Tibiofemoral joint-surface motions in weight-bearing and non-weight-bearing movement

Context: Analyses of the path of instant center of rotation (PICR) can be used to infer joint-surface rolling and sliding motion (arthrokinematics). Previous PICR research has not quantified arthrokinematics during weight-bearing (WB) movement conditions or studied the association of muscle activity with arthrokinematics. Objective: To examine tibiofemoral arthrokinematics and thigh-muscle EMG during WB and non-weight-bearing (NWB) movement. Design: 2 × 9 repeated-measures experiment. Setting: Laboratory. Participants: 11 healthy adults (mean age 24 years). Main Outcome Measures: Tibiofemoral percentage rolling arthrokinematics and quadriceps: hamstring EMG activity. Results: WB percentage rolling (76.0% ± 4.7%) exceeded that of NWB (57.5% ± 1.8%) through terminal knee extension (F_8,80 = 8.99, P < .001). Quadriceps:hamstring EMG ratios accounted for 45.1% and 34.7% of the variance in arthrokinematics throughout the WB and NWB movement conditions, respectively (P < .001). Conclusions: More joint-surface rolling occurs through terminal knee extension during WB movement and is associated with an increase in hamstring activity.