Teaching Case

A 14-year-old girl presents at the emergency department with a swollen left ankle and weight-bearing inability after falling 2 meters from a playground tower. The fall caused an inversion/supination trauma of the ankle, resulting in significant tenderness of the distal tibia during examination.

Conventional radiographs of the left ankle revealed an oblique tibial fracture running from lateral to medial on the anteroposterior (AP) and mortise views, distal to the physis, without significant displacement nor intra-articular gap (Figure 1a). The lateral view, however, showed a subtle vertical fracture line, through the posterior malleolus with intra-articular hydrops and soft tissue swelling (Figure 1b).

To evaluate the extent of involvement of the physis, subsequent computer tomography (CT) was performed and revealed three distinct fracture lines. The first fracture runs para-sagittally in the epiphysis of the lateral distal tibia, extending to the anterior physis with an intra-articular gap (Figure 2a). The coronal plane showed a second fracture line, running from the anterior central physis to the joint’s medial aspect (Figure 2b). Lastly, a vertical fracture line separated the posterior malleolus from the ankle joint on the posterior aspect of the distal tibia (Figure 2c).

A triplane ankle fracture, also known as a Marmor–Lynn fracture, is a type of fracture of the distal tibia that predominantly affects children between the ages of 12 and 15. It is most commonly caused by sports or playground injuries [1]. This epiphyseal fracture has fracture lines in three planes: sagittal, coronal and axial. This triplanar nature is a result of the sequence of distal tibial physis closure during early adolescence, commencing anteromedially at Kump’s bump, and extending medially before finishing laterally towards the syndesmosis (Figure 3). During this time, unfused segments of the growth plate are prone to fracture, while the fused parts become relatively stable in trauma. Due to the importance of ongoing physeal closure, this fracture type is also referred to as a “transitional fracture” [1–3].

The intricate triplanar pattern does not allow complete visualisation using conventional AP and lateral radiographs. These fractures mimic Salter–Harris type III fractures on an AP view and Salter–Harris type II fractures on lateral view, making it challenging to estimate displacement accurately. Further evaluation, diagnosis, and pre-operative planning require CT [1,2,4,5].

When intra-articular displacement is limited to 2mm, conservative treatment using cast immobilisation is an option. Any greater displacement, however, requires open reduction and internal fixation, either using lag screws (which can sometimes be placed percutaneously) or plate osteosynthesis [1,2]. Thus, CT imaging is indispensable for pre-operative planning. According to a study conducted by Eismann et al., in up to 41% of cases, surgeons changed their proposed strategy for internal fixation after analysis of the CT images [5].

Triplane ankle fractures continue to pose a challenge for emergency physicians, radiologists, and orthopaedic surgeons. Fractures involving the distal tibia growth plate in adolescents demand careful consideration, and when uncertainty arises, additional evaluation through CT imaging is essential to avoid overlooking indications for surgery. Existing literature emphasises the importance of using multiplanar imaging techniques in nearly all cases of triplane fractures, as they enhance diagnostic accuracy and pre-operative decision-making [2,4,5].

Written informed patient consent for publication has been obtained.