Anatomy of the posterior malleolar fracture

W. Marlow, A. Molloy, L. Mason

Introduction: There is an increasing acceptance that the clinical outcomes following posterior malleolar fractures are less than satisfactory. Current ankle classification systems do not account for differences in fracture patterns or injury mechanisms, and as such, the clinical outcomes of these fractures are difficult to interpret. The aim of this study was to analyse our posterior malleolar fractures to better understand the anatomy of the fracture.

Methods: In a series of 42 consecutive posterior malleolar, who all underwent CT imaging, we have described anatomically different fracture patterns dictated by the direction of the force and dependent on talus loading.

Results: We found 3 separate categories. Type 1 - a rotational injury in an unloaded talus resulted in an extraarticular posterior avulsion of the posterior ligaments. This occurred in 10 patients and was most commonly associated with either a high fibular spiral fracture or a low fibular fracture with Wagstaffe fragment avulsion. The syndesmosis was usually disrupted in these patients. Type 2 - a rotational injury in a loaded talus resulting in a posterolateral articular fracture, of the posterior incisura. This occurred in 16 patients and was most commonly associated with a posterior syndesmosis injury, low fibular spiral fracture and an anterior collicular fracture of the medial malleolus. Type 3 - axially loaded talus in plantarflexion causing a posterior pilon. This occurred in 16 patients and was most commonly associated with a long oblique fracture of the fibular and a Y shape fracture of the medial malleolus. The syndesmosis was usually intact in these patients.

Conclusion: In conclusion, the anatomy of the posterior malleolar should not be underestimated and requires careful consideration during treatment and categorisation in outcome studies to prevent misinterpretation.