Introduction
Normal ambulation is a complex process made possible by the architecture of the foot and by the machinery of the neuromuscular axis. Amputation of any portion of the foot will alter the process of ambulation in degrees ranging from trivial to prohibitive, depending not simply on the amount of tissue removed, but also on the existing health and functional status of the patient. For any given patient, ambulation will be impaired in direct proportion to the amount of tissue removed. Further consideration of this concept will be included in the discussion of each amputation level in the ensuing paragraphs. The most commonly employed levels of amputation are the phalangeal and transmetatarsal, each of which can be single or multiple, and are sometimes performed in combination. Less common are amputations performed through the midfoot (Chopart and Lisfranc), and hindfoot (Syme) (Fig. 1).

Anatomy of the Foot and Toes
The complexity of the foot is illustrated by an accounting of its components: 26 bones, 33 joints, and over 100 muscles, ligaments, and tendons, in addition to fatty tissue, vessels, and nerves, and its investing envelope of skin. These structures are somewhat artificially divided into three zones: the forefoot, including the phalanges, sesamoids, and metatarsals of the five digits; the midfoot, composed of the five tarsal bones, and the hindfoot, made up of the talus and calcaneus. The range of motion of the foot includes plantar flexion, powered by the posterior compartment muscles (tibialis posterior and flexor digitorum), and innervated by the posterior tibial nerve. Extension of the foot, also called dorsiflexion, is enabled by the anterior compartment muscles (tibialis anterior and extensor digitorum), innervated by the anterior tibial (deep peroneal) nerve. Eversion is performed by the peroneus muscles and is rather limited in range. Inversion derives from the posterior muscles and is equally limited in range. The intrinsic muscles of the foot (lumbricals and interossei) complement the extrinsic forces to maintain balance, allow for finer movements of the toes, and contribute signficantly to preserving the normal architecture. Multiple ligaments including the large plantar fascia are essential to create and maintain joint stability. Sensory innervation is supplied by five nerves: the superficial peroneal for the dorsal surface; the deep peroneal for a very small area of the first web space; the sural for the posterior and lateral areas; the saphenous for the medial aspect; and the posterior tibial for the plantar surface. Of these nerves, only the posterior tibial is crucial for normal function, as it provides protective sensation on the weight-bearing surface. Arterial supply derives from the posterior tibial artery, the dorsalis pedis (a continuation of the anterior tibial), and the peroneal artery. The latter vessel ends in smaller branches at the ankle, but the two tibial vessels extend into the foot to form the plantar arches and directly nourish the forefoot and toes. Each toe has medial and lateral digital arteries and nerves.

Phalangeal Amputation
The hallux has two phalanges, and the other four digits have three, with the distal phalanx being the smallest. Beyond this simple anatomic difference, the hallux overshadows the other digits in functional importance by virtue of its roles in balance of the forefoot and in push-off during ambulation. Although the second toe can adapt to some extent in the absence of the great toe, patients who have lost the hallux invariably notice a substantial difference in the mechanics of walking, especially after transmetatarsal amputation. Amputations of the great toe should be performed for only the strictest and most carefully considered indications. Although amputation of only the distal part of a toe is technically possible, there is little functional advantage to having half or two-thirds of a toe, even the great toe. Certainly in any situation where perfusion is abnormal, digital amputations are best performed through the base of the proximal phalanx, leaving a relatively short stump with a better likelihood of healing.