Triplane ankle fracture

Abstract

Triplane ankle fractures, accounting for 5 to 7% of paediatric ankle fractures, are intra-articular with potentially significant functional sequelae if the diagnosis is missed. We present a case of a previously well adolescent boy who sustained this injury during sports through a benign mechanism. This case report discusses key considerations in clinching the diagnosis in an ambulatory care setting and highlights essential factors that inform subsequent definitive management.

Introduction

Triplane ankle fractures occur in all three planes of the distal tibia and involve the epiphysis, metaphysis, and diaphysis, usually arising from ankle inversion. The most common mechanism of injury is supination and external rotation, and less commonly due to adduction.^1,2 They are transitional ankle fractures that tend to arise before complete physeal closure, which takes 18 months, occurring at the ages of 12 to 16 years in girls and 14 to 19 years in boys. ³ This accounts for 5 to 7% of paediatric ankle fractures. ⁴ We present a case of an otherwise well adolescent boy who sustained a triplane ankle fracture despite a relatively benign mechanism of injury, requiring open reduction and surgical fixation. This case demonstrates the importance of maintaining a high clinical index of suspicion for unstable fractures in this demographic; and of obtaining adequate views on plain radiographs to avoid a missed diagnosis.

Case presentation

A 14-year-old boy presented to the Children’s Emergency Department for right ankle pain after stepping on his teammate’s hockey stick during a hockey match. The hockey stick was withdrawn, and the child sustained an ankle inversion injury. There was no direct blunt force or penetrating trauma involved. The child was otherwise previously well with no predisposing risk factors for pathological fractures. He had no previous ankle injuries or surgical instrumentation.

On examination, he was unable to weight bear on the right lower limb. There was right lateral ankle swelling with tenderness over the anterior talofibular ligament and inferior to the medial malleolus. There was no bony tenderness elsewhere, no skin tenting and no clinical signs of ankle instability. The distal neurovascular status was intact.

The initial ankle X-rays are shown below (Figure 1(a)–(c)). What is the diagnosis?

Figure 1.

(a) Anterior view, (b) Lateral view, (c) Mortise view.

Image interpretation

The radiographs revealed a right ankle triplane fracture with a displacement of more than 2 mm, best demonstrated on the mortise and lateral views. Preoperative Computed Tomography (CT) (Figure 2(a)–(d)) showed a vertical fracture through the tibial epiphysis extending to the tibiotalar joint, extending postero-medially to involve the medial malleolus. There was also a horizontal fracture through the distal tibia lateral physis and a coronal plane fracture in the tibial metaphysis which extended inferiorly across the physis to the epiphysis.

Figure 2.

(a) Vertical fracture, (b) Horizontal fracture, (c) Coronal plane fracture, (d) Coronal plane fracture.

Diagnosis

A Salter Harris IV closed intra-articular triplane fracture of the right distal tibia with a 0.3–0.4 cm displacement in all planes was diagnosed.

Clinical course

The limb was kept immobilised in a below knee backslab before surgical fixation the same night. The child underwent open reduction and surgical fixation of the right distal tibia triplane fracture with two partially threaded screws and was discharged well the next day. Serial postoperative X-rays confirmed satisfactory alignment. The child was converted to a below knee cast for 1 month before progressing to partial weight-bearing with a walker boot and crutches for the next month. He was then allowed to full weight bear with a walker boot. He returned to non-competitive sports at 3 months post-op and was back to competitive sports by 5 months post-op. The implants were removed at 9 months post-op as the fractures had fully healed. He was given an open dated appointment.

Discussion

Diagnosis

Despite the benign mechanism of injury of low velocity as described by the child, clinicians should consider obtaining radiological imaging to confirm the presence of potentially unstable intra-articular fractures, especially in the presence of bony tenderness and/or inability to weight bear. Although less common, depending on the clinical sites of tenderness and deformity, a concomitant distal fibula fracture should also be suspected and evaluated for radiologically. ⁵

The Ottawa Ankle Rule, ⁶ validated for patients ≥2 years old, is a useful guide for such clinical decision making. Our patient fulfilled criteria for X-ray imaging as he was unable to weight bear. This case also demonstrates the utility of obtaining a dedicated mortise view (Figure 1(c)) to appreciate the presence of a vertical fracture on the plain radiograph, which is a more readily available imaging modality in the ambulatory setting.

