The foot may be amputated through the midtarsal or tarsometatarsal joints. Ordinarily they give unsatisfactory stumps owing to the heel being pulled up by the tendo calcaneus (Achillis), and the shape of the inner part of the tarsal arch. This causes the patient to walk on the end of the stump, which soon becomes painful.

To perform these operations skilfully it is essential that one be familiar with the lines of the joints. Plantar flaps are used because the skin of the sole is tougher than that of the dorsum and the cicatrix is out of the line of pressure.

Midtarsal (Chopart's) Amputation

This is made through the midtarsal joint. The guides to the joint are the tubercle of the scaphoid (navicular) on the inside and the ridge on the anterior end of the os calcis, midway between the external malleolus and the fifth metatarsal bone, on the outer side. A short dorsal and a long plantar flap are cut. The plantar flap is longer on its inner side to allow for the greater thickness of the foot on that side. It is easier to begin the disarticulation on the inside, going in just behind the tubercle of the scaphoid (navicular). This part of the joint is convex forward. On reaching the outer edge of the astragalus (talus) care should be taken not to slip posteriorly between the astragalus and os calcis, but to continue laterally. The extensor tendons are to be sutured to the end of the stump and frequently the tendo calcaneus (Achillis) is cut in an attempt to prevent subsequent elevation of the heel. (Fig. 592).

Fig. 592.   Chopart's midtarsal amputation of the foot.

Fig. 592. - Chopart's midtarsal amputation of the foot.

Fig. 593.   Lisfranc's tarsometatarsal amputation of the foot.

Fig. 593. - Lisfranc's tarsometatarsal amputation of the foot.

Carelessness may result in opening the joint in front instead of behind the scaphoid (navicular).

Tarsometatarsal (Lisfranc's) Amputation

The guide to this joint is the tuberosity of the fifth metatarsal bone on the outer side and the ridge on the base of the first metatarsal on the inner side. This latter is about 4 cm. (1 1/2 in. ) in front of the highest point of the tubercle of the scaphoid.

The joint is best entered from the outer side. The knife is to be passed first forward and then carried inward. Trouble is usually experienced when the base of the second metatarsal is to be disarticulated. It lies behind the others and some surgeons advise skipping it and opening the first metatarsal joint and then completing the disarticulation by opening the second last. The sawing off of the projecting internal cuneiform bone as proposed by Hey is objected to on account of weakening the attachment of the tibialis anterior tendon. The same precaution is to be taken of making the plantar flap longer on its inner side, as was advised in Chopart's amputation, on account of the greater depth of the foot on this side. The line of the joint is best understood by reference to the position of the bones (Fig. 578). Tenotomy of the tendo calcaneus (Achillis) is not so often resorted to in this amputation as in that through the midtarsal joint (Fig. 593).