Bilateral activation failure of ankle dorsiflexors in patients with hip osteoarthritis undergoing total hip arthroplasty.

The study aimed at investigating voluntary activation of ankle dorsiflexors in patients with hip osteoarthritis before and after total hip arthroplasty (THA). Twenty-six subjects with unilateral end-stage hip osteoarthritis were assessed for voluntary activation level (VAL) of ankle dorsiflexors of operative and non-operative sides using twitch interpolation technique. Maximal isometric force (MVIC), intrinsic electrically-evoked force (EF) and rate of force development (RFD) at 50 ms, 100 ms and 200 ms during voluntary contractions were also collected. Patients were assessed on the preoperative and third postoperative days and data were compared to 26 age-matched healthy subjects. Patients revealed lower VAL (before surgery: MD 7.7 %, CI95 0.4, 14.9; after surgery: MD 12.4 %; CI95 5.5, 19.2), MVIC, EF and RFD than healthy subjects on the operative side. On the nonoperative side, patients revealed lower postoperative VAL than healthy subjects (MD 9.0 %, CI95 2.4, 15.6) as well as lower evoked force and RFD before and after surgery. Bilateral activation failure of ankle dorsiflexors was found in patients undergoing THA. Such impairments were accompanied by deficits in maximal, evoked and explosive force. These findings confirmed impairments in neuromuscular function of muscles that do not surround the affected joint and may depend on supraspinal pathophysiological mechanisms and learned non-use.