Patho-anatomy

Distal tibial physeal closure starts centro-medially and progresses laterally along the posterior tibia before reaching the anterolateral tibia. While the traditional school of thought posits that the pattern of physeal closure is the key factor in determining the fracture pattern across different age groups, a recent retrospective multicentre cohort study ⁷ on triplane fracture mapping demonstrated a characteristic Y-pattern in fracture morphology regardless of age and gender. Another retrospective cohort study by Hadad et al. ⁸ corroborates with similar fracture pattern findings at the epiphysis, whereas at the metaphysis, fracture patterns do not conform to the expected sequence of physeal closure. It is postulated that the role of the insertions of tibiofibular ligaments are more important determinants of the triplane fracture pattern. ⁷

Management

Transitional ankle fractures can lead to angular deformities, arthritis, growth arrest and limb-length discrepancies. Hence, to ensure anatomical alignment, they minimally require closed reduction in cases of undisplaced or minimally displaced fractures less than 2 mm; or surgical fixation (i.e., percutaneous pinning or open fixation) if ≥ 2 mm displacement is present.^9,10 The role of CT imaging in management of patients with suspected triplane fractures has been debated in the literature. ¹⁰ In our patient, the diagnosis of a triplane fracture necessitating surgery (>2 mm displacement) was established on plain radiographs. CT imaging is useful for preoperative planning to characterise the complexity of the fracture, which includes appreciating the number of fracture fragments and the extent of displacement between fragments. It also facilitates planning of the screw trajectory. Postoperatively, the limb should be immobilised in a cast for 4 weeks to prevent rotation, ¹¹ followed by a walking boot for an additional 2 weeks. ⁴

However, in patients in which the diagnosis of a triplane fracture is established on X-rays, but displacement is less than 2 mm, advanced imaging in the form of a CT scan aids in surgeon decision making regarding operative treatment. A 10-year retrospective review of triplane fractures at a level 1 paediatric trauma centre suggested that conventional radiographs could underestimate the actual articular displacement of triplane fractures. Metaphyseal displacement >1 mm, which can be measured on a lateral X-ray, is strongly predictive of clinically relevant articular displacement on CT that calls for operative treatment. ¹²

Surgical approaches

If deemed to require open reduction, three commonly adopted approaches are: open reduction with cannulated screws; open reduction with percutaneous pinning; and arthroscopic assisted fracture fixation. Cannulated screws were used in this case. Percutaneous pinning done with K-wires will usually require removal in 6 weeks in the ambulatory setting. Arthroscopic assisted fracture fixation is a recently-described approach involving arthroscopic-assisted visualisation of the joint surface, removal of any blocks to reduction i.e., the periosteum, application of a fracture reduction clamp, followed by stab incisions to insert cannulated screws.

Complications

A residual displacement of less than 2 mm is generally acceptable in terms of functional prognosis,^4,9,10 particularly, to avoid post-traumatic arthritis. Recent studies have shown an incidence rate of growth arrest of 25%–40%. ¹³ Premature physeal closure leading to growth arrest and limb-length discrepancy will be relevant in children with at least 3 years of remaining growth potential, necessitating periodic serial radiographs to ensure bilateral growth symmetry before discharge. ¹¹

Conclusion

As the first safeguard against a missed diagnosis, clinicians should maintain a high index of clinical suspicion for transitional ankle fractures in the adolescent age group, even in cases with a low-velocity or benign mechanism of injury. Adequate views on plain radiographs, including anterior-posterior, lateral and mortise views of the ankle, are crucial to clinch the initial diagnosis of a triplane fracture. Advanced imaging in the form of CT scans can help to guide management between operative and non-operative treatment, and aid in pre-operative planning should operative treatment be adopted. Finally, as these fractures involve the articular surface, anatomical alignment with minimal to no residual displacement is required to ensure good long-term functional outcomes.