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Total Knee Arthroplasty in Severe Valgus Deformity
The typical patient with a severe valgus deformity is an elderly woman ( Fig. 4.1 ). She usually is in her seventh or eighth decade and reports that she has had “knock-knees” her entire life. She also may give a history of patellofemoral problems through adolescence and young adulthood. These problems might be symptoms of chondromalacia or recurrent subluxation episodes. As the valgus deformity progresses, loss of lateral compartment joint space and gradual attenuation of the medial collateral ligament (MCL) occur ( Fig. 4.2 ). A skyline view of the patella often shows patellofemoral involvement and possibly patellar dysplasia, with a very thin patella that is partially dislocated laterally, developing a concave shape to the lateral facet that mates with the convex shape of the lateral femoral condyle ( Fig. 4.3 ). Patella alta often is present and can be appreciated on both the anteroposterior and lateral radiographs. Chondrocalcinosis is a frequent finding with calcification of the menisci or articular cartilage. A long film of the tibia will usually show a valgus bow. This valgus tibial deformity is problematic if the surgeon uses intramedullary tibial alignment devices ( Fig. 4.4 ). The long film is necessary for template placement to show where to enter the tibia for the intramedullary device and may even show that its use is contraindicated.
Typical patient is an elderly woman in her seventh or eighth decade.
Note the loss of lateral joint space and attenuation of the medial collateral ligament.
Patellofemoral involvement is common.
Valgus tibial bow makes the use of tibial intramedullary alignment devices problematic.
The clinical diagnosis generally is osteoarthritis, although severe valgus also can be seen in patients with rheumatoid arthritis. The patient with osteoarthritis usually has a hypermobile knee and possibly hyperextension. The patient with rheumatoid arthritis can share this clinical picture or may have a stiff knee and a flexion contracture (see Chapter 6, Chapter 7 ).
Valgus knees have several clinical features distinct from those of varus knees. In my experience, patients with valgus deformity and lateral compartment disease often can tolerate significant structural damage better than those with varus knees of comparable severity. I have seen patients with 20-degree valgus deformities complain more about secondary trochanteric bursitis than about pain and disability from the knee itself. If a patient has “windblown” knees (varus on one side and valgus on the other), the varus knee is almost always more symptomatic than the valgus knee and should be operated on first unless bilateral simultaneous procedures are contemplated (see Chapter 11 ).
Another distinction between the valgus and the varus knee is the source of the deformity. In varus knees, the medial tibial plateau is deficient and the tibial joint line is in significant varus. The femoral joint line, however, retains valgus between 5 and 9 degrees (see Chapter 3 ). In valgus knees, however, the valgus deformity comes from the femur. The tibial joint line is usually in neutral or even in the classic 2 to 3 degrees of varus, and the femoral joint line is in marked valgus ( Fig. 4.5 ). This deformity is caused by hypoplasia of the lateral femoral condyle, which is seen both distally and posteriorly ( Fig. 4.6 ). Occasionally, a valgus femoral metaphyseal bow also may be present. As the valgus progresses, the MCL becomes attenuated, allowing the deformity to increase, and at times the lateral femoral condyle erodes the lateral tibial plateau in its central portion ( Fig. 4.7 ). The peripheral aspect of the lateral plateau remains intact so the resultant defect is contained. In the varus knee, the progressive erosion of the medial tibial plateau involves the periphery of the plateau; thus the defect is not contained and is more structurally significant.
Valgus deformity comes from the femur rather than the tibia.
Lateral femoral condyle is hypoplastic both distally and posteriorly.
Sometimes the femoral condyle erodes into the central portion of the lateral tibial plateau.
Lateral Femoral Condyle Hypoplasia
As noted earlier, the typical severe valgus knee demonstrates hypoplasia of the lateral femoral condyle. This hypoplasia exists both distally and posteriorly. When performing the distal femoral resection in a valgus knee, the surgeon must resist the temptation to resect back to the level of this deficiency ( Fig. 4.8 ); instead, the deficient lateral side must be augmented. The consequence of excessive distal femoral resection in a valgus knee is twofold. First, the extension gap can end up being extremely large because of the extra distal medial resection coupled with a normal tibial plateau resection and an attenuated MCL. Second, the joint line is elevated, distorting the kinematics of the collateral ligaments and often resulting in midflexion laxity. Both distal femoral and proximal tibial resections in a severe valgus knee should initially be conservative. It is not unusual for the distal lateral resection to be zero or even less. Augmentation methods (see Chapter 10 ) include cement alone, cement and screw augmentation, or metal wedge modular augments ( Fig. 4.9 ).
