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 pressur e was minimal (2 +/- 1 mmHg). However, when the foot and ankle were positio ned in full eversion, mean tarsal tunnel pressure increased to 32 +/- 5 mmH g (P less than or equal to 0.005); in full inversion, mean pressure increas ed to 17 +/- 5 mmHg (P less than or equal to 0.05). There was no significan t difference in mean tarsal tunnel pressure between the everted and inverte d positions. These results support the hypothesis that increased pressure w ithin the tarsal tunnel when the foot is moved into the everted or inverted position may aggravate posterior tibial nerve entrapment. These findings m ay also provide an explanation for clinically observed aggravation of sympt oms in these positions, night pain, and improvement of symptoms with neutra l immobilization in some patients with tarsal tunnel syndrome.