Hawkins type III talar neck fracture dislocation with neurovascular and tendon entrapment in a toddler

Abstract

Paediatric displaced fracture of the neck of talus is extremely rare injury with variable outcomes. We report our experience in managing a Hawkins type III talar neck fracture dislocation with neurovascular and tendon entrapment in a 3-year-old boy. We describe the emergency presentation, radiological findings, orthopaedic management and clinical and functional outcomes in this toddler following the injury with review of the current literature.

Background

Fractures of talus in a paediatric age are rare, with a reported incidence between 0.01% and 0.08%.¹ The talus in younger children has more resistance to torsional forces than the adults due to its cartilaginous nature and flexibility of foot.^{2 3} The most common location of fracture in children is the neck of talus followed by talar body. Non-operative treatment is acceptable for undisplaced fractures; however, displaced fractures of the talus require reduction and surgical fixation to reduce the risk of osteonecrosis due to severance of its tenuous blood supply.^3–5 Until now a Hawkins type III fracture at the age of 3 years has not reported in the literature. We highlight such a rare injury with an urgent situation requiring immediate intervention to address and prevent a potential neurovascular compromise.

Case presentation

A 3-year-old boy presented to the emergency department after fall of a heavy object (motorbike) on his left foot. He was unable to bear weight on his left leg. It was an isolated injury with no concerning medical or surgical history.

Clinical examination revealed a grossly swollen left ankle and foot, with no open wounds. A bruise measuring 3×2 cm was present on the posteromedial aspect of the left ankle. He was reluctant to move his ankle and toes due to pain. Dorsalis pedis artery pulsations were palpable, but the posterior tibial artery could not be clinically felt behind the medial malleolus. Following triage and administration of analgesia titrated to his body weight, anteroposterior and lateral radiographs of left ankle were obtained (figure 1). These confirmed displaced talar neck fracture (Hawkins type III neck of talus fracture with subtalar dislocation).

Figure 1.

Anteroposterior and lateral radiographs of left ankle showing Hawkins type III fracture dislocation.

Differential diagnosis

Clinically and radiologically, the injury was due to trauma with fracture dislocation of neck of left talus with neurovascular compromise of the foot.

Treatment

The serious, limb threatening nature of the injury was explained to the parents of the child. The foot and the ankle was splinted in a plaster of Paris backslab for support. He was admitted to the hospital for analgesia, elevation, monitoring and planned for emergency surgery. An open reduction and internal fixation of the talar neck fracture dislocation was scheduled imminently due to concerns of neurovascular compromise of the foot. After general anaesthetic induction, a posteromedial approach to the ankle was performed without the use of limb tourniquet. Surgery was performed within 6 hours to injury. On superficial dissection, the posterior tibial neurovascular bundle was found to be lying behind the dislocated talar body fragment along with the posterior tibial, flexor hallucis longus and flexor digitorum longus tendons leading to the vascular compromise (figure 2A). As soon as the fracture dislocation was reduced and temporarily stabilised by ‘Kirschner’ wires, the posterior artery perfusion returned within few minutes (figure 2B). Definitive fixation of the fracture was undertaken with the use 2×4 mm cannulated compression screws (figure 3). Postoperatively, a below knee plaster was given for 6 weeks and non-weight bearing mobilisation was advised.

Figure 2.

Intraoperative picture showing displaced fracture talus (A) fracture reduction and temporary fixation with Kirschner wires (B).

Figure 3.

Anteroposterior and lateral radiographs of the left ankle on first postoperative day.

Outcome and follow-up

He was regularly followed-up in our fracture clinic for wound care and radiological monitoring. Passive and active ankle range of motion exercises were started at 6 weeks. At 12 weeks, ankle range of motion was pain free and radiographic union of fracture was evident (figure 4A). Weight bearing was allowed and started at this time. However, at 6-month follow-up visit after the index surgery, radiographic evaluation revealed one of the screw had loosened and hence was removed. After 18 months on plain radiographs, avascular necrosis (AVN) of talar body was found (figure 4B). Clinically, however, the child had pain-free functional ankle range of motion (neutral dorsiflexion to 40° plantar flexion) with no restriction of activities of daily living (figure 5A–D). The parents were counselled about the complex nature of the injury with the guarded prognosis but reassured that a satisfactory outcome may ensue in the child due to articular remodelling considering his age. They were provided with a future clinical appointment if any symptoms arose as he grew into his adulthood.

