Tarsal tunnel syndrome; posterior tibial nerve entrapment
A 65 year old female presented with a one week history of right knee and right foot pain associated with numbness and tingling sensation on the plantar surface of her right foot. Past history reveals a recent knee replacement surgery and a well-healed incision in the anterior line of the knee on physical examination. She reported her symptoms started shortly after the surgery. Further evaluation revealed mild vascular changes but did not meet Budapest criteria that would qualify for complex regional pain syndrome. Electromyography and nerve conduction studies were ordered and revealed posterior tibial nerve entrapment. Positive Tinel sign inferior to the medial malleolus was also noted, further supporting the diagnosis. A posterior tibial nerve block with a corticosteroid was recommended and provided relief of symptoms.
The clinical presentation of tarsal tunnel syndrome can vary depending on the exact segment of the tibial nerve or its branches (calcaneal, medial and lateral) that are involved. Electromyography and nerve conduction studies demonstrate high sensitivity and specificity. Nerve conduction studies in this patient revealed prolonged distal onset latency and reduced amplitude in the right tibial motor nerve.
Detailed electrodiagnostic testing in addition to clinical evaluation can prove to be a powerful diagnostic tool in diagnosis of tarsal tunnel syndrome. This case highlights the clinical importance of electromyography and nerve conduction studies to determine idiopathic causes of tarsal tunnel syndrome that have not responded to conservative management.