A 24 year-old male presents with right foot pain after falling off of a 12 foot ladder, his foot locked in supination, with obvious deformed (Figure 1). Pulses, sensation, and motor function intact distally. X-rays are ordered (Figure 2).
This is a rare injury; it accounts for approximately 1 – 2% of all dislocations. This can look similar to an ankle dislocation on examination, but the tibiotalar joint and mortise are intact.
These injuries typically from a high energy mechanism such as a fall from height or high energy motor vehicle collision (MVC). Typically to cause this dislocation, an axial load is applied when the patient has a plantar flexed foot. Patients may get these injuries from lower energy mechanisms such as sport injuries or fall from standing, especially if the patient is elderly or obese. Most injuries tend to be male (3:1 ratio) and in the third decade of life.
Subtalar dislocation is the disruption of the articulation of both the talocalcaneal and the talonavicular joints with an intact ankle joint mortis. This involves disruption of the surrounding ligaments: interosseous talocalcaneal ligament (most important), anterior talocalcaneal ligament, posterior talocalcaneal ligament, lateral talocalcaneal ligament, and medial talocalcaneal ligament.
Approximately 25% of these injuries are open upon presentation to the ED. There is high risk of skin necrosis from tenting over malleolus or talar head, which can convert these injuries to open dislocations.
Types of Subtalar Dislocations
The vast majority of subtalar dislocations are either medial (85%) or lateral (15%). Anterior and posterior dislocations can also occur.
Medial Subtalar Dislocation
This is the most common type of subtalar dislocation. It typically results from an inversion injury with a plantar flexed foot. It is sometimes called “basketball foot” as this is a common mechanism. Another term for this injury is “acquired clubfoot.” On physical exam, you will find that the foot is inverted, the calcaneus is displaced medially, and the foot is locked in supination.
On AP x-ray, the calcaneus will be displaced medially (Figure 3). Lateral x-ray will show that the talar head is superior to the navicular (Figure 4).
Lateral Subtalar Dislocation
Lateral subtalar dislocations account for around 15% of subtalar dislocations. On physical examination, you will find that the foot is everted, the calcaneus is lateral to talus, and the foot is locked in pronation. AP x-ray will show lateral displacement of the calcaneus (Figure 5). On lateral views, the talar head with be inferior to the navicular (Figure 6). Lateral dislocations tend to result from higher mechanism injuries; therefore, these injuries are more likely to be open and have more associated injuries.
Anterior and Posterior Dislocations
There are case reports of anterior and posterior dislocations, but these are exceedingly rare. They account for around 1% of subtalar dislocations.
Reduction should be attempted rapidly due to the threat of skin necrosis if dislocation is prolonged. Reduction should occur prior to obtaining radiographs (either immediately upon presentation to the ED or in the field) if the foot has obvious neurovascular compromise such as absent or thready dorsalis pedis or posterior tibial pulse, decreased capillary refill, or lack of sensation to the bottom of the foot. Obtaining a thorough vascular and sensory exam of the foot before and after any reduction attempts is key. Often procedural sedation is necessary to perform this procedure. The approach to reduction is as follows:
Knee bent at 90 degrees to relax gastrocnemius and soleus muscles
Apply traction at heel and counter-traction to thigh
Accentuate deformity followed by reversal.
Medial dislocations: Further invert, pull traction, and then evert
Lateral dislocations: Further evert, pull traction, and then invert
Apply a splint – short posterior slab splint with side gussets
If reduction is successful, then obtain post-reduction x-rays and CT scan of foot and ankle. It is recommended that the patient is non-weight bearing in short leg cast for 4 to 6 weeks.
Given that most of these injuries occur from a high degree force to the foot, it is not surprising that many of patients have other foot and ankle injuries in addition to the subtalar dislocation. Approximately 55% of medial subtalar dislocations and 72% of lateral dislocations have associated injuries. Common associated injuries include osteochondral lesions of the talus, subtalar debris, ankle fractures, 5th metatarsal fracture, navicular fracture, and cuboid fracture. Given the high percentage of associated injuries and that some of the associated injuries are difficult to see on plain radiographs, it is recommended to get a CT scan of the ankle and foot after reduction. In a case series of 9 patients, CT scan showed additional injuries missed on plain film in 100% of cases, and the CT changed the treatment in 44% of the cases. Fortunately, neurovascular injury and chronic subtalar joint instability are rare complications.
Approximately 30% of injuries are not reducible by closed means. In medial dislocations, the capsule of the talonavicular joint, peroneal tendons, or the extensor digitorum brevis (EDB) muscle can block reduction. The talar head can “button hole” through the EDB which blocks reduction. In lateral dislocations, the posterior tibialis tendon, flexor halluces longus, or flexor digitorum longus can be interposed into the joint space and block reduction. These injuries are also associated with contusions or lacerations of the posterior tibial artery and nerve.
Open subtalar dislocations have an infection rate of approximately 30% even with aggressive irrigation in the OR. Appropriate antibiotics prophylaxis should be given immediately upon recognizing an open fracture. Cefazolin is sufficient coverage for skin flora in most cases without obvious contamination and with minimal soft tissue damage. If the patient is high risk for MRSA, vancomycin coverage can also be added. For patients with severe soft tissue injury or gross contamination coverage should be expanded to ampicillin-sulbactam, cefoxitin, or cefotetan. If there is exposure to water, then Pseudomonas coverage should be added with an agent like cefepime. If fecal contamination is possible or there is concern for clostridial exposure (agricultural injuries), then high dose penicillin should be used as an adjunct.
There also is a risk of avascular necrosis of the talus or navicular after a subtalar dislocation. This is a rare complication more likely to occur after lateral subtalar dislocation. This is more common with tibiotalar dislocation when the ankle mortise is disrupted.
Many patients will go on to have chronic pain in their ankle (30 - 63%); intraarticular debris fragments and open injuries increase the risk of this.
Take Home Points
Subtalar dislocations often occur after a high mechanism injury to the foot while it is plantar flexed
Medial subtalar dislocations are more common
Lateral subtalar dislocations are more likely to be open and to have other associated injuries
Open dislocations have very high infection risk even with prompt and appropriate care
Fast reduction is key. Put the knee at 90 degrees, apply traction, recreate the injury and then reverse it
Get appropriate antibiotics on board quickly for open fractures
Approximately 30% of the time, closed reduction is impossible as the dislocated bone is caught on adjacent structures
Get a CT scan after reduction to look for other injuries
Faculty Reviewer: Dr. Mark Greve
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