A 58-year-old Asian female presented with a gait disturbance for six months. The patient had progressive weakness in the eversion of the right foot and a gait disturbance which had lasted six months. There was no history of trauma. She denied having numbness, pain, or impaired sensation in the right lower extremity. The patient had undergone pacemaker implantation surgery for sick sinus syndrome several years ago. The patient denied any family history of peroneal neuropathy. A physical examination disclosed severe atrophy of the lateral calf muscles and decreased evertor strength in the right foot, graded 1/5 on the Medical Research Council scale. It was noted that she walked with a wide-based gait and with inversion of the right foot during the stance phase of the gait cycle for every step taken. A sensory examination which tested for light touch, pinprick and proprioception sensation showed that sensation in the lower extremities was intact, and the patellar reflex and ankle jerk reflex tests for both legs were normal. Routine blood analysis revealed the following: White blood cell count, 6.8 × 103/μL [reference range: (3.3-9.9) × 103/μL]; red blood cell count, 2.69 × 106/μL [reference range: (3.78-5.11) × 106/μL]; hemoglobin, 9.9 g/dL (reference range: 11.0-15.0 g/dL); and platelet count, 324 × 103/μL [reference range: (157-392) × 103/μL]. Liver function and kidney function were normal (serum creatinine, 0.77 mg/dL; epidermal growth factor receptor, 77; aspartate transaminase, 29 U/L; alanine aminotransferase, 26 U/L). Electrodiagnostic (EDX) testing was performed with findings compatible with subacute neuropathy of the right common peroneal nerve at the level of the fibular head, preferentially affecting the muscular branch of the superficial peroneal nerve. A neuromuscular ultrasound revealed atrophy of the right peroneal longus and peroneal brevis muscles, graded 3/4 on the modified Heckmatt scale[]. Swelling of the right common peroneal nerve just proximal to an incidentally found fabella was also identified by means of ultrasound imaging. Atrophy of the right peroneus longus and peroneus brevis muscles was also disclosed by means of a computed tomography scan of the lower extremities, with decreased muscle cross-sectional area and decreased radiodensity at the level of the mid-calf compared to the asymptomatic contralateral side. Surgical excision of the fabella was performed through a dorsolateral incision between the biceps femoris muscle and the iliotibial band. The common peroneal nerve was isolated. The fabella was removed and measured 25 mm × 19 mm × 27 mm.