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of the tibia. The small posterior surface of the talus is felt distal and posterior to ad the medial malleolus, at the anterior part of the hollow between it and the heel. In effusions into the ankle-joint the hollows in front and behind the malleoli are obliterated, and the extensor tendons are raised from the front of the joint.
A finger's breadth distal to the tip of the medial malleolus is the sustentaculum tali; 1 in. in front of the sustentaculum, and midway between the dorsal and plantar margins of the medial aspect of the foot, is the tuberosity of the navicular (the medial landmark in Chopart's amputation), which is generally visible, and always distinctly palpable. The calcaneo-taloid joint lies immediately above the sustentaculum, while close above it the tendon of the tibialis posterior may be rendered visible, as it extends from behind the tip of the medial malleolus to the tuberosity of the navicular. An inch and a half in front of the tuberosity of the navicular is the joint between the first cuneiform and the first metatarsal; the ridge at the base of the first metatarsal furnishes a good guide to the articulation. The first metatarso-phalangeal joint lies a little in front of the middle of the ball of the great toe.
A finger's breadth vertically below the tip of the lateral malleolus is the trochlear process of the calcaneus, and midway between the two is the calcaneotaloid joint; the trochlear process is, when present, a trustworthy guide to the level at which the two peronæi tendons cross the lateral surface of the calcaneus. The
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greater process of the calcaneus is felt in the triangular interval between the tendons of the peronæus brevis and tertius; the calcaneo-cuboid joint-the lateral landmark in Chopart's amputation-is placed a little in front of the mid-point between the tip of the lateral malleolus and the base of the fifth metatarsal bone. To open the lateral tarso-metatarsal articulations, the knife, entered behind the projecting base of the fifth metatarsal bone, should be directed forwards as well as medially. On the dorsum of the foot the tarsal joints are obscured by the extensor tendons. The synovial layer of the ankle-joint is prolonged on to the neck of the talus, and care must be taken to avoid opening the ankle-joint in performing Chopart's amputation.
The line of the tarso-metatarsal joints extends nearly 1 in. further forwards on the medial than on the lateral border of the foot; between these points the jointline takes a zigzag course on account of the second metatarsal bone extending backwards between the first and third cuneiform bones. The joint between the second metatarsal and second cuneiform is nearly in. behind that between the first metatarsal and first cuneiform, and nearly in. behind that between the third metatarsal and the third cuneiform. The strong transverse interosseous ligament (Lisfranc's ligament), which connects the lateral surface of the first cuneiform with the base of the second metatarsal, must be divided in the tarso-metatarsal amputation of Lisfranc. In order to preserve the insertions of the two tibial and the three peroneal muscles, it is advisable, when possible,
instead of disarticulating at "Lisfranc's joint," to saw through the metatarsal bones just in front of their bases.
The metatarso-phalangeal articulations are situated 1 in. behind the web of the toes. In disarticulating a toe, the transverse metatarsal ligament, which unites the heads of the metatarsal bones, should not be injured.
The tendon of the tibialis posterior may be felt, and, by inverting the foot, seen, as it extends from behind the tip of the medial malleolus to the tuberosity of the navicular; it crosses the talus immediately above the sustentaculum tali.
In the commonest form of club-foot, viz., talipes equino-varus, the tuberosity of the navicular is approximated to the medial malleolus, so that tenotomy of the tendon should be performed through a puncture a little distal to the tip of the medial malleolus ; if the knife, after dividing the tendon, is carried down to the bone, the plantar calcaneonavicular ligament will be divided and the talo-navicular joint opened, a procedure which is called for before the foot can be brought into good position.
Crossing the front of the ankle-joint, from medial to lateral side, are the following tendons, viz.: the tibialis anterior, the largest and most prominent; the extensor hallucis longus, the extensor digitorum longus, and the peronæus tertius. The extensor digitorum brevis gives rise to a fleshy pad which overlies the dorsal aspect of the calcaneo-cuboid joint. When the foot is everted, the tendon of the peronæus brevis may be seen extending from the tip of the lateral malleolus to the base of the fifth metatarsal bone; immediately below it is the tendon of the peronæus longus, which, as it winds round the cuboid, is obscured by the fleshy fibres of the abductor digiti quinti muscle. The abductor hallucis muscle, although described along with the sole, forms a fleshy pad along the medial border of the foot below the sustentaculum tali.
An incision, extending from the tuberosity of the navicular to the middle of the medial border of the heel, will expose the various tendons, vessels, and nerves, as they pass from the medial malleolus into the sole, beneath the abductor hallucis.
The dorsalis pedis artery may be mapped out on the surface by drawing a line from a point opposite the ankle-joint, midway between the tips of the two malleoli, to the posterior end of the first interosseous space; the vessel may be compressed against the medial column of the tarsal bones. The great saphenous vein and the saphenous nerve lie between the anterior border of the medial malleolus and the tendon of the tibialis anterior; the small saphenous vein and the nervus suralis take the same course as the tendon of the peronæus brevis.
The medial plantar vessels and nerves lie along the medial intermuscular septum, which corresponds to a line drawn from the inferior surface of the medial tubercle of the calcaneus to the interval between the first and second toes. The lateral plantar vessels and nerves may be exposed by an incision along the lateral intermuscular septum, which runs in a line extending from the middle of the inferior surface of the heel to the fourth toe (Kocher); to map out the course of the plantar arch, draw a line across the sole from the medial side of the base of the fifth metatarsal bone to the proximal end of the first interosseous space.