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Knee Fusion for Irretrievably Failed Total Knee Replacement

Jerome D. Wiedel, M.D.

Over the past 30 years, the increasing success of total knee arthroplasty has gradually replaced arthrodesis as the procedure of choice in most conditions causing severe joint destruction. Instead of a primary procedure, arthrodesis is now considered a salvage procedure relegated to cases where total knee replacement may he contraindicated, e.g. sepsis, neuropathic joint, and youth, or for an irretrievably failed total knee replacement (3,8,9).

Considering all causes of total knee replacement failure, infection is the most common indication for knee fusion (3,4,9). In a small number of cases, the infected arthroplasty may he salvaged by debridement and long-term antibiotics, either retaining the original prosthesis, or removal, and later performing a second prosthetic arthroplasty. The chances of succeeding with this technique may be very slim, at best. The success reported for salvage of infected total hip replacements has not been duplicated for the infected total knee replacement.

Failures of total knee replacement on the basis of aseptic loosening, instability, fractures, and prosthetic wear or breakage are usually managed satisfactorily by a revision arthroplasty. The purpose of this chapter is to discuss the indications and techniques for arthrodesis after a failed total knee, including some of the difficulties and pitfalls as well as alternatives to fusion.

Indications

Although this chapter addresses "irretrievably failed" total knee replacements which by definition preclude further consideration of total knee arthroplasty, when considering knee fusion in the context of failed arthroplasty, it is appropriate first to consider failed total knee replacements in general.

Whenever the orthopaedist faces a failed total knee replacement, the most common considerations are first revision surgery and second salvage fusion. In planning for such a situation, great consideration must be given not only the upcoming operation, but also to that procedure which would follow if the NEXT one failed also.

With an eye toward fusion as the end stage operation, the basic requirements for satisfactory fusion must be kept in mind. First, adequate bone stock must be present in order for there to be satisfactory likelihood of healing. Secondly, excessive shortening, as a result of repeated resection of distal femur and proximal tibia, should be avoided to the extent possible. While most modern prostheses used for primary total knee replacement fulfill the general conditions of minimal bone resection, many of these prostheses used for revision surgery with bulky stems with or without housings do not fulfill these requirements.

The basic concern is that leading a patient down a path of multiple unsuccessful arthroplasties may well leave him with an unsalvageable limb and inevitable amputation when earlier more prudent acceptance of knee fusion would have preserved lower limb function. The success of obtaining a fusion after total knee replacement differs significantly when comparing failed nonconstrained prostheses (80%) with failed hinges (35%)(3). Success rates as low as 21% have been reported for attempted fusion upon removal of hinged prostheses (7).

Other factors have to be considered when choosing between revision arthroplasty or arthrodesis: the patient's age, medical status, activity level, the basic disease process and the condition of other joints, particularly the hips and contralateral knee. We are not particularly concerned about revision arthroplasty that will still allow preservation of sufficient bone stock for subsequent arthrodesis. However, revision arthroplasty that would require the use of a bulky stemmed prosthesis which, if failed, would not allow a salvage procedure short of probable amputation, must be considered only under dire circumstances. Furthermore, we are not, at this time, considering the failed, infected total knee replacement.

With this in mind, the younger and more active patient with a normal life expectancy and with reasonably good neighboring joints should be considered more strongly for an arthrodesis. On the other band, if the patient is quite elderly and debilitated, an arthrodesis may be impractical, making revision arthroplasty the procedure of choice. Similarly, patients with rheumatoid arthritis and multiple joint involvement tolerate knee fusions poorly.

The patient with a contralateral knee fusion presents a particularly difficult problem. If one were to fuse the ipsilateral knee, a situation may be created whereby the patient completely loses the ability to transfer from sitting to standing positions. This situation most likely will exist in the patient with polyarthropathy where the upper extremities are so severely involved that they cannot be used to assist in transfer. If faced with this situation, every effort should be made to avoid an arthrodesis.

Resection arthroplasty should be considered as an alternative to knee fusion which should be considered when faced with the patient who is very inactive and severely disabled. Consideration of this alternative may be especially appropriate if the patient has multiple joint involvement.

Resection arthroplasty can provide some flexion, allowing a patient to sit in a more comfortable and convenient position as well as providing extension for standing. Although the resection arthroplasty alone may not be stable enough for weightbearing, external brace support can be an acceptable method of controlling instability for the purpose of walking.

