Total fibula dislocation: A rare variant of a Bosworth fracture-dislocation injury

Abstract

To our knowledge and from our review of the literature, this is a previously unreported variant of a Bosworth fracture – total fibula dislocation. A 45 year old male presented after a high energy external rotation injury to his lower leg and was diagnosed with a total fibula dislocation with the distal fibula dislocated and incarcerated posteriorly to the tibia. Definitive management was operative with fixation of the proximal tibiofibular joint and repair of the posterolateral corner structures as well as fixation distally of the syndesmosis injury. A graded rehabilitation programme was followed and 6 months postoperatively the patient was hill walking and jogging. Bosworth fracture-dislocations are rare injuries that can often be missed during the initial presentation, especially when there is no fracture associated with a dislocation. An underappreciation for the severity of this injury can have major sequelae and the clinician should have a high index of suspicion when diagnosing this injury. An appreciation for Bosworth fracture dislocations and their variations are important for the trauma surgeon.

1. Introduction

1.1. Case report

A 45 year old male pedestrian presented to the emergency department after being involved in a road traffic accident when he was struck by a car. He sustained a high energy external rotation injury to the left leg and was immediately unable to weight bear due to pain and swelling to his left ankle and knee.

Clinical examination revealed a grossly swollen ankle and knee with bruising and ecchymosis to both joints. Sensory function, motor function and vascular status distally were intact.

Initial anteroposterior and lateral radiographs of the ankle revealed a subluxed ankle joint and widened syndesmosis without any evidence of an associated fracture at the level of the ankle (image 1.1)

1.1.

AP and lateral radiograph of left ankle joint (pre-reduction).

Radiographs of the ipsilateral knee joint revealed a widened proximal tibiofibular joint with a posteriorly subluxed fibula (image 1.2).

1.2.

AP and lateral radiographs of left proximal tibiofibular joint.

Closed reduction was attempted in the emergency department under conscious sedation. This resulted in the talus being reduced underneath the tibial plafond but the ankle syndesmosis remained widened. The leg was splinted in an above knee backslab with the knee flexed to 10° and plantargrade position of the ankle (image 2.1, 2.2).

2.1.

AP radiograph of left ankle (post reduction), 2.2 Lateral radiograph of left ankle (post reduction).

Computed Tomography (CT) scan of the ankle and knee was performed. Axial images at the level the ankle revealed a posteriorly dislocated fibula behind the posterolateral ridge of the tibia (image 3.1). Axial images of the proximal tibiofibular joint revealed posterior dislocation of the fibula associated with a fracture of the proximal fibula head (image 3.2) which are further demonstrated in the 3D reconstruction images (image 3.3)

3.1.

Axial CT image at level of ankle syndesmosis.

3.2.

Axial CT image at level of proximal tibiofibular joint.

3.3.

3D Reconstruction images of left ankle syndesmosis demonstrating posterior dislocation of fibula.

(Note: patient had previous intramedullary nailing of contralateral right tibia)

Magnetic Resonance imaging (MRI) was performed to assess the posterolateral corner ligamentous structures associated with the proximal fibula as well as the proximal fibula fracture and proximal tibiofibular joint. This revealed a rupture of the lateral collateral ligament and avulsion fracture of the biceps femoris tendon from its distal insertion onto the fibula head (image 4.1, 4.2).

4.1–4.2.

Coronal T2 images of left knee demonstrating diastasis at the proximal tibiofibular joint.

After MDT discussion, operative management was planned on a dual consultant trauma operating list with syndesmosis fixation and knee soft tissue reconstruction (lateral ligament reconstruction).

Examination under anaesthesia revealed subluxation and dislocation of the proximal and distal tibiofibular joints as well as laxity at the knee joint on varus stress at 30° of flexion. Dial test was positive at 30° of flexion.

The procedure was completed under general anaesthesia and a tourniquet was used.

A lateral approach was utilised to the proximal tibiofibular joint and posterolateral corner (image 5.1). The common peroneal nerve was identified and protected throughout. Injury to the proximal peroneal muscles was identified. The proximal tibiofibular joint was reduced and temporarily fixed with a 2mm k-wire.

Image 5.1.

Lateral approach to knee posterolateral corner/proximal tibiofibular joint. Common peroneal nerve protected with yellow sling.

Distally, a lateral approach to the ankle syndesmosis was performed. The anterior inferior tibiofibular ligament (AITFL) was intact. The fibula was found to be reduced in the notch. The syndesmosis was reduced using a mantis clamp with the foot in dorsiflexion.

