EFFECT OF ANKLE BRACES ON PREVENTING DYNAMIC FORCED ANKLE INVERSION

Participants: M. L. Ubell, J. P. Boylan, J. A. Ashton-Miller, E. M. Wojtys

Keywords: ankle, muscles, ankle braces

Introduction

Ankle injuries account for a large portion of athletic injuries, with ankle inversion during landing being the most common cause of such injuries. According to some estimates, over two million people are affected by ankle injuries in the United States each year (Soberoff et al., 1984). In an effort to avoid ankle injuries, many athletes use ankle braces. The effectiveness of different ankle braces has largely been examined in non-weight bearing situations, but few studies have examined their effectiveness in situations in which the ankle is subjected to a dynamic force, particularly during landing on a hard surface. This study simulates an unexpected landing which would cause the foot to invert and examines the ability of different braces to prevent ankle inversion during such a landing. It tests the hypothesis that ankle braces provide no increased protection against dynamic forced inversion of the ankle compared to the unbraced state.

Materials and Methods

Eleven male subjects (mean (SD) age=25.5(4.0) years; range of 21 to 36) with no history in the past six months of ankle injury volunteered for this study. In order to cause a dynamic inversion of the ankle, a detachable sole was designed that produced an inversion of 24 degrees when the outside of the sole touched down. With either a stimulus sole or a flat control sole attached to the shoe, subjects jumped onto a force plate so that they landed with a force of twice body weight. Three braces were tested: Swedo^TM, Aircast^TM, and Bledsoe’s Ultimate Ankle^TM. In order to reduce relative motion between the shoe and braces, and thereby ensure that a touchdown of the outside of the foot indeed signified an inversion of nearly 24 degrees, Velcro was affixed to the bottom of the Swedo^TM and the Aircast^TM, as well as to an orthotic which was worn when no braces were used. Velcro was also attached to the top and bottom of the insole and to the inner sole of the shoe so that the insole was held in place. The Ultimate Ankle^TM is designed to be affixed to the inner sole of the shoe with Velcro, so no modifications were made to its design. The Optotrak 3-D tracking system was used to monitor the kinematics of the shoe, foot, and tibia. Two markers were placed on the shoe, two were placed on a stick attached to the calcaneous, and two were placed on the posterior midline of the leg (10 and 16 mm below the fibular head). This system also gathered data from a force plate and recorded circuit closures caused by touchdown of the outside of the foot. The first trial block of 15 jumps was without a brace, the next three were with each of the three braces, presented in randomized order, and the last trial block was again without any brace. The outcome measure was the success rate of preventing touchdown on the outside of the foot.

Results

There was no statistical difference between the two unbraced states, thereby demonstrating an absence of a learning effect (p=0.267). Compared to the unbraced state, the increase in success rate of the Aircast was statistically significant (p=0.025), the Bledsoe brace closely approached significance (p=0.058), while the Swedo brace did not reduce the probability of full ankle inversion during landing (p=0.294).

Conclusions

The primary goal of this study was to determine whether braces offered increased protection during a dynamic forced inversion and, if possible, to identify differences in various braces’ ability to do so. The results show that two of three braces tested increased the likelihood of preventing full forced inversion upon landing on a hard foreign body under the medial aspect of the foot. The two most rigid braces (Bledsoe and AirCast) significantly increased ankle protection.

References

Soberoff SH, et al.: Benefits, risks, and costs of alternative approaches to the evaluation and treatment of severe ankle sprains. Clinical Orthopaedics 183: 160-68, 1984.