A triplane fracture is a complex and relatively uncommon ankle injury that occurs almost exclusively in adolescents nearing the end of skeletal growth. This fracture pattern involves the distal tibia, the end of the long bone, and is named for the three distinct planes in which the bone breaks. Because the injury violates the growth plate (physis), it presents a unique challenge for orthopedic specialists compared to fractures in fully grown adults or younger children.
The Anatomy and Mechanism of Injury
The triplane fracture occurs at the distal end of the tibia, where it meets the ankle joint. It is considered a “transitional fracture” because it happens during the brief 18-month period when the growth plate is closing permanently. The distal tibial physis does not fuse all at once; closure typically begins centrally and progresses toward the lateral side.
During this transitional period, the medial side of the growth plate is already fused, while the lateral side remains open and weak. A sudden, forceful twisting motion, most commonly a supination-external rotation injury, causes the fracture to propagate through this vulnerable, partially open growth plate. The average age for this injury is 13 to 14 years, correlating with this asymmetrical closure pattern. This mechanism results in a fracture that combines features of two types of growth plate injuries, often categorized as a complex Salter-Harris Type IV fracture.
Understanding the Triplane Nature
The term “triplane” refers to the three different anatomical planes the fracture lines follow.
The first component is vertical, or in the sagittal plane, passing through the epiphysis, the rounded end of the bone that forms the joint surface. This fragment is typically visible on an anterior-posterior (AP) X-ray view.
The second component is a horizontal separation running along the growth plate itself, across the axial plane, where the physis has not yet fused.
The third line of fracture runs obliquely or vertically through the metaphysis, the wider part of the bone shaft, in the coronal plane. This metaphyseal fracture is often best appreciated on the lateral X-ray view. This combination of breaks separates a segment of the ankle joint into two, three, or sometimes four distinct fragments, each existing in a different orientation.
Diagnosis and Imaging Essentials
Diagnosing a triplane fracture can be difficult based on standard X-ray images alone because each view only reveals one of the three fracture components. For instance, a standard AP view might suggest a simpler Salter-Harris Type III fracture, while the lateral view may resemble a Type II injury. This discrepancy highlights why X-rays are often insufficient for accurately characterizing the full extent of the damage.
A Computed Tomography (CT) scan is the preferred imaging modality to fully assess the injury. The CT scan provides a three-dimensional view of the ankle, allowing the orthopedic surgeon to visualize the number of fragments, their exact orientation, and the degree of displacement. This detailed information is necessary for determining the severity of the fracture and planning the surgical approach to restore the alignment of the joint surface.
Treatment Approaches and Recovery
Treatment for a triplane fracture depends primarily on the amount of displacement, especially at the joint surface. Fractures that are minimally displaced (less than two millimeters of separation or step-off) can often be managed without surgery. Non-surgical treatment involves a closed reduction, where the fragments are manually realigned, followed by immobilization in a long leg cast for several weeks.
If the fracture fragments are displaced by two millimeters or more, or if acceptable alignment cannot be achieved through closed reduction, surgical intervention is necessary. The goal of surgery, often Open Reduction Internal Fixation (ORIF) or percutaneous screw fixation, is to achieve anatomical alignment of the joint surface to prevent long-term issues like arthritis. Following treatment, the patient will spend several weeks immobilized in a cast or walking boot, with a full return to activities occurring over several months. Due to growth plate involvement, patients require follow-up monitoring to check for potential complications such as growth arrest.