Thursday, December 31, 2009

Subtalar Dislocation


Subtalar Dislocation
By Joel Horning, MD; John DiPreta, MD
ORTHOPEDICS 2009; 32:904
Subtalar dislocations are relatively rare, accounting for approximately 1% to 2% of all joint dislocations. This article reviews the diagnosis and management of subtalar dislocations.
Subtalar dislocations represent a relatively rare injury, accounting for approximately 1% to 2% of all joint dislocations.1 First described in 1811 by Judey and Dufaurest, the subtalar dislocation, also referred to as a subastragalar or peritalar dislocation, involves the disruption of the talocalcaneal and talonavicular joints, while the calcaneocuboid joint remains intact.2-5 Because of its rarity, few large series have been published, and a majority of the literature are case reports. This article describes the diagnosis and management of subtalar dislocations.

Anatomy

The subtalar dislocation occurs through the disruption of 2 separate bony articulations, the talonavicular and talocalcaneal joints. These joints act as a hinge that transmits load and movement from the foot to the ankle. There is triplaner movement across the joint: a combination of flexion, supination, and adduction or extension, pronation, and abduction.1 The talocalcaneal, or subtalar, joint is composed of 3 separate articulations. The anterior, middle, and posterior facets provide bony stability to the joint, while ligamentous attachments provide added strength. The majority of the ligamentous stability of the subtalar joint, however, is attributed to the interosseous ligaments found within the sinus tarsi. Medially and laterally, the deep deltoid ligament and the calcaneofibular ligaments, respectively, provide restraint to eversion and inversion forces.
The talonavicular joint’s bony architecture provides the majority of its stability, while relatively weak capsular and ligamentous structures augment its stability. Comparatively, the talonavicular and talocalcaneal ligaments and capsules are weaker than those of the calcaneocuboid joint, explaining the pattern of subtalar dislocation where the calcaneonavicular joint remains intact as the talonavicular and talocalcaneal joints fail.6
The blood supply to the talus is derived from branches of the dorsalis pedis, peroneal artery, and posterior tibial artery. The majority of the dorsal blood supply is contributed by branches of the dorsalis pedis. The lateral and inferior blood supply arises from branches of the dorsalis pedis and peroneal arteries as they course through the sinus tarsi, while the medial talus is supplied by the posterior tibial artery as its branches pass within the tarsal canal.

