ObjectiveTo evaluate anatomical variations in the lateral ankle and their relationships with pathological conditions of the peroneal tendon on magnetic resonance imaging (MRI) in symptomatic patients.Materials and methodsSixty-nine ankles MRIs of 60 adult patients with symptomatic ankles were included. The presence and sizes of peroneal tubercle and retrotrochlear eminence (RTE), the prevalence of peroneus quartus (PQ), os peroneum, and boomerang-shaped peroneus brevis (PB) tendon, the shape of the retromalleolar fibular groove (RMFG), and the location of the PB muscle-tendon junction were evaluated. The relationships of these variations with peroneal tendinopathies were assessed. The correlations between pathological peroneal conditions on MRI and clinical findings were evaluated.ResultsPeroneal tubercle (mean size, 3.2mm) and RTE (mean size, 4.5mm) were identified in 58 (84%) and 69 (100%) ankles respectively. PQ muscle, os peroneum, and boomerang-shaped PB tendon were found in 9 (13%), 7 (10%), and 24 (34.8%) ankles respectively. The RMFG was concave, flat, convex, and irregular in 14 (20.3%), 40 (58%), 13 (18.8%), and 2 (2.9%) ankles respectively. Sixteen (23.2%) patients had low-lying PB muscle belly. Only boomerang-shaped PB tendons showed a significant relationship with peroneal tendinopathies. MRI and clinical findings had a poor correlation in pathological peroneal conditions and both had low sensitivity in diagnosis.ConclusionLateral ankle anatomical variations are common and cannot be attributed to pathological conditions of the peroneal tendon, except for boomerang-shaped PB tendons. Both clinical and MRI findings have low sensitivity in the diagnosis of peroneal tendinopathies, which are often incidental findings on MRI.