Growth plate or physeal fractures are common injuries in skeletally immature children and adolescents. Most fractures in skeletally immature individuals involve the physis as this cartilaginous growth center is the weakest part of the bone and therefore more susceptible to injury. Triplane ankle fractures are complex traumatic Salter-Harris IV fractures with involvement of the metaphysis, physis, and epiphysis. The term “triplane” refers to the different orientation of the fracture lines in the distal tibia and represents a frequent diagnostic challenge. The epiphysis is fractured in the sagittal plane and is visible on the anteroposterior (AP) radiograph. The posterior aspect of the metaphysis is fractured in the coronal plane and appreciated on the lateral radiograph. The physis becomes separated in the axial plane. Treatment is closed reduction or surgical fixation depending on the degree of fracture displacement and articular step-off. Prognosis is excellent, given the triplane ankle fracture is identified and appropriately treated.
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. 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). Medial triplane injuries are rare and occur secondary to an adduction force.
Ankle injuries are common in children and rank second only to injuries to the hand and wrist in those aged 10 to 15 years old. Ankle fractures occur twice as frequently in males and represent 5% of all pediatric fractures and 9% to 18% of all physeal injuries. Triplane fractures specifically account for 5% to 15% of pediatric ankle fractures and occur in adolescents with a mean age 13 years and 5 months, range 10 to 17 years. Tillaux fractures classically occur in older adolescents with more resulting physeal closure.
Skeletal growth typically continues until 16 years in males and 14 years in females. 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. Once closure of the distal tibia physis begins, there is an 18 to a 20-month transitional period where closure is incomplete. 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.
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. 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.
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 with the AP view revealing 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. 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.
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. 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.
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. Care should be taken to place screws as perpendicular 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.
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 must be taken to ensure all screw threads are past the fracture if using partially threaded screws. [Level V]
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.
Triplane ankle fractures are classified based on the number of parts as well as the pattern.
Classification by Parts:
Classification by Pattern:
Appropriately identified and treated triplane ankle fractures have an excellent prognosis. Physeal damage or premature closure occurs in 7% to 21% of cases. 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 remaining should be followed clinically. Cooperman et al. reported a series of 14 triplane ankle fractures with three growth disturbance complications. All occurred in patients with more than two years of growth remaining.
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.
A provider should not assume a pediatric ankle injury is simply a ligamentous sprain. The ligamentous stabilizers of the ankle are stronger than the physis making physeal fracture much more common. In appropriately aged patients, scrutinize orthogonal radiographic views in patients with apparent distal tibia Salter-Harris II or III fractures to avoid missing a more significant Salter-Harris IV triplane ankle fracture.
Treatment strategies of triplane ankle fractures depend on the residual displacement following reduction. Post-reduction CT scans should be obtained to assess the quality of reduction and articular step-off. Ertl et al. demonstrated in a series of 23 triplane ankle fractures managed nonoperatively at a single institution (Level IV) that residual articular displacement of more than 2 mm results in poor outcomes if managed nonoperatively.
Triplanar ankle fractures require an interprofessional team approach. The primary care practitioner should immediately enlist an orthopedist for evaluation and eventual treatment. Following any procedure, or with non-operative management, an orthopedic specialty-trained nurse is invaluable. They can assist during surgery, provide post-surgical care, and help with conservative, non-operative management, monitoring progress and coordinating with physical therapy when necessary, serving as a coordination point between the treating clinician and other providers. This type of interprofessional collaboration will result in better outcomes and improved patient care. [Level V]
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