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C h e c k o u t A B M P 's l a t e s t n e w s a n d b l o g p o s t s . Av a i l a b l e a t w w w. a b m p . c o m . 89 The path of the plantar digital nerves between the superfi cial and deep transverse metatarsal ligaments is quite narrow. At the same time, these nerves must pass between the metatarsal heads, and that makes 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. Another factor leading to potential entrapment of the plantar digital nerves is an anatomical anomaly in the division of nerve fi bers. There can be a connecting branch between some of the adjacent digital nerves originating from the medial and lateral plantar divisions. When this connecting branch is present, it increases the potential for compression pathology because the nerve group is not as mobile. There are other key biomechanical factors that routinely lead to Morton's neuroma, and we'll look at these next. BIOMECHANICS AND NERVE COMPRESSION Plantar digital nerve compression affects women more commonly than men. In fact, one study found women were 10 times more likely to develop this problem. 1 One reason for this is because of high-heeled shoes. 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, which increases compression on structures 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. The narrow toe box is most prevalent in dress shoes for both men and women, but also can occur in other shoes like cowboy boots. Other complications in the foot can also lead to digital nerve entrapment without the narrow toe box being a key factor. Fractures or dislocations can narrow the tunnel through which the nerve travels and make nerve compression more likely. Nerve compression may also result from pregnancy, conditions involving poor circulation, fl uid retention in the lower extremities, or ganglion cysts that may develop in the region. 2 The biomechanics of the foot during locomotion also play a prominent role in digital nerve compression. During the push-off phase of the gait cycle, there is hyperextension at the metatarsophalangeal (MTP) joints (Image 3). When the toes are hyperextended, the plantar digital nerves are bowstrung against the deep transverse metatarsal ligament and are pulled taut. This foot position increases irritation of the nerve, especially if it is already being compressed by adjacent structures. As a result, clients often complain of increased pain when the toes are extended in the push-off phase of gait. 3 Toes in hyperextension during push off. KEY SYMPTOMS The plantar digital nerves are sensory nerves, so when they are compressed, the primary symptoms include numbness, paresthesia, and, most commonly, shooting electrical or burning sensations into the toes. The pain is usually described as very sharp and specifi c in nature, not the dull or diffuse aching that is common with other disorders in the region. The most common region for digital nerve entrapment is between the third and fourth metatarsal heads, so most symptoms occur in the third and fourth toes. It is certainly possible to have digital nerve compression in other toes, but it is much less frequent.