Injection of the Abductor Hallucis Muscle in the Diagnosis and Treatment of Distal Tarsal Tunnel Syndrome.

Background: Tarsal tunnel syndrome (TTS) can be divided into proximal TTS and distal TTS (DTTS). Research on methods to differentiate these two syndromes is sparse. A simple test and treatment is described as an adjunct to assist with diagnosing and providing treatment for DTTS.

Methods: The suggested test and treatment is an injection of lidocaine mixed with dexamethasone administered into the abductor hallucis muscle at the site of entrapment of the distal branches of the tibial nerve. This treatment was studied with a retrospective medical record review in 44 patients with clinical suspicion of DTTS.

Results: The lidocaine injection test and treatment (LITT) was positive in 84% of patients. Of patients available for follow-up evaluation (35), 11% of those with a positive LITT test (four) had complete lasting symptom relief. One-quarter of patients with initial complete symptom relief at LITT administration (four of 16) maintained this level of symptom relief at follow-up. Thirty-seven percent of patients evaluated at follow-up (13 of 35) who had a positive response to the LITT experienced partial or complete symptom relief. No association was found between level of symptom relief maintenance and the immediate level of symptom relief (Fisher exact test = 0.751; P = .797). The results showed no difference in the distribution of immediate symptom relief by sex (Fisher exact test = 1.048; P = .653).

Conclusions: The LITT is a simple, safe, invasive method to help diagnose and treat DTTS, and it provides an additional method to assist with differentiating DTTS from proximal TTS. The study also provides additional evidence that DTTS has a myofascial etiology. The proposed mechanism of action of the LITT suggests a new paradigm in diagnosing muscle-related nerve entrapments that may lead to nonsurgical treatments or less invasive surgical interventions for DTTS.