Dorsomedial Approaches to the Metatarsophalangeal Joint of the Great Toe
The dorsomedial approach makes possible most surgeries to the metatarsophalangeal joint of the great toe for the treatments of bunions or hallux rigidus.
The dorsomedial skin incision provides access to the exostosis on the metatarsal head without much skin retraction; it does have drawbacks, however. The bursa covering the exostosis may have become inflamed, complicating the surgery. As well, the skin on the medial aspect of the metatarsophalangeal joint is thinner than on the dorsum of the joint, and may not heal as well.
The major advantage of the skin incision is that it gives direct access to the exostosis and is anatomically farther away from the terminal branches of the saphenous nerve.
Its use includes the following:
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Excision of exostosis of the first metatarsal (bunionectomy)
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Excision of the proximal part of the proximal phalanx of the hallux (Keller procedure)
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Procedures on the medial joint capsule, including reefing and V-Y plasties
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Arthrodesis of the metatarsophalangeal joint
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Insertion of total joint replacements
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Dorsal wedge osteotomy of the proximal phalanx in cases of hallux rigidus
Position of the Patient
Landmarks and Incision
The head of the first metatarsal bone and the metatarsophalangeal joint are palpable on the ball of the foot and on its medial border. In cases of bunion, the metatarsal head is prominent medially.
Palpate the extensor hallucis longus tendon on the dorsum of the foot. When it is tight, it stands out upon passive flexion of the great toe in the plantar direction.
Begin the dorsomedial incision just proximal to the interphalangeal joint on the medial aspect of the great toe. Curve it over the medial aspect of the metatarsophalangeal joint, remaining medial to the tendon of the extensor hallucis longus muscle. Then, curve the incision back by cutting along the medial aspect to the shaft of the first metatarsal, finishing some 2 to 3 cm from the metatarsophalangeal joint (Fig. 12-74).
Internervous Plane
There is no true internervous plane. The bone is subcutaneous; the two tendons close to the dissection—the extensor hallucis longus and the abductor hallucis—receive their nerve supply proximal to this approach, thus cannot be denervated by it.
Superficial Surgical Dissection
Incise the deep fascia in line with the incision. Then approach the dorsomedial aspect of the metatarsophalangeal joint using sharp dissection. The dorsal digital branch at the medial cutaneous nerve may be visible in the upper flap of the wound. Retract it laterally with the skin flap on the lateral edge of the wound. Next, make an incision into the joint capsule. The positioning of the incision depends on the surgical procedure to be carried out. A longitudinal incision or U-shaped incision is standard. Ensure that you leave the capsule attached to the proximal end of the proximal phalanx (Figs. 12-75 and 12-76).
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Figure 12-74 Dorsomedial skin incision for the medial approach to the metatarsophalangeal joint of the great toe. Note the proximity of the dorsal digital nerve to the incision.
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Figure 12-75 Incise the deep fascia. Develop a joint capsule flap. Protect the dorsal digital branch of the medial cutaneous nerve.
Deep Surgical Dissection
Incise the periosteum of the proximal phalanx and the first metatarsal bone longitudinally. Using sharp and blunt instruments, strip the coverings of the bone, taking care not to damage the tendon of the flexor hallucis
longus muscle, which lies in a fibro-osseous tunnel of the plantar surface of the proximal phalanx, between the sesamoid bones. The extent of deep dissection depends on the procedure. Strip only a minimum of periosteum of the bone. Take great care not to strip all the soft tissue attachments of the first metatarsal bone if the distal osteotomy of that bone is to be performed, because the metatarsal head may be rendered avascular by stripping.
Dang
The tendon of the extensor hallucis longus muscle, which lies on the lateral edge of the wound, should not be cut during the approach. Indeed, in cases of bunion, the tendon bowstrings laterally across the metatarsophalangeal joint and is considerably more lateral to the incision. Protect the dorsal digital nerve if it can be seen (see Figs. 12-71 and 12-74).
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Figure 12-76 Make a U-shaped incision into the joint capsule, leaving the capsule attached to the proximal end of the proximal phalanx.
The tendon of the flexor hallucis longus muscle is vulnerable as you strip tissue from the base of the proximal phalanx. The tendon lies in a groove on the plantar surface of the proximal phalanx so close to the
How to Enlarge the Approach
Careful and systematic stripping of the structures of the bone provides an adequate view of the joint. The approach cannot be extended usefully to other joints in the foot, but may be extended proximally for access to the shaft of the first metatarsal.
