Purpose of the study: High tibial osteotomy (HTO) is a routine procedure for medial gonarthrosis. Mid-term results are known to be satisfactory, but they deteriorate with longer follow-up. The authors present a long term survival analysis of 109 out of 111 consecutive HTO with a minimal potential follow-up of ten years.
Material and methods: 111 patients were consecutively operated on for isolated primary varus gonarthrosis between 1977 and 1985: 57 men and 54 women, with a mean age of 53 years (range, 27 to 79 years). X-ray measurements were done on stance, hip-ankle view. Global axial deformation was defined as the angle between mechanical axes of femur and tibia. The respective part of congenital and degenerative tibial deformation was assessed according to Dejour. The angle between femoral and tibial bicondylar lines, representing lateral instability, was added to the tibial degenerative deformation to represent the total degenerative deformation. The goal of correction was a 3 to 7 degree mechanical valgus angulation. At the time of bone healing, 82 patients (74 per cent) had an optimal correction. Two patients were excluded from the follow-up study because of a severe complication (1 bacterial arthritis and 1 tibia non union) which could interfere with the long term result. The 109 remaining patients were followed for a minimal period of 1 year (mean: 8.4 years). GUEPAR pain grading and the occurrence of a revision were prospectively analyzed. 57 non reoperated patients could be re-examined at a mean maximal follow-up of 13.5 years (range, 10 to 18 years). Failure was defined as either the occurrence of a grade 2 or 3. GUEPAR pain during the whole follow-up, or a clinical or functional Knee Society score < 80 points at final follow-up, or revision. Failure and revision rates were calculated according to Kaplan and Meier.
Results: 11 patients were reoperated on before final examination (10 per cent): 2 medial unicondylar and 9 total knee prostheses. At final follow-up, the mean clinical and functional scores were respectively 87.0 points (range, 24 to 100 points) and 86.3 (range, 45 to 100 points). The cumulative failure rate was 33 per cent after 10 years and 54 per cent after 15 years; the respective revision rates were 9 per cent and 19 per cent. A pre-operative total degenerative deformation superior to 3 degrees led to a 3.5 fold increased failure rate (p < 0.000,1). A pre-operative medial joint space narrowing over the half of the normal, lateral one led to a 2.2 fold increased failure rate (p = 0.014). An optimal post-operative correction led to a 3.2 fold decreased failure rate (p = 0.000,1). For a given total degenerative deformation, patients with a congenital deformation superior to 5 degrees had a significant lower failure rate (p < 0.000,1). No factor significantly influenced the revision rate.
Discussion: Ideal patients for HTO, with an expected survival rate of 100 per cent after 13 years, have moderate degenerative changes and a congenital deformation superior to 5 degrees. Patients with advanced degenerative changes and no congenital deformation experienced a 35 per cent failure rate after 10 years. In this population, unicondylar replacement should be considered as a valuable alternative.