Classification

In 1852, Broca first classified subtalar dislocations as “inward,” “outward,” or “backward” in a paper presented to the Societe de Chirurgie.4 In 1856, Malgaigne and Beurger expanded Broca’s original classification to include anterior dislocations.1 The classification system today is similar, as it describes anatomically the position of the foot with respect to the talus.
The medial dislocation, sometimes referred to as an “acquired clubfoot,” is the most common of all subtalar dislocations, comprising approximately 80% to 85% of cases.7-9 Described by Grantham10 as the “basketball foot,” the medial dislocation occurs through forceful inversion of the forefoot with the talar neck pivoting on the sustentaculum tali, which acts as a fulcrum to lever the calcaneus from the talus.7,11 Initially, it is believed that the talonavicular joint is the first to dislocate, followed by rotary subluxation through the subtalar joint, with the talar head finally coming to rest between the extensor hallucis longus and the extensor digitorum longus on either the cuboid or navicular (Figure 1).12
Figure 1A: The posteromedial position of the foot relative to the talusFigure 1B: The posteromedial position of the foot relative to the talus
Figure 1C: Radiograph of the patient following closed reductionFigure 1D: Radiograph of the patient following closed reduction
Figure 1: AP (A) and lateral (B) radiographs of a 47-year-old man demonstrating a medial subtalar dislocation after he sustained an inversion-type injury by stepping in a hole in his yard. Of note is the posteromedial position of the foot relative to the talus. AP (C) and lateral (D) radiographs of the patient following closed reduction under local anesthesia (hematoma block) and mild narcotic sedation. The subtalar joint was stable postreduction with no intra-articular fracture as documented on CT. The patient was immobilized in a well-padded posterior splint and discharged nonweight bearing on the affected extremity.
The lateral is the second most common subtalar dislocation, occurring in 15% to 20% of dislocations.8,9 Also known as an “acquired flatfoot,” the lateral dislocation typically results from the forceful eversion of the foot with the anterolateral talus pivoting over the anterior calcaneal process.7 The talar head is often displaced through the talonavicular capsule. Buckingham and LeFlore12 described injury to the deep deltoid and calcaneofibular ligaments in the lateral and medial subtalar dislocations, respectively, with sparing of the spring ligament. The lateral subtalar dislocation is historically associated with higher-energy trauma as compared with medial dislocations such as motor vehicle accidents and falls from a height (Figure 2).
Figure 2A: Open lateral subtalar dislocationFigure 2B: Open lateral subtalar dislocationFigure 2C: The capsule was also closed
Figure 2D: Reduction of the lateral subtalar dislocationFigure 2E: Removal of fragments from the sinus tarsi
Figure 2: AP (A) and lateral (B) radiographs of a 25-year-old woman who presented with open lateral subtalar dislocation. The dislocation was reduced in the emergency department, and the wound was irrigated and debrided in the operating room. The fragments seen in the area of the sinus tarsi were removed during the irrigation and debridment procedure. At the time, the capsule was also closed (C). AP (D) and lateral (E) radiographs showing reduction of the lateral subtalar dislocation and removal of fragments from the sinus tarsi.
First described in 1907 by Luxembourg, the posterior dislocation accounts for <1% of all subtalar dislocations.13The posterior dislocation most commonly occurs as the foot is excessively plantarflexed. The talar head becomes perched on the navicular and the foot does not have much medial or rotational deformity on frontal radiographs.14This has rarely been described in the literature.
The least common of all subtalar dislocations is the anterior dislocation, which results from forces being transmitted through an excessively dorsiflexed foot.13,15 The posterior facet of the talus comes to rest on the calcaneal tuber, and there may be some lateral displacement of the foot on frontal radiographs.

Diagnosis

The patient sustaining subtalar dislocations typically presents with significant pain and deformity to the affected extremity. The dislocation commonly results from motor vehicle accidents, falls from a height, sporting activities, jumping, running, or twisting.16 Men are affected more commonly than women (6:1), and mean patient age is 38.11,16 High-energy mechanisms are often associated with open injury, although this has not been shown to occur more frequently with medial or lateral dislocations.16
There is a higher incidence of associated fracture about the ankle in lateral dislocations, with the talus most commonly affected.3,16 In addition, the ipsilateral extremity and spine must be evaluated carefully, especially with high-energy injury.
All areas of concern should be evaluated radiographically in orthogonal planes. With respect to the subtalar dislocation, both frontal and sagittal views should be obtained to document the position of the foot and associated fractures of the foot and ankle. Following radiographic evaluation, the subtalar dislocation should be promptly reduced using the techniques described below.

