Muscle activation features of the osteoarthritic knee with patellar lateral subluxation

The aim of the study was to compare the muscle activation feature of vastus medialis obliquus (VMO) and vastus lateralis (VL) between the osteoarthritic knee patients with patellar lateral subluxation (Group 1B) and without patellar lateral subluxation (Group 1A).

Isokinetic muscle strength of the knee extensor was evaluated using a CYBEX NORM dynamometer with angular velocities of 80, 120 and 240 degrees/second (°/sec) respectively, contraction activities of VMO and VL muscle were recorded with synchronized surface electromyography (sEMG). Age-matched healthy subjects were recruited and served as control group (Group 2). The VMO/VL ratio of EMG between Group 1A, Group 1B and Group 2 were compared.

The peak torque in Group A was 40.7 ± 12.9, in Group B was 39.6 ± 12.9 and in Group C was 60.2 ± 9.5 respectively at 80°/sec angular velocity (p < 0.01). There were no significant difference between Group 1A and Group 1B in the three trial of tested velocities (p > 0.01). The sEMG ratios of VMO/VL of Group 1B calculated at angular velocities of 80/sec was 0.769 ± 0.15, 120°/sec was 0.818 ± 0.22 and 240°/ sec was 0.850 ± 0.22, all those were lower than Group 1A and Group 2 (p<0.01).

Musculature imbalance of VMO and VL may explain the different muscle activation pattern in osteoarthritic knee patients with and without patellar lateral subluxation.