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BACKGROUND: Tarsal tunnel pressure is increased when the foot and ankle are positioned in eversion or inversion from neutral, aggravating symptoms of tarsal tunnel syndrome in some patients. Space-occupying lesions may cause tarsal tunnel syndrome. We hypothesized that positional change of the foot and ankle from neutral to eversion or inversion causes decreased tarsal tunnel compartment volume that may aggravate symptoms of posterior tibial nerve entrapment.
METHODS: MRI of 13 ankles in nine healthy subjects in three positions (neutral, eversion, inversion) were obtained with respect to the malleolar-calcaneal plane; this plane was defined by the distal tip of the anterior colliculus of the medial malleolus, the medial tubercle of the posterior calcaneal tuberosity, and the lateral tubercle of the posterior calcaneal tuberosity. The borders of the tarsal tunnel noted on the MRI were traced with a computer digitizing apparatus to determine the cross-sectional area of the tarsal tunnel on each image, and the slice thickness and interspace distance for the seven central images were used to calculate tarsal tunnel volume.
RESULTS: The mean tarsal tunnel volume was significantly greater when the foot and ankle were in neutral position (21.5 +/- 0.9 cm(3)) than in either full eversion (18.0 +/- 0.9 cm(3); p =/< 0.001) or inversion (20.3 +/- 1.0 cm(3); p =/< 0.001).
CONCLUSIONS: The results support the hypothesis that eversion and inversion of the foot and ankle cause decreased compartment volume of the tarsal tunnel and increased tarsal tunnel pressure that may contribute to symptoms of posterior tibial nerve entrapment in tarsal tunnel syndrome.
CLINICAL RELEVANCE: Neutral immobilization of the foot and ankle may relieve symptoms of posterior tibial nerve entrapment in tarsal tunnel syndrome by minimizing pressure on the nerve and maximizing tarsal tunnel compartment volume available for the nerve.
The Effect of HyProCure® Sinus Tarsi Stent on Tarsal Tunnel Compartment Pressures in Hyperpronating Feet
Michael E. Graham, Nikhil T. Jawrani, Vijay K. Goel Journal of Foot an Ankle Surgery
Tarsal tunnel syndrome is characterized by increased pressure in the tarsal tunnel. In hyperpronation, there is excessive abnormal pronation resulting from partial displacement of the talus on the calcaneus. In this study, we hypothesized that hyperpronation caused by talotarsal instability will lead to increased pressure in the tarsal tunnel and porta pedis. We also hypothesized that the pressure in these compartments will decrease following an extra-osseous talotarsal stabilization procedure using HyProCure®. Pressures in the tarsal tunnel and porta pedis were measured in 9 fresh-frozen cadaver specimens using an intracompartmental pressure monitor system. Pressures were measured with the foot in neutral and hyperpronated position, before and after stabilization using HyProCure. For the tarsal tunnel, pressure in the neutral position with and without HyProCure was 3 ± 3 mm Hg and 4 ± 3 mm Hg, respectively (P = .159). However, for the hyperpronating foot, the pressure decreased from 32 ± 16 mm Hg to 21 ± 10 mm Hg (P < .001) following the placement of HyProCure. In the porta pedis, pressure in the neutral position with and without HyProCure was 2 ± 2 mm Hg and 2 ± 2 mm Hg, respectively (P = .168). However, for the hyperpronating foot, the pressure decreased from 29 ± 15 mm Hg to 18 ± 11 mm Hg (P < .001) following the placement of HyProCure. The pain caused by compression of the posterior tibial nerve in the tarsal tunnel and its branches in the porta pedis, owing to hyperpronation, may be alleviated by implantation of HyProCure.
The results of surgical treatment for tarsal tunnel syndrome have been suboptimal, especially in the absence of space-occupying lesions. We attribute this to a poor understanding of the detailed anatomy of the `tarsal tunnel' and potential sites of nerve compression.
This study involved the dissection of 19 cadaveric feet. All findings and measurements were documented with digital photography and digital calipers.
This study demonstrated three well-defined, tough fascial septae in the sole of the foot. In addition to the flexor retinaculum and the abductor hallucis, two of these septae represented potential sites of compression of the posterior tibial nerve and its branches. The medial plantar nerve may be entrapped under the medial septum. However, in 16 of 19 feet, the medial plantar nerve did not traverse beneath the septum. The lateral plantar nerve traversed beneath the medial septum in all specimens. The nerve to abductor digiti minimi may be trapped under the medial and intermediate septum.
We detailed the anatomical relationship of the nerve branches relative to the fibrous septae and found that the medial plantar nerve did not traverse a septae in all specimens.
We believe better understanding of the anatomical relationships of the tarsal tunnel and a clear communication system among anatomists, neuroradiologists and foot and ankle surgeons will facilitate accurate preoperative localization of the site of nerve compression possibly leading to better outcomes