Figure 4.

Anteroposterior and lateral radiographs of the left ankle seen on 12 weeks from primary fixation (A); avascular necrosis of talar body was evident on 18 months after the index surgery (B).

Figure 5.

(A–D) Clinical photographs at 18-month follow-up showing functional outcome.

Discussion

Fracture of the talus is a rare injury in paediatric age group.

The most frequent mode of injury tends to be due to high velocity trauma after motor vehicle accident or a fall from a height. A component of dorsiflexion of the foot with axial loading of the talus against the anterior tibial plafond appears to be the most common mechanism of injury.^{3 6} Both of above elements appear to have caused the talar neck fracture in our patient.

Commonly described talar neck fractures in paediatric age group tend to be of undisplaced (Hawkins type I) or Hawkins type II with considerably favourable outcome.⁵ What is unusual is nature of displacement and the severity of the injury in our child. It could perhaps be explained by the fall of the heavy motorbike on a small sized foot with the fracture dislocation occurring as the force continued beyond the elastic resistance of the skeletally immature bone leading to a displaced fracture. Consequently, the severity of the displacement was such that the talar body had retropulsed on the posterior tibial neurovascular structures causing vascular compromise of the foot. Though reports of high rate of complications following talar neck fractures have been described in the literature, it is critical to recognise this imminent danger to nerves, vessels and tendons with early diagnosis and focused vascular examination. Early treatment is needed to identify and release neurovascular and tendon entrapment as well as to minimise risk of complications such as AVN, non-union, talar dome collapse and ankle arthrosis.^{5 7} The debate of using tourniquet in ankle surgery has evaluated in the literature with concerns of reperfusion injury.⁸

In adults, the reported incidence of AVN for Hawkins type III fractures is 80%–90%. Though lower incidence of AVN in paediatric age has been noted, it has been observed that the incidence of displaced talus fractures, as well as complications increases with patient age.^{5 7 9}

Meier et al studied the long-term outcome of all Hawkins type fractures with different treatment modalities.⁵ Hawkins types III and IV fractures were treated by open reduction and internal fixation with Kirschner wires, screws and external fixation or combination of these fixation devices. Patients with open injuries and Hawkins types III and IV showed more complications, including vascular necrosis, arthrosis and deep infection, than Hawkins type I or type II.

Smith et al in their study observed that 33% children with Hawkins type III fractures went on to develop AVN.⁷

Kızılay and Aytan reported a low-energy Hawkins type III fracture dislocation with neurovascular and tendon entrapment in a 9-year-old child. Open reduction of fracture was done using two 4.5 mm cannulated screws. However, at 2-year follow-up, they observed AVN of the talar head.¹⁰ They also stressed the importance of soft tissue structures entrapment between fracture fragments, as seen in our child. Pereles et al also reported AVN with partial collapse of body of talus 8 months after internal fixation of fracture dislocation of neck of talus in a 10-year-old child despite protection from weight bearing for 8 months after surgery.¹¹ Authors suggest such injuries have a guarded prognosis.

This case highlights the need for early recognition of displaced fracture dislocation of neck of talus, which can lead to imminent vascular compromise and tendon entrapment. Urgent intervention can avoid acute limb threatening complication. Though the delayed complication of AVN cannot be completely prevented or predicted, a good functional outcome may be achieved with early stabilisation of the fracture and the remodelling resilience in a growing skeleton.

Learning points.

• Displaced fracture-dislocation of neck of talus is a rare injury in toddlers and children.

• These can be associated with neurovascular compromise and tendon entrapment.

• Emergent surgery is necessary to obviate this limb threatening injury and prevent vascular complication.

• Avascular necrosis of the talus may occur due to its precarious blood supply, but a good functional outcome may ensue in children due to articular remodelling.