Biomechanical Comparison of 3 Ankle Braces With and Without Free Rotation in the Sagittal Plane

Context:

Various designs of braces including hinged and nonhinged models are used to provide external support of the ankle. Hinged ankle braces supposedly allow almost free dorsiflexion and plantar flexion of the foot in the sagittal plane. It is unclear, however, whether this additional degree of freedom affects the stabilizing effect of the brace in the other planes of motion.

Objective:

To investigate the dynamic and passive stabilizing effects of 3 ankle braces, 2 hinged models that provide free plantar flexion–dorsiflexion in the sagittal plane and 1 ankle brace without a hinge.

Design:

Crossover study.

Setting:

University Movement Analysis Laboratory.

Patients or Other Participants:

Seventeen healthy volunteers (5 women, 12 men; age = 25.4 ± 4.8 years; height = 180.3 ± 6.5 cm; body mass = 75.5 ± 10.4 kg).

Intervention(s):

We dynamically induced foot inversion on a tilting platform and passively induced foot movements in 6 directions via a custom-built apparatus in 3 brace conditions and a control condition (no brace).

Main Outcome Measure(s):

Maximum inversion was determined dynamically using an in-shoe electrogoniometer. Passively induced maximal joint angles were measured using a torque and angle sensor. We analyzed differences among the 4 ankle-brace conditions (3 braces, 1 control) for each of the dependent variables with Friedman and post hoc tests (P < .05).

Results:

Each ankle brace restricted dynamic foot-inversion movements on the tilting platform as compared with the control condition, whereas only the 2 hinged ankle braces differed from each other, with greater movement restriction caused by the Ankle X model. Passive foot inversion was reduced with all ankle braces. Passive plantar flexion was greater in the hinged models as compared with the nonhinged brace.

Conclusions:

All ankle braces showed stabilizing effects against dynamic and passive foot inversion. Differences between the hinged braces and the nonhinged brace did not appear to be clinically relevant.Key Words: ankle–foot complex, inversion, joint motion, ankle stabilization

Key Points

• Both the hinged and nonhinged braces appeared to sufficiently restrict dynamically and passively induced foot inversion.
• Other than the existence of a hinge, factors related to brace design, material, or application seemed to be responsible for differences in movement restriction.
• The Ankle X brace provided the greatest amount of restriction against dynamic inversion.

With a prevalence of 20%, ankle sprains are the most frequent injuries in athletes and often happen during running and jumping activities,¹ most often during direct contact with an opponent.² Taping and ankle braces are the most advocated interventions to prevent ankle injuries.^1,3–8 Braces differ in design, material, and movement restriction of the ankle-foot joint–complex (eg, semirigid and lace-up braces)^9–11; the goals are to provide sufficient protection but also sufficient flexibility of the ankle during sports and activities of daily living. Consequently, the stabilizing effects of braces need to be evaluated.¹² Semirigid braces use a stirrup design consisting of a thermoplastic material¹³ and are recommended for dynamic conditions, eg, sports, in which the primary goal is to restrict foot inversion but not plantar flexion and dorsiflexion.¹⁰ Therefore, among the semirigid brace models, hinged braces have been designed to allow free rotation in the sagittal plane for almost the entire range of dorsiflexion and plantar flexion of the ankle. However, soft and semirigid braces that allow more plantar flexion were associated with greater inversion velocity on a tilting platform as well as greater amplitude of passively induced inversion.¹⁰ Furthermore, wearing an ankle brace with a subtalar locking system was notably effective in limiting foot inversion during passive as well as dynamic inversion compared with a functional hinged brace and a lace-up brace.¹⁴ Therefore, less-restricted plantar flexion may imply less stabilization in associated foot displacement because it is related to some degree to hindfoot inversion.¹⁵Rapidly induced inversion movements are usually evaluated with tilting platforms or trapdoor mechanisms and may provide information about the stabilizing effect of ankle braces under dynamic loading conditions that simulate inversion trauma.^10,16–18 Passive testing usually involves the application of an external force or moment to the ankle-foot joint–complex so that the stabilizing effect of ankle bracing in other movement directions (plantar flexion, dorsiflexion, eversion, external and internal rotation) can be assessed. These directions are also considered relevant in the evaluation of ankle braces.^10,19 This method does not represent the actual injury mechanism because it lacks the dynamic load application of a real-life trauma situation.¹⁰ However, a high correlation (r = 0.78; P = .0031) was reported¹⁰ between dynamically and passively induced inversion, thus confirming that both methods provide information about various aspects of the stabilizing effects of ankle braces.The aim of our study was to compare the stabilizing effects of 3 ankle braces: 2 hinged models with free rotation in the sagittal plane (Body Armor Embrace [DARCO (Europe) GmbH, Raisting, Germany] and Ankle X [McDavid, Woodridge, IL]) and 1 model without free rotation in the sagittal plane (Aircast AirGo [DJO LLC, Vista, CA]), during a rapidly induced foot-inversion movement on a tilting platform, as well as during passively induced movements in 3 anatomical planes (6 directions) of the ankle-foot joint–complex. We hypothesized that all ankle braces would restrict ankle movements during rapidly induced inversion and passively induced movements of the ankle compared with the unbraced condition. Furthermore, we hypothesized that the hinged braces would provide less stabilization during a rapidly induced inversion and result in larger joint angles during passively induced movements of the ankle and foot compared with the unhinged brace.