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ELECTIVE SURGERY OF THE KNEE


by D.W. LENNOX, L.H. RILEY Jr, D.S. HUNGERFORD, M.A. JACOBS,

Th. JUDET and K.A. KRACKOW

In: Atlas of Orthopaedic Surgery
Volume 3
Lower Extremity;
Editors: Laurin, CA, Riley Jr. LH, Roy-Camille R

Reprinted with permission from Masson, copyright Masson, Paris, 1991


1. Synovectomy of the knee

by D.W. LENNOX and L.H. RILEY Jr.


Synovectomy of the knee is performed through a long anterior, midline incision (Fig. 15-I). The capsule and tendon of the knee extensors are opened in the medial parapatellar region, taking care to spare the muscle fibres (Fig. 15-2). The patella is reflected lateral to the lateral femoral condyle permitting the knee to be flexed beyond 90 degrees (Fig. 15-3). The infrapatellar fat pad and overlying synovium are removed and the medial one third of the patellar tendon insertion into the tibial tubercle may be divided to facilitate patellar eversion. Sufficient exposure is thus achieved to permit a complete synovectomy.

Fig. 15-1. - The skin incision extends from just superior to the musculo-tendinous junction of the knee extensors across the medial one third of the patella and ends just distal to the tibial tubercle.
Fig. 15-2. - The capsule and knee extensors are incised in the medial parapatellar region.
Fig. 15-3. - The patella is reflected lateral to the lateral femoral condyle permitting the knee to the flexed beyond 90°. The infrapatellar fat pad is removed.


With the knee in full extension, the synovium of the suprapatellar pouch is identified and sharply dissected from the underlying soft tissues and the anterior condyles of the femur (Fig. 15-4). Proximally, the fibres of the retractor synovialis which insert into the synovium are sharply divided. As the synovial layer is dissected distally care is taken to avoid injury to the fat which separates the synovium from the underlying femur. The knee is then flexed to 90° to permit the synovium to be sharply dissected from the medial femoral condyle and from the medial capsular pouch. At this stage, the patella and lateral capsular pouch are reflected to permit dissection of the synovium from the lateral femoral condyle. Care must be taken to remain in the proper plane over the medial and lateral femoral condyles to prevent transection of the femoral attachments of the medial and lateral collateral ligaments which can be damaged if the dissection is carried down to bone. The synovial flap is detached at the femoral joint line and, inferiorly as dissection is extended in the plane between the synovium and the capsule medially and laterally, down to the capsular attachments to the tibia (Fig. 15-5).

Fig. 15-4. - With the knee in full extension, the synovium of the suprapatellar pouch is sharply dissected from the underlying soft tissue to the articular surface of the femoral condyles.
Fig. 15-5. - Synovium is sharply dissected from the medial and lateral femoral condyles: the dissection is extended in the plane between the capsule and synovium to their tibial attachments.


The synovium of the posterior medial compartment is visualized with the knee in 90° of flexion through a curved incision in the capsule, just posterior to the medial collateral ligament, and can be removed with sharp dissection or with pituitary forceps (Fig. 15-6). The synovium in the posterolateral compartment is removed in a similar fashion through a curved capsular incision just posterior to the lateral collateral ligament with the knee flexed beyond 90° (Fig. 15-7).

Fig. 15-6. - Exposure of the posteromedial compartment and synovial excision.
Fig. 15-7. - Exposure of the posterolateral compartment and synovial excision.

The synovium covering the cruciate ligaments is removed with sharp dissection or with pituitary forceps.

Suction drains are left in the medial and lateral compartments. The capsule is closed with interrupted nonabsorbable sutures; the subcutaneous fascia is closed with fine interrupted sutures and the skin is closed with either a running stitch of nonabsorbable suture or with skin staples (Fig. 15-8). A compression dressing is applied. When incisional healing is assured, the knee is placed in a continuous passive motion machine and 90° of motion are usually regained within seven days. Extension exercises are begun on the first postoperative day and continued throughout the rehabilitative period. Protected weight-bearing is permitted as soon as muscle control is sufficient.

Fig. 15-8. - Wound closure.


2.    Technique of total knee replacement

by D.S. HUNGERFORD


Technical inaccuracy is the most common cause of aseptic loosening following total knee replacement. Indeed, even relatively constrained designs, which have subsequently been superseded by more anatomical and kinematically physiologic designs, have shown long term durability when properly implanted with perfect alignment, component positioning and ligamentous stability.

Initially, instruments to implant total knee components were overly simple and relied mostly on free visual referencing by the surgeon. The technical achievement varied considerably from case to case, and surgeon to surgeon, since the alignment references were incompletely visualized. Instrumentation systems have gradually become more sophisticated and comprehensive leading not only to the proper triaxial placement of each component, but also assisting in ligament balancing with intimate contact between the individual prosthetic components and the host bone. The latter is of critical importance for the cementless prostheses.

Different surgeon/engineer groups have chosen different routes to achieve common goals. However, they all stress the importance of proper alignment, ligament balance, and prosthetic bone contact. It is beyond the scope of this chapter to review all the instrumentations system currently available since they are based upon different premises and, to a certain extent, differing alignment criteria. However, there is more in common among various systems than there are differences. The purpose of this section is to review the alignment requirements for a well functioning total knee replacement, and to review in some detail the specific operative sequence that the author is currently using.

ALIGNMENT IN TOTAL KNEE REPLACEMENT

1° Axial alignment

When alignment in total knee arthroplasty is discussed, most people first think of long axial alignment or the overall orientation of the leg in the frontal plane (Fig. 15-9). Alignment of the normal leg averages 6° of valgus between the femoral shaft and the tibial shaft. (Insall, Kapandji). During single leg stance, the joint line is horizontal and it makes, on average, an 81° angle with the femoral shaft. The mechanical axis, a line from the center of the femoral head to the center of the ankle, normally passes through the center of the knee. It is more difficult to obtain a standard measurement when using the tibial shaft as a reference, since the proximal tibial diaphysis may not be in the same line as the distal diaphysis. Therefore, the line between the center of the knee and the center of the ankle is often substituted for the tibial shaft axis. The tibial shaft axis or mechanical axis makes, on average, an 87° medial angle with the joint line. In a normal population, the joint line is virtually never perpendicular to the mechanical axis.

Fig. 15-9. - Schematic drawing showing normal leg alignment with the lower extremities positioned for single leg stance. HKA: Mechanical axis. SKA: Anatomical axis. TT: Transverse axis. V: Vertical axis.

Several instrumentation systems recommend cutting the proximal tibia perpendicular to the mechanical axis and compensating for this relative valgus cut on the tibia by making a 6° cut on the femur. In fact, if this is carried out on the normal knee, it results in removing a 3° laterally based wedge from the tibia which is compensated by the 3° medially based wedge on the femur (Fig. 15-10 a). However, this balance occurs only with the knee in full extension, and is not compensated for when the knee is in flexion unless the femoral cutting block is also rotated into external rotation (Fig. 15-10 b). This practice is recommended by Insall and the instrumentation of Scott and Thornhill for the PFC knee provides an adaptation to laterally rotate the femoral component 3° while using the medial posterior condyle as a rotational reference. We prefer to make a 9° valgus femoral cut and a 3° varus tibial cut to achieve normal alignment in the frontal plane (Fig. 15-11). However, the whole issue of alignment is much more complex than only axial alignment.

Fig. 15-10. - a) Line drawing showing the offsetting medial femoral wedge and lateral tibial wedge when the femur is cut in 6° of valgus and the tibia in 0°,

Fig. 15-10. - b) External rotation of the distal femoral cutting block to compensate in flexion for the laterally based wedge resection of the tibia.
1. Mechanical axis; 2. Tibial cut at 90° to mechanical axis.

Fig. 15-11. - Long standing X-rays of a total knee replacement with 9° valgus femoral cut and 3° varus tibial cut. The joint line is horizontal.
The right knee is in varus.

2° Rotational alignment

Femoral component

The rotational position of the femoral component will define the posterior joint line which will influence medial and lateral compartment stability when the knee is in flexion, as well as the orientation of the trochlea. Trochlear position will influence the stability and tracking of the patellofemoral joint. Therefore, correct rotational position of the femoral component is important to the functional kinematics of the replaced knee. Available references for correct rotational alignment include the posterior condyles, the “skyline” view appearance of the trochlea, with the lateral facet projecting more anteriorly than the medial facet, and the level of the epicondyles (Fig. 15-12). Of these, the level of the posterior condyles is probably the most reliable, but may be subject to variability in instances of fracture, severe deformity or osteonecrosis. In such cases the secondary alignment references will also be employed. In fact, the secondary references should always be used to check the validity of the primary reference.

