Isolated Flexor Hallucis Longus Weakness Caused by a Popliteal Ganglion Cyst Compressing the Tibial Nerve: A Case Report.

CASE: A 43-year-old woman presented with left foot numbness and progressive difficulty flexing the great toe. Examination revealed isolated flexor hallucis longus (FHL) weakness. Plain radiographs of the left knee showed no degenerative changes. MRI showed a multiloculated ganglion cyst in the left popliteal fossa with increased FHL signal intensity, suggestive of denervation edema. Cyst aspiration resulted in immediate FHL recovery, but the cyst recurred 3 months later, and complete recovery was achieved after surgical excision. At the 3-year follow-up, the patient remained symptom-free with full FHL strength (MMT 5/5) and no cyst recurrence.

CONCLUSION

An extraneural popliteal ganglion cyst can cause selective fascicular compression of the tibial nerve, resulting in isolated FHL weakness, with durable functional recovery achievable through surgical excision.