Pertinent Insights On Proximal Bunionectomies
First, ensure the patient is in a supine position on the operating table. Typically, one places a small bump under the ipsilateral hip to slightly internally rotate the leg until the foot is in the appropriate anatomical plane. Place a pneumatic tourniquet around the ankle or thigh, depending on the type of anesthesia and whether one is addressing associated reduction of an equinus deformity. Make an incision from the base of the proximal phalanx medial to the extensor hallucis longus, extending proximally to the lateral aspect of the medial cuneiform. Take care to identify and retract the medial dorsal cutaneous nerve.
Gain access to the metatarsocuneiform joint by performing a linear capsulotomy, creating a dorsal lateral and plantar medial flap. Employing a Freer elevator at the joint line facilitates identification of the periosteal/capsular layer. Start dissection at the joint line, extend it proximally and then distally. Take particular care to identify and avoid damaging the neurovascular bundle and perforating artery as well as the second metatarsal medial cuneiform ligament (Lisfranc ligament). It is also important to avoid cutting the tibialis anterior tendon medially at its insertion.
The crucial step is the denudation of the adjacent articular surfaces at the first metatarsocuneiform joint. We prefer to use curettage and an osteotome technique for preparation of the fusion site. Use saw resection for “feathering” of the subchondral bone ends. Also, in regard to severe deformities, one can utilize planal resection with a saw for correction and alignment. Take care with this technique as shortening and dorsiflexion can easily occur, and lead to a poor result. A lamina spreader or Hintermann retractor can assist with joint exposure. Take care to remove all cartilage dorsal, plantar, distal and proximal in equal amounts. Due to the shape of the metatarsal and cuneiform, there is a propensity to take more bone dorsally than plantarly, causing distal elevation and dorsiflexion of the first ray.
Once subchondral bone is exposed, it is imperative to break through the subchondral plate. Fenestrate the subchondral plate with either a 2.0 mm drill or 0.62 K-wire until bleeding bone is visible. It is our preference to use the 2.0 mm drill to decrease thermal necrosis and retain the bone from the drill bit to use as a bone graft. Oftentimes, one can resect the lateral eminence of the base of the first metatarsal to prevent abutting the second metatarsal during reduction.
Before reducing the deformity, perform a distal metatarsophalangeal joint capsulotomy in the dorsal medial MPJ capsule. We typically delay resection of the dorsal medial eminence until the last step of the surgery. This discourages staking of the metatarsal head and the complication of hallux varus. Surgeons may perform a lateral release when indicated.
Reduce the first intermetatarsal angle manually or with a large reduction clamp situated on the medial aspect of the first metatarsal and the lateral aspect of the second metatarsal. Then perform dorsiflexion of the first MPJ to enable the windlass mechanism to plantarflex the first ray. Employ temporary fixation and confirm reduction of the deformity using direct visualization and image intensification fluoroscopy.
At this point, place a wire across the fusion site from the dorsal midshaft of the metatarsal to the plantar base of the medial cuneiform. In the opposing manner, place a wire from the dorsal medial cuneiform to the plantar lateral base of the first metatarsal. Employ a 3.5 or 4.0 mm cannulated lag screw across the fusion site. Alternatively, one can place fully threaded cortical lag screws in a similar fashion.
After placing the screws, evaluate the foot for any intercuneiform/intermetatarsal instability. Surgeons commonly utilize a third screw, oriented from the proximal shaft of the first metatarsal to the base of the second metatarsal, to further stabilize the construct.