The position, orientation, and relative size of the fibularis longus tubercle in normal patients: A weightbearing CT assessment.

The fibularis longus attaches to the base of the first metatarsal at the fibularis/peroneus longus tubercle (FLT/PLT). Theoretically, differences in FLT morphology may reflect changes in the function of the fibularis longus. This study defines the normal limits of the FLT position, orientation, and size in patients with morphologically normal foot anatomy. A retrospective analysis of 131 feet without deformity in 72 patients undergoing weightbearing CT (WBCT) at a single center was conducted. The position and morphology of the FLT was assessed with novel measurements including tubercle-floor distance, tubercle-metatarsal angle, and the angle between the floor and a line bisecting the FLT (bisecting angle). Roundness of the FLT was compared to a triangle limiting its shape (triangular ratio), with lower values indicating increasing roundness. We also report relative size of the FLT to the first metatarsal (X/Y ratio), and relative size of the first metatarsal and FLT to the second metatarsal (XY/Z ratio). There were no significant side to side differences for any measurement (p > 0.05). Mean values were: tubercle-floor distance 28.02 ± 2.63 mm, tubercle-metatarsal angle 32.7 ± 6.32 degrees, bisecting angle 65.58 ± 6.27 degrees, triangular ratio 0.69 ± 0.04, X/Y ratio 1.13 ± 0.20, and XY/Z ratio 3.44 ± -0.72. Bisecting angle strongly correlated with tubercle-metatarsal angle (Pearson correlation 0.840, p < 0.001) suggesting FLT rotation occurred independent of foot position. ICC was >0.943 for all measurements. This study reports the morphology of the FLT in individuals with normal feet. This normative data may be used in future studies examining differences between groups of patients with foot pathology, helping us better understand the role of fibularis longus in the development and treatment of foot disorders.