Abstract
INTRODUCTION
Osteochondral lesions of the first metatarsal head have long been recognized in patients with degenerative arthritis 4 possibly resulting from trauma to the joint. 9 Treatment for widespread damage of the joint is either fusion or resection arthroplasty. 3,6 –8,10 When the damage is localized to the dorsal third of the joint, a simple cheilectomy suffices to remove the lesion and allows excellent results. While cheilectomy for a more dorsal cartilaginous lesion works well for the more common hallux rigidus, the central defect is low in the metatarsal head and too much joint surface would be removed if a cheilectomy were done. Alternative treatments include simple debridement, subchondral drilling, joint decompression osteotomy, or modified Keller interposition arthroplasty.
A young active patient with a persistently painful defect in the middle of the metatarsal head poses a difficult treatment scenario. The patient often does not want a fusion, and the resection arthroplasty may lead to weakness and transfer metatarsalgia. 5 The ability to harvest bone from one portion of the joint and insert it into a more centrally loaded and damaged part of the joint thus holds great promise.
Normal articular cartilage rarely is restored with debridement, subchondral drilling, microfracture, or bone grafting. In the hallux, results after subchondral drilling have been less than rewarding. Osteochondral autograft transplant provides an articular plug that may restore normal biomechanics to the metatarsophalangeal joint, potentially minimizing joint degeneration. Originally done with focal osteochondritis dissecans lesions in the weightbearing surface of the femoral condyles, the OATS procedure has increasingly become an option for similar defects elsewhere in the body. Long-term results have been promising in the knee and in selected patients for talar osteochondritis dissecan lesions. The authors have experience with the Arthrex OATS instruments (Arthrex, Inc., Naples, FL) for ankle cartilage repair and used only this system. It seemed reasonable to apply this technique to the metatarsal head for focal central lesions for which no good alternative therapy currently exists.
The OATS procedures bring hyaline cartilage to the area of defect, whereas drilling, microfracture, or abrasion of the lesion produces fibrocartilage. 1 The technical aspects of the cartilage transfer have been formidable, leading to the development of a system that harvests a donor plug of bone and cartilage to precisely fit the recipient site. The importance of precise fit and plug insertion has been established. 2 The technical indications and risks for a mosaicplasty (multiple smaller grafts) compared to an OATS procedure with one or two larger grafts is still being determined. The authors have preferred the OATS procedure for talar lesions in an effort to maximize hyaline cartilage surface.
Since the dorsal quarter to third of the metatarsal head is commonly removed by a cheilectomy, this area seemed an ideal donor site for harvesting an osteochondral plug. The articular surface in this area closely resembles the convex geometry of the central metatarsal head. The OATS is indicated when the defect is isolated and dorsal cartilage of the first metatarsal head is in excellent condition (Figure 1).
OPERATIVE TECHNIQUE
The technique begins as usual for a cheilectomy, with a dorsal incision lateral to the dorsomedial cutaneous nerve but medial to the extensor hallucis longus (EHL) tendon. The joint capsule is incised medial to the EHL tendon sheath (in our experience preservation of the intact sheath seems to give less postoperative pain).
An arthrotomy is performed with section of enough collateral ligament to adequately see the metatarsal head. An oblique dorsal cheilectomy of the dorsal proximal phalanx aids in exposure of the metatarsal head and assists with increased joint dorsiflexion. This procedure usually is done with a rongeur. When an isolated lesion is found, the cartilage is trimmed to healthy edges, and the lesion size is determined with the round sizer (usually 5 mm) on the instrument set (Figure 2). The dorsal cartilage donor site is then selected and viewed with the correspondingly larger round sizer. The bone and cartilage plug is then harvested, taking care to match the cartilaginous contour. The plug is taken to a depth of 12 mm (Figure 3). This may require a surprisingly forceful mallet tapping.
Anteroposterior radiograph of foot with minimal degenerative changes.
Sizing recipient site defect. Note healthy dorsal cartilage.
Replacing some bone from donor site to ensure proper depth at recipient site.
The recipient site is then harvested to 10 mm. If the two resected cylinders of bone meet (that is, if the recipient harvest hole extends to the donor hole) some of the recipient bone or some further harvested bone from the cheilectomy must be used to limit the depth of the recipient site to 10 mm. This can be checked with the solid sizing rod in the instrument set. The donor plug is then tamped into the recipient site to a slight 1-mm proud position (Figures 4 and 5). The joint is then compressed with gentle axial loading and then dorsiflexion to ensure an even gliding surface. A cheilectomy of the metatarsal head is then performed with a chisel at the margin of the donor site (Figure 6). The metatarsophalangeal joint dorsiflexion is then checked, and a Moberg dorsiflexion wedge osteotomy of the proximal phalanx should be considered if dorsiflexion is significantly limited. The capsule is then repaired with 2-0 Vicryl (Ethicon, Parsippany, NJ) absorbable suture, the subcutaneous tissues with 4-0 Vicryl suture, and the skin with 4-0 monocryl suture, which helps prevent inflammation at the operative site. A compressive dressing is applied, and a postoperative shoe is used with heel weightbearing for the first 2 weeks. Progressive activity and return to normal shoe wear is then permitted as tolerated.
OATS plug after initial insertion, still prominent.
Intraoperative view. The plug is left only slightly prominent.
Final intraoperative appearance after cheilectomy.