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| DURACON® TOTAL KNEE SYSTEM |

Using Monogram® Knee Instruments*
Surgical Technique

The following surgeons have contributed extensively to surgical techniques associated with Duracon prostheses and Monogram instrumentation:

Lester S. Borden, MD
Head of Adult Reconstructive Surgery
Cleveland Clinic Foundation, Cleveland, OH

Edward T. Habermarin, MD
Professor and Chairman
Department of Orthopaedic Surgery
Albert Einstein College of Medicine
Orthopaedic Surgeon-in-Chief
Montefiore Medical Center
Albert Einstein College of Medicine, Bronx, NY

Anthony K. Hedley, MD, FRCS
Chairman, Department of Orthopaedic Surgery
St. Luke's Medical Center, Phoenix, AZ

David S. Hungerford,  M.D.
Chief, Division of Arthritis Surgery
Professor of Orthopaedic Surgery
Johns Hopkins University, Baltimore, MD
Chief of Orthopaedic Surgery
Good Samaritan Hospital Baltimore, MD

Kenneth A. Krackow, M.D.
Professor of Orthopaedic Surgery
State University of New York at Buffalo
Department Head
Department of Orthopaedic Surgery
Buffalo General Hospital, Buffalo, NY

This publication sets forth procedural highlights for using Howmedica devices and instruments. It offers guidance that you should heed, but, as with any such technical guide, each surgeon must consider the particular needs of each patient and make appropriate adjustments when and as required. The surgeon can refer to other Duracon publications for a more detailed description of the surgical technique. Some of these references include:

6640-0-011 Tibial Components Using Monogram Total Knee Instruments.

6640-1-l05 Duracon Primary Femoral and Patellar Components (with Stabilizer Box Option) Using Monogram Total Knee Instruments.

US Patent Nos, 4,550,448; 4,646,729; 4,653,488; 4,668,290; 4,714,468; 4,787,383; 4,825,857; 4,834,756; 4,944,756; 5,035,71)0; 5,192,324; 5,441,537; 5,541947; and US Design Patent Not. 273,894-95; 274,(NU-95; 274,161-62. Other Parents Pending.


| INTRODUCTION |

The goal of the Duracon® Total Knee System is to enhance durability and minimize polyethylene wear through articular conformity and balanced patellofemoral tracking. By increasing the conformity and contact between femorotibial and patellofemoral articulating surfaces, point contact stresses generally associated with accelerated wear are reduced. And by achieving balanced, stable anatomic tracking and normalized quadriceps and patellar tendon tension, stresses that may also lead to accelerated wear are reduced.

While implant design is critical, it is widely established that instrumentation plays an important role in the success of knee arthroplasty. To this end, Howmedica has developed the Monogram® Knee Instrument System.

  • The Monogram Knee Instruments are a hallmark series of instruments which allow surgeons to customize total knee surgery to their preferences.
  • The Monogram Knee Instruments and the design of the Duracon components work together to assure compatibility and ease of transition throughout the range of total knee arthroplasty cases: primary, stabilizer, and revision.
  • The Monogram Knee Instruments promote accuracy efficiency, and reproducibility.

The following pages present highlights of the Duracon surgical technique, incorporating the Monogram instrumentation and the Duracon components.


| FEMORAL PREPARATION |

Orientation of the Central Drill Hole

The intercondylar drill guide and stepped drill are used to make the initial intercondylar hole in the distal femur for the distal femoral alignment guide and intramedullary rod (Figure 1). The hole should be placed approximately 0.5cm to 1cm anterior to the origin of the posterior cruciate ligament.

Using the Distal Femoral Alignment Guide

The intramedullary bushing is set for right or left knee at the preoperatively determined valgus position. The locking knob is tightened. The IM rod is slid into the bushing, and the assembly is placed on the distal femur.

The axial alignment tower and long alignment pin are attached to the guide, and used to verify the position of the distal femoral alignment guide relative to flexion/extension, varus/valgus, and rotation (Figure 2).

