Case Reports

Bosworth Ankle Fracture-Dislocation

Anthony Silverio, DO, Eric Rebich, DO, Michael Basso-Williams, DO, Nicolas Vardiabasis, DO, and Matthew Robinson, DO
Department of Orthopaedic Surgery
Riverside County Regional Medical Center, Moreno Valley, CA

Abstract
The Bosworth fracture-dislocation is a rare and potentially problematic ankle injury. On initial clinical exam and radiographs, it appears to be a routine ankle fracture. In a Bosworth fracture, however, the proximal aspect of the distal fibula lodges posteriorly to the tibia, making closed reduction nearly impossible. This potential oversight can lead to improper treatment in the emergency room and a poor outcome for the patient. If recognized, however, these injuries can be successfully treated via early open reduction and internal fixation. This rare injury is presented in the following case of a 35-year-old male who underwent an open reduction and internal fixation after multiple failed closed reduction attempts.

Introduction
Ankle fracture-dislocations are common injuries that have long been noted by the medical community and patients alike. Case reports date back to 1836 in which the fibula was dislocated posteriorly in an ankle fracture.2 Practitioners have methodically improved treatment protocols for this injury, effectively reducing the risk of complications, which include severe soft tissue swelling, compartment syndrome, skin necrosis, and unsuccessful attempts at close reduction. Misdiagnosis or mistreatment has historically left patients disabled, in pain, arthritic, unsatisfied, and in need of more drastic surgical options.

Bosworth ankle fracture-dislocation is a rare yet severe injury that was originally described in 1947 by David Bosworth, M.D.1 This fracture-dislocation was described as an irreducible dislocation of the proximal aspect of the distal fibula posterior to the tibia. Five patients were described in the original paper: two fracture-dislocations were not recognized, leading to malunion and eventually requiring arthrodesis; one fracture-dislocation was recognized late but appropriately treated with satisfactory results; and the remaining two fracture-dislocations were recognized and treated, leading to excellent results.1

Approximately sixty Bosworth fracture-dislocation cases have been documented since Bosworth’s initial description.2,3 New information has been presented with several of these publications including age variations, cases with intact fibulas, level of the fracture in relationship to the syndesmosis, mechanism of injury, cases with successful close reduction, and additional injury.2,3 Yet this fracture-dislocation is often misdiagnosed and mistreated, potentially leading to devastating consequences. With the pressure for more middle level practitioners, the possibility for more unrecognized diagnosis is inevitable. A case report is presented below to help accurately diagnose and treat the Bosworth ankle fracture-dislocation.

Case Report
A 35-year-old male was transferred to our facility for higher level of care, complaining of a left ankle fracture sustained while playing soccer the previous day. On the date of injury, the patient was playing soccer at an indoor facility equipped with synthetic turf with typical soccer cleats. The mechanism of injury was a "slide tackle" in which a soccer player leaves his feet with one leg extended in the hopes of taking the ball away from an opposing player, a move the patient was comfortable with. Patient claims that his cleats gripped the turf and twisted his ankle in an external rotation fashion.

Closed reduction was attempted at the transferring institute under conscious sedation with minimal improvement of bony alignment. The patient was complaining of 8/10 throbbing pain in his left lower extremity with associated swelling and the inability to bear weight on the extremity.

On examination of the patient's left ankle, there was an equinus and external rotation deformity. There was moderate left ankle swelling with associated medial ecchymosis and a 2 cm medial fracture blister. Pulses were weakly palpable, but the foot was warm and the capillary refill was brisk. Gross motor was intact. There was some decreased sensation in the distribution of the first web space.

