Pressure changes in the medial and lateral plantar and tarsal tunnels related to ankle position: A cadaver study

Background: Pressure in the tarsal tunnel has been shown to be elevated when the ankle is pronated. We hypothesized that this also would be true for the medial plantar and lateral plantar tunnels because they also are potential sites of nerve compression. Additionally, we hypothesized that decompression surgery, including a release of the superficial and deep fascia of the abductor hallucis muscle and excision of the septum between the medial and lateral plantar tunnels, would decrease the pressure in all three tunnels. Methods: Twelve fresh cadaver legs were obtained, and pressure measurements were made in a variety of ankle positions in the tarsal and medial and lateral plantar tunnels before and after decompression surgery. For the medial and lateral plantar tunnels, pressures were obtained after tunnel roof (deep fascia of the abductor hallucis) incision and after both roof incision and excision of the septum between the two tunnels. Results: Pressures were significantly elevated in all tunnels with ankle pronation, were significantly decreased in all positions in the tarsal tunnel after decompression, and significantly decreased in most positions in the medial and lateral plantar tunnels after decompression. Septum excision led to additional significant decreases in pressure in some positions. Conclusions: Pressures within the medial and lateral plantar tunnels and the tarsal tunnel increase significantly with changes in ankle subtalar position. These pressure changes can be significantly decreased by operative release of each of these three tunnels, including excision of the septum between the medial and lateral plantar tunnels. Clinical Relevance: Symptoms related to chronic compression of the tibial nerve and its branches at the ankle may be relieved by an operative strategy that targets release of multiple anatomic regions of tightness in the medial ankle rather than focusing on the tarsal tunnel alone.