Augmentation on the tibial side in severe valgus knees is occasionally necessary if the valgus is caused by a depressed lateral plateau fracture, or erosion of the femoral condyle into the central portion of the tibial plateau is present. Augmentation also may be necessary if the valgus is caused by overcorrection after tibial osteotomy (see Chapter 8 ). Any central lateral plateau deficiency can be filled with cement with or without a supporting screw, depending on the discretion of the surgeon. Because the bone surface is greatly sclerotic, I do not recommend bone grafts for these defects.
The wear pattern in the lateral compartment usually is posterior. The appropriate level of tibial resection generally is sufficiently distal to eliminate this deficiency.
I prefer a 4-degree or 5-degree valgus angle resection for valgus knees. In severe valgus, it is tempting to cut the distal femur in as much as 7 degrees of valgus because it is then easier to balance the lax medial side. I do not advocate this for two reasons.
The first reason to choose 5 degrees or less of valgus is to attempt to overcorrect the deformity slightly so that the pathologically stretched and abnormal MCL and capsule are put under less tension during weight-bearing. The less overall valgus, the less tension is placed on the medial side. Some surgeons prefer to diminish the valgus angle to as little as 2 or 3 degrees. The result, however, is a need for more lateral release to balance the lax medial side.
A second reason to choose 5 degrees or less of valgus for distal resection is because some of these knees have a distal metaphyseal valgus bow ( Fig. 4.10 ). If the surgeon follows the center of the shaft from its midpoint to the joint line, it becomes apparent that the center shaft alignment exits medial to the true center of the intercondylar notch. Unless the surgeon enters the medullary canal at this medial position, the valgus angle chosen on the cutting jig will actually result in a few more degrees of valgus imparted to the resection (see Chapter 2 ).
Ligament balancing involves creating symmetric (rectangular) flexion and extension gaps. Unlike the varus knee, the valgus knee can be balanced in flexion independent of the balancing in extension. The flexion gap is balanced by proper rotational alignment of the femoral component (see Chapter 13, Chapter 2, Chapter 5 ). In my experience, the lateral tissues in severe valgus knees are not extremely tight, and the medial tissues are not as lax in flexion as they are in extension ( Fig. 4.11 ). After the conservative distal femoral resection is performed, the knee is flexed 90 degrees, and medial and lateral laminar spreaders are placed to tense the tissues. I still draw the Whiteside line and transepicondylar axis as reference points. Using the tensed flexion gap method, the femoral component is almost always externally rotated to establish symmetry. In extremely rare cases, the lateral collateral ligament (LCL) must be partially released from the femur to open the lateral side of the flexion gap. This type of situation will always be present in the severe valgus knee that results from overcorrection of the tibial osteotomy (see Chapter 8 ). In these cases, I accept the fact that internal rotation of the femoral component is necessary to establish symmetry, and I avoid release of the LCL to open up the lateral side in flexion. In my experience, this internal rotation of the femoral component (as much as 5 degrees in some cases) has not led to maltracking of the patella.
For the severe valgus knee in extension, the problem that needs to be resolved is pathologic medial laxity combined with pathologic lateral contracture. Medial laxity in extension can be resolved by advancement of the medial structures, lateral release of the tight structures, or a combination of both techniques. Healy and colleagues published a technique of medial advancement that I find attractive because the location of the femoral attachment of the MCL is not distorted. The origin of the ligament is freed from the femur attached to a block of bone. This bone block with the ligament attached is then advanced to the metaphysis of the femur at the appropriate tension and secured with anchoring sutures that pass through and are tied over the lateral epicondyle ( Fig. 4.12 ). I have no experience with this technique, but it would be my first choice should I elect to perform a medial advancement.
I believe that mediolateral imbalance and extension can be resolved in almost all cases by performing a lateral release to balance the lax medial side. Through the years, I developed a simple inverted cruciform release of the lateral structures that has worked even in extremes of deformity. The advantages of the technique are its simplicity and effectiveness. The disadvantages of any lateral release are the resultant slight lengthening of the limb and a very small incidence of transient peroneal palsy.
During a preoperative discussion of the risks involved with total knee arthroplasty (TKA), I rarely mention peroneal palsy except in the patient with a severe valgus deformity. I inform these patients that in correcting their alignment, their leg will be lengthened (enough that they may desire a lift in the opposite shoe) and that the nerve that travels down the outside of their leg is always stretched. Sometimes this results in a transient palsy. I have never seen it to be permanent, but this is certainly a possibility. All patients having TKA should undergo neurovascular evaluation in the postoperative care unit. If peroneal palsy is detected, the patient’s dressing should be loosened and the knee flexed 50 to 70 degrees to relieve tension on the nerve. I have noted that even with careful monitoring, palsies may not appear until 24 to 48 hours after the procedure.
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