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some people, the nerve branches out after passing through the tunnel instead of before entering it. Several other structures pass through the tunnel, including the tendons of the tibialis posterior, f lexor digitorum longus, f lexor hallucis longus, and the posterior tibial artery and vein. Tarsal tunnel syndrome results when compressive or tensile stress irritates the nerve in the tunnel. Compression can occur from extrinsic factors outside the tunnel, such as a direct blow to the medial side of the ankle or fractures or dislocations that compress the nerve. Nerve compression also occurs from intrinsic factors, such as inf lammation, space- occupying lesions, or ganglions, which press on the nerve within the tunnel. Tensile (pulling) forces on the nerves in the tarsal tunnel may also cause symptoms. Neural tension results from either a sudden stretch of the nerves or from biomechanical distortion, such as a calcaneal valgus foot alignment that stretches the nerves. Peripheral neuropathies like tarsal tunnel syndrome are linked to diabetes, muscular sclerosis, rheumatoid arthritis, and hyperthyroidism. Some medications may cause sensitivity in the distal lower extremity nerves that could be mistaken for compression or tension pathologies in the tarsal tunnel. Morton's Neuroma Morton's neuroma is a nerve compression pathology involving the digital plantar nerves. The digital nerves are the terminal extension of the medial and lateral plantar nerves, which are divisions of the tibial branch of the sciatic nerve (Image 3). The metatarsal heads are bound together by the deep and superficial transverse metatarsal ligaments, which create a small opening or tunnel between the metatarsal heads. The plantar digital nerve branches course through these small tunnels between the metatarsal heads. The path of the plantar digital nerves between the superficial and deep transverse metatarsal ligaments is relatively narrow. At the same time, these nerves must pass between the metatarsal heads, making their tunnel of passage even smaller. While nerves can be compressed between any pair of metatarsal heads, the most common location for plantar digital nerve entrapment is between the third and fourth metatarsals. The space between these metatarsal heads is smaller than between any other pair. Plantar digital nerve compression affects women more commonly than men. High- heeled shoes are one likely reason for that difference. When the heel is lifted higher than the forefoot, it essentially jams the foot into the front portion of the shoe, thus squeezing the metatarsal heads tightly together and increasing compression on the nerves between the metatarsal heads. Narrow-toe box shoes are a frequent contributor to plantar digital nerve compression. Any shoe with a narrow toe box can increase nerve compression by squeezing the metatarsal heads together. A narrow toe box can occur in all types of shoes—from athletic shoes to dress shoes to cowboy boots. Baxter's Neuropathy A potential cause of plantar foot pain often mistaken for plantar fasciitis is compression of the inferior calcaneal nerve under the foot's arch. The inferior calcaneal nerve is a branch of the lateral plantar nerve on the bottom surface of the foot. The nerve is also sometimes called Baxter's nerve, named after the fi rst physician to describe this nerve compression as a specifi c cause of foot pain. Compression pathology of this nerve is therefore called Baxter's neuropathy. As noted previously, the tibial nerve divides into two primary branches, the medial and lateral plantar nerves, as it passes around the medial side of the ankle in the tarsal tunnel. The first smaller branch that splits off from the lateral plantar nerve is the inferior calcaneal nerve (Image 2). In Baxter's neuropathy, there are two potential locations of entrapment of the inferior calcaneal nerve. The first is between the deep fascia of the abductor hallucis muscle and the quadratus plantae muscle. The second is along the medial 3 Plantar digital nerves affected in Morton's neuroma. Image courtesy of Complete Anatomy. 24 m a s s a g e & b o d y wo r k j a n u a r y/ fe b r u a r y 2 0 2 3 Medial plantar nerve Lateral plantar nerve