Arthrodesis of the Knee - Clinical Tree

Indications and Results

With the success of total knee arthroplasty, knee arthrodesis seldom is performed as a primary operation and usually is reserved for those few patients who are not candidates for total knee replacement. Occasionally, arthrodesis may be more appropriate than arthroplasty in a young patient with severe arthrosis because of the patient’s weight, occupation, or activity level. Other possible indications for primary arthrodesis include painful ankylosis after infection, loss of the extensor mechanism, tuberculosis, trauma, severe deformity in paralytic conditions, neuropathic arthropathy, and malignant or potentially malignant lesions around the knee. The most frequent indication for knee arthrodesis is currently salvage of a failed total knee arthroplasty, most often secondary to infection.

Most current series of knee arthrodesis report successful fusion in most patients, up to 100% in some series. Most properly selected patients are satisfied with a fused knee, especially with the decrease in pain postoperatively; however, some patients report functional difficulty and continued pain. Arthrodesis as a salvage procedure after failed total knee arthroplasty can be expected to have some inferior results compared with primary knee arthrodesis, including lower fusion rates, higher infection rates, and shortening (often 2 to 5 cm in this setting).

Frequent concerns expressed by patients after knee fusion include the attention they attract in public, difficulty riding public transportation, difficulty sitting in theaters and stadiums, and difficulty getting up after a fall. Patients should be counseled about these difficulties preoperatively. Some patients may benefit psychologically from a preoperative trial of long-leg immobilization (cast or brace) to decide if they can manage with a fused knee. Harris et al. found that walking speeds and efficiency are similar after amputation, arthrodesis, and arthroplasty for tumors around the knee. Although patients with arthrodeses had the most stable limbs and could perform the most demanding physical work and recreational activities, they had difficulty sitting and were more self-conscious about the limb than were patients with arthroplasty.

Above-knee amputation is another procedure for treating chronic prosthetic joint infections. Arthrodesis should still be considered first because it allows better function and ambulation compared with amputation.

Techniques

Numerous techniques have been described for knee arthro-desis, and these can be categorized by the type of fixation used. The amount and quality of bone present are important in determining appropriate fixation and the need for bone grafting. The selection of arthrodesis technique also is based on the individual patient and the surgeon’s experience.

Arthrodesis can be performed as a one- or two-stage procedure, depending on the circumstances. Arthrodesis has been found to be more predictable with a two-stage method.

Published arthrodesis techniques for the knee include compression with external fixation, intramedullary nailing, plate, screws, or various combinations of the above.

Compression Arthrodesis With External Fixation

Compression arthrodesis is generally indicated for knees with minimal bone loss and broad cancellous surfaces with adequate cortical bone to allow good bony apposition and compression. Advantages of compression arthrodesis include the application of good, stable compression across the fusion site and the placement of fixation at a site remote from the infected or neuropathic joint. Some series suggest that the recurrent infection rates may be lower when using external fixation compared with intramedullary nailing (e.g., 4.9% compared with 8.3% reported by Mabry et al.) for arthrodesis after infected total knee replacement.

Disadvantages of external fixation include external pin track problems, poor patient compliance, and the frequent need for early removal and cast immobilization. Several studies have demonstrated reduced fusion rates after external fixation compared with intramedullary nailing (29% to 67% vs. 91% to 95%, respectively) in arthrodesis for failed total knee replacement. These patients differ from those with primary arthrodesis in whom fusion has been reported in up to 100% with the use of external fixation. A variety of monolateral, bilateral, and ring multiple-pin fixators are now used, with fusion rates ranging from 31% to 100%. Stability, limited tissue damage, and high patient comfort are the cited advantages of using anterior unilateral external fixation.

Single-plane and biplane external fixators have similar fusion rates, although complications are numerous with both devices. Despite biomechanical advances in external fixator design, knee arthrodesis remains difficult to achieve in patients who have had multiple previous procedures, a failed total knee arthroplasty, or an infected total knee arthroplasty with significant bone loss. One series reported successful arthro-desis for treatment of sepsis using augmented external fixation with crossed Steinmann pins. No recurrences of infection were noted over a mean follow-up of 8.2 years. Other authors have used fine wire external fixation, Ilizarov external fixation, or a similar device for treatment of septic failure of total knee arthroplasty, persistent knee sepsis, or septic sequelae after knee trauma. Fusion was obtained in 77%, 96%, and 100%, respectively. Achieving fusion in the face of major bone loss can be particularly challenging and may be facilitated by using the Ilizarov device and bone transport. Ilizarov-type devices do have the advantage of bone lengthening.

Compression Arthrodesis Using External Fixation

Technique 8.1

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When extensive exposure is necessary, use an anterior longitudinal incision; otherwise, a transverse incision can be used. For arthrodesis after total knee arthroplasty, approach the knee through a midline incision or through previous scars when appropriate.
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Split the quadriceps and patellar tendons and excise the patella.
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Detach the joint capsule from the tibia anteriorly and divide the collateral ligaments.
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Flex the knee so that the capsule and quadriceps mechanism fall posteriorly on each side.
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Remove the synovium and excise the menisci, cruciate ligaments, and infrapatellar fat pad.
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With a power saw, cut the superior surface of the tibia exactly transverse to the long axis of the bone, and remove a wafer of cartilage and bone 1 cm thick.
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Remove an appropriately sized segment of bone from the distal femur so that raw bony surfaces are apposed with the knee in the desired position. We have found total knee instruments useful in making these bone cuts.
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If arthrodesis is performed after failed total knee arthroplasty, do not remove more bone from the femur and tibia but thoroughly clean the surfaces and attempt to interdigitate irregular surfaces to give the best possible contact.
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Charnley recommended a position of almost complete extension for cosmetic reasons; we prefer arthrodesis with the knee in 0 to15 degrees of flexion, 5 to 8 degrees of valgus, and 10 degrees of external rotation.
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Insert the appropriate pins for the compression device. Tighten the clamps so that a compression load of 45 kg is attained.
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Close and dress the wound. If a compression clamp is used, a long leg cast incorporating the clamp is applied; if a more rigid external fixator is used, the cast can be omitted.
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The compression device is removed after 6 to 8 weeks, and either a long leg or a cylinder cast is applied; graduated weight bearing is initiated. The cast is worn until fusion is solid, usually another 6 to 8 weeks.
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If a multiple-pin, biplanar fixator is used, place three parallel transfixation pins through the distal femur and three through the upper tibia ( Fig. 8.1A ); if bony surfaces are adequate, fixation usually is sufficient. If anteroposterior instability is present, insert additional half-pins above and below the knee at angles different from the initial pins ( Fig. 8.1B ). Connect all pins to the frame and apply compression.
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A triangular frame configuration also can be used, with 6.5-mm half-pins placed at a 45-degree angle to the anteroposterior and mediolateral planes ( Fig. 8.1C ). This configuration provides rigid stability and is tolerated by the patient.

Postoperative Care

The triangular frame configuration usually is rigid enough to allow early weight bearing and should be left in place for 3 months. After removal of the triangular frame, the patient is allowed protected weight bearing with crutches until clinical and radiographic union is noted.

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