Treatment

After confirmation of subtalar dislocation, attention should be turned to prompt reduction of the dislocation. Typically, this can be undertaken in a closed manner. Early cases described operating room reduction under general anesthesia. Prior to 1920, open reduction and talus removal were advocated by some for the treatment of subtalar dislocation.2 Plewes and McKelvey2 described 2 cases of subtalar dislocation reduced in the operating room under general anesthesia with Steinman pin placement through the calcaneus, through which traction was applied over a Böhler frame for over an hour prior to reduction. In addition, Böhler’s maneuver was used where the foot was forcibly reduced over a block.17
Today, the majority of subtalar dislocations can be reduced in a closed manner in the emergency department with the use of local anesthesia and procedural sedation. After appropriate anesthesia and analgesia, the reduction maneuver is completed with the patient’s knee flexed to 90° to release tension from the gastrocnemius. With an assistant providing counter-traction, the foot deformity is recreated, longitudinal traction is applied, and the foot is then directed into its appropriate position with the foot in plantarflexion to open the subtalar joint. This should be completed without excessive force. Manual pressure can be applied on the talar head to aid in reduction. Following confirmation of reduction, the leg should be immobilized and a computed tomography (CT) scan obtained to confirm absence of osteochondral fractures and stability of the subtalar joints. Neurologic and vascular status of the foot should be assessed and documented pre- and postreduction.
No consensus exists in the literature as to which type of immobilization should be used. Treatment has been described with initial nonweight bearing in a short posterior splint, short leg cast, and long leg cast lasting between 4 and 6 weeks.1,3,9,11,18,19 Care must be taken when choosing the method of immobilization with regard to the patient’s swelling. It may be prudent to initially immobilize the patient in a posterior splint and change to cast immobilization once the swelling has begun to subside. Patients can begin partial weight bearing at that time. This course is altered by the presence of associated fractures of the foot and ankle. There has been support in the literature for early range of motion after an initial period of immobilization of 3 weeks to minimize the incidence of fibrosis.20 The ability to engage in this aggressive rehabilitation is due to the inherent stability of the subtalar and midtarsal joints postreduction.
Failed reduction by closed means occurs in 10% to 20% of cases of medial and lateral dislocations.3,21 A number of anatomic explanations exist for failed closed reduction. Historically, irreducible medial dislocations have been attributed “buttonholing” of the talar head through the extensor digitorum brevis, extensor retinaculum, talonavicular ligaments, or joint capsule. Talonavicular impaction and interposition of the extensor digitorum brevis have also been implicated. Heck et al22 found in a cadaveric study that the talar head tended to come to rest dorsal to the extensor digitorum brevis, making buttonholing unlikely. They observed entrapment of the extensor retinaculum and talonavicular impaction and also obstruction by the deep peroneal nerve, which was not previously reported.
The posterior tibial tendon, talar head impaction, and entrapment of the joint capsule have been described as causes of irreducible lateral dislocations. In 1954, Leitner23 initially proposed a mechanism by which the flexor retinaculum is disrupted, allowing the tendon to drape over the talar head and preventing reduction. This was later challenged by Mulroy,17 who presented a case of an irreducible lateral dislocation where the flexor retinaculum was still intact. Subsequent cadaveric studies have supported Leitner’s23 original theory.24