Positioning the Cutting Jig

The cutting jig is positioned on the distal alignment guide at the 10mm resection level for most sizes. The cutting jig should be set at the 12mm mark for the XL and XXL components. The jig is secured with two 1/8" drill pins through the holes marked "STD" (Figure 3).

The distal femoral cutting jig permits +2mm incremental adjustment. It has additional sets of drill holes for smaller bones. It also provides a drill hole marked "X" into which a drill pin can be placed to stabilize the jig (Figure 4).

The distal femoral cut can be made on the surface of the open cutting jig or, alternatively, through the slots of the slotted cutting jig (Figure 5).

Femoral Component Alignment

After confirming correct medial/lateral and rotational orientation of the femoral positioning jig, the fixation pins are impacted (Figure 6).

For a neutral femoral cut, the neutral drill guide bushing is inserted into the femoral positioning jig, and the 3/16" holes drilled with a stepped drill (Figure 7a).

For a 3° externally rotated femoral cut, the 3° drill guide bushing is placed into the femoral positioning jig with the word "left" or "right" indicating the operative limb, facing the surgeon (Figure 7b).

Femoral Component Sizing

The femoral marking stylus placed on the femoral positioning jig references the prominent aspect of the anterior cortex.

The edge of the marking stylus identifies the appropriate size of the femoral component. In this example, a medium component is indicated (Figure 8).

If the marking stylus indicator points to a scribe line, the next larger block should be used to avoid notching the anterior cortex.

NOTE: The marking stylus should only be used in anatomic alignment, not with classical alignment.

To determine the final component sizing, use the femoral reference gauge. The gauge is placed in the two 3/16" fixation holes previously made. Slide the femoral sizing indicator or a .050" thick blade through the slot(s) to choose the best femoral component size (Figure 9).

A/P and Chamfer Bone Cuts

NOTE: All cuts made with the slotted blocks are done with a .050" Howmedica sawblade. The block handles can be removed.

The Monogram® Instruments provide three options for making the final femoral preparation.


OPTION A - Ceramic Blocks

The ceramic cutting blocks are designed to reduce blade-to-block contact area. The combination of ceramic rails and reduced contact area minimizes heat generation,+ provides for extremely accurate cutting, and offers the potential for reduced intraoperative wear debris. These blocks are available in both open and slotted styles.

With the impactor in place, impact the ceramic femoral cutting block #1 into the previously made holes in the distal femur. The impactor is removed and the sawblade is guided along the rails of ceramic cutting block #1 to complete the anterior chamfer cut and the resection of the posterior condyles (Figure 10).

+Data on file at Howmedica Osteonics.

Ceramic femoral cutting block #2 is impacted onto the cut femur. The previous cuts are visually checked for accuracy. The anterior resection is made first on block #2. The posterior chamfer is then resected (Figure 11).


OPTION B - ABCTM Blocks

The ABCTM cutting blocks and corresponding chamfer blocks provide a unique method for making the four final femoral cuts, utilizing surface blocks or "captures." The blocks can be used with or without the capture mechanism. (Capture mechanisms are not shown above.)

The chamfer cutting block is used first. The A/P block is used next. Both blocks are impacted into the holes previously made on the distal femur before making the appropriate cuts (Figure 12).

Planers are also available.


OPTION C - 4-in-1 Blocks

The slotted 4-in-1 blocks provide a quick, guided mechanism through which all four cuts can be made. The 4-in-1 block is impacted into the previously made holes on the distal femur. Drill pins can be used for additional stability. The cutting sequence begins with the A/P cuts. The chamfer cuts are made last (Figure 13).

Stabilizer Preparation (Optional)

If a Duracon Stabilizer is to be used, the surgical technique is identical to that of the primary component with the following simple, final bone preparation steps. Place the appropriate sized box guide on the distal femur in the previously prepared holes. Use a 1/4" or 1/2" osteotome or .050" Howmedica sawblade to make the initial square cut. Then use the box chisel to finish the preparation (Figure 14).

If using a Modular Stabilizer component, the stepped drill finishes the distal holes to make room for the screws on the modular box (Figure 15).


TIBIAL PREPARATION

Positioning the Tibial Alignment Jig

There are two options for the tibia: extramedullary referencing alignment and intramedullary alignment.


