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Ankle Inversion Injuries

The Role of the Dynamic Defense Mechanism

Department of Orthopedic Surgery, Sports Medical Division, Gentofte Hospital

Michael Voigt, MSc, PhD

Department of Functional Anatomy, the Panum Institute, University of Copenhagen, Copenhagen, Denmark

Charlotte Hojsgaard, MD

Department of Functional Anatomy, the Panum Institute, University of Copenhagen, Copenhagen, Denmark

We investigated the role of a muscular defense in the stabilization and protection of the ankle joint against sudden forced inversion. Ten volunteers with mechan ically stable ankles were tested in different standing and walking situations using a trap door model and lower extremity electromyography and electrogoniom eters. Peroneal electromyographic activity was ob served 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. Quad riceps and hamstring muscle electromyographic activ ity occurred 68 msec after the ankle inversion stimulus. Evidence of active eversion was seen 176 msec after sudden inversion. Active changes in knee and hip joint angles occurred even later. In contrast, the trap door rotated 30° in approximately 80 msec. We conclude that the reflex reaction to sudden inversion is initiated at a peripheral level by the inversion motion followed by a reaction pattern mediated by spinal or cortical motor centers. Both peripheral and central reactions, however, seem too slow to protect the ankle in case of sudden inversion occurring at the time of heel contact.

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