S93.316A Dislocation of tarsal joint of unspecified foot, initial encounte
Subtalar Dislocation Etiology / Epidemiology / Natural History
High-energy (MVC, fall from height) or sports injury.
Subtalar Dislocation Anatomy
Blood supply: the artery of the tarsal canal(posterior tibial artery) is the main blood supply to the body of the talus. It forms an anastomotic sling with the artery of the tarsal sinus (peroneal). Others=superior neck vessels from anterior tibial artery, Deltoid artery(post tibial) (Mulfinger JBJS 1970;52B:160), (Gelberman RH, Foot Ankle 1983;4:64).
60% covered with articular cartilage, no muscle originate from or insert into talus.
Lateral process: a wide, wedge-shaped prominence extending from the lateral aspect of the body of the talus; consists of two distinct articular facets: the dorsolateral and the inferomedial. The dorsolateral facet articulates with the distal fibula; the inferomedial facet forms the anterolateral portion of the subtalar joint. The lateral process is the site of insertion of the lateral talocalcaneal ligament.
Posterior process: composed of a medial and a lateral tubercle(Stieda’s process) which are separated by a groove within which lies the flexor hallucis longus tendon. The Y-shaped, bifurcate talocalcaneal ligament forms a roof over this grooveand inserts onto each tubercle. The posterior talofibular ligament inserts onto the lateral tubercle of the talus. The posterior talotibial portion of the deltoid ligament inserts onto the medial tubercle.
Os trigonum: located directly posterior to the lateral tubercle(Stieda's process). It is an accessory bone that arises from a secondary ossification center between the ages of 8 and 11 years. Generally fuses to the lateral tubercle within 1 year of its appearance. May persist as a separate ossicle, attached to the talus by a cartilaginous synchondrosis. (Grogan DP, JPO 1990;10:618)
Medial subtalar dislocation (Swivel fracture-dislocation) -more common than lateral; 75% of subtalar dislocations. -Usually can be reduced closed. If no fx or defects are seen on post-reduction xray ---Treatment = closed reduction (with sedation / spinal anesthetic) followed by CT scan. Reduction manuever = knee flexion (held by assistant), Longitudinal traction applied to foot/heel with foot in plantar flexion. Slight accentuation of deformity with pressure on the talar head. SLC for 4 wks. Late instability is rare. -Irreducible medial dislocations are caused by the talar head "buttonholed" through the extensor retinaculum or extensor digitorum brevis; can be blocked from reduction by an interposed short extensor muscle, deep peroneal neurovascular bundle, peroneal tendon, or talonavicular joint capsule; or can become impacted on a sharp border of the navicular.
Lateral subtalar dislocation -High energy, frequently associated with small osteochondral fx. -Less common then medial subtalar dislocations. -Treatment = closed reduction (with sedation / spinal anesthetic) followed by CT scan. The reduction maneuver involves longitudinal traction, hyperpronation and lastly supination. The knee should be flexed and an assistant should supply countertraction under the thigh.Large fragments should be fixed, small fragments excised. -Irreducible lateral subtalar dislocations caused by posterior tibial tendon (most common), flexor hallucis longerus, flexor digitorum longus tendons onto the lateral neck of the talus or by impaction fractures around the talar head. -Lateral subtalar instability: if fails conservative treatment calcaneofibular ligament reconstruction is indicated.