Background/Objectives: Posterior tarsal tunnel syndrome is a compressive neuropathy of the tibial nerve at the level of the ankle within the tarsal tunnel. However, there is no established gold standard for the diagnosis of tarsal tunnel syndrome to date. High-resolution ultrasound could add important value in this setting. But up to date, to the best of our knowledge, only six clinical studies have investigated the use of ultrasound for the diagnosis of tarsal tunnel syndrome, with partially conflicting results. Most authors identify nerve swelling at the level of anatomical compression as the key ultrasonographic criterion, whereas at least one study and some expert opinions instead emphasize nerve compression at the site of entrapment. Methods: We performed a retrospective observational study of high-resolution ultrasound of the tibial nerve in patients with typical clinical and electrophysiological characteristics of tarsal tunnel syndrome. Results: A cohort of 26 feet with clinically and electrophysiologically confirmed tarsal tunnel syndrome was collected. Nerve ultrasound demonstrated a moderate sensitivity of 65% for the detection of abnormalities of the tibial nerve when applying the commonly used cut-off of 11.8 mm2 for the tibial nerve at the level of the tarsal tunnel entry or within the tarsal tunnel. In all but one of the cases classified as pathological on ultrasound, an increase in tibial nerve CSA in the tarsal tunnel was observed compared with the CSA measured 5–10 cm proximal to the tarsal tunnel entry (by a factor of 1.6 ± 0.53). A secondary cause was found in only 12% of the cases. But this study also suggests that ultrasound may remain unremarkable in approximately one third of patients with tarsal tunnel syndrome. Conclusions: Establishing the diagnosis of tarsal tunnel syndrome remains challenging. Our study supports the hypothesis proposed in previous publications that tarsal tunnel syndrome appears to be an exception among compression neuropathies on ultrasound: sonography demonstrates nerve swelling not proximal to the site of compression, but at the level of the anatomical compression. Further prospective data would be of substantial clinical relevance.
Holtz et al. (Tue,) studied this question.