Transmetatarsal forefoot amputations preserve normal weight bearing. The principal indication is gangrene of several toes or the great toe, with or without soft tissue infection or osteomyelitis. The gangrene should have spread beyond a level that could be treated by a two-ray amputation; there must be no evidence of spreading infection within the foot; and the plantar skin must be healthy. Patients who do not meet these criteria require a higher amputation.
The incision creates a generous plantar flap. There is no dorsal flap. On the plantar surface, the incision is continued medially to laterally just proximal to the metatarsophalangeal crease. The metatarsal bones are divided with the medial and lateral shafts cut shorter than those in the middle to preserve the normal architecture of the foot and assist with orthotic fitting postoperatively, and the tendons are pulled down and transected as high as possible.
Transmetatarsal amputation produces an excellent functional result. Walking requires no increase in energy expenditure, and the gait is usually smooth. A prosthesis is not mandatory, but to achieve optimal gait, the shoes must be modified. Lamb’s wool or custom-molded foam can be used to fill the toe portion of the shoe. A spring steel shank in the sole of the shoe approximates the action of the longitudinal foot arch during the toe-off phase of walking.
Open transmetatarsal amputations are occasionally necessary in the presence of infection. After the wound has contracted, a split-thickness skin graft may be used for skin coverage. The prosthetic fitting and rehabilitation of these patients are delayed and more difficult, because preservation of the skin graft becomes a primary concern. An ankle-foot orthosis may be necessary.
Chopart’s amputation (transtarsal amputation of the forefoot through the talonavicular-calcaneo-cuboid joint), Lisfranc’s amputation (through the tarsometatarsal joint), and Piroff’s amputation (removal of the talus and rotation of the calcaneus) are unpopular procedures because they produce an imbalance in the remaining muscles of the foot. This results in equinovarus deformity of the foot, with a tender scar and unsatisfactory weight bearing. The Achilles tendon can be transected in an attempt to improve the situation. Ambulation in these patients is somewhat limited. However, limb salvage may be greater when unconventional foot amputations are used.