Tibial alignment

Rotational alignment of the tibia will primarily affect patellofemoral tracking, but marked rotational malalignment will also affect the relative position of the collateral ligaments and hence tibio-femoral stability. Alignment references for the proximal tibia are less well-defined than for the distal femur, but include the posterior margin of the tibial plateau, the tibial tubercle, and the transmalleolar axis (Fig. 15-13). In general, the final selection of tibial rotation will usually be made after provisional trial reduction.

Fig. 15-12. - End on view of the distal femur. The posterior margins of the condyles mark the coronal plane (1). The medial epicondyle is slightly anterior to the lateral epicondyle. The lateral trochlear facet is anterior to the medial facet.
Fig. 15-13. - Top view of the tibial plateau. The tibial tubercle is slightly lateral to the midline. In general, the posterior margin of the plateaus parallels the transverse axis of the tibia.

Patellar component

Dome type patellar components require no rotational orientation. The original anatomical PCA patellar component requires rotational orientation after the coronal cut of the facets is made. The orientation of the longitudinal ridge separating the medial and lateral facets is noted prior to the patellar resection, and the patellar resurfacting component will be aligned in this plane. The dome patella is not rotationally constrained, and precise rotation is not critical.

3° Flexion-extension alignment

Femoral component

1° Flexion. - Because of the curvature of the femoral condyles, minor flexion-extension malalignment of the femoral component will be tolerated relatively well. The flexion-extension alignment reference is the long axis of the femoral shaft seen from the side (Fig. 15-14). Early alignment systems used external guides. Many current systems use an intramedullary rod. Significant tilting of the femoral component in flexion will tend to bring the posterior condyles of the femoral component more anteriorly and contribute to instability in flexion. In addition, most total knee components allow only limited heperextension and excessive flexion of the femoral component will impose a fixed flexion contracture on the definitive prosthesis. With marked flexion of the femoral component, the anterior patellar flange could project even more anteriorly than the femoral cortex and could interfere with the quadriceps mechanism.

Fig. 15-14. - The long axis of the femur, as seen from the side, serves as the flexion extension alignment reference (1) for the femoral component.

2° Extension. - Extension of the femoral component will lead to hyperextension of the knee. The patient may also develop functional instability when the knee is in anatomical full extension since the prosthetic components will not be fully extended and, therefore, be less stable. Additionally, extending the femoral component will likely lead to notching of the anterior femoral cortex.

Tibial component

The flexion-extension attitude of the tibial component is much more critical to proper knee functioning than the femoral component. The natural, posterior inclination of the tibial plateau decreases the distance between the femoral and tibial-fibular attachments of the collateral ligaments during knee flexion (Fig. 15-15). The collateral ligaments are therefore relaxed in flexion which allows rotation between the tibia and the femur to take place. This possible rotation is important when changing direction during gait. This means that rotational movements, which will naturally be imposed in everyday living, will be dissipated by rotational movement between the femur and the tibia, or, in the case of total knee replacement, between the femoral and tibial components. In the absence of rotational freedom, torsional forces will be resisted by the components and lead to shear forces at the prosthesis-bone interface.

There are, basically, two ways to duplicate this important anatomical configuration. The first is to slope the tibial cut in the same way as the natural proximal tibia is sloped, i.e. 7° to 10° posteriorly. The second way is to cut the tibia perpendicular to the longitudinal axis and tighten the radius of curvature of the femoral component to offset the difference between the amount of posterior tibial bone that is resected and the amount that is replaced by the tibial prosthesis (Fig. 15-16). Sloping the tibial cut posteriorly has the disadvantage of resecting more posterior bone than would, otherwise, be necessary. Secondly, a posteriorly sloped cut will frequently result in transection of the tibial attachment of the posterior cruciate ligament, particularly if there is already significant bone loss on either of the tibial plateaus.

Fig. 15-15.  - The posterior slope of the tibial plateau contributes to the decreased distance between the femoral and tibial attachments of the collateral ligament in flexion (a) compared to extension (b).
Fig. 15-16. - Composite drawing of the resected bone replaced by the prosthesis to eliminate the posterior wedging phenomenon.

For the PCA prosthesis, we have chosen to cut the tibia perpendicalar to the longitudinal axis, thus protecting the posterior cruciate attachment to the tibia and preserving stronger subchondral posterior tibial bone. It is important that the user be familiar with the design of the particular prosthesis that he chooses, since variation in the orientation of the tibial cut from that which is designed for the specific prosthesis will lead to undesirable flexion and extension characteristics of the replaced knee.

If the tibial component is cut with an anterior slope (extension), instability in extension will be produced. If a sufficiently thick tibial component is used to produce stability in extension, the knee will be too tight in flexion. This will occur whether the design of the prosthesis calls for a transverse tibial cut or one which is sloped posteriorly. If the tibial cut is sloped more posteriorly than intended for the specific prosthesis, the knee will be unstable in flexion. If a sufficiently thick tibial component is used to stabilize the knee in flexion, a fixed flexion contracture will be introduced.

Patella

There are few guidelines for the proper flexion­extension attitude of the patellar cut. It is, therefore, important that osteophytes around the patella be debrided and that the marginal insertions for the quadriceps tendon, the retinaculae and the patellar tendon be well identified. Failure to cut the patellar facets in the coronal plane will lead to patellar instability if too much patellar bone is resected; if too little bone is excised, a tightening of the patellar tendon-quadriceps tendon mechanism results in loss of flexion.

4° Proximal-distal and anterior-posterior component position

Femoral component

There have been two schools of thought concerning femoral component positioning in these planes. Prior to the introduction of the Universal instruments in 1978, the common way was to first make a minimal resection of the proximal tibia followed by a variable resection from the posterior and distal femoral condyles to produce equal flexion and extension gaps. The Universal instruments introduced the concept of measured resection, whereby an amount, equal to the thickness of the prosthesis, is resected from the distal and posterior condyles, using the non-eroded femoral condyle as a reference (Hungerford). This results in positioning the femoral component close to the level of the original joint line, thus allowing the retained ligaments, including the posterior cruciate ligament, to function in a kinematically normal way throughout the full range of motion.

Similar results may be obtained using the common flexion-extension gap method as long as the prosthesis is not moved too far from the original joint line. One pitfall that must be avoided in the common gap method is the prevention of the free movement of ligaments by osteophytes or scar. For example, if, after having made the flexion gap, the extension gap is then determined with retained posterior osteophytes (or scarred posterior capsule), the distal femoral resection will be excessive; while the knee will be stable in full extension, as soon as the knee flexes a few degrees and the posterior capsule is no longer under tension, the knee will be unstable. Within reasonable limits it is probably acceptable to move the joint line proximally (by removing more femoral bone distally) and anteriorly (by removing more femoral bone posteriorly) by equal amounts, offsetting the additional resection with the use of a thicker tibial component. Likewise, it is probably permissible to move the joint line slightly distally and an equal amount posteriorly, with an offsetting thinner tibial component. It must, however, be realized that moving the joint line proximally, but not anteriorly, will lead to instability in extension or tightness in flexion depending upon the thickness of the tibial component; moving the joint line anteriorly, but not proximally, will lead to instability in flexion or a fixed flexion contracture, again dependent upon the choice of the thickness of the tibial component. If the femoral component is moved excessively proximally and anteriorly, the replaced knee will only be stable at 0° and 90° and not in the midrange of flexion.

Tibia

Anterior posterior positioning potential of the tibial component will be very limited if the size of the tibial component has been correctly selected. If a prosthesis is chosen which sacrifices the posterior cruciate ligament, anterior posterior position of the tibial component will not have much effect on knee stability. However, when retaining the posterior cruciate, anterior malpositioning of the tibial component will tighten the posterior cruciate, since the tibial attachment of the PCL is moved posteriorly. This could result in premature tightening of the posterior cruciate ligament and limit flexion of the knee.

