Medial subtalar dislocation

Clinical History

The patient twisted his right ankle when his moped was hit by a slow moving car.

Imaging Findings

The patient was hit from behind by a slow moving car while driving a moped and fell, twisting his right ankle. He was not wearing any protective gear. There was no significant past medical history.

On examination of his right ankle there was obvious deformity with the hind foot angulated medially (Fig. 1a). There were two superficial small abrasions over the lateral malleolus (Fig. 1b). The dorsalis pedis was well felt. There was no skin tenting or any distal neurovascular deficit.

Radiographs of the right foot and ankle showed a medial subtalar dislocation with dislocation of the talonavicular joint (Fig. 2). There was also a possible fracture of the talus and a chip fracture of the cuboid. The patient was sedated and closed reduction of the subtalar joint was achieved (Fig. 3). A below-knee back slab was applied. Post-reduction radiographs showed satisfactory reduction of the subtalar and talonavicular joints and the talus fracture. The fracture was treated in a non-weight-bearing below-knee cast for six weeks, followed by full mobilisation of the ankle and subtalar joint with physiotherapy. The follow-up was uneventful.

Discussion

Subtalar joint dislocations are uncommon (1) and require a high degree of suspicion as lateral ankle views do not show the dislocation clearly. Subtalar joint dislocation is associated with talonavicular joint dislocation. An inversion injury of the foot causes the talus to lever over the sustentaculum tali and dislocates the talonavicular joint followed by subluxation and dislocation of the talocalcaneal joint. Low energy injuries causing pure subtalar dislocations, treated nonoperatively, have a better long-term outcome (2).

Letonoff et al. in their case report of internal fixation of a fracture of the posteromedial process of the talus, after a medial subtalar dislocation, show that internal fixation of these fractures may reduce post-traumatic arthritis to the ankle and subtalar joints (3). Bibbo et al. showed that CT scanning identified associated injuries better and suggested that it should be performed in all cases of subtalar dislocations (4). There have been reports (1,5) of subtalar joint stiffness, but generally subtalar joint dislocation does not affect the mobility of the patient much.

Differential Diagnosis List

Final Diagnosis

Medial subtalar dislocation of right foot

URL:	https://www.eurorad.org/case/2040
DOI:	10.1594/EURORAD/CASE.2040
ISSN:	1563-4086