POPLITEUS FUNCTION IN ACL-DEFICIENT PATIENTS

Anterior cruciate ligament (ACL) injuries commonly result in anterolat eral rotary instability and a 'pivot shift' phenomenon. Since popliteu s muscle stimulation causes a pivot shift, some postulate the popliteu s muscle plays a role in causing pivot shifts. To see if patients with pivot shifts exhibited excessive popliteus muscle activity, we studie d fine-wire EMGs of the popliteus in 16 normal subjects and 10 ACL-def icient subjects. Subjects performed six activities (level walking and jogging, ascending walking and jogging, and descending walking and jog ging). Except for minor timing differences in ascending treadmill and ascending jogging, the signals were similar for injured and uninjured limbs; similar variance ratios suggested similar pattern variability. Thus, we observed only minor popliteus EMG signal differences in this group of patients. We conclude that the popliteus muscle does not acti vely contribute to instability in the studied activities.