5° On the order of bone cuts

There are some systems which require a specific order of bone cuts. In general, these are systems which balance the ligaments by creating a common gap in flexion and extension. We believe that there are some inherent problems in using the common flexion­extension gap method. If certain precautions are utilized, this can result in a satisfactorily aligned and balanced prosthesis. The two precautions are: 1) the joint line must not be moved excessively from its original location; 2) all blocks to the free movement of the retained soft tissues must be released or removed prior to the creation of the common gaps. This can sometimes be difficult because access to all areas of the knee is limited prior to making the cuts. The disadvantage of making the tibial cut first is that posterior structures cannot be adequately exposed, particularly the posterior cruciate attachment to the tibia. In addition, the alignment references for the proximal tibia are not as apparent prior to resecting the posterior femoral condyles and subluxing the tibia anteriorly. There are few disadvantages to cutting the femur first, which is the method we prefer. The single disadvantage is that it does require 90° of knee flexion. In the knee which is rigid or ankylosed, this can be difficult or impossible, requiring that the tibial cut be made first. The advantages of cutting the distal and posterior femur first include: 1) all of the alignment references for all of these cuts are available as long as the knee can be flexed to 90°; 2) with the femoral cuts completed, exposure for the tibial cuts is greatly facilitated. For most total knee systems there is only one configuration of femoral component for a given size. For some systems, the thickness of the distal and posterior aspects of the prosthesis may vary between sizes and for other systems they remain constant. However, if the distal and posterior joint lines are to be re-established, it is important that the amount of bone resected from the distal and posterior femur be equal to the dimensions of the prosthesis. This may require choosing the correct femoral size prior to making any of the cuts. With the original PCA prosthesis the amount of distal and posterior resection is constant among all of the sizes available with the variation in size being anterior and medial­lateral. This allows the distal and posterior femoral cuts to be made prior to selecting the ultimate femoral size, and also allows a larger size to be changed to a smaller size without affecting the stability of the joint in extension or flexion. The theory for the PCA system is that, if the level of the joint line is used as a reference and recreated, then the radius of curvature of the prosthesis will match the radius of curvature of the natural knee, and the collateral ligaments will function under physiologic tension throughout the range of motion. This premise appears, in fact, to be true for the vast majority of knees, but the final test is with the trial reduction when collateral ligament tension is balanced both medially and laterally, in flexion and in extension.

There is a fundamental separateness between the order of the bone cuts and the balancing of ligamentous tension. Although, in most instances, both will take place simultaneously, they can, in fact, be done as completely separate steps. It is important to realize that one must not compensate for ligamentous imbalance by selective malalignment of the prosthesis. Such malaligment will lead to its own separate set of problems, which have already been addressed.

6° Ligamentous balance

For the moderately severe arthritic knee, ligamentous balance will be virtually automatically achieved by debriding the knee during exposure, removing osteophytes, loose bodies, scarred synovium, and releasing retracted capsule, as long as alignment is correct in all of the planes. Ligamentous instability, however, can also be imposed by individual component malalignment. Moreover, offsetting malalignments usually produce stability in only one degree of flexion, leaving asymmetrical ligament tightness throughout the rest of the range of motion. Therefore, the first step, in assuring ligamentous balance throughout a functional range of motion, is correct individual component placement. Any residual instability at the time of trial reduction is then a rather straightforward procedure of tightening the loose side or releasing the tight side.

A section describing the special techniques for dealing with severe deformity appears following the section on the standard surgical technique. The first section of this chapter presented the rationale for total knee arthroplasty technique with review of some of the consequences of failure to achieve those technical goals. Whatever system is chosen must be carefully studied and understood along with the specific characteristics of the implant and the instruments.

EXPOSURE

A nearly midline, straight skin incision, slightly towards the medial side, avoids being directly over the patella or the tibial tubercle. The quadriceps tendon is split at the medial one third, central one third junction, and is carried distally, through the medial retinacular, to the tibial tubercle (Fig. 15-17).

Fig. 15-17. - The knee is approached through a longitudinal midline skin incision, followed by a medial para-patellar capsular incision. The quadriceps tendon is incised longitudinally, allowing eversion and dislocation of the patella laterally.

1° Cutting the distal femur

With the knee at 90° flexion, the menisci and peripheral osteophytes are removed, an intercondylar drill hole is made, anterior to the femoral attachment of the PCL.

The intramedullary alignment rod with a distal femoral cutting guide attached is passed to the level of the isthmus. The bushing to align the varus-valgus orientation of the cut is selected with preoperative templates. The extramedullary guide confirms correct alignment and can be used if the intramedullary space is not free (THR, plate/screws, etc.) (Fig. 15-18).

Before fixing the distal femoral cutting block to the anterior femur, the alignment jig must be properly rotated. Posterior condyles are primary guides with epicondyles and trochlea as secondary references.

With the distal femoral cutting jig flush against the prominent condyle, the position of the cutting block will insure that the thickness of the distal resection is equal to the distal thickness of the prosthesis (Fig. 15-19).

The N° 2 jig references off the posterior condyles. If one condyle is defective posteriorly (rare), a space will be created equal to the defect. The reference 3/16” drill holes will properly align the femoral component for rotation, medial-lateral, and anterior-posterior positions (Fig. 15-20). The posterior condylar resection is the same for all prosthetic sizes. Size variability adjusts at the level of the anterior resection.

The N° 3 cutting block size is chosen so that the anterior cut will not notch the anterior femur. The size of the posterior cut is constant (Fig. 15-21).

The chamfer cuts complete preparation of the femur. The posterior chamfer cut is constant for all sizes. The anterior cut is specific to each size (Fig. 15-22).

With the femoral cuts completed, the femoral component can be tried for fit. The proximal margin of the posterior condyle should be marked with a curved osteotome. Failure to remove posterior osteophytes will result in lack of full extension and may also block full flexion (Fig. 15-23).

Fig. 15-18. - The long axial guide and long alignment pin are used to verify the position of jig I-A relative to flexion-extension, varus-valgus, and rotational planes.
Fig. 15-19. -The distal femoral cutting block has been positioned to allow the cut to be made not only in the proper varus-valgus, flexion-extension and rotational axes, but also at the proper level to re-establish the distal joint line.
Fig. 15-20. - a and b) The femoral jig II assures the proper anterior-posterior, medial-lateral and rotational position of the condylar fixation drill holes.
Fig. 15-21. - a) The size of jig III will determine the level of the anterior cut (A, B, C).
b) Jig III is used to make the anterior and posterior femoral cuts.
Fig. 15-22. - Anterior and posterior femoral chamfer cuts are made.
Fig. 15-13. - A curved osteotome is used to remove posterior osteophytes that may prevent component seating and/or full flexion.

One common error is to underresect the anterior femur, particularly as the cut approaches the anterior cortex. The consequence will be to cause the femoral component to flex as it approaches full seating. This should be looked for and corrected before the posterior bone is crushed.

With the femoral cuts made, the tibia can be subluxed in front of the femur.

The posterior horns of the two menisci are removed and the tibial attachment of the posterior cruciate ligament is identified. Residual peripheral osteophytes, particularly postero-medial, are also removed.

The tibial cutting jig controls the varus-valgus, flexion-extension and rotational aspect of the tibial cut (Fig. 15-24 a to e).

Fig. 15-24. - a) The long pin of the proximal tibial alignment rod jig V-A is lightly seated on proximal tibia and rotational adjustments are mad.
Fig. 15-24. - b) Flexion-extension alignment is adjusted and the distal locking screw is tightened.
Fig. 15-24. - c) Proper flexion-extension alignment when the jig is parallel to the midcoronal plane of the tibia (and not to the anterior border of the tibia).
Fig. 15-24. - d) After initial alignments are verified, the two proximal fixation pins are fully seated.
Fig. 15-24. - e) The middle thumbscrew is tightened to secure jig V alignment.

The long fixation pin of the assembly is inserted into the middle of the tibial plateau and the ankle clamp fits around the distal tibia. The two points define the mechanical axis. Flexion-extension attitude can be adjusted by moving the distal part of the assembly forwards or backwards. The assembly should be lined up with the midlateral longitudinal axis of the lower leg, not with the anterior tibial crest. Rotational alignment is checked by using the transverse axis of the tibial plateau, the position of the tibial tubercle (slightly lateral to the midline) and the transmalleolar axis as rotational references. Once triaxial alignment has been assured and finally checked, the top piece is driven down, engaging the short pin which will prevent rotation. There remains only to determine the level of the tibial cutting block and to secure it to the tibia with 1/8” drill pins. Once this is done, the tibial cutting assembly is removed leaving the cutting guide in place. Care in cutting is necessary to avoid damage to collateral and posterior cruciate ligaments.

Trial reduction

The initial trial reduction is done on the N° 7 jig, which is the drill guide for the final fixation holes for the tibial component (Fig. 15-25). This jig determines the final medial-lateral, anterior-posterior, and rotational position of the tibial component. It is important to avoid medial overhang of the prosthesis as this might cause painful conflict with the medial collateral ligament. In general, rotation will be in the same orientation as the tibia was cut. However, some rotational change is still possible. Internal rotation of the component must be avoided. Different degrees of rotation can be tested prior to selection of the final orientation.