The proximal and distal tibiofibular joints were both checked and found to be reduced. Proximal soft tissue repair was performed using a pre-loaded suture anchor (TwinFix, Smith & Nephew) in the fibula head to reduce the biceps femoris tendon and a Syndesmosis Tightrope (Arthrex) to reduce the proximal tibiofibular joint.

Distal fixation was with 3 fully threaded tetracortical screws through a 5-hole third tubular plate (image 6.1, 6.2).

6.1 & 6.2.

intraoperative image intensifier images AP and lateral of ankle syndesmosis fixation.

Final assessment of the lateral and posterolateral corner structures as well as the proximal and distal fibula revealed satisfactory reduction and a stable proximal and distal tibiofibular joint (image 7.1, 7.2).

7.1 & 7.2.

intraoperative image intensifier images AP and lateral of proximal tibiofibular joint fixation.

Postoperatively, the patient was monitored clinically for compartment syndrome for 36 hours prior to discharge and then kept non weight bearing on crutches for 12 weeks. Rehabilitation was to commence at 2 weeks with a hinged knee brace and increasing flexion gradually by 15° every week. Distal common peroneal nerve function was intact immediately postoperatively.

He underwent a graded physiotherapy and rehabilitation regime and 6 months postoperatively had resumed hill walking and jogging.

2. Discussion

Bosworth fractures are a rare occurrence.¹ Bosworth fracture dislocations were first described by David Bosworth in 1947.² In his seminal paper, he described a case series of 5 patients with fracture-dislocation of the ankle joint with a posteriorly displaced and incarcerated distal fibula fragment that was not reducible by closed methods. Woods et al. subsequently described the first case report in the published literature of a posteriorly dislocated fibula behind the tibia without an associated fracture.³

Since then, there have been many cases that have been cited in the literature that are different in definition and anatomy to Bosworth's original description. However, they all share the same finding of a posterior dislocation of the fibula behind the distal tibia. These are all termed Bosworth variants but to our knowledge and from our review of the literature, no previous cases of “total fibula dislocation” (proximal and distal tibiofibular joint dislocation) have been reported.

The mechanism of injury that we have observed is similar to that described in previous Bosworth variants: a violent, high energy external rotation mechanism. Since Bosworth's original description in 1947 and further case reports that we have reviewed in this paper, these rare injuries are now increasingly being recognised in the acute setting. This is especially the case since the wider utilisation of advanced radiographic imaging such as CT scanning. In the largest review of cases in the published literature, Bartoníček et al. (2017) reviewed 108 Bosworth fracture variants with 48 of these being reported since 2007. There is a clear trend towards using CT scanning and 3D CT reconstruction images to visualise the dislocated/fractured fragments in the more recently published cases.⁴

Bosworth fracture dislocation variants are difficult to recognise and require a high index of suspicion, particularly when not associated with a fracture. They are usually caused by a supination external rotation (SER) mechanism with an abnormal amount of external rotation that is often associated with high energy. Many variants of Bosworth fracture dislocation have been described in the literature. They all share the common finding of a locked posterior dislocation of the distal fibula but can be associated with a number of other injuries including Maisonneuve type injury, distal fibula fracture, medial malleolus fracture and proximal fibula fracture. There is no consensus on optimal treatment protocol,¹ largely due to the heterogeneity of the variants of this type of injury and associated injuries. Evidence is limited to case reports or case series.

There is no consensus on the exact nature and classification of the injury although several authors have tried to define the sequence of failure of structures around the ankle.^2,5,6 Downey et al.¹ have summarised these in the table below:

Study	Mechanism
Bosworth, 19472	1.Leg pushes forward and rotates externally with the talus moving from its anatomical position from under the tibia and putting increased force on the lateral collateral ligaments drawing the fibula behind the tibia. 2.If there is adequate amount of force, the fibula then breaks against the posterior tibial border and stays fixed on the posterior tubercle
Bartonicek. et al., 20074	1.Children and adolescents intact fibula with epiphyseolysis of the fibula and tibia (Salter Harris type I) 2.Young patients with closed distal tibia physis, the fibula will dislocate without fracture due to increased elasticity of osseous structures 3.Middle aged and older dislocation occurs with fibula fracture either distally or proximally due to increased elasticity
Perry. et al., 19835	1.Rupture/avulsion of Anterior Inferior Tibiofibular Ligament (AITFL) 2.Rupture/avulsion of Posterior Inferior Tibiofibular Ligament (PITFL) 3.Rupture of the anteromedial part of the capsule followed by rupture of the interosseus ligament 4.Interosseous membrane tears at a point 4–6 cm proximal to the ankle joint 5.External rotation continues, the fibula is then forcefully pushed posterior by the intact lateral collateral ligaments causing the fibula to be entrapped behind the posterolateral ridge of the tibia 6.Talus continues to rotate around the intact deltoid and medial malleolus, causing the fibula to undergo a supination external rotation type fracture at the level of the ankle joint 7.Medial malleolus fracture or rupture of the deltoid ligament
Schatzker. et al., 19776	1.Posterior dislocated talus 2.External rotation of talus 3.Ruptures of the AITFL and PITFL 4.Fracture of the fibula
Meyers. et al., 19577	1.Forward momentum of the leg 2.Eversion of an adducted foot