OPTION A - Extramedullary Referencing

The proximal tibial cutting assembly has two parts: the ankle clamp and the proximal alignment guide. These are assembled first (Figure 18). Then the tibial cutting jig is positioned over the thin section of the proximal guide assembly shaft slid proximally, and locked into position (Figure 16).

The system offers a O° and a 2.5° tibial cutting jig. If a 3° externally rotated femoral cut was made, the O° tibial cutting jig should be used; or, if the neutral femoral cut was made, the 2.5° tibial cutting jig should be used.

The cutting jig, available in left and right configurations, is designed to avoid soft tissue impingement (Figure 17).

Flexion/Extension Alignment

The long fixation pin of the proximal alignment guide is partially seated in the proximal tibia to stabilize the assembly.

Flexion I extension alignment is correct when the long axis of the assembly parallels the midcoronal plane of the tibia. Flexion I extension alignment can be further confirmed by seeing that the long axis of the assembly is parallel to the fibula. Distal locking knob "A" is then tightened (Figure 18).

Rotational Alignment

With flexion/extension alignment defined, rotational alignment is now established. Rotate the entire assembly so that a 1/8" drill pin placed in the medial anterior pin hole of the ankle clamp is parallel to the plane of the malleoli, oriented 25° to the coronal plane (Figure 19).

Medial/Lateral Alignment

Medial/lateral offset can be adjusted using distal locking knob "B" (Figure 20). The assembly is slid medially until the jig shaft intersects the center of the tibia.

Once triaxial alignment is achieved, fully tighten the midshaft locking knob. Fix the whole assembly in place by striking the proxirnal end of the alignment rod with a mallet securing the two fixation pins.


OPTION B - Intramedullary Referencing

A 5/16" hole is drilled in the location determined by the preoperative X-rays (Figure 21).

Slowly pass the N rod into the canal, clearing the canal. Remove the rod then reinsert it into the body of the N alignment jig. The assembly is then inserted into the canal and the N rod is passed into the canal until the isthmus is engaged (Figure 22).

Rotational Alignment

With the body of the IM jig resting on the proximal tibia, proper rotational alignment is achieved by rotating the instrument about the IM rod so that the tibial tubercle appears slightly lateral to the vertical mounting bar. The headed nail is impacted, fixing rotational alignment (Figure 23).

Varus/Val gus Alignment

Assemble the appropriate tibial cutting jig (left or right) onto the mounting bar, and lightly tighten the locking knob on the face of the cutting jig. Attach the alignment handle to the cutting jig, and slide a long alignment pin through the neutral tibial "NT" alignment hole. When varus/valgus alignment is correct the pin should be centered over the ankle.

If varus/valgus adjustment is needed, locking knob "1" is loosened. The mounting bar is pulled toward the surgeon, and the jig is rotated until proper varus/valgus orientation is achieved (Figure 24). Once the alignment pin is centered over the ankle, the locking knob is securely tightened.

Flexion/Extension Alignment

If additional posterior slope is required (keeping in mind that all tibial cutting jigs incorporate a 3° posterior slope), loosen locking knob "2" and set the appropriate level of slope. Once the correct slope is attained, securely tighten locking knob "2" to set the final position of the jig (Figure 25).


Fixing the Depth of the Tibial Cut
[The following applies to both extramedullary and intramedullary alignment.]

The tibial marking stylus attaches to the tibial cutting jig, with the "9mm" end referencing the lowest level of the rnidplateau on the unaffected compartment (Figure 26). 9mm of bone will be resected. Altematively if the 0mm end of the tibial marking stylus is used, the amount of bone resected will be in line with the tip of the stylus.

Two 1/8" drill pins are placed into the "N" [neutral] holes, fixing the level of the tibial cutting jig. The extramedullary ankle clamp and proximal alignment guide or the IM rod and the intramedullary alignment jig are removed, leaving the cuffing jig in place. If additional stability of the jig is required, utilize the oblique "X" hole.

Cutting the Proximal Tibia

Resection of the proximal tibia is now completed (Figure 27). The pin puller is then used to remove the tibial cutting jig.

