Subtalar dislocations (eponym 'basketball' foot)
A subtalar dislocation, aka peritalar dislocation, refers to the dislocation of the talocalcaneal and talonavicular joints. These joints represent the distal articulation of the talus bone.
A subtalar dislocation can occur in any direction. However, it is reported that approximately 85% are medial dislocations and 15% are lateral dislocations.A medial dislocation, named for the direction of the distal boney structures, refers to a medially displaced calcaneus relative to the talus. This type of dislocation is usually associated with an inversion injury to the foot and low-energy forces.A lateral dislocation refers to a laterally displaced calcaneus relative to the talus. This type of dislocation is usually associated with an eversion injury to the foot and high-energy forces.
Upon presentation, the patient's foot is grossly deformed in appearance.Up to 40% of lateral dislocations may present as an open injury usually secondary to the talar head damaging the surrounding soft tissues. In closed dislocations, the skin can appear tight or stretched over the boney deformity making the skin susceptible to tissue breakdown.For this reason, prompt reduction of the injury is important. In addition to the skin exam, a thorough neurovascular evaluation should be performed.
Due to the gross deformity of the foot it may be difficult to obtain accurate AP and Lateral radiographs.However, x rays need to be taken for complete evaluation of the foot and ankle. Commonly, fractures are missed upon initial review of the x rays.CT evaluation may be warranted if a fracture is suspected.
Prompt reduction of a closed subtalar dislocation is important to prevent necrosis of the surrounding tissues which lie superficial to any gross deformity. The following list is a brief summary of the steps to reduce a closed subtalar dislocation if encountered in the emergency room or office:
1. conscious sedation for the patient
2. patient should lie supine (if using sedation)
3. flex the leg of the affected side to remove stress from the Achilles tendon (which could pose tension against your reduction maneuver)
4. place traction on affected foot while an assistant induces counter traction onto the thigh of the affected side
5. with continuous traction, the examiner should exaggerate the deformity of the foot to free up the bones within the foot
6. with continuous traction, reverse the direction of the deformity until reduction is achieved
7. place a posterior splint with foot in neutral position and ace wrap until further evaluation in office
Occasionally, you can feel a 'clunk' which may validate the reduction maneuver.However, the reduction may be satisfactory if the deformation appears resolved and no 'clunk' was felt. Although, any closed reduction procedure should be confirmed with post reduction radiographs to verify that the joint surfaces are now congruent.The post reduction films may also be better for evaluating if any bones of the foot were fractured with the injury.
Sometimes closed reduction may not be possible due to structural abnormalities associated with the injury. In this situation, open reduction is usually required to alleviate the impinging structure.For medial dislocations, the extensor digitorum brevis(EDB) and the capsule of the talonavicular joint are common offenders and can obstruct the foot from a closed reduction procedure. For lateral dislocations, more commonly it is the posterior tibial tendon.
Prognosis for the patient who suffers a subtalar dislocation depends on the mechanism of injury.Therefore, lateral subtalar dislocations typically have a worst prognosis since they are associated with high energy injuries. Thus, they carry a higher incidence of associated trauma.
After closed reduction, subtalar dislocations, barring any serious injuries to the foot, can be treated in a posterior splint for a short duration followed by early active range of motion (ROM). Sometimes, physical therapy may be warranted to help a patient regain strength and confidence in the function of their foot.
Mark D. Miller, ed.Review of Orthopaedics. 4th ed. : Elsevier 2004:566.
Robert W. Bucholz, James D. Heckman, Charles Court-Brown, eds.Rockwood and Green's Fractures in Adults. 6th ed.: Lippincott Williams & Wilkins; 2006:2282-2288.