Fig. 15-25. - Trial reduction is done initially with the N° VII jig which allows confirmation of the orientation of the tibial cut and selects the position of the tibial fixation holes. That determines medial-lateral, anterior-posterior and rotational positions of the tibial component.

Trial reduction may detect medial-lateral, rotational, or anterior-posterior instability. In such cases, the first place to look is for obstacles to the free travel of soft tissue stabilizers. Posterior condyles and the posteromedial tibia are the first place to check for retained osteophytes or tight capsule. It is also possible that the distal femur was underresected. If this were so, the trial reduction, with the tibial spacer that provided stability in flexion, would show a fixed flexion contracture. Any fixed flexion contracture, which is evident at the time of trial reduction, may be either on the basis of tight soft tissue structures requiring either resection of those things which are blocking free excursion of those soft tissues, or release of the soft tissues. On the other hand, the fixed flexion contracture may be indicative of the need to recess the femoral component proximally. This technique is described under the section “Management of severe fixed deformity”.

4° Patellar resection

The patellar facets are resected at the level of the attachment of the quadriceps tendon and the retinaculae into the “equator” of the patella. Final trial reduction includes a trial patellar component and a tibial base plate, which allows reduction of the extensor mechanism to check for range of motion, stability, ligament balance and patellar tracking.

SPECIAL TECHNIQUES FOR DEALING WITH SEVERE DEFORMITY

1° Fixed valgus deformity

Type I valgus deformity. - This type of deformity involves loss of bone stock from the lateral side, usually with equal amounts of bone deficiency from the tibia and the femur. The deformity may be passively correctable or fixed. However, the medial ligamentous structures must be intact and the standing X-ray will not show any opening of the medial joint space. If a type I patient has a fixed valgus deformity, lateral soft tissue release will allow the leg to be passively aligned correctly while maintaining medial soft tissue stability (Fig. 15-26 a).

2° Type II valgus deformity. - The elements of type I deformity are all present, i.e. lateral bone stock loss with or without lateral structure contracture. The criteria of demarcation for type II deformity, however, is that the medial soft tissue stabilizers are attenuated and elongated. On the standing film, the medial joint line is significantly opened. In these cases, the lateral soft tissue structure will have to be released not only to allow the leg to be aligned, but also to allow the tibia to be sufficiently distracted away from the femur to stabilize the attenuated medial structures. Alternatively, the medial structures will be reconstructed and shortened (Fig. 15-26 b).

Fig. 15-26. - a) Type I valgus deformity: Bone loss on the lateral side but no medial instability.
Fig. 15-26. - b) Type II valgus deformity: Attenuation of the medial soft tissue stabilizer is evident both clinically and radiologically.

Lateral soft tissue release

There are six soft tissue structures which stabilize the lateral side of the knee: the iliotibial band, the popliteus muscle, the biceps muscle, the lateral head of the gastrocnemius, the lateral collateral ligament and the posterior lateral capsule (Fig. 15-27). Four of these six stabilizers are musculotendinous complexes, which, we believe, explains the tendency for valgus deformity to become fixed. The lateral release is best done at the time of trial reduction because it is only at that time that one can adequately assess which structures require releasing. We prefer to limit the release to those structures which are tight rather than to simply carry out an extensive and complete release. In most cases, complete release is not necessary. Prior to any lateral release, it is important to make sure that all femoral and posterolateral tibial plateau osteophytes have been removed. The most common structure requiring release is the iliotibial band. We prefer to Z-plasty lengthen this structure rather than to simply transect it. The popliteus muscle can be transected, if necessary. The lateral collateral ligament should be released from its femoral origin as an osteo-periosteal slide.

Fig. 15-27. - The lateral soft tissue stabilizers and their levels of transection.
1. Iliotibial band; 2. Parapatellar release; 3. Popliteus tendon; 4. Fibulectomy (rarely necessary); 5. Lateral collateral ligament; 6. Biceps femoris tendon; 7. Lateral head of gastrocnemius.

If the deformity is so severe as to require lengthening of the biceps tendon and/or the lateral head of the gastrocnemius, it is safer to utilize a separate, posterolateral incision, to identify and protect the peroneal nerve. In rare instances, it may be necessary to resect the fibular head to decompress the peroneal nerve. In most instances of severe valgus deformity, the medial structures will be attenuated and stretched. We prefer, in such cases, to limit the lateral release to that which allows correction of the deformity, and then to carry out a medial ligamentous reconstruction. In most instances, only the iliotibial band and the posterolateral capsule will need to be released. Further lateral decompression can be accomplished by modest femoral shortening, which is described under fixed flexion contracture. Femoral shortening, however, should not be considered unless the surgeon is already committed to also carry out a medial reconstruction.

Medial soft tissue advancement

This procedure is only necessary for severe (type II) valgus deformities. The median, parapatellar skin incision must be extended 5 cm distally in order to expose and reflect the proximal half of the pes anserinus insertion. This exposes the attachment of the superficial collateral ligament to the tibial metaphysis (Fig. 15-28). All of the soft tissues attached to the proximal medial tibial metaphysis are reflected posteriorly to the insertion of the semimembranous tendon, as a single ligamentous and capsular flap. Dissection is facilitated by having the knee in 90° of flexion and progressively externally rotating the tibia.

Fig. 15-28. - a and b) The skin incision is extended distally and the top half of the pes anserinus tendons are reflected distally to expose the superficial medial collateral ligament.
1. Pes tendon group; 2. Medial collateral ligament.

Distal re-attachment of the capsular ligamentous flaps is performed only after the components are permanently in place. The tibial component thickness that is selected should stabilize the posterior cruciate ligament and the lateral ligamentous structures-throughout the range of motion. With the knee in 10-15° of flexion and the tibia in neutral rotation, the capsular ligamentous flap is pulled distally and slightly anteriorly. It is fixed to the medial tibial metaphysis by staples, supplemented by heavy sutures inserted through and tied over bone (Fig. 15-29). It is important to be careful not to selectively tighten the anterior portion of the medial capsule or closure of the median parapatellar incision will be difficult or impossible. To protect against this, it is helpful to place holding sutures at the proximal and distal margins on the median side of the patella to make sure that the capsule can be closed. The pes anserinus is then re-attached to cover the soft tissue repair. Standard postoperative care consists in routine physical therapy with active and active-assisted range of motion excretes, and ambulation in a posterior splint to protect the repair.

Fig. 15-29. - The medial capsular ligamentous structures are pulled distally and slightly anteriorly where they are re-attached to the tibia.
2. Medial collateral ligament; 3. Staples; 4. Prostheses.

2° Fixed varus deformity

Bone resection alone on the tibia will allow the axial deformity to be corrected, but will exacerbate the relative laxity on the lateral side. Theoretically, the same possibility exists as for a fixed valgus deformity. However, the lateral side is dynamically stabilized since four of the six structures stabilizing the lateral side are attached to muscles and mild to even moderate lateral instability is well tolerated. Therefore, release of the medial structures usually suffices to both correct the deformity and balance the soft tissue stabilizers. Since the medial release must include the superficial medial collateral ligament, the entire medial side of the tibia needs to be exposed; all osteophytes are removed and the fibres of the deep medial collateral ligament are sharply detached from the medial metaphysis 2.5 cm distal to the joint line. This degree of release will be sufficient for the vast majority of cases.

A more extensive medial release involves exposure and elevation of the medial ligamentous capsule in a manner identical to that described under medial soft tissue advancement. It is not, however, always necessary to reflect the pes anserinus since the exposure can be done blindly with a periosteal elevator. For a varus deformity, the medial stabilizers are recessed while they were advanced for a severe valgus deformity.

The need for lateral soft tissue advancement is extremely rare and will not be described in detail. Basically, the fibular head, with the attached lateral collateral ligament and biceps tendon is mobilized after transecting the fibular neck. It is then drawn distally to assess the appropriate length of the fibular neck that must be resected to restore tightness in the lateral structures; the fibular head is then fixed to the shaft, using an intramedullary, cancellous bone screw.

3° Fixed flexion contracture

The first step in treating severe fixed contracture is to minimize the fixed flexion contracture preoperatively. This includes serial casting, bracing, stretching and physical therapy. The vast majority of fixed flexion contractures can be reduced by at least 50% through one or a combination of these modalities. Any fixed flexion contracture of more than 30° should be considered for an attempted preoperative reduction.

