SLR - May 2016 - Pegah Samouhi

Title: Arterial Anatomy of the Posterior Tibial Nerve in the Tarsal Tunnel

Reference: Manske MC, McKeon KE, McCormick JJ, Johnson JE, Klein SE. Arterial Anatomy of the Posterior Tibial Nerve in the Tarsal Tunnel. J Bone Joint Surg Am. 2016 Mar 16; 98 (6): 499 -504

Scientific Literature Review  

Reviewed By: Pegah Samouhi, DPM
Residency Program: Cedars Sinai Medical Center, Los Angeles, CA   

Podiatric Relevance:  Tarsal tunnel syndrome is a neurologic condition affecting the posterior tibial nerve and its associated branches at the medial aspect of the ankle. This syndrome often causes aching or burning pain, dysesthesias, and paresthesias on the medial border and plantar aspect of the foot. It is considered the most common nerve-compression disorder of the foot and ankle. Hence, advancing the understanding of the arterial anatomy supplying the posterior tibial nerve and its branches may provide insight into the cause and treatment of tarsal tunnel syndrome.

Methods: Thirty matched pairs of adult cadaveric lower extremities were obtained, for a total of sixty cadaveric lower extremities used in this study. Macroscopic evaluation was performed on thirty specimens that were previously frozen but not embalmed. Fresh specimens obtained within seventy-two hours of death were used in the microscopic evaluation. Limbs were excluded if they had evidence of foot or ankle deformity or had undergone surgery or trauma.

An 8-French triple-lumen catheter was inserted into the anterior tibial, posterior tibial, and peroneal arteries and injected with dye. Macroscopic evaluation was achieved by chemical debridement of the soft tissues, including the vascular walls, by the sodium hypochlorite, casts of the vessels created by the latex, became visible. The location of the vessels entering the posterior tibial nerve (PTN) relative to the tip of the medial malleolus and abductor hallucis fascia was measured and recorded. Microscopic evaluation was achieved and each nerve was evaluated using a stereoscopic microscope. The locations of all entering vessels relative to the bifurcation of the PTN into the MPN and LPN were recorded. As part of the microscopic analysis, the number of vessels per centimeter was calculated as a representation of the density of vessels entering each nerve.

Results: The mean vascular density (the number of vessels per centimeter) was 0.17 ± 0.07 for the PTN, 0.31 ± 0.13 for the medial plantar nerve, and 0.36 ± 0.14 for the lateral plantar nerve. There was a significant difference (p < 0.05) in vascular density between the PTN and each of its branches, with the branches having a greater vascular density. Both macroscopically and microscopically, the PTN, the MPN, and the LPN were observed to have an abundant arterial supply.

On both macroscopic and microscopic evaluation, the PTN and the medial and lateral plantar nerves were observed to have multiple entering vessels within the tarsal tunnel. On microscopic evaluation, a vessel was observed to enter the nerve at the bifurcation of the PTN into the medial and lateral plantar nerves in twenty-two (73 percent) of the thirty specimens. There was a significant difference (p < 0.05) in vascular density between the PTN and each of its branches.

Conclusions: This study revealed the location of vessels entering the PTN relative to the medial malleolus and the location of vessels entering the MPN and the LPN relative to the abductor hallucis fascia, these reference points are easily identifiable surgical landmarks. The microvascular evaluation of the PTN provides podiatric surgeons with valuable information that this rich vascular network may render the PTN and its branches susceptible to nerve compression related to vascular congestion. The combination of vascular and structural compression may also elicit neurologic symptoms. It can be concluded that hyperemia can lead to tarsal tunnel syndrome and should be considered in diagnostic evaluation and treatment planning. 

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