If the patient finds the resection arthroplasty unsatisfactory because of instability or pain, an arthrodesis can still be attempted. Furthermore, delaying an arthrodesis may be advantageous if infection is present and not well controlled or if the patient is not mentally prepared for a knee fusion.

Basically, the main indications for performing an arthrodesis after an irretrievably failed total knee replacement is to provide a stable, pain-free extremity particularly in the ambulatory patient.

Surgical Techniques

There have been many operative techniques described for arthrodesis of the knee joint (2, 5, 6, 11-15, 17, 18). Methods that lend themselves to usage after total knee replacement failure are compression arthrodesis, either external or internal, and intramedullary nail fixation.

External compression arthrodesis remains the most commonly used procedure and has been reportedly more successful than other methods (3, 19). The success of arthrodesis depends mainly on two factors: apposition of large congruent trabecular surfaces and rigid fixation. The former, no doubt, is the most important, which accounts for the success of primary arthrodesis when little, if any, fixation is used. Unfortunately, this situation rarely exists after a failed total knee replacement. Therefore, rigid fixation becomes even more important.

Figure 18.1. (A) infected total knee arthroplasty. (B) Twelve weeks after removal of prosthesis and application of external compression device. (C) Fusion at 16 weeks. Figure 18.2. (A) Infected stemmed prosthesis. (B) Failed fusion after removal of prosthesis and attempted external compression arthrodesis.

The patterns of femoral and tibial surfaces remaining after preparation for different types of prostheses varies significantly (10). Resurfacing prostheses without large pegs or stems will leave the greatest surface area, (Fig. 18.1, A-C), while the bulky prostheses with large central stems or pegs substantially diminish the remaining area (Fig. 18.2, A and B).

Other factors further reducing this area include osteoporosis and subchondral cysts, anchoring holes drilled for cement fixation, and further erosions of bone at the bone cement interface in loosened prostheses. All of these circumstances clearly emphasize the importance of choosing a primary or revision prosthesis which requires minimal bone resection to optimize the chances of performing a successful salvage procedure, whether it be a revision prosthetic arthroplasty or arthrodesis.

Two situations may exist which require special attention and modification of arthrodesis techniques: severe osteoporosis and bone loss. Both of these situations create a particular problem in gaining rigid fixation: osteoporosis, because of the difficulty in gaining rigid bone purchase of the fixation device, and bone loss, because of the residual small, irregular bony surfaces. Obtaining rigid fixation in all planes is even more critical in these situations than when the bone is of good quality and when large congruent surfaces are present.
Figure 18.3. Standard quadralateral external fixation device.
 Figure 18.4.  (A and B) Two types of external fixation ion devices with addition of anterior pin placement.

The conventional compression device, using single pin above and below the fusion site, does not provide adequate stability in the AP plane for most cases of total knee replacement failure. Even multiple pin placement, using the standard quadralateral frames (Fig. 18.3) will not adequately control anteroposterior (AP) motion when there has been significant bone loss. Further pin placement anteriorly in the femur and tibia will help stabilize this plane of motion (Fig. 18.4, A and B).

External fixation devices do have their undesirable features, however. They are large, cumbersome, and frequently heavy. The multiple pin hole arrangements in osteoporotic bone may invite fracture. Pin tract infections are fairly common, and these devices are initially quite expensive. Despite this substantial list of negative features properly applied external fixation provides good stability at the fusion site and serious complications among the list above are quite rare.

Figure 18.5. Double-plating for knee arthrodesis.

 

Internal compression arthrodesis, using double-plating techniques, is an alternative method of securing rigid internal fixation (Fig. 18.5). This method maybe specifically indicated where external skeletal compression fixators are undesirable. Osgood, in 1913, and Lucas and Murray, in 1961, published their techniques of double-plating for immobilization of the knee (15, 17). Scranton, in 1980, further modified the technique by using compression plating. He also reported on the use of this technique for the failed total knee replacement (18).

Internal fixation, using double-plating, does have the advantage of not requiring external support devices and eliminating the problems associated with percutaneous pins. The technique is, however, technically very demanding. Accurate bending of the plates to conform to the femoral and tibial contours is critical. Obtaining the appropriate fusion also has to be accurate because, once the plates are secured, there is no way of changing the position short of replacing the plates. Here the use of external fixation systems has an advantage in that position changes can be made by adjusting the external fixation device.