Theoretically, any severe fixed flexion contracture can be treated by a generous resection of the distal femur and proximal tibia. However, aside from violating the basic principles of removing as little bone as is absolutely necessary, overzealous bone resection is unsatisfactory for two reasons. Firstly, the knee which extends only on the basis of bone resection will only be stable in extension, since the stability in extension will only be provided by the posterior capsule. As soon as the knee flexes a few degrees, the posterior capsule will relax and the knee will be completely unstable. Bone resection alone, to correct fixed flexion contracture, can only be used with completely intrinsicly stabilized knee components and is not satisfactory for standard unconstrained components.

Posterior osteophytes and capsule

One of the most common causes of a persistent fixed flexion contracture after the standard bone cuts is the presence of significant posterior femoral osteophytes (Fig. 15-30). The osteophytes deform the posterior capsule causing the capsule to be prematurely tight prior to full knee extension. Resection of all posterior marginal osteophytes is essential to correct a fixed flexion contracture.

Fig. 15-30. - Posterior femoral osteophytes are visible on the lateral preoperative X-ray. They distract the posterior capsule in extension leading to flexion contractures.

At the time of trial reduction, if the knee does not extend fully, the cause of this lack of extension must be determined. If the collateral ligaments become tight prior to the knee extending fully, then the distal femur can be shortened. If, however, the lack of full extension is caused by premature tightening of the posterior capsule, then the capsule can be divided under direct vision with the knee at 90° of flexion.

The capsular layer should be identified and incised away from the midline to avoid damage to the posterior tibial or popliteal neurovascular structures. Dissection with a curved clamp can separate the capsule from the gastrocnemius muscle allowing its transverse division under direct vision. In rare instances, the origins of the heads of the gastrocnemius muscle may be stripped from the femur with a periosteal elevator.

Resecting the distal femur

Using the Universal total knee instrumentation system, it is easy to resect additional bone from the distal femur. The 1/8” pins, which were used to fix the N°  1B primary distal femoral cutting jig, are reinserted into the distal femur. The 5B jig is placed upon these drill pins and the distal femur is recut. This resects exactly 2 mm of additional femur. If additional femoral resection is necessary, the axillary N° 5 jig can be inserted onto the drill pins and another 2 mm of distal femur can be resected. Additional distal femoral resection will have to be followed by recutting the chamfer cuts of the anterior femoral cut, but not the posterior cut. Distal femoral resection recesses the femoral component proximally only, thereby producing additional space for extension, but, since the femoral component stays in the same anterior-posterior plane, stability in flexion is not affected.

AVOIDING EXTENSOR MECHANISM PROBLEMS

Most series report a two to five percent incidence of significant extensor mechanism problems. Complications include patellar tendon rupture, quadriceps tendon rupture, patellar fracture, patellar subluxation, and dislocation. Many aspects of total knee replacements, other than those directly involved with the extensor mechanism, impact on the functioning of the quadriceps mechanism. This begins with exposure in the tight knee with limited flexion preoperatively. Excessive traction or leverage on the extensor mechanism must be avoided. If sufficient exposure cannot be achieved through the standard median patellar approach, then a reflection of the tibial tubercle may be necessary to facilitate exposure. Excessive retraction, particularly with retractors with long leverage handles, may result either in patellar fracture or patellar tendon avulsion. The latter complication is to be avoided at all costs.

Instability of the patella is a multifactorial problem and can be caused by malposition of either the femoral or the tibial component. Internal rotation of the femoral component displaces the trochlear groove medially and increases the likelihood of patellar dislocation. Underresection of the anterior femur with the implantation of an unnecessarily large femoral component pushes the extensor mechanism anteriorly, tightens the lateral retinaculum and predisposes to lateral patellar subluxation. Internal rotation of the tibial component lateralizes the tibial tubercle, thereby increasing the quadriceps angle and predisposes to patellar subluxation. Underresecting the patella, also, displaces the patella anteriorly tightening the lateral retinaculum and predisposing to dislocation.

When using a dome patellar button, the medial margin of the button must be coated with the medial margin of the cut patella. The normal patella is broader in the medial-lateral plane than in the proximal-distal plane. The patellar button, which does not overhang proximally or distally, will not fully cover the patella medial-laterally. Since the center of the dome is symmetric and since the central ridge on the normal patella is asymmetrically displaced towards the medial side, placing the dome symmetrically on the cut surface of the patella functionally lateralizes the central ridge of the dome compared to the original anatomic position. This increases the Q angle and predisposes to subluxation-dislocation. Therefore, in order for the dome to be concentrically located in the prosthetic patello-femoral groove, the patellar button should be slightly displaced medially.

Finally, older people may heal tendinous soft tissues more slowly than younger patients. Dissolvable sutures placed in the retinacular and quadriceps tendon repair may lose their strength before these tissues have sufficiently healed. We, therefore, prefer to use nonabsorbable sutures in the central third of the extensor mechanism repair. Attention to all of these details will minimize the likelihood of patello-femoral problems. We do not believe that it is necessary to do routine lateral releases. However, during the trial reduction, if there is any tendency of the patella to sublux while no pressure is applied to the patella to keep it located, a lateral release should be carried out.

BIBLIOGRAPHY

  1. GREENBERG R.L., KENNA R.V., HUNGERFORD D.S., KRACKOW K.A. - Instrumentation for total knee arthroplasty. In: HUNGERFORD D.S., KRACKOW K.A., KENNA RVTotal knee arthroplasty’: A comprehensive approach. 35-70. Williams and Wilkins, Baltimore, 1984.
  2. HUNGERFORD D.S., KRACKOW K., KENNA RV - The porous-coated anatomic total knee system. Orthop. Clin. North. Am., 13, 103-122, 1982.
  3. HUNGERFORD D.S., KRACKOW K.A., KENNA RV - Total knee arthroplastv: A comprehensive approach. Williams and Wilkins, Baltimore, 1984.
  4. INSALL J.A. - Surgery of the knee. Churchill Livingstone, New York, 1984.
  5. INSALL J.N., TRJA A.J., SCOTT W.N. - The total condylar knee prosthesis: The first five years. C/in. Orthop., 145, 68, 1979.
  6. KAPANDJI I.A. - The physiology of the joints, Vol. II. 74-75. Churchill Livingstone, New York, 1970
  7. KRACKOW K.A. - Management of fixed deformity at total knee arthroplasty: General principles. In: HUNGERFORD D.S., KRACKOW K.A., KENNA RVTotal knee arthroplastv: A comprehensive approach, 163-166. Williams and Wilkins, Baltimore. 1984.
  8. KRACKOW K.A. - Management of fixed deformity at total knee arthroplasty: Fixed flexion contracture. In: HUNGERFORD D.S., KRACKOW K.A., KENNA RVTotal knee arthroplastv: A comprehensive approach, 193-201. Williams and Wilkins, Baltimore, 1984.
  9. LASKIN R.S. - Management of fixed deformity at total knee arthroplasty: Fixed varus deformity. In: HUNGERFORD D.S., KRACKOW K.A., KENNA RVTotal knee arthroplastv: A comprehensive approach, 179-192. Williams and Wilkins, Baltimore. 1984.
  10. MORELAND J.R., BASSETT L.W., HANKER G.J. - Radiographic analysis of axial alignment of the lower extremities. J. Bone Joint Surg., 69A, 745-749, 1987.
  11. MORELAND JR., THOMAS R.J., FREEMAN M.A.R. -ICLH replacement of the knee: 1977 and 1978. Clin. Orthop.. 145, 47, 1979.
  12. SCOTT R.D., THORNHILL T.S. - Press fit condylar total knee replacement. Technique Orthop., 4, 41-58, 1987.
  13. SIDLES JA, MATSEN F.A., GARBINI IL.. LARSON RV, LARSEN J.M. - Total knee arthroplasty: Functional effects of tibial resection level. Transactions of 32nd Orthopaedic Research Society. 11, 263, 1986.

3. Revision knee arthroplasty

by M.A. Jacobs


Indications for revision total knee arthroplasty include joint sepsis, component loosening, and ligamentous instability. Joint infection is diagnosed by arthrocentesis and culture. Once an infection has been diagnosed, treatment may be removal of components and a staged reimplantation. Sequential radiographic demonstration of component migration is proof of septic or aseptic component loosening. Careful history and physical examination are usually sufficient to diagnose significant ligamentous instability. Pain alone in the absence of any definable cause is not an indication for revision knee arthroplasty. It is incumbent upon the orthopaedist to clearly identify a  surgically correctable cause of the pain prior to recommending revision knee arthroplasty.