Figure 1 A, Anteroposterior radiograph showing increased tibiofibular overlap. B, Lateral radiograph showing tibiotalar as well as distal tibiofibular subluxation. C, Mortise radiograph

The initial radiographs showed a tibiotalar dislocation with a bimalleolar equivalent ankle fracture (Fig. 1A-C). The initial radiographs can be scrutinized for what appears to be an overly externally rotated lateral radiograph, an AP radiograph which shows increased tibiofibular overlap, and a nearly normal mortise view. Post-reduction x-rays showed a failed reduction attempt with minimal change in bony alignment (Fig. 2A-C).  Given the irreducible nature of the fracture, the patient was admitted and taken to the operating room for open reduction and internal fixation.

During surgery, the distal fibula was approached in a standard posterior lateral incision. Once the fracture site was exposed, it was noted that the proximal aspect of the distal fibula was entrapped behind the posterior lateral edge of the tibia (Fig. 3). The fibula was released and reduced anatomically in relation to the distal tibia and stabilized with a one-third tubular plate. The syndesmosis appeared stable on stress radiographs, and therefore a syndesmotic screw was not inserted (Fig. 4A-C). The patient was placed in a three-sided splint and kept non-weight bearing. At week six, weight bearing in a CAM (controlled ankle motion) walker boot was initiated. Patient currently has full range of motion and is able to weight bear without significant pain. Figure 5 A-C show 6-week post operative x-rays with maintenance of reduction and a healing fracture.

Figure 2, Radiographic ankle series demonstrating failed closed reduction

Figure 3, Intraoperative photo

Figure 4 A-C, Fluoroscopic images demonstrating open reduction with internal fixation of fibula

Figure 5 A-C, 6 week post-operative x-rays

Discussion
Differentiating a Bosworth ankle fracture-dislocation from a typical ankle fracture is difficult. It is recommended that good quality radiographs be obtained. Given the external rotation position of the ankle, adequate radiographs can be difficult to obtain. Some authors argue that radiographs that include the knee and ankle on one film will allow for a more accurate interpretation of the fracture pattern.3 It has also been described that computed tomography may play a role in diagnosis.5 If there is any doubt after good quality radiographs have been obtained, a CT with thin cuts and 3D reconstruction will definitively show if the proximal aspect of the distal fibula is entrapped behind the tibia. A pathognomonic radiographic sign has also been described in recent literature. “The Axilla sign”, a cortical density in the axilla of the medial tibial plafond, was determined to be present exclusively in Bosworth fractures.4 The presence of this cortical density should alert the practitioner to a potential Bosworth fracture. Once the diagnosis has been made, treatment can proceed in a straightforward manner. After open reduction of the entrapped proximal fibula fracture, fixation via interfragmentary compression and a neutralization plate will provide adequate fixation. The need for syndesmotic reduction and fixation will be determined intraoperatively. During our review of the literature, all Bosworth fractures required syndesmotic fixation; however, in our case, the syndesmosis was appropriately stressed and did not require fixation.

Conclusion
While the diagnosis of a Bosworth fracture can be challenging, having a high index of suspicion will allow for prompt recognition and early open reduction and internal fixation. This will ultimately provide the patient with the best possible outcome.

References

1. Bosworth DM. Fracture-dislocation of the ankle with fixed displacement of the fibula behind the tibia. J Bone Joint Surg AM 1947; 29:130-5.
2. Bartonicek, J, Fric, V, Svatos, F, Lunacek, L. Bosworth-type fibular entrapment injuries of the ankle: Bosworth lesion. A report of 6 cases of literature review. J Orthop Trauma 2007;21:710-717
3. Hoblitzell, RM, Ebraheim, NA, Merritt, T, Jackson, WT. Bosworth fracture-dislocation of the ankle. A case report and review of the literature. Clinical Orthopaedics and Related Research. 1990; 255:257-262.
4. Khan, F, Borton D. A constant radiological sign in Bosworth’s fractures: “the axilla sign”. Foot Ankle Int 2008; 29:55-57.
5. Wright SE, Legg A, Davies MB. A contemporary approach to the management of a Bosworth injury. Injury 2012; 43:252-253.