Ultrasound Imaging and Prevalence of Intrasheath Peroneal Tendon Subluxation in Asymptomatic Volunteers

CATEGORY: Ankle; Other INTRODUCTION/PURPOSE: Intrasheath peroneal tendon subluxation is typically an incidental finding in athletes with sports-related injuries and is characterized by a temporary reversal in the anteroposterior positions of the peroneus longus (pL) and peroneus brevis (pB) tendons within their common tendon sheath. It is currently unclear whether intrasheath subluxation represents normal physiologic or pathologic tendon motion. This study aims to determine the normal variation in motion of supramalleolar pB and pL tendons in multiple ankle positions and to determine the overall prevalence of intrasheath tendon subluxation in asymptomatic volunteers. METHODS: Static sonographic images of the peroneal tendons in 22 asymptomatic volunteers were collected in the neutral position, in eight fixed ankle positions (active and passive pronation, dorsiflexion, supination, and plantarflexion), and during dynamic ankle circumduction. The center of each tendon in relation to the lateral fibular cortex and in relation to each other was measured in each position and used to calculate absolute and percentage displacement. Two-way ANOVA was used to determine the significance of passive versus active motion and two-tailed paired sample t-test was used to compare the mean displacement of pL and pB in active and passive positions. RESULTS: Intrasheath subluxation was not visualized in any static position but was visualized in 33% of patients during active ankle circumduction, regardless of direction or laterality. Percent displacement was greatest in active ankle plantarflexion (55%) for pB and in active pronation (34%) for pL. A statistically significant difference in the tendon positions in relation to each other was found in the anteroposterior direction (p=0.026), but there were no statistically significant differences between active and passive motions or with ankle positioning. A non-painful ankle 'snap' was palpated by the sonographer in all cases of intrasheath subluxation. CONCLUSION: Intrasheath subluxation is a fairly common occurrence seen in one third of our volunteers. Our results suggest that a snapping ankle in otherwise asymptomatic patients is highly suggestive of intrasheath peroneal tendon subluxation and can be well-documented with dynamic ultrasound. Establishing the normal ranges of motion of supramalleolar peroneal tendons may assist in the evaluation of patients with lateral ankle pain.