A careful preoperative plan is essential and includes evaluation of previous surgical incisions and the need for special implants or bone graft material and special instruments that will be necessary for surgery. Previous skin incisions should be used whenever possible. Parallel incisions and V-shaped incisions should be avoided. Consultation with a plastic surgeon is sometimes helpful to plan the incision. Once the knee is open, it may be necessary to increase exposure. This may be done either proximally or distally. Proximally, a Coonse-Adams patellar turndown, or a modification as described by Scott (Fig. 15-31), may be performed. The theoretical disadvantage of these maneuvers is that they may devascularize the patella and the patellar flap. An alternative is to perform a tibial tubercle osteotomy (Fig. 15-32). Potential complications relate to tibial tubercle osteosynthesis; tendon ruptures, tibial fractures, and avulsion of the tubercle are other complications of this maneuver. Although both maneuvers have potential complications, they are sometimes necessary since forcibly flexing the knee, to increase exposure, may result in patellar tendon avulsion.

Fig. 15-31. - The patellar turn-down technique will permit increased exposure of the knee.
Fig. 15-32. - a) The patellar retinaculum and capsule are incised, and a hinge osteotomy of the tibial tubercle is made.
Fig. 15-32. - b) The patella, patellar tendon, and hinged tibial tubercle are reflected laterally to increase exposure.
Fig. 15-32. - c) The hinged tibial tubercle is re-attached with a screw.
1. Prostheses; 2. Cement; 3. Medullary plug.

Removal of the components

Removal of the components that are not loose may be a difficult problem. It is essential to free all bone cement or bone-metal interfaces prior to applying a significant distraction force to the implant. Flexible osteotomes, which are much thinner than rigid osteotomes, are essential. By applying excessive distraction force to the implant, through a specialized extraction tool, the surgeon runs a significant risk of removing excessive amounts of bone. This is particularly true with components that were applied in a cementless fashion.

Reconstruction, Implants and Bone Grafting

In attempting to reconstruct the knee joint, it is necessary to consider several fundamental rules of primary knee replacement and to supplement them with several other principles. In primary total knee arthroplasty, the three fundamental principles are the creation of accurate overall knee alignment, the attainment of accurate bone cuts, and the achievement of correct ligamentous balance. In revision knee arthroplasty, the additional fundamental principle is the reconstitution of an anatomically accurate joint line which is necessary to achieve the proper function of the patient’s remaining ligaments and to avoid producing either a patella alta or a patella baja.

In some cases, this may require significant bone grafting of large defects. In other situations, special prostheses with augmentation may be necessary. Revision femoral implants are available that have augmentations both distally and posteriorly (Fig. 15-33). Augmented prostheses must be available in various sizes. These implants can be used in conjunction with bone grafting of smaller defects on the distal femur.

Significant bone loss in the proximal tibia may require implants with medial and/or lateral plateau build-up to restore tibial stock. If a shell of bone remains on which the implant can be placed, these special implants may be used in conjunction with various bone grafts to fill smaller defects within the shaft of the tibia itself. The use of massive tibial bone allografts on which the tibial component is supported has not been shown to be a satisfactory technique.

Ligamentous instability

Significant anterior-posterior instability due to ligamentous inadequacy may be present. This is particularly true when the posterior cruciate ligament and the posterior capsular structures are severely weakened. This situation may require the use of a nonhinged, stabilized prosthesis (Fig. 15-34). Several types of knee revision systems are available that incorporate these options. The selection of the correct one for each patient should be part of the surgeon’s preoperative plan.

Fig. 15-33. - Distally and posteriorly augmented femoral components are available in either (a) one-piece units or (b) modular units
Fig. 15-34. - A tibial post articulates with the femoral housing to provide anterior-posterior stability.

Ligamentous balance must be achieved in any successful knee arthroplasty. Releasing the tight side is the traditional and preferred way of achieving correct balance (Figs. 15-35 and 15-36). Rarely, it may also be necessary to advance the loose side. With extreme lateral instability, the lateral colateral ligament must be exposed to the fibular head (Fig. 15-37). A section of fibular neck may be resected and the fibular head reattached with a screw to the fibular shaft. This has the effect of tightening the fibular collateral ligament. When performing this maneuver, the peroneal nerve must be carefully isolated and protected. The need for lateral ligament advancement must be determined after the medial side has been maximally released and trial reduction with a plastic spacer has been performed.

In medial ligament laxity, the lateral side is maximally released and trial reduction is performed. If significant medial laxity still remains, the medial capsular structures are transected at the level of the pes anserinus. With the appropriate trial implants in place, the medial structures are advanced distally and fixed with staples or screws (Fig. 15-38).

Fig. 15-35. - Lateral structures which may require release or lengthening.
1. Iliotibial band; 2. Parapatellar release; 3. Lateral head of gastrocnemius; 4. Lateral collateral ligament; 5. Biceps femoris tendon; 6. Popliteus tendon.
Fig. 15-36. - The lateral collateral ligament and the popliteus tendon may be divided from the femur.
1. Lateral collateral ligament; 2. Popliteus tendon.

Fig. 15-37. - The lateral ligament may be advanced by removing a portion of the fibula distal to the fibular head (a) and securing the advanced fibular head and attached lateral collateral ligament with a screw (b).
Fig. 15-38. - Medial capsular structures are advanced and fixed with staples.
1. Prostheses; 2. Medial collateral ligament; 3. Staples.


Postoperative care

This is an important part of revision knee replacement. Because of the uniqueness and complexity of each case, therapy must be adjusted to accommodate individual variations. Patients who have huge angular deformities and significant ligamentous modifications may require postoperative bracing and may be poor candidates for continuous passive motion. Similarly, patients with distal tubercle osteotomies or patellar tendon turndowns may require other restrictions. It is incumbent upon the surgeon to communicate these specifics to the therapist.

Conclusion

In summary, revision total knee replacement is a difficult problem that requires careful preoperative planning to be certain that the proper equipment is present at the time of surgery and to minimize the actual surgical time. Great care must be taken to choose the correct skin incision and create accurate overall axial alignment. The use of specialized revision knee systems as well as judicious use of bone grafts are essential to reconstitute an accurate joint line and maximize the chance of the best possible result.

BIBLIOGRAPHY

  1. COONSE K., ADAMS J.D. - A new operative approach to the knee joint. Surg. Gvneco!. Obstet., 77. 344-347. 1943.
  2. HUNGERFORD D.S., KRACKOW K.A., KENNA RV - Total knee arthrop!asty: A comprehensive approach. Williams and Wilkins, Baltimore, 1984.
  3. INSALL J.N. - Surgery of the knee, 635-644. Churchill Livingstone, Edinburgh, 1984.
  4. JACOBS M.A, HUNGERFORD D.S., KRACKOW K.A., LENNOX D.W. - Revision of septic total knee replacement. Clin. Orthop. Rel. Res., 236, 103-110, 1988.
  5. SCOTT RD, SILISKI J.M. - The use of a modified VT quadriceps-plasty during total knee replacement to gain exposure and improve flexion in the ankylosed knee. Orthopedics. 8, 45-48, 1985.

4.  Distraction arthroplasty of the knee

by TH. JUDET


The aim of a distraction arthroplasty of the knee is to provide motion to an ankylosed knee without implant interposition.

The principles are the following: extensive arthrolysis, complete freeing of the quadriceps, contoured bony resections, a distraction apparatus that will temporarily stabilize the pseudarthrosis while maintaining the bony surfaces apart and permit early mobilization.

This operation is usually indicated for fibrous or bony ankylosis following resistant infections in young patients or in patients where the use of a prosthesis is not indicated.

Installation of the patient

The patient is supine on an ordinary table and a tourniquet is preferable.

Soft tissue surgery

The arthrolysis and freeing of the quadriceps are achieved by medial and lateral incisions.

The extensive lateral approach will permit complete dissection of the quadriceps from the anterolateral and anteromedial aspects of the entire femur.

Bony resection

The bony resection is usually performed via the medial incision using osteotomes to free the patella from the distal femur (Fig. 15-39) in order to dislocate the extensor mechanism laterally. Whenever possible, the level of the femoral and tibial resections are at the original joint line; if the latter is completely obliterated, the level of the patellar tendon insertion will serve as a reference point.

The tibial resection is usually performed first (Fig. 15-40). A straight osteotome is used to expose cancellous bone at both tibial plateaus which are contoured slightly concave in all directions to provide some stability, preserving, whenever possible, a central, sagittal ridge at the level of the former tibial spines.

Femoral resection is achieved with curved osteotomes and a Putti, curved gouge for the posterior femoral condyles, attempting to achieve an outline that resembles the original, distal femur (Fig. 15-41).

Fig. 15-39. - Bony ankylosis of the knee involving the femur, tibia and patella. Patello-femoral osteotomy via a medial arthrotomy.
Fig. 15-40. - Tibio-femoral ostotomies. Insert: amount of bony resection
Fig. 15-41. - Modelling of the neoarticular surfaces.

