Effect of foot and ankle position on tarsal tunnel compartment pressure

Tarsal tunnel intracompartment pressures were determined in 10 fresh-frozen normal human adult cadaver specimens. With the foot and ankle held in mild plantar-flexion and neutral eversion-inversion, mean tarsal tunnel pressure was minimal (2 +/- 1 mmHg). However, when the foot and ankle were positioned in full eversion, mean tarsal tunnel pressure increased to 32 +/- 5 mmHg (P less than or equal to 0.005); in full inversion, mean pressure increased to 17 +/- 5 mmHg (P less than or equal to 0.05). There was no significant difference in mean tarsal tunnel pressure between the everted and inverted positions. These results support the hypothesis that increased pressure within the tarsal tunnel when the foot is moved into the everted or inverted position may aggravate posterior tibial nerve entrapment. These findings may also provide an explanation for clinically observed aggravation of symptoms in these positions, night pain, and improvement of symptoms with neutral immobilization in some patients with tarsal tunnel syndrome.