[Z-plasty for valgus deformity in total knee arthroplasty].

PURPOSE OF THE STUDY: Several options for treatment of valgus deformity in total knee arthroplasty (TKA) have been described. In 2002 the lateral approach to the valgus knee with Z-plasty of the articular capsule involving part of Hoffa's fat pad started to be used in our department. In this study the surgical technique, including steps for gradual deformity correction, is described and shortterm results are evaluated.

MATERIAL: A total of 1136 TKAs were carried out in the period from 1994 to 2004; of these 131 (11 %) were performed on valgus knee. After a visit to the Schulthess Klinik and personal communication with Dr. med. T. Drobny, we began to use the lateral approach to the valgus knee, with Z-plasty of the articular capsule and involvement of Hoffa's fat pad. Forty-two patients (35 women and 7 men) were treated by this technique. The average age of this group was 71 years, and the average preoperative valgus deformity was 20.5 degrees.

METHODS: A skin incision is made along the midline and, in its lower part, it is led toward the lateral border of the tibial tubercle. The joint capsule is incised in the superficial layer at about 2 cm lateral to the patella. Dissection of the superficial and deep layers of the capsule is made laterally, extending up to 4 cm. After joint exposure, the fat pad is separated from the medial attachment and preserved, on a lateral pedicle, with the patellar ligament. If needed, this flap can be used to close a defect in the distal articular capsule. By including both parts of the joint capsule produced by Z-plasty, medial transposition of the patella is achieved after suture. The deformity is corrected in a sequential manner according to its severity and the effect of release in each step, as follows: 1) Point incisions of the iliotibial band at a 5-cm distance above the articular fissure (piecrusting). 2) Subperiosteal elevation of the iliotibial band attachment from Gerdy's tubercle. 3) Release of the posterolateral capsule. 4) Subperiosteal release of the femoral attachment of the lateral collaterall ligament and dissection of the popliteal muscle. 5) Release of the lateral head of the gastrocnemius muscle. The evaluation of patients was based on the Knee Society Clinical Rating System.

RESULTS: Using this surgical technique, correction of deformity was achieved in all patients. The knee axis after surgery improved to 6.6 degrees on the average. The more extensive dissection of lateral structures resulted in larger blood losses, which were on average 1150 ml, and the procedure also required a longer tourniquet application (55 min). The patients were followed up on average for 22 months. The Knee Score assessment in the whole group (42 knees) was on average 90.6 points, with 92.0, 93.3 and 87.9 for rating system categories A, B and C, respectively. The average range of motion was 0 to 118 degrees , and none of the patients reported femoropatellar problems. Revision surgery for hematoma was performed in one patient and puncture of the knee joint had to be done in several patients. Redress for postoperative motion restriction was carried out in three patients and one patient underwent repeat surgery for infection.

DISCUSSION: The lateral approach with Z-plasty of the capsule and fat pad involvement provides maximal release of and access to the lateral structures, reduces the risk of insufficient blood supply of the patella and also resolves patellar subluxation. This technique thus allows us to reduce the probability of developing femoropatellar problems that are frequently responsible for poor TKA outcomes in the valgus knee.

CONCLUSIONS: The technique described here is an effective approach to the valgus knee requiring total replacement. It provides good access to exposed lateral structures and, with the use of Z-plasty, permits correct alignment and tracking of the patella. In addition, it minimally interferes with blood supply to the patella and completely avoids problems associated with suture of the articular capsule.