Bone mass distribution of 892 distal tibiae and implications for the treatment of medial malleolar fractures.

Background: The medial malleolus is involved in up to 50 % of ankle fractures. When surgery is required, a thorough understanding of bone mass distribution within the distal tibia is crucial for selecting and positioning screws to ensure stable fixation. Despite its clinical significance, data on the bone mass distribution in the distal tibia remains limited.

Methods: A total of 892 anonymized computed tomography data sets were analyzed to assess bone mass distribution in the distal tibia. Patients were categorized based on age, sex and stratified into those with normal (Hounsfield units (HU) ≥ 122) and reduced (HU < 122) bone density. Utilizing color-coded thermal maps, bone density and bone mass distribution in the distal tibia was visualized. Subsequently, simulation of potential screw trajectories for medial malleolar fracture treatment were conducted and bone density along those trajectories measured.

Results: Patients exhibiting reduced bone density (n = 442) were significantly older (69 (IQR 60-78)) than those with regular bone density (n = 450) aged (62 (IQR 47-72)) and more often female (p < 0.0001). The highest bone density was located within the proximal one centimeter from the distal tibial articular surface. Another region of dense bone was found at the transition from the distal tibia to the medial malleolus. Bone density was lowest at the distal tibial shaft region beginning at around 30 mm (in females) and 33 mm (in males) from the tip of the medial malleolus.

Conclusion: Our data highlights the areas with the highest bone density in the distal tibia. When fixing medial malleolar fractures with unicortical partially threaded screws, this data suggests that screws with a length between 36 and 41 mm should be used at the anterior colliculus and intercollicular. However, regardless of our findings, fracture morphology must be considered, and the AO principles of fracture fixation should be adhered to.

Level Of Evidence: III.