Eight to twelve millimeters of bone are usually resected to obtain a satisfactory range of motion. While the remains of the collateral ligamentous attachment to the tibia are spared, the cruciate ligaments are almost always sacrificed.

It is then usually preferable to release the tourniquet so as to free the quadriceps (in particular the vastus lateralis from the intertrochanteric line and the rectus femoris from the anterior, inferior iliac spine).

Complete passive knee mobilization must be obtained at the expense of instability which will be subsequently controlled by the distractor.

Distractor apparatus

Because of the changing instant centre of rotation in the knee, the apparatus has two centres of rotation (Fig. 15-42).

The surgical steps are the following (Fig. 15-43): - temporarily identify the two centres of rotation by pins in the distal femur. Two transverse pins are first inserted in the anterior and posterior portions of the femoral condyles, corresponding to the site of axes of rotation in flexion and extension;

Fig. 15-42. Schematic axes of tibio-femoral rotation.
Fig. 15-43. - Application of the distractor apparatus.

- the distractor is then constructed around these two axes;

- the femoral component is fixed to the femur via two pins inserted in the distal femoral metaphysis;

- two other pins are inserted in the tibial epiphysis, and side plates of appropriate length are then selected;

- the two pins corresponding to the future axes of rotation are then removed and the entire distractor is interconnected. Final adjustments (Fig. 15-44) in the length of the distractor plates are then made as the knee is passively mobilized, ensuring that there is always a 10 mm gap between the femur and the tibia during the full range of motion.

Fig. 15-44. - Attachment of side plates to maintain distraction during full, passive mobilization.

Postoperative care

Daily re-adjustments of the apparatus are usually necessary.

Non weight-bearing is permitted on the second week.

Removal of the distractor after 75 days is followed by gradual weight-bearing.

Physiotherapy is usually necessary for at least six months.



5.    Arthrodesis of the knee

 by K.A. KRACKOW

Preoperative consideration

There are numerous techniques to achieve a knee arthrodesis. The currently available techniques differ principally in terms of fixation and may be described as: 1) limited internal fixation and casting; 2) intramedullary rod fixation; 3) double bone plating; 4) external fixation. Each of these approaches has its advantages and disadvantages as delineated in table 15-I.

TABLE 15-I.
Fusion type
Advantages
Disadvantages
Limited internal fixation and cast
  1. Possibly smaller surgical exposure
  2. Freedom from pin tract problems
  3. Technically simple
  1. Poor stability and healing in failed total knee salvage
  2. Foreign body in case of possible infection
  3. Poor stability in obese leg
Imtramedullary rod
  1. Excellent varus-valgus and flexion-extension stability, less rotational stability
  2. Freedom from pin tract problems
  1. Technically difficult
  2. Require special rod
  3. Potential spread of infection
  4. questionable rotational stability
Double plating
  1. Freedom from external fixator and pin problems
  1. Questionable stability with poor bone stock
  2. Relative contraindication in infection
  3. Larger surgical exposure
External fixation
  1. Potential stability even with poor bone stock
  2. No permanent implant
  1. Potential pin tract problems
  2. Bulky, cumbersome and expensive apparatus

Double plating and intramedullary techniques should not be used when infection is present or suspected. In cases of primary fusion with good bone stock, limited fixation plus casting, or external fixation has been selected. In primary fusions with infection, or in total knee arthroplasty salvage situations, with or without infection, external fixation is preferable.

Operative planning

 Infection. - Planning is outlined in table 15-II. When treating a failed total knee arthroplasty, infection should always be considered, and ruled in or out, by aspiration, biopsy, and gallium scanning, so that appropriate antibiotic therapy can be instituted. When infection is present and fusion has been elected, it may be performed as a single stage procedure, or as a two stage procedure.

TABLE 15-II. - PREOPERATIVE PLANNING
  1. Infection: aspiration, biopsy, Gallium 67 scanning
  2. Axial alignment: 5-7° valgus tibiofemoral angle
  3. Rotational alignment: normal intermalleolar axis
  4. Knee flexion angle: 5-20°; consider shortening and ankle dorsiflexion
  5. Bone grafts: allograft, local, iliac crest
  6. Prosthesis extraction instruments
  7. primary total knee arthroplasty instrumentation for controlled distal femoral and proximal tibial cut.

2° Instrumentation. — Adequate instrumentation must be available for component removal in total knee arthroplasty salvage situations, especially if metal­backed tibial trays have been used. Exact knowledge of the inner surface geometry of the implant to be removed is mandatory. It is helpful to have previously discarded, representative, components present in the operating theater to refer to. Total knee replacement instrumentation may also be used to make well aligned, flat distal femoral and proximal tibial bone cuts.

3° Grafting. — Consideration must be given to bone grafting, especially in the presence of large defects.

Alignment. — Position and alignment of the arthrodesis can be described in terms of axial alignment, i.e. tibio-femoral angle, rotational alignment, and flexion angle. While no recognized clinical disadvantage is seen with minimal aberration in the tibio-femoral angle, seek to preserve a normal tibio-femoral angle of 5-7° valgus. Rotational alignment must be achieved so that the foot points normally during gait.

Various recommendations exist regarding the proper flexion angle at the arthrodesis site. Recommendations between 50 150 are common as minimal knee flexion may help when rising from a seated position and facilitate hip extension in a more normal fashion. Additionally, one must recognize that 1.5 to 2 cm of relative shortening at the operative side is necessary for the foot to clear objects on the floor and to facilitate swing of the fused leg. However, one must guard against excessive shortening.

An additional point to consider when planning flexion at the knee fusion site is the impact of fixed knee flexion on the position and kinematics of the ankle. For a patient to stand with a plantigrade foot on an extremity with the knee fused requires that the ankle dorsiflexe. Furthermore, as the patient steps forward on the opposite foot, ankle dorsiflexion on the operative side must increase further.

Surgical technique

1° Rotational alignment. — Prior to surgical exposure, it is desirable to identify reference points for both femoral and tibial rotational alignment.

2°Femur. - In cases of primary knee fusion without pre-existing femoral malrotation, the axis formed by the posterior femoral condyles can be used to define neutral rotation (Fig. 15-45).

Where femoral malrotation exists, this should be assessed preoperatively whenever possible, so that appropriate compensation can be made. A CT scan of both femurs can be used to establish malrotation of the operative side in comparison to the normal rotation of the contralateral extremity (Fig. 15-46).

3° Tibia. — The apparent rotation of the tibia should be evaluated in terms of general appearance, the orientation of the foot, and the position of the intramalleolar axis (Fig. 15-47 a and b).

The axes of femoral and tibial rotation are identified before the joint surfaces are excised, so that rotational alignment of the entire lower extremity is correct (Figs. 15-46 and 15-47).

4° Exposure. - Preexisting incisions are used when possible. If none are present, or if only a transverse one is present, a midline, longitudinal exposure is used (Fig. 15-48).

The capsular incision is made longitudinally in the quadriceps tendon, then extended in a routine medial parapatellar fashion (Fig. 15-49).

Fig. 15-45. - End-on view of distal femur.
1. Trochlear grove; 2. Axis of neutral rotation; 3. Medial femoral condyle; 4. Axis of posterior femoral condyles; 5. Lateral femoral condyle.
Fig. 15-46. - a) Normally rotated femur: 3. Medial femoral condyle; 4. Transcondylar axis in neutral rotation; 5. Lateral femoral condyle.
Fig. 15-47. - a) and b) Tibial joint surface from above.
1. Tibial tubercle (slightly lateral to mid-center line); 2. Axis of neutral tibial rotation; 3. Fibular head; 4. Medial and lateral malleolus; 5. Intermalleolar axis.
Fig. 15-48. - Skin incisions.
Fig. 15-49. - Capsular incision.

Exposure of the joint surfaces is not difficult unless massive intra-articular adhesions are present. Mobilization of tissues anteromedially and anterolaterally over the femur is necessary if flexion of the knee is to be achieved.

If one is dealing with an ankylosed knee in good position for fusion, the distal femur and proximal tibial joint surfaces are excised parallel to one another and the fixation is applied, holding the knee in the desired position.

Most commonly, extensive exposure is necessary. The patellar tendon is elevated from the tibial tuberosity if necessary, and dissection is extended between the quadriceps mechanism and the anteromedial as well as the anterolateral aspects of the femur to allow knee flexion. Thickened, scarred tissue is removed to facilitate eversion of the patella.

