The objective of this study was to determine the mechanisms of injury and pattern of associated foot and ankle injuries and systemic injuries associated with subtalar dislocations, and, correlate these data with the radiographic and clinical/functional outcome of patients after subtalar dislocation.

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.