Muscle activation features of the osteoarthritic knee with patellar lateral subluxation.

OBJECTIVE: 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). METHODS: 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. RESULTS: 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). CONCLUSION: Musculature imbalance of VMO and VL may explain the different muscle activation pattern in osteoarthritic knee patients with and without patellar lateral subluxation.

Relationship between the EMG ratio of muscle activation and bony structure in osteoarthritic knee patients with and without patellar malalignment.

OBJECTIVE: The aim of this study was to compare muscle activation patterns and patellofemoral joint morphologies between patients with knee osteoarthritis with and without patellar malalignment. SUBJECTS: The subjects were divided into 3 groups. Group A comprised 11 patients with symptomatic knee osteoarthritis without patellar malalignment. Group B comprised 14 patients with symptomatic knee osteoarthritis with patellar malalignment. Group C comprised 10 age-matched subjects with non-knee osteoarthritis as controls. METHODS: Isokinetic dynamometry with surface electromyography was used to measure maximal muscle activity in terms of vastus medialis oblique/vastus lateralis ratios. Merchant's view was taken to analyse the bony anatomy of the patellofemoral joint. Recordings were made at angular velocities of 80, 120 and 240 masculine/sec. RESULTS: The electromyographic ratios of group B were lower than groups A and C for all testing velocities (p<0.05). Group B also had larger sulcus angles, lateral patellar tilt and displacement. The electromyographic ratios correlated negatively with sulcus angles. CONCLUSION: Subjects with knee osteoarthritis with patellar malalignment exhibited an imbalance in quadriceps contraction, as confirmed by altered vastus medialis oblique/vastus lateralis ratios associated with larger sulcus angles of the patellofemoral joints. The sulcus angle may be an important contributing factor in causing abnormal patellar tracking in knee osteoarthritis.