The purposes of this study were to determine the effect of a rigid ankle orthosis (Aircast Air-Stirrup) and lateral ankle ligament anesthesia on ankle joint proprioception. Twelve noninjured subjects attempted to match nine reference ankle joint positions with their eyes closed before and after application of the ankle brace and before and after one or two of the lateral ankle ligaments (anterior talofibular and calcaneofibular) were anesthetized. Three-dimensional ankle joint orientations were recorded with a Motion Analysis system. No significant differences in the constant, variable, or absolute error were seen between subjects in the non-anesthetized and anesthetized conditions (P > 0.05), regardless of whether one or two ligaments were anesthetized. Thus, it appears that ligament mechanoreceptors contributed little to ankle joint proprioception, and that the afferent feedback from skin, muscle, and other joint receptors was adequate for the positioning task of the present study. Both the variable and absolute error in matching the reference positions were significantly less with the orthosis than without (P < 0.05). Application of an orthosis may increase the afferent feedback from cutaneous receptors in the foot and shank, which may in turn lead to an improved ankle joint position sense.

The purpose of this study was to determine the effect of plantar flexor and dorsiflexor fatigue on postural sway amplitude during unilateral, or one-legged, stance. It was hypothesized that plantar flexor and dorsiflexor fatigue would increase unilateral postural sway amplitude. Eight uninjured male subjects participated in pre- and postfatigue unilateral stability tests. Selected parameters describing medial-lateral (ML) and anterior-posterior (AP) postural sway were measured on a Chattecx Balance System before and after an isokinetic fatigue protocol. The fatigue protocol resulted in a significant increase in ML postural sway amplitude (p< 0.05) and an increase in AP sway amplitude (p= 0.065). Previously, links have been established between increased postural sway amplitude and ankle joint injury. Thus, fatigue of the plantar flexors and dorsiflexors, which increased postural sway amplitude, may render the ankle joint susceptible to injury. Induced ankle muscle fatigue may represent a valid paradigm to study the causes of traumatic ankle joint injury.

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