When 90° of flexion has been achieved, a 1/8” Steinmann pin is placed transversely across the distal femur, oriented in neutral femoral rotation (Fig. 15-50) and at 90° to the vertical axis (Fig. 15-51) or, if possible, at an angle, relative to the femoral shaft that corresponds to the orientation (varus-valgus) of the planned distal femoral cut (Fig. 15-51). Utilizing the Universal Total Knee Instruments the distal femoral cut is at a 9° valgus angle (81° complementary angle), when the tibial cut is at an angle of 3° varus, for a final tibio-femoral angle of 6° valgus (Fig. 15-52). With a perpendicular tibial cut, a distal femoral cut of approximately 6° valgus (84° complementary angle) will be necessary.

A 1/8” tibial rotation pin is placed in neutral rotation at an angle corresponding to the angle of the tibial cut (either 3° varus or perpendicular, according to whether the femoral cut is to be 9° valgus or 6° valgus) (Fig. 15-53). When a cemented tibial component blocks the placement of this pin, the pin is inserted after component removal.

Fig. 15-50. - Guide pin as reference for femoral bone cut.
1. 1/8" Steinmann pin; 2. Axis of neutral femoral rotation (transverse axis).
Fig. 15-51. Different femoral and tibial cuts to achieve proper anatomical axis:
1. Femoral shaft axis; 2. Femoral pin (transverse axis) (neutral rotation and 90° to vertical axis).
Fig. 15-52. Angle of femoral and tibial cuts resulting in an anatomical axis of 6° valgus. Femoral and tibial cuts in relation to femoral and tibial shaft axes. In relation to the vertical axis, the femoral cut is in 9° of valgus and the tibial cut is in 3° of varus. Hence, a tibio-femoral axis of 6° of valgus.
Fig. 15-53. - Angle of femoral cut to achieve 6° of valgus when tibia is cuts at 90°. Tibial cut at 90° to tibial shaft axis. The femoral cut is then at 84° to the femoral shaft axis and the anatomical axis of the knee is in 6° of valgus.

When the indication for fusion is a failed total knee arthroplasty, the femoral and tibial components are removed sequentially being careful to preserve as much bone as possible. Total knee arthroplasty instruments may be used to align and facilitate the performance of accurate, flat distal femoral and proximal tibial bone cuts. The femoral instrument is placed in neutral rotation according to the femoral rotational pin and is adjusted to be neutral or in the desired degree of flexion for the femoral cut. A flat, well aligned distal resection is made with a reciprocating saw (Fig. 15-54).

Similarly, a transverse proximal tibial cut is made with total knee replacement instruments positioned in neutral rotation and with the desired degree of anterior to posterior slope so that when the femoral and tibial surfaces are approximated, the desired total amount of flexion will be achieved (Fig. 15-54).

The joint excision space is examined as the surfaces are temporarily apposed to assess the accuracy of contact and fit (Fig. 15-55). After total knee arthroplasty, especially after revision total knee arthroplasty, it is frequently necessary to elevate soft tissues from the posteromedial, posterolateral, and posterior tibial cortex to allow the cut surfaces of the femur and tibia to approximate (Fig. 15-56 a and b).

This maneuver is necessary due to a blocking effect of the bulging soft tissue sleeve. The peripheral displacement of this sleeve is impeded by its attachment to the cortices at the resection level.

Attention is next directed to the patella, which may either be: 1) excised and discarded; 2) excised and morcelized as bone graft; 3) left attached and incorporated into the fusion area. The patella should not be left free as patellofemoral symptoms can develop. It is possible to leave the patella attached to the lateral soft tissues and to fix it to the fusion site as a vascularized bone graft utilizing a lag screw (Fig. 15-57). However, this technique requires pulling the patella distally and can make wound closure more difficult.

Fig. 15-54. - a) Neutral distal cut. 1. Plane of neutral cut. b) Distal cut flexed 5°. 2. Plane of 5° cut.
Fig. 15-55. - Verification of accuracy of bone cuts for optimal contact and correct alignment.
Fig. 15-56. - a) Bone approximation impaired by redundant capsular-ligamentous sleeve.
b) Soft tissues stipped away from tibia to allow bone approximation.
1. Site of soft tissue elevation
Fig. 15-57. - Patella fixed across fusion site.

Fixation

1° Limited internal fixation plus cast. - In the case of primary fusion with good bone stock and a very “castable” lower extremity, the femoral and tibial surfaces are apposed, being certain to align the femoral and tibial rotational pins parallel to one another. The bones are internally fixed with lag screws. Bone grafting is performed if desired; the patella is handled according to the surgeon’s preference and the wound is closed. A cylinder cast is carefully applied.

2° External fixation. - Before inserting the external fixator pins, the femoral and tibial rotational pins are removed and replaced transcutaneously so that wound edge approximation is possible with these rotational pins in place. It is convenient to substitute 7/64” Steinmann pins at this stage as they will easily pass through the previously drilled pin tracks.

To avoid tension at the skin puncture sites of the external fixator pins, the wound edges are temporarily approximated with towel clips, before repositioning the femoral and tibial rotation pins.

Femoral transfixion pins are generally placed from medial to lateral for maximal control on the side of the femoral artery. Tibial pins are generally placed from lateral to medial similarly to have maximum control with respect to the peroneal nerve. In cases of severe bone loss, where conical bone ends exist at the distal femur and/or proximal tibia, the transfixion pins are situated farther away from the arthrodesis site to provide greater stability. In extreme cases, safe positioning of proximal, femoral pins may require exposure of the femoral artery.

Medial to lateral transfixion pins provide excellent stability against varus-valgus stress, but poor stability against flexion and extension and anterior “half pins” may be used. At least two femoral and two tibial half pins are placed through the anterior and posterior cortices. A lateral intraoperative X-ray is taken to be certain that these half pins do not protrude beyond the posterior cortex.

The external fixator frame is assembled taking care to keep the femoral and tibial sets of transfixion pins parallel to one another in the rotational axis, while the femoral and tibial bone surfaces are approximated. The bone cuts themselves guide the amount of flexion and the varus-valgus alignment. The parallel transfixion pins assure proper rotation of the tibia with respect to the femur and correct varus-valgus alignment.

Bone grafting

Except for patellar cortico-cancellous bone, the author does not routinely add a bone graft in noninfected cases. However, substantial pieces of iliac crest can be used peripherally to establish cortical continuity or improve mechanical stability. The use of large autogenous bone grafts into vacuous tibial and/or femoral spaces should be avoided. When central cancellous bone is largely or totally absent, morsalized bone grafts are also placed peripherally (Fig. 15-58).

Fig. 15-58. - Peripheral bone grafting in the presence of central bony defects.
1. Femur; 2. Defect; 3. Bone graft peripherally; 4. Tibia.

Patella

The patella is dealt with last, either removing it as bone graft material, removing and discarding it, or fixing it to the distal femur over the level of fusion.

Wound closure

Wounds have been successfully closed primarily in the presence of infection. Closure is performed after thorough debridment with complete removal of all components, cement, and old suture material. Where radio-opaque cement has been implanted, an intra­operative X-ray is taken to document that the cement has been completly removed.

Wound closure, except in cases of primary fusion, may be difficult. This is due to the tissue bulging effect mentioned earlier. Minimal, buried suture material is used only at the capsular level. Absorbable chromic or polyglycolic acid materials are employed. Meticulous skin closure with interrupted nylon is performed, utilizing retention sutures since no subcutaneous or subderrnal sutures are inserted.

Postoperative care

For routine, noninfected cases, prophylactic intravenous antibiotics, i.e. penicillinase resistant penicillins or cephalosporins, are continued for 48 hours. In cases which are presumably infected after failed total knee arthroplasties, antibiotics are continued longer until the peroperative cultures show no growth.

If the operative culture reveals infection, or when dealing with a known infection, parenteral antibiotics are continued for three to six weeks according to the severity of infection, and the “nature” of the infected organism. Oral antibiotics are continued for another three months.

Pin care is routine, with once or twice daily cleansing of pin sites, utilizing hydrogen peroxide or saline, followed by the application of bacitracin antibiotic ointment. Iodine containing solutions or ointments should be avoided. Local pin tract infections are usually successfully treated by short courses of oral antibiotics.

Weight-bearing and immobilization

The postoperative weight-bearing status depends upon the type of fixation as well as the bone quality and stability at the fusion site. Patients with limited internal fixation and casts are not allowed to bear weight for one to three months, followed by progressive weight-bearing for the next two to three months with cast removal at 4-6 months once union is demonstrated.

Conclusion

While conceptually, a simple and basic orthopaedic procedure, knee arthrodesis may be quite difficult due to exposure problems, implant removal, preparation of a satisfactory fusion site and achievement of stable fixation in excellent position.