Triplane Ankle Fracture

Etiology

Triplane ankle fractures occur secondary to ankle trauma in an adolescent during a transitional period of partial physeal closure. Similar to Tillaux fractures (transitional Salter-Harris III ankle fracture), a supination-external rotational force is often the reported mechanism.[1] Lateral-sided triplane injuries are the most common as the lateral physis is the weakest and the point of insertion of the stout anterior inferior tibiofibular ligament (AITL).[2] Medial triplane injuries are rare and occur secondary to an adduction force.[3]

Epidemiology

Ankle injuries are common in children and rank second only to injuries to the hand and wrist in those aged 10 to 15 years.[4][5][6] Ankle fractures occur twice as frequently in males and represent 5% of all pediatric fractures and 9% to 18% of all physeal injuries.[3][5][7][8][9] Triplane fractures specifically account for 5% to 15% of pediatric ankle fractures and occur in adolescents with a mean age of 13 years and 5 months and a range of 10 to 17 years.[10] Tillaux fractures classically occur in older adolescents with more resulting physeal closure.[2]

Pathophysiology

Skeletal growth typically continues until 16 years in males and 14 years in females.[2][3] Physeal closure is driven by the hormone estrogen, which gets produced at a younger age in females. Physeal closure occurs in a predictable pattern beginning centrally and progresses anteromedially, posteromedially, and finally laterally.[2] Once closure of the distal tibia physis begins, there is an 18 to 20-month transitional period where closure is incomplete.[11] The unfused portions of the physis are at risk for transitional ankle fractures (triplane and Tillaux) during this period of incomplete growth plate closure. As the lateral aspect of the physis is the last to close, lateral epiphysis fractures are much more common than medial patterns.[2]

History and Physical

Adolescents typically report a twisting injury often during a sporting activity with resulting ankle pain and inability to bear weight. The most common injury mechanism is supination and external rotation, while the uncommon medial triplane fracture occurs with an adduction force.[1][3] Swelling or ecchymosis are commonly appreciated, but angular deformity can present in severe injuries. Gross instability is rarely appreciated. Patients will be tender to direct palpation of the physis circumferentially. As in all ankle injuries, the clinician should perform and document a thorough neurovascular exam.

Evaluation

Triplane ankle fractures are often under-appreciated with plain radiographs as each view typically only reveals a single fracture line. AP, mortise, and lateral views are essential. The AP view reveals the sagittal fracture line in the epiphysis (Salter-Harris III), and the lateral view demonstrating the coronal fracture line in the posterior metaphysis (Salter-Harris II). The mortise radiograph is the best way to appreciate articular displacement on plain films. Computed tomography (CT) is a vital tool for assessing the exact fracture pattern, degree of displacement, and articular step-off. Jones et al. demonstrated that all surgeons surveyed changed the starting point and trajectory of planned screw fixation after reviewing the CT scan versus relying on plain radiographs in a series of triplane ankle fractures.[12] Of note, the rare medial triplane fracture differs from the lateral injury in that the metaphyseal fracture occurs in the sagittal plane and the epiphysis injury is more medial and coronally oriented.

Treatment / Management

The treatment of triplane ankle fractures depends on the amount of fracture fragment displacement and degree of articular step-off visualized on CT. Nondisplaced and minimally displaced (less than 2 mm) injuries can effectively undergo management with long leg cast immobilization.[3] The reduction maneuver for the classic triplane ankle fracture pattern is ankle internal rotation with a post-reduction CT scan used to assess residual displacement and articular step-off. Rapariz et al. reported excellent outcomes in a series of triplane fractures displaced less than 2 mm, while displaced injuries developed chronic pain and ankle degenerative changes.[13]

Surgery is reserved for triplane fractures with over 2 mm of displacement or injuries that lost reduction during attempted nonoperative management. Fixation is typically achieved with one or two screws placed parallel to the physis. Screw placement can be in the metaphysis, epiphysis, or both depending on the fracture pattern. Screw types utilized for fixation vary widely no evidence suggesting the superiority of cannulated versus non-cannulated or fully threaded versus partially threaded screw fixation in triplane ankle fractures. Congruity of the articular surface must be restored to optimize outcomes.[11] Care is necessary to place screws perpendicularly as possible to fracture lines to maximize compression and maintain reduction. Clinicians and researchers have described both closed reduction and open reduction techniques with universally good outcomes.[14][15](B2)

Several clinicians' preferred technique includes percutaneous reduction via small incisions and fixation with one or two non-cannulated partially threaded 3.5 mm screws placed parallel to the physis. The epiphyseal fracture is usually amenable to anterolateral to posteromedial placed screws, while the metaphyseal fragment usually gets captured with direct anterior to posterior based screws. Care is also necessary to ensure all screw threads are past the fracture if using partially threaded screws. [Level 5]

Differential Diagnosis

Differential diagnoses of adolescent ankle pain include sprain, Tillaux fracture, triplane fracture, syndesmosis injury, ankle dislocation, subtalar dislocation, calcaneal fracture, talus fracture, malignancy, and infection.

Staging

Triplane ankle fractures are classified based on the number of parts as well as the pattern.

Classification by Parts

• 2-part
  • Part 1: anterolateral and posterior epiphysis
  • Part 2: anteromedial epiphysis
• 3-part
  • Anterolateral epiphysis
  • Posterior epiphysis
  • Anteromedial epiphysis
• 4-part
  • Comminuted

Classification by Pattern

• Lateral
  • Most common
  • Epiphyseal fracture: sagittal plane
  • Physeal fracture: axial plane
  • Metaphyseal fracture: coronal plane
• Medial
  • Epiphyseal fracture: coronal plane
  • Physeal fracture: axial plane
  • Metaphyseal fracture: sagittal plane
• Intramalleolar
  • Type I: intraarticular, involving weight-bearing surface
  • Type II: intraarticular, not involving weight-bearing surface
  • Type III: extraarticular

Prognosis

Appropriately identified and treated triplane ankle fractures have an excellent prognosis. Physeal damage or premature closure occurs in 7% to 21% of cases.[16][17][18][19] Many have questioned the significance of preserving the physis, given the limited remaining growth potential. The clinician should clinically follow patients with more than two years of expected growth should be followed clinically. Cooperman et al. reported a series of 14 triplane ankle fractures with three growth disturbance complications.[20] All occurred in patients with more than two years of growth remaining.[20]

Complications

Complications during nonoperative management include loss of reduction requiring operative fixation, nonunion, malunion, and persistent pain. Surgical adverse events are rare and include bleeding, infection, nonunion, painful hardware, and transient neuropathy.