A prospective study of 5-year outcomes and predictors in high tibial osteotomy

Purpose: To determine 5-year outcomes and predictors of clinically important improvement after medial opening wedge high tibial osteotomy (HTO). Methods: Patients with medial knee OA and varus alignment undergoing medial opening wedge HTO with external fixation were recruited from one centre specializing in realignment surgery. Patient-reported outcomes, hip-to-ankle standing antero-posterior x-rays and gait analysis were completed before, 6 months and 5 years after HTO. Mean changes with 95% confidence intervals (95%CI) quantified effect sizes. Logistic regression tested the associations between maintaining an increase ≥10 in the Knee injury and Osteoarthritis Outcome Score (KOOS4) at 5 years and the following potential predictors: preoperative KOOS4, sex, age, x-ray severity in the medial and lateral compartments, mechanical axis angle (MAA), peak external knee adduction moment (EKAM) during walking, and surgical change in MAA and EKAM (i.e. difference between preoperative and 6-month values). Results: A total of 244 patients received HTO. 50 patients who subsequently had a second HTO on the opposite limb, and 24 patients who subsequently had HTO converted to total knee arthroplasty, were excluded from the present analysis. In 170 patients (135 males, age = 46 ± 9 years, BMI = 29.4 ± 4.9 kg/m2), mean changes (95%CI) were as follows. KOOS4: +14.2 (10.8, 17.6), MAA: +8.2 deg (7.6, 8.8), EKAM: -1.45 %BW*Ht (-1.31, -1.49). While adjusting for other independent variables (adjusted Odds Ratios (OR); 95%CI), the preoperative KOOS4 (OR 0.96; 0.94, 0.98), 6-month MAA (OR 1.23; 1.01, 1.49), change in MAA (OR 0.85; 0.74, 0.99), preoperative EKAM (OR 0.41; 0.24, 0.73) and change in EKAM (OR 3.06; 1.46, 6.42) were associated with improvements in KOOS4 scores ≥10. Conclusions: Substantial improvements in patient-reported outcome, lower limb varus alignment and the medio-lateral distribution of load on the knee during walking were maintained 5 years after medial opening wedge HTO. Pre-operative age, sex, x-ray severity and BMI were not associated with outcomes in the present sample. The amount of alignment correction and especially the extent of re-distribution of load on the knee during walking were associated with 5-year clinically important improvement.