Results

Outcomes following closed reduction of isolated subtalar dislocation have been favorable. Several long-term studies with long-term follow-up have shown minimal disability despite significant loss of subtalar motion.3,7 As much as 80% of subtalar dislocations have restriction in motion after healing, and 50% to 80% have radiographic evidence of post-traumatic subtalar arthritis.25 Associated fractures are common in nearly 50% of cases and are most often intra-articular, osteochondral fractures.3,6
Monson and Ryan7 reported a series of 11 patients with medial subtalar dislocations treated over a 9-year span. They found minimal disability, pain mainly localized to the talonavicular joint, and significant loss of subtalar motion.
DeLee and Curtis3 described 17 subtalar dislocations, 3 open, that were treated with immobilization in a short leg cast for 3 weeks when there was no associated fracture. They also found a significant decrease in subtalar motion in all patients, especially those with associated fractures immobilized >6 weeks. This is despite the early mobilization of the subtalar joint as described by McKeever.20
Zimmer and Johnson9 described 9 patients treated for subtalar dislocations, most commonly resulting from a fall, with a 56-month average follow-up. Patients were treated with cast immobilization for an average of 6 weeks. Five patients reported a sensation of instability, and radiographs showed degenerative changes in 2 patients with no incidence of avascular necrosis. As a result, they proposed lengthier immobilization for younger, more active patients, along with inversion and eversion strengthening.9
Perugia et al1 reported a large series of 45 patients who sustained closed subtalar dislocations with an average follow-up of 7.5 years. All patients were treated with closed reduction and placed in a short leg cast, and CT scans were obtained. Patients were immobilized and nonweight bearing for 4 weeks, after which aggressive rehabilitation was performed. The patients had a mean AOFAS score of 83.8 and reported minimal or no limitation in daily or recreational activity. The patients reported discomfort on stairs, inclines, and uneven ground. Only 1 patient went on to subtalar fusion due to instability and pain.1
Goldner et al19 described long-term follow-up of 15 Gustilo grade III open subtalar dislocations treated with urgent irrigation and debridement followed by reduction and immobilization, nonweight bearing in an above-the-knee cast initially for 4 to 6 weeks. They were then transitioned into a below-the-knee walking cast for an additional 6 weeks. Seven of these patients were unstable following reduction, and a Steinman pin was placed across the subtalar joint. The early course was complicated by wound infections in 2 patients and causalgia in 7 lateral dislocations, where the tibial nerve was observed to be injured. Five patients were observed to have osteonecrosis of the talus that required ankle arthrodesis in 1 patient, and 2 patients sustained large osteochondral fractures at the subtalar joint that required subsequent subtalar fusion as late complications. All patients demonstrated loss of motion at the ankle, subtalar joint, and midfoot in addition to difficulty walking on uneven ground.19
Finally, Bibbo et al16 presented a series of 25 patients with acute subtalar dislocation, the majority of whom sustained their injury through a high-energy mechanism. They found an association between high-energy mechanism and open dislocation, but found no correlation between direction of dislocation and mechanism of injury. A high radiographic incidence of degenerative changes was noted, and a significant decrease in AOFAS score was observed.

Authors’ Preferred Method

When presented with a patient with an acute dislocation of the subtalar joint, especially one that resulted from a high-energy mechanism such as a motor vehicle accident or fall from a height, care must be taken to ensure a proper evaluation as described by ATLS protocol. In addition, a complete secondary survey and judicious evaluation for associated musculoskeletal injuries must be completed. Following the initial assessment, thorough evaluation of the patient’s neurovascular status and skin must performed, including appropriate radiographic imaging. Closed injuries should be promptly reduced under either local anesthesia or procedural sedation, followed by repeat radiographic assessment and CT scans to evaluate for associated osteochondral fractures.
Failed closed reduction attempts are brought to the operating room, where closed reduction should be attempted under general anesthesia. Failure to achieve closed reduction in this setting necessitates open reduction with removal of any impediments to reduction should this attempt fail. The reduction is tested for stability, and additional percutaneous fixation is added as necessary. Open dislocations are urgently brought to the operating room, where irrigation and debridement are performed with copious pulsatile lavage, reduction, and closure of the wound. Standard intravenous antibiotics and tetanus vaccination are administered at presentation and for a course of 48 hours.
Open dislocations and those associated with significant swelling are initially immobilized in a posterior splint to aid in skin evaluation. Subsequently and following those successfully reduced in a closed fashion, the patient is placed nonweight bearing into a below-the-knee cast for 4 weeks, followed by progressive mobilization and rehabilitation.

Conclusion

Subtalar dislocations are rare, accounting for only 1% to 2% of all dislocations. The majority of these cases can be treated in a closed manner with a period of nonweight bearing and immobilization with satisfactory results. Occasionally, especially in cases as a result of high-energy trauma and open dislocations, open reduction is necessary. While radiographic evidence of subtalar degenerative change is often present, rarely is the patient symptomatic. Subtalar arthrodesis is an option for patients with refractory subtalar pain and instability.

References

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Authors

Drs Horning and DiPreta are from the Division of Orthopedic Surgery, Albany Medical Center, Albany, New York.
Drs Horning and DiPreta have no relevant financial relationships to disclose.
Correspondence should be addressed to: John DiPreta, MD, Division of Orthopedic Surgery, 1367 Washington Ave, Albany, NY 12206.
doi: 10.3928/01477447-20091020-17