Subtalar joint axis in patients with symptomatic peritalar subluxation compared to normal controls.

BACKGROUND: The etiology of peritalar subluxation (PTS) is poorly understood and likely mutifactorial. An anatomic predisposition for posterolateral subluxation of the hindfoot has not been previously described or investigated. The aim of the current study was to describe the morphology of the subtalar joint axis (STJA) in patients with symptomatic PTS compared to normal controls.

METHODS: We identified patients with symptomatic PTS who had undergone operative correction from hospital records. The angle of the axis of the posterior facet of the subtalar joint was made on simulated weight-bearing CT (SWBCT) scans. A control group of patients who had no foot deformity on standing films was used for comparison. The STJA was defined as the angle between the superior talar dome and the posterior facet of the talus on coronal CT scan. The mean, maximum, and minimum STJAs were calculated for each cut from anterior to posterior across the posterior facet. The trend in progression across the posterior facet was also examined.

RESULTS: After exclusions, 22 feet in 20 patients were included in the study group and compared to 20 control subjects. It was seen that patients with PTS had an increased valgus orientation of the subtalar joint. In patients with PTS the STJA began in valgus and progressed to even greater valgus from anterior to posterior across the posterior facet. The STJA in control subjects was seen instead to begin in slight varus and transition to valgus at the junction of the anterior and middle third and then increase in valgus as the joint progressed posteriorly.

CONCLUSIONS: The valgus orientation of the coronal plane of the subtalar joint may represent an anatomic contribution to the etiology of PTS.

LEVEL OF EVIDENCE: Level III, comparative series.