Michael W. Downey. et al. “The Bosworth Ankle Fracture: A Retrospective Case Series and Literature Review”. EC Orthopaedics 3.1 (2016): 243–253.¹

After initial presentation and assessment and management of life or limb threatening injuries in the acute setting, standard radiographic assessment of ankle injuries include anteroposterior (AP) mortise view and lateral radiographs. Clinical assessment of the joint above should alert the clinician to a possible proximal injury and a very low threshold for obtaining anteroposterior and lateral radiographs of the knee and proximal tibiofibular joint should be made. This is particularly the case with Maisonneuve type injuries. In suspected Bosworth type variants, we would recommend full length AP and lateral knee to ankle radiographs to assess the proximal and distal joint for diastasis, subluxation and/or dislocation as has been recommended by previous authors.^6,8,9

Some authors have described “the axilla sign” which is a unique visible cortical radiodensity on the medial tibial plafond of post injury radiographs.^10,11 There are several parameters when interpreting ankle radiographs that should alert the clinician to an injury including decreased tibiofibular overlap (normal >6mm) and increased medial clear space (normal <4mm on mortise view). On a lateral ankle radiograph, posterior dislocation of the fibula behind the tibia can be seen although this is not always apparent if the radiograph is not a true lateral view.

In isolation or if associated with a dislocated ankle joint, initial attempts can be made in the acute setting to reduce the ankle by closed methods (with sedation and analgesia) followed by splinting the ankle and knee joint in an above knee backslab. However as seen in previously reported cases this is not always successful, especially in the case of a dislocated fibula that is incarcerated behind the tibia.

After initial reduction and splinting, reassessment of the neurovascular status should be performed and the limb elevated. As with Maisonneuve type injuries, these high energy injuries are associated with significant swelling and increased risk of compartment syndrome and therefore require careful observation.

We advocate further investigations in the form of CT scan and/or MRI scan in order to define the injury further and to help guide definitive management of this rare injury. Most cases of Bosworth variant injuries describe distal injuries that can include distal fibula fracture, medial malleolar fracture and syndesmosis injury. These injuries are managed with open reduction of the dislocated fibula into its native position at the incisura and then anatomic reduction and internal fixation of the fractured fragments using AO principles and stabilisation of the ankle syndesmosis.

Our case adds to the literature a previously unreported variant of Bosworth fracture dislocation. This was a significant injury at the proximal tibiofibular joint and the knee that included dislocation of the proximal tibiofibular joint, a lateral collateral ligament injury and an avulsion fracture of the fibula head – essentially a total fibula dislocation. This has been cause by a high energy injury including likely disruption or tear of the interosseous membrane (similar to Maisonneuve injury) and the severity of the injury should not be underestimated by the clinician. The proximal injury was initially recognised on initial radiographs and then subsequent CT and MRI scan helped to define the injury further and guided the definitive management.

3. Conclusion

Bosworth fracture-dislocations are rare injuries that can often be missed during the initial presentation, especially when there is no fracture associated with a dislocation. An underappreciation for the severity of this injury can have major sequelae and the clinician should have a high index of suspicion when diagnosing this injury.

Complete assessment of the whole tibia and fibula including the knee and ankle joint should be made clinically and radiographically with a low threshold for the utilisation of advanced imaging such as CT and MRI.

For optimal results, restoration of native anatomy and stabilisation of the ankle, syndesmosis, knee and associated soft tissue structures such as ligaments is paramount.

Consent

Written and verbal patient consent has been obtained for publication of this case whilst maintaining confidentiality of patient's personal information and details.

Declaration of interests

No competing interests to declare.

Financial Support

None.

CRediT authorship contribution statement

Moez Asaid Zeiton: Conceptualization, Writing - case report, literature review, final proof reading. Rafik Yassa: Final proof reading. Haris Naseem: Final proof reading.