Hip abduction moment and protection against medial tibiofemoral osteoarthritis progression

Objective. To test the hypothesis that a greater peak internal hip abduction moment is associated with a reduced likelihood of ipsilateral medial tibiofemoral osteoarthritis (OA) progression. Methods. Fifty-seven persons with knee OA (by definite osteophyte presence and symptoms) were evaluated. Baseline assessments included kinematic and kinetic gait parameters, obtained with an optoelectronic camera system and force platform, with inverse dynamics used to calculate 3-dimensional moments at the joints; pain, using a separate visual analog scale for each knee, and alignment, using full-limb radiographs. Radiographs of the knee in a semiflexed position, with fluoroscopic confirmation of tibial rim alignment, were obtained at baseline and 18 months later. Disease progression was defined as worsening of the grade of medial joint space narrowing. Logistic regression obtained with generalized estimating equations was used to estimate odds ratios (ORs) for progression per unit of hip abduction moment, after excluding knees with the worst joint space grade at baseline (which could not progress). Results. The 57 participants (63% women) with mild to moderate OA had a mean age of 67 years and a mean body mass index of 29. A greater internal hip abduction moment during gait was associated with a reduced likelihood of medial tibiofemoral OA progression, with OR/unit hip abduction moment of 0.52 and a 95% confidence interval (95% Cl) of 0.32-0.85. This protective effect persisted after adjustment for age, sex, walking speed, knee pain severity, physical activity, varus malalignment severity, hip OA presence, and hip OA symptom presence, with an adjusted OR of 0.43 a 95% CI of 0.22-0.81. Conclusion. A greater hip abduction moment during gait at baseline protected against ipsilateral medial OA progression from baseline to 18 months. The likelihood of medial tibiofemoral OA progression was reduced 50% per 1 unit of hip abduction moment.