LONG-TERM SURVIVAL ANALYSIS AFTER HIGH TI BIAL OSTEOTOMY FOR VARUS GONARTHROSIS

Purpose of the study High tibial osteotomy (HTO) is a routine procedur e for medial gonarthrosis. Mid-term results are known to be satisfacto ry, but they deteriorate with longer follow-up. The authors present a long term survival analysis of 109 out of 111 consecutive HTO with a m inimal potential follow-up of ten years. Material and methods 111 pati ents were consecutively operated on for isolated primary varus gonarth rosis between 1977 and 1985: 57 men and 54 women, with a mean age of 5 3 years (range, 27 to 79 years). X-ray measurements were done on stanc e, hip-ankle view. Global axial deformation was defined as the angle b etween mechanical axes of femur and tibia. The respective part of cong enital and degenerative tibial deformation was assessed according to D ejour. The angle between femoral and tibial bicondylar lines, represen ting lateral instability, was added to the tibial degenerative deforma tion to represent the total degenerative deformation. The goal of corr ection was a 3 to 7 degree mechanical valgus angulation. At the time o f bone healing, 82 patients (74 per cent) had an optimal correction. T wo patients were excluded from the follow-up study because of a severe complication (1 bacterial arthritis and 1 tibia non union) which coul d interfere with the long term result. The 109 remaining patients were followed for a minimal period of 1 year (mean: 8.4 years). GUEPAR pai n grading and the occurance of a revision were prospectively analyzed. 57 non reoperated patients could be re-examined at a mean maximal fol low-up of 13.5 years (range, 10 to 18 years). Failure was defined as e ither the occurance of a grade 2 or 3 GUEPAR pain during the whole fol low-up, or a clinical or functional Knee Society score < 80 points at final follow-up, or revision. Failure and revision rates were calculat ed 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 funct ional scores were respectively 87.0 points (range, 24 to 100 points) a nd 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 incr eased failure rate (p < 0.000,1). A pre-operative medial joint space n arrowing over the half of the normal, lateral one led to a 2.2 fold in creased 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 t otal 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 I deal patients for HTO, with an expected survival rate of 100 per cent after 13 years, have moderate degenerative changes and a congenital de formation superior to 5 degrees. Patients with advanced degenerative c hanges and no congenital deformation experienced a 35 per cent failure rate after 10 years. In this population, unicondylar replacement shou ld be considered as a valuable alternative.