Intramedullary nail fixation is another alternative to consider for immobilization of the knee in an attempt to gain fusion of the knee after failed total knee replacement. It may be most useful when severe osteoporosis makes screw or pin fixation impractical. Intramedullary nail fixation does have the disadvantage of not allowing a choice of knee fusion position, and it may not provide rigid stabilization, particularly with regard to rotation. The presence of an ipsilateral hip arthroplasty would necessarily preclude the use of this method.

The preparation of the bone ends for arthrodesis after a failed total knee replacement deserves special attention. This aspect of the procedure demands surgical experience and skills that will allow the surgeon to modify conventional techniques and improvise when necessary. Unexpected findings make such appropriate modifications quite frequently necessary.

When preparing the femur and tibia for arthrodesis, some basic principles should be followed:

Preserve Bone Stock. Special care should be taken in removing the prosthesis and cement so that bone is not inadvertently removed. Remove only that bone which is necessary to obtain good contact surfaces and proper alignment. If infection is present, debride all granulation tissue and devitalized tissue, but do not attempt to resect bone solely for the purpose of eradicating the infection.

Develop Congruent Trabecular Surfaces. Whenever possible, large areas of trabecular bone should be fashioned for congruent fitting with the opposing surface. This may be no more than a peripheral rim or bridging surfaces.

Form Inherent Stability. Irregular and different sized surfaces may have to be opposed. If this situation exists, an attempt should be made to interlock the irregularities to gain stability and increase the contact surfaces. When dealing with two surfaces of unequal size, inserting one into the other like a press-fit can provide a way of gaining stability and surface contact. This technique is particularly useful when attempting a resectional arthroplasty.

In cases of significant bone loss preventing suitable opposing surfaces, bone grafting maybe considered. The patella may be available; however, the best bone graft for filling a void as well as providing osteogenesis is probably iliac bone.

The position of fusion must also be considered when preparing the bone. The position must be determined preoperatively, based upon the individual patient's needs. The AP alignment should match that of the patient's other knee, if normal, and will usually be in slight valgus. The Universal alignment instruments, used for total knee replacement, make excellent guides for establishing correct AP alignment.

The position of flexion generally is best at 10-15°. This position is particularly critical if there is bilateral involvement. The patient with bilateral fusions functions best with the maximum allowable practical flexion, probably up to 20°(16). If the contralateral knee is less involved and the patient remains ambulatory, the fusion should be in more extension so as to provide a more functional position from the standpoint of walking rather than sitting. Also, if shortening is a problem, full extension maybe advantageous to maintain as much length as possible.

Although some shortening is advantageous for a knee fusion to allow for an easier swing phase, in salvage fusions for failed total knee replacement, unacceptable shortening may occur, particularly from failed binge prostheses. The amount of acceptable shortening must be determined with each patient. Obviously, any amount of shortening can be corrected by shoe lifts or prostheses, but this may be impractical or unacceptable because of shoe size, weight, and appearance. The other aspect of too much softening is the inability to obtain fusion. This is well documented in reports by Arden (1), DeBurge (7), and Hagemann et at. (9).

Bone grafting to make up for bone less, causing unacceptable shortening, has marked limitations. The relative indications here would be the situation where preservation of a stable, functional limb was necessary because of young age and a demanding activity level. The slow replacement of a graft bridging a large gap would necessarily require prolonged immobilization and would most certainly not be practical in an elderly or severely disabled patient. In the face of marked bone loss or minimal trabecular bone contact surfaces, electrically induced osteogenesis may be of benefit with or without bone grafting.

Summary

Arthrodesis of the knee for irretrievably failed total knee replacement may very well become a more frequently performed procedure as the number of patients with total knee replacements, the length of follow-up, and the number of revisions increase.

The type of prostheses for primary and revision arthroplasties must be carefully selected, keeping in mind that the success of fusion depends, to a large degree, on the type of prosthesis implanted. The minimally constrained resurfacing types of prostheses without large stems or pegs allow for apposition of large trabecular surfaces and a fusion rate approaching that of a primary arthrodesis; whereas, the large, bulky prostheses with long stems, causing excessive methaphyseal bone loss, are associated with a significantly lower fusion rate.

External compression arthrodesis is the technique of choice in the majority of cases. In the presence of infection, this method clearly is preferred over internal fixation.

The surgical technique of fusion following failed total knee replacement is difficult and demanding. Careful removal of the prosthesis and cement, preservation of bone stock and creation of large contact surfaces, increase the chances of a successful fusion.

Resectional arthroplasty may be an acceptable alternative in selected cases.

References

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