Influence of Hip External Rotators during Hip Flexion

Abstract

The purpose of this study was to investigate the influence of extension of hip external rotators on passive hip flexion. Hip flexion angle was measured in sixty normal healthy volunteers (thirty females and thirty males) with their hip joint rotated internally/externally in the saggital plane. Flexion angle decreased significantly in conjunction with increasing internal rotational angle (p<0.001). The hip flexion angle of a donated fresh cadaver was measured after cutting each hip posterior muscle in turn. The flexion angle was particularly increased after cutting the piriformis and obturator internus muscles. Because both the piriformis and obturator internus muscles are hip external rotators, we concluded that these muscles restrict hip flexion. Therefore, in the treatment of restricted hip flexion, the range of internal rotation should also be taken into consideration.