Dimensions of the Lateral Malleolar Fossa and Its Potential Violation With Lateral Distal Fibular Plate Fixation

A previously undescribed pitfall of lateral distal fibular locking plates is the risk of violating the lateral malleolar fossa (MF). No previous study has described the dimensions of this fossa. All cases using a lateral distal fibular plate for a fibula fracture from December 2012 to December 2015 (n=365) at a single institution were reviewed. Screws that violated the medial fibular cortical density corresponding to the MF were identified as "at-risk" screws. Available preoperative computed tomography (CT) scans were reviewed (n=69) to measure MF dimensions. Of 365 patients, 115 (31.5%) patients had distal fibular screws at risk of MF violation. There were no significant differences between MF violation and non-violation groups in terms of age, sex, open fracture, syndesmotic fixation, and Weber classification. The MF dimensions were measured on CT scans. Mean height was 12.96 mm (SD, 2.09 mm; range, 9.0-17.3 mm). Mean width was 7.52 mm (SD, 1.37 mm; range, 4.2-10.4 mm). Mean depth was 8.32 mm (SD, 1.59 mm; range, 5.3-11.8 mm). Mean ratio of MF to total fibular width was 0.46 mm (SD, 0.07 mm; range, 0.3-0.65 mm). Mean MF to total fibular depth was 0.42 mm (SD, 0.07 mm; range, 0.28-0.58 mm). There was a difference in dimensions of patients with screws at risk of MF violation compared with those without (MF height: 13.77 vs 12.56, P=.02; MF width: 7.98 vs 7.30, P=.05; MF to fibula width ratio: 0.49 vs 0.44, P=.01; MF to fibula depth ratio: 0.43 vs 0.42, P=.05). The MF violation is a previously unreported but potentially prevalent pitfall of lateral distal fibular plate fixation. Surgeons should be aware of the MF size and exhibit caution when placing screws in the distal locking holes during fibula fixation. [Orthopedics. 2020;43(3):e141-e146.].