78. DOES TRANSFER OF THE ANTERIOR TIBIAL TUBEROSITY FAVOUR LONG-TERM DEVELOPMENT OF MEDIAL FEMOROTIBIAL OSTEOARTHRITIS?

Abstract

Purpose of the study: Transposition of the anterior tibial tuberosisty (ATT) is often performed during the treatment of periodic dislocation of the patella. The purpose of this retrospective study was to evaluate the rate of medial femorotibial osteoarthritis and medial patellofemoral osteoarthritis after ATT transfer.

Material and method: We reviewed 129 knees in 106 patients who underwent surgery from 1988 to 2004. The patients were reviewed at mean 9 years follow-up, minimum 2 years. Three groups were defined:

1. isolated descent (n=15),

2. isolated medial shift (n=19), and

3. descent and medial shift (n=95).

The degree of the medial shift and the descent depended on the distance from the tibial tuberosity to the trochlear notch and the Caton-Deschamps index measured preoperatively. Patients who underwent surgery for chronic anterior laxity and/or meniscal lesions were excluded (n=3). All patients were free of osteoarthritis before surgery. A complete radiographic series was available for 102 knees. Unilateral periodic dislocation of the patella was present in 60 patients whose knee x-rays were obtained bilaterally.

Results: All patients in group 2 were free of osteoarthritis. In group 2, the rate of medial femorotibial osteoarthritis was 10.5%; the rate of medial patellofemoral osteoarthritis was 21%. In group 3, the rate of medial femorotibial osteoarthritis was 7% and that of medial patellofemoral osteoarthritis 14%. For patients with unilateral periodic patellar dislocation, only the operated knees exhibited medial patellofemoral osteoarthritis (12%). The rate of medial patellofemoral osteoarthritis was significantly greater for knees with a medial shift of the ATT. The rate of medial femorotibial osteoarthritis was 6.8% for knees with medial shift versus 8.3% for the index knees. There was no significant difference between the medial shift knees and the index knees for medial femorotibial osteoarthritis.

Discussion: Biomechanical studies have shown increased stress forces on the medial compartment after medial shift of the ATT. However, these studies were performed with normal knees free of the morphological anomalies generally present in knees exhibiting periodic patellar dislocation (abnormally high tibial tuberosity femoral notch distance, trochlear dysplasia. In our series, regarding the rate of medial femorotibial osteoarthritis, there was no significant difference between the knees which underwent a medial shift of the ATT and healthy knees. Consequently, medial shift of the ATT should be avoided when unnecessary; the morphology of the trochlea (depth, morphology of the medial component) can induce increased medial stress on the patellofemoral joint.