Weight-bearing flexion angle correlates significantly with severity of knee osteoarthritis

This study evaluated flexion angles and mechanical loads at the knee during weight-bearing deep flexion in patients with knee osteoarthritis (OA). Thirty-eight knees of 26 patients (mean age, 73 years; range, 58-81 years) with medial knee OA and 16 knees of 8 healthy volunteers (mean age, 63.4 years; range, 60-65 years) were enrolled. Patients were subdivided into two groups based on Kellgren and Lawrence OA grade: moderate OA (grade 2, 17 knees) or severe OA (grade 3 or 4, 21 knees). Motion analysis was performed while rising from maximal knee flexion with one leg for each subject. Maximum knee flexion angles and net quadriceps moments in the weight-bearing motion were compared among the two OA groups and healthy subjects. Mean maximum flexion angle in patients was 91 ± 9°. Angles were about 30% smaller than passive range of motion (ROM). Mean angles in healthy subjects, moderate OA and severe OA were 102.7 ± 5.0°, 95.6 ± 7.7° and 86.5 ± 7.2°, respectively, and net quadriceps moments during motion were 5.5 ± 1.2%BW*Ht, 4.5 ± 1.7%BW*Ht and 3.9 ± 1.3%BW*Ht, respectively. Angles and moments were significantly lower in OA patients than in healthy subjects. Maximum flexion angles during weight-bearing rising correlated significantly with HSS score (r = 0.63; 95% confidence interval, 0.40-0.78) and were significantly lower in severe OA patients compared to moderate OA. This measurement may offer an important clinical index for knee OA.