Toes are the most frequently amputated parts of the body. Over two-thirds of amputations in diabetics involve the toes and forefoot. The indications include gangrene, infection, neuropathic ulceration, frostbite, and osteomyelitis limited to the middle or distal phalanx. Good blood flow is required.
Contraindications to digit amputation include indistinct demarcation, infection at the metatarsal level, dependent rubor, and ischemia of the forefoot. Important principles pertaining to digit and ray amputations include the following:
The first metatarsal head is important for patient balance and should be preserved if possible.
Amputation that leaves only one or two remaining digits (unless the first) does not facilitate normal foot function but complicates functional footwear. Patients often develop pressure lesions of the remaining digits due to neuropathy.
Resection of metatarsal heads in diabetic patients with malperforans ulcers often transfers the pressure point responsible for the initial lesion to the adjacent metatarsal head. Therefore, without adequate protection with orthotic shoes or inserts (along with patient compliance), recurrence of these lesions is the rule rather than the exception. This is particularly likely in obese diabetic patients. Several clinical series of toe amputations in diabetic patients have demonstrated the necessity of another toe amputation in up to two-thirds of cases, and below-knee amputation was eventually required in 15–20% of patients.
Digit and ray amputations should be carried out through the shafts of bones because joint cartilage will secrete fluid into the wound and retard healing.
Tendons are avascular structures and should be divided as proximally as possible.
For dry, uninfected gangrene of one or more toes, autoamputation may be allowed to occur. During this process, epithelialization occurs beneath the eschar, and the toe spontaneously detaches, leaving a clean residual limb at the most distal site. Although preferable in many patients (and especially frostbit patients), autoamputation sometimes requires months to complete.
Ray or wedge amputation includes removal of the toe and metatarsal head; occasionally, two adjacent toes may be amputated by this method. As with toe amputation, there is modest cosmetic deformity and a prosthesis is not required. Ray amputation of the great toe leads to unstable weight bearing and some difficulty with ambulation resulting from loss of the first metatarsal head.
The extents of toe and ray amputations
For distal resections, a circular incision is made at the midpoint of the proximal phalanx, and the phalanx is resected at about its midpoint. If it is necessary to remove the entire phalanx or to excise the distal portion of the metatarsal, the incision is extended proximally over the metatarsal, and the bone is divided behind the metatarsal head. Not uncommonly, the incision must be left open to heal by second intention owing to the presence of local infection.
Complications that may require amputation at higher levels include infection, osteomyelitis of remaining bone, and nonhealing of the incision. These complications have been reported in up to one-third of diabetic patients.