Ankle inversion injury and hypermobility: effect on hip and ankle muscle electromyography onset latency

Changes in reflexes associated with chronically sprained ankles were examined by measuring the reflex response latency of hip and ankle muscles during instantaneous ankle/foot inversion.

Randomized trials.

All studies were performed in the Research Department laboratories at a major rehabilitation center in a large metropolitan area.

Twenty subjects were assigned to 2 groups (normal and hypermobile) based on goniometry testing. Subjects were recruited from hospital and University staff and had a mean age of 31 +/- 5 years.

Subjects stood on a platform constructed such that either foot/ankle could be instantaneously inverted. Latency was measured by EMG surface electrodes placed over the right and left gluteus medius and peroneal muscles. Two-factor analysis of variance was calculated to determine significant muscle onset latency differences (p < .01) between groups.

Significant EMG latency differences were found in comparing right gluteus medius of the hypermobile group (127.35 +/- 6.02msec) with the normal group (150.49 +/- 6.49msec) during right ankle perturbation, and the left gluteus medius of the hypermobile group (120.71 +/- 6.16msec) with the normal group (136.24 +/- 5.88msec) during left ankle perturbation.

These data suggest that there is decreased latency of hip muscle activation after ankle inversion in the hypermobile population. In treating ankle instability, clinicians must decide to address the altered hip muscle recruitment pattern or accept this recruitment pattern as an injury-adaptive strategy and thus accept unknown long-term consequences of premature muscle activation (ie, possible articular predisposition to degenerative changes, altered joint reaction forces, and muscle imbalances).