Morphology of the Posterior Malleolar Fracture Associated With a Spiral Distal Tibia Fracture

OBJECTIVE: To define the pathoanatomy of the posterior malleolus fracture associated with a spiral distal tibia fracture to guide clamp and implant placement when treating these common injuries. DESIGN: Retrospective cohort. SETTING: Level I trauma center. PATIENTS/PARTICIPANTS: One hundred twenty-two spiral infraisthmal tibia fractures identified from a cohort of 922 tibia fractures undergoing intramedullary nailing over a 7-year period. MAIN OUTCOME MEASUREMENTS: We collected instances of intra-articular extension seen on preoperative, intraoperative, or postoperative imaging. For patients with a posterior malleolus fracture and computed tomography imaging, we used an axial image 2-3 mm above the articular surface to create a fracture map. RESULTS: Intra-articular extension was present in 84 patients (68.9%), with posterior malleolus fractures occurring most commonly (n = 59, 48.4%). Other fractures included plafond fractures (n = 8), medial malleolus fractures (n = 7), anterior-inferior tibiofibular ligament avulsions (n = 5), and other anterior fractures (n = 5). Forty-one of 44 (93%) posterior malleolus fractures with cross-sectional imaging were Haraguchi type I (posterolateral-oblique type) with an average angle of 24 degrees off the bimalleolar axis. The remaining 3 were type II (transverse-medial extension type) fractures. Posterior malleolus fractures were visible 61% of the time on preoperative radiographs. DISCUSSION: Posterior malleolus fractures occur in approximately half of spiral distal tibia fractures and are consistently posterolateral in their morphology. This study can be used to enhance evaluation of the posterior malleolus intraoperatively (eg, ∼25 degrees external rotation view), and if the typical variant of posterior malleolus is identified, clamps and lag screws might be applied accordingly.