Select the appropriate size tibial template, and lock it onto the tibial alignment handle. The short posterior tabs on the tibial template help stabilize the template at the posterior cortical surface (Figure 28).

Verifying Alignment

The alignment handle verifies rotational, varus/valgus, and flexion/extension alignment (Figure 29). Rotational alignment is correct when the drill bit placed in a hole from the previous step parallels the handle (Figure 30). Varus/valgus and flexion/extension alignment are verified with a long alignrnent pin.

Holes are located on the anterior face and the posterior surface of the template. Headed nails or drills through these holes may be used to temporarily fix the template.


TRIAL REDUCTION

The proximal tibial template accepts the trial inserts for an open trial reduction. The alignment handle may be left in place and utilized for an open trial reduction, or the handle may be removed to allow the template to serve as a trial for a closed trial reduction. Trial baseplates are also available when the scenario dictates their use.

With the knee in 90° of flexion, the appropriate tibial trial insert is carefully inserted into the proximal tibial template. Forcing the trial spacer into place can cause it to break. The trial femoral component is carefully impacted onto the distal femur

With the femoral trial component fully seated, the knee is carefully extended, noting medial and lateral stability as well as overall alignment in the A/P and M/L planes (Figure 31).

When trial reduction has been completed, the femoral prosthesis finishing holes are drilled through the trial component with a 5/16" stepped drill (Figure 32).

NOTE: Trials are available for add-on components (Wedges, Stem Extenders, etc.), if required.


IMPLANT DESCRIPTION

Femoral Components

There are several types of Duracon® femoral components:

  • Standard Monolithic: Beaded and Non-Beaded
  • Modular (pegs): Beaded and Non-Beaded
  • Modular Stabilizer: Beaded and Non-Beaded
  • Standard Monolithic Stabilizer
  • Stemmed Monolithic Stabilizer

Spacers and Stem Extenders are also available for use with the appropriate femoral components.

Patellar Components

Both metal-backed and all-plastic Asymmetric resurfacing patellae are part of the Duracon System. An all-plastic Symmetric Patella for resurfacing and insetting applications is also available. A bone-sparing Inset Patella without pegs is an additional option (used with the Patellar Milling Instrumentation).

Tibial Components

There are two metal Baseplate designs: Universal and Cruciform. Both designs have beaded and non-beaded styles.

Inserts of the A/P Lipped and Condylar styles work with both the Universal and Cruciform Baseplates. The Stabilizer Inserts are used only with the Universal Baseplate. An all-plastic Symmetric Tibial Component is included in the system.

Stem Extenders and Tibial Wedges are also available. Stem Extenders work only with the Universal Baseplates.

Cancellous bone screws can be used with the Universal Baseplate.


FINAL BONE PREPARATION

Howmedica® Universal Baseplate

The stem punch guide is placed in the corresponding locking holes in the tibial template (Figure 33a). Attach the stem punch to the sliding hammer assembly. The stem punch fits into the cutout on the guide.

During insertion/impaction, the stem punch must be maintained perpendicular to the resected surface. Slowly impact the stem punch to allow expansion of the bone (Figure 33b).

The Universal stem punch plunger is inserted into the hole of the stem punch. Impaction of the plunger creates a bone plug at the stem tip (Figure 34).

Duracon® Cruciform Baseplate

The Cruciform template, punch guide, and stem punch are used as described in "Universal Baseplate" (Figure 35). (The Cruciform Instruments are not the same catalog numbers as the Universal Instruments.)

The Cruciform Baseplate has no stem plug plunger.

Duracon® A/P Lipped All-Plastic Tibial Component

The tibia must first be prepared to accept the Universal Baseplate (Figures 33a, 33b, and 34) prior to preparation for the All-Plastic Component.

The all-polyethylene stem compactor is used to enlarge the cutout for the stem (Figure 36). Alignment perpendicular to the cut tibia must be maintained. This provides space for a cement mantle around the stem.

Tibial Stem Extenders Optional)

The stem reamer guide is placed onto the Universal tibial template after preparation for the primary stem. The distal locking knob is tightened, securing the assembly (Figure 37).

