ANKLE INVERSION INJURIES - THE ROLE OF THE DYNAMIC DEFENSE-MECHANISM

We investigated the role of a muscular defense in the stabilization an d protection of the ankle joint against sudden forced inversion. Ten v olunteers with mechanically stable ankles were tested in different sta nding and walking situations using a trap door model and lower extremi ty electromyography and etectrogoniometers. Peroneal electromyographic activity was observed 54 msec after the detection of ankle inversion. This latency was shorter when the ankle was already in inversion and longer with the ankle in eversion. Quadriceps and hamstring muscle ele ctromyographic activity occurred 68 msec after the ankle inversion sti mulus. Evidence of active eversion was seen 176 msec after sudden inve rsion. Active changes in knee and hip joint angles occurred even later . In contrast, the trap door rotated 30 degrees in approximately 80 ms ec. We conclude that the reflex reaction to sudden inversion is initia ted at a peripheral level by the inversion motion followed by a reacti on pattern mediated by spinal or cortical motor centers. Both peripher al and central reactions, however, seem too slow to protect the ankle in case of sudden inversion occurring at the time of heel contact.