To start our review of common foot and ankle problems, we begin with some basic anatomy. There are many bones in the foot, and there is no need to memorize the names of all of them, but it is helpful to know the names of the groups of bones (Figures 5-1,5-2,5-3,5-4,5-5,5-6). From distal to proximal, we start with the phalanges, the bones in our toes. Each toe has a distal, a middle, and a proximal phalanx, except the big toe, which only has a distal and a proximal phalanx. Just proximal to the phalanges is the second group of foot bones, the long, slender metatarsal bones. The metatarsals and phalanges account for what is often referred to as the forefoot. Just proximal to the metatarsal bones are a group of small, short bones called the tarsal bones, which make up the midfoot. The hindfoot bones are the talus and the calcaneus, and the talus is the bone that is the “ball” of the ball-and-socket of the ankle. The “socket” of the ankle joint is actually two separate bones. The tibia contributes the roof and the medial sidewall of the socket, and the distal tip of the fibula accounts for the lateral sidewall. At the sidewalls of the ankle joint, the tibia and fibula become a bit thicker and a bit more prominent, creating the hard, bony features of the ankle that we call the medial and lateral malleoli. That’s a grand total of 28 bones in the foot and ankle (not including the two tiny sesamoid bones under the big toe!). It seems intuitive that our hands would have a disproportionately high number of bones in them, given the large array of complex motions they have evolved to perform, but why the skeletal structure of our feet is so complex is harder to understand.

Despite this apparent overabundance of bones, there aren’t any muscles in the foot and ankle that are important enough to deserve mention in an anatomic review as basic as this one. In simplest terms, the foot and ankle only move in four directions: flexion (up), extension (down), inversion (toward the midline, sometimes called supination), and eversion (away from the midline, sometimes called pronation). For the most part, these four motions result from forces applied to the foot and ankle by the calf muscles via their specific tendons. For example, the downward motion of ankle flexion (sometimes referred to as plantar flexion) occurs when the calcaneus is pulled proximally by the Achilles tendon and the gastrocnemius and soleus muscles attached to it. Similarly, ankle upward extension (sometimes referred to as dorsiflexion) results from contraction of the tibialis anterior muscle (see sidebar), and inversion/supination and eversion/pronation result from contraction of the tibialis posterior and peroneal muscles, respectively.

The only ligaments worth noting in this discussion are the ankle-stabilizing ligaments. The ankle joint moves freely in the flexion-extension plane of motion but does not move much from side to side. This side-to-side motion occurs primarily at the hindfoot joint below the ankle, between the talus and the calcaneus, and is limited at the ankle joint by the ankle-stabilizing ligaments. There are three ligaments on the lateral side of the ankle joint and one on the medial side (Figure 5-7). These ligaments are covered in more detail in the ankle sprain section of this chapter.

Figure 5-8 shows how the medial and lateral plantar nerves branch into the common digital nerves, which then branch into the proper digital nerves to provide sensory innervation to the medial and lateral sides of the toes. On the distal end of each metatarsal bone, there is a bulbous mass of bone known as the metatarsal head. The common digital nerves pass between the metatarsal heads as they bifurcate into their terminal branches: the proper digital nerves. As we walk, there is movement between adjacent metatarsal heads, and that movement can create the inflammatory changes that result in a Morton’s neuroma. While this can occur between any two adjacent metatarsal heads, it is most common in the webspace between the third and fourth toes, where the nerve is sandwiched between the third and fourth metatarsal heads (see sidebar). Figure 5-9 shows an inflamed, swollen Morton’s neuroma in the third webspace. Patients with a Morton’s neuroma usually complain of pain that “feels like a pebble” on the bottom of their foot. The pain may radiate into the toes distal to that webspace, and symptoms are usually worse in high-heeled shoes or shoes with a narrow toe box. The nerve may malfunction, causing numbness or tingling.

Physical Exam

The mass may be large enough to splay the toes (Figure 5-10). You may detect a loss of sensation to light touch, and some of the bigger masses can be palpated on physical exam. If you hold the metatarsal heads of two adjacent toes and move them in opposite directions, up and down several times, you can often re-create the patient’s pain. This is called the metatarsal shift test.

Imaging Studies

X-rays aren’t likely to show anything, other than, perhaps, a widening of the space between the metatarsal heads. A magnetic resonance image (MRI) may show inflammatory changes in and around the neuroma.

Medical Treatment

Shoes that subject the metatarsal heads to high stress can precipitate impingement of the nerve and result in a Morton’s neuroma (Figure 5-11). High-heeled shoes are known for loading the metatarsal heads, and the toe box on these shoes is typically narrow, crowding the metatarsal heads against one another. Narrow, high-heeled shoes create the perfect environment for the development of this condition. Changing to a wide shoe with a low heel can make a big difference, as can adding a metatarsal support (Figure 5-12). Metatarsal supports can be applied to the skin of the foot, as in Figure 5-12, or built into the shoe. These supports transfer weight-bearing forces off the metatarsal heads and into the arch. A cortisone injection into the space between the metatarsal heads can decrease inflammation and help the symptoms of a Morton’s neuroma resolve. (See Chapter 9 for the injection technique for Morton’s neuroma.)

Surgical Treatment

The surgical treatment of Morton’s neuroma involves making a small incision over the involved webspace on the dorsum of the foot, exposing the neuroma, and then resecting it (Figure 5-13). The entire neuroma is removed by cutting the proximal common digital nerve and both of the distal digital nerve branches. Numbness on one side of each toe results, but most patients prefer this to the pain of the neuroma. No motor deficit results because this is a purely sensory nerve.

Running along the plantar surface of our feet is a tough, stiff band of dense connective tissue called the plantar fascia (Figure 5-14). It originates from the plantar surface of the calcaneus and inserts onto the plantar surfaces of the metatarsal heads. Like the string on a bow, it spans the space between the hindfoot and forefoot, and it helps maintain the arch of the sole of the foot. In the condition known as plantar fasciitis, the plantar fascia becomes inflamed, usually at its attachment to the calcaneus, and this creates pain that can be quite intense. The condition usually affects patients who are over the age of 40, and men are more likely to be affected than women. The classic symptom is one of heel pain that is worse on first putting weight on the heel in the morning (see sidebar).