Injury Characteristics and the Clinical Outcome of Subtalar Dislocations: A Clinical and Radiographic Analysis of 25 Cases

Abstract

Twenty-five patients with a subtalar dislocation were identified over a seven year period. The mean patient age was 38 years. Males (n=19) comprised 76% of patients, with a mean age of 36 years. High energy mechanisms (motor vehicle accidents, falls) accounted for 68% of subtalar dislocations. Although high energy mechanisms showed a strong trend toward open subtalar dislocations, the association was not statistically significant (p=0.0573, Fisher's exact test). Closed dislocations predominated (75%). Left and right-sided dislocations were nearly equally distributed, even among motor vehicle accidents. Medial dislocations predominated (65%): these were not influenced by mechanism of injury and did not result in statistically lower AOFAS ankle/hindfoot scores. Subtalar dislocation was irreducible (requiring open reduction) in 32%, with higher energy mechanisms of injury being statistically associated with an irreducible subtalar dislocation (p=0.0261, Fisher's exact test). Block to reduction was evenly distributed among soft tissue elements (posterior tibial tendon, flexor hallucis longus tendon, capsule, extensor retinaculum) and osseous elements. Eighty-eight percent of patients incurred concomitant injuries to the foot and ankle (95% of which were closed injuries), namely, the ankle and talus. Systemic injuries occurred in 88% of patients. At a mean follow-up of five years, the mean AOFAS score of the subtalar dislocation side was significantly lower (mean=71 vs. 93, p=0.0007, unpaired Student's t-test). No statistical relation was found between the number of associated extremity injuries and AOFAS score (Spearman correlation coefficient, r=(-)0.236, p=0.331). Radiographic follow-up demonstrated 89% of ankles with radiographic changes (31% symptomatic); however, the majority of these patients (61%) had an associated ankle injury. The subtalar joint demonstrated radiographic changes in 89% of patients, with 63% being symptomatic; 75% of patients with subtalar joint changes incurred a fracture about the subtalar joint at the time of dislocation. Four patients went on to subtalar fusion at an average of 8.8 months post-dislocation. The midfoot showed radiographic changes in 72% of patients, with only 15% of these patients being symptomatic. All patients with midfoot symptoms were well controlled by nonsurgical measures.