Fix the reamer guide assembly to the tibial template, and ream with the bushing in place to the proper depth (Figure 38).

TECHNICAL HINT: When a situation calls for a Stem Extender, especially the 155mm length, it is recommended to use only the neutral (0°) tibial cutting jig.


Tibial Bone Wedges (Optional)

The wedge drill guide is attached by tightening the locking knob to the anterior face of the tibial template. Two 1/8" drill bits are placed through the guide. The tibial wedge cutting jig is then placed on the 1/8" drill bits.

The tibial wedge cutting jig allows accurate defect resection to provide full bony contact for the configured component (Figure 39).

The tibial wedge cutting jig offers four options: a 12° or 24° angled wedge resection, and a 5mm or 10mm flat wedge resection (Figure 40).


PATELLAR PREPARATION

NOTE: Patellar Milling Instruments are also available. Please refer to surgical technique #6640-1-125. The following technique refers only to resurfacing preparation

Remove all osteophytes and synovial insertions around the patella, and measure thickness using a caliper. After determining the depth of the cut with a caliper, affix the stylus in the appropriate slot to the patellar resection guide, and capture the patella between the jaws of the saw guide. Using a .050" Howmedica sawblade, resect the patella (Figure 41).

Center the chosen patellar drill guide over the patella with the handle perpendicular to the trochlear groove. Drill three fixation holes with the appropriate stepped drill (Figure 42).


IMPLANTATION

Implantation of the Metal Tibial Component

If utilized, Stem Extenders are screwed and tightened on the Baseplate with the wrench instruments and are torqued to 60-80in/lb; Wedges are cemented to the Baseplate.

Lock the "feet" of the tibial impactor under the posterior lip of the component.

Turn the wing nut clockwise to secure the anterior lock.

Use the driver to impact the component. Ensure that the undersurface of the component always remains parallel to the cut surface of the tibia during insertion (Figure 43).

If implanting the baseplate with 6.2mm cancellous screws, use a 1/8" drill bit and drill guide to create the pilot holes (Figure 44a). Insert four screws of a preoperatively determined length (Figure 44b). Clear excess cement.

Assembly of the Plastic Insert

NOTE: Once assembled onto the Baseplate, the insert cannot be removed and reassembled. One-time use only! To properly assemble the Tibial Insert to the Baseplate, the Insert must be slid fully posterior into the two posterior pockets of the Baseplate before attempting to snap down the anterior portion of the Insert (Figure 45a).

When the Insert is slid fully posterior, snap down the anterior locking tab by applying thumb pressure, or by light impaction with the tibial insert impactor (Figure 45b). Make certain that pressure is applied in a distal-posterior direction. Once properly assembled to the Baseplate, the Insert should not be removed and reseated.

When using the Stabilizer Insert, the locking screw must be tightened to 60-80in-lb of torque after the plastic insert has been snapped into the baseplate.

Insert and hand tighten the screw using the adaptor handle and the 4mm locking screw adaptor (Figure 46a). Final tightening torque can be applied two ways: when using the T-handled torque wrench (Figure 46b), torque is applied in a clockwise direction until a definitive drop in resistance is felt signifying the pre-set torque level has been reached (between 60 and 80in-lb). When using the Cantilever torque wrench (Figure 46c), apply tightening torque until the indicator reads between 60 and 80in-lb. The baseplate counter-wrench should be used with both methods to apply an opposing force during tightening.

Failure to tighten locking screw to 60-80in-lb may result in screw loosening.

Implantation of the All-Plastic Tibial Component

Use the designated impactor to seat the All-Plastic Tibial Component (Figure 47).

Implantation of the Femoral Component

Modular Spacers, Stabilizer Boxes, and/or Stem Extenders are secured with fixation pegs or screws.

When using Modular Femoral Components, prior to implantation, the modular fixation pegs or screws must be tightened to the recommended torque of 60in-lb minimum to 80in-lb maximum.

The femoral impactor guides the femoral component and ensures proper placement (Figure 48).

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| FEMORAL PREPARATION |