Can CT-based assessment of lateral malleolus anatomy indicate when and how to perform an intramedullary fixation in distal fibula fractures? An analysis of 150 ankles

Purpose The primary aim was to analyse the lateral malleolus morphology with a focus on the shape of the distal fibula for IM fixation of the fibula in infra- and transsyndesmotic fracture patterns. The secondary aim was to propose a treatment algorithm according to the lateral malleolar anatomy. Methods 77 healthy, skeletally mature volunteers underwent CT scanning of the ankle. The fibula medullary canal and its cortical thickness were quantitatively analysed at 4 different levels measured from the fibular tip (1.5 cm, 3.0 cm, 4.5 cm, and 6.0 cm). A geometric classification was proposed, and a decision algorithm was developed. Statistical significance was set at a p-value < 0.05. Results The smallest diameter of the medullary canal of the fibula was at 6.0 cm from the tip of the fibula, in 98.2% of the ankles. The distal fibula can be classified into triangular and rectangular type, according to the cortical thickness index (p < 0.0001). In 16.7% ankles, the internal diameter of the fibula at 6.0 cm was equal or narrower than 3.5 mm (p < 0.05). Conclusion The shape of the distal fibula as evaluated by CT-guided analysis allows for IM osteosynthesis of the lateral malleolus in 83% of individuals. In our study, the smallest diameter of the medullary canal of the fibula was located 6.0 cm from the tip of the lateral malleolus. Coronal CT evaluation is advantageous in indicating which type of IM implant should be used safely for infra- and transsyndesmotic fracture patterns, potentially reducing intraoperative risks.

Automated summary

The aim of this study was to analyze the morphology of the lateral malleolus and propose a treatment algorithm based on its shape for IM fixation of fibular fractures. CT scans of the ankle were performed on 77 healthy volunteers, and the fibular medullary canal and cortical thickness were analyzed at different levels. A geometric classification and decision algorithm were developed. The results showed that the shape of the distal fibula allows for IM osteosynthesis in 83% of individuals. The smallest diameter of the fibular medullary canal was located 6.0 cm from the tip of the lateral malleolus. Coronal CT evaluation can help determine the appropriate IM implant for infra- and transsyndesmotic fracture patterns.