Due to the diaphyseal location of the osteotomy and the degree of distal segment displacement often required to achieve correction, surgical dissection is minimized to maintain the vascular supply to the osseous segments (5,6,7,8 and 9). The skin approach is through the classic dorsomedial linear incision (Fig. 29.4B). After incision of the superficial fascia, a limited dissection interval is developed between the superficial and deep fascia along the dorsomedial first metatarsal. The capsular incision is dorsomedial and can employ removal of a wedge of redundant capsular tissue at closure, often with oblique “load sutures” to help maintain rectus hallux alignment. The periosteal incision is extended onto medial cortical bone and continues proximally toward the base slightly above the midline of the shaft. The periosteum is carefully elevated medially along the shaft from the periosteal incision line and extended dorsally to view the exit site of the long upper wing of the osteotomy proximally, thereby avoiding injury to the extensor hallucis longus (EHL) tendon. Once raised, the periosteal-capsular plane can be extended distally exposing the metatarsal “transitional bone” and medial eminence (Fig. 29.4C). Care is taken to preserve the integrity of the capsular tissues for subsequent closure. This can be facilitated by initiating the dissection proximally with a sharp periosteal elevator, then taking down the medial collateral ligamentous complex from beneath the epicondyle of the metatarsal head. The plantar and dorsal capsular recesses are preserved to minimize postoperative adhesions that can restrict range of motion (Fig. 29.4C-H).

The lateral release, if required, is next accomplished. We employ a percutaneous approach just distal to the metatarsophalangeal joint (MTPJ) with care to preserve the lateral metaphyseal vascular plexus. A “vertical puncture dissection” interval is developed between the sling component of the extensor hood and the subcutaneous tissue plane. Two Senn retractors can facilitate exposure with the rake end of one retracting the EHL medially and the deep end of the other protecting and retracting the contained subcutaneous neurovascular elements laterally (Fig. 29.4D). Distal traction on the hallux defines a puckering of the joint capsule that is entered with a scalpel blade delivered deeply hugging the flare of the proximal phalangeal base as the plantar lateral capsular tissues are released including the extensor sling, collateral ligament, combined adductor hallucis tendon, and, in severe deformity, the lateral head of the flexor hallucis brevis tendon. This maneuver can be facilitated by applying a simultaneous adductory force to the great toe tensioning the tissues. A small curved hemostat is then placed within this capsular rent directed proximally beneath the vertical sesamoidal ligament and just above the fibular sesamoid. The ligament is tensioned and released with a scalpel from inside out. As noted earlier, if the fibular sesamoid is pathologically enlarged, arthritic, or offers an obstruction to lateralization of the distal fragment, it can be removed.

Attention is now directed to the medial capital fragment. The phalanx is subluxed laterally and the dorsal capsular fold is retracted to directly visualize the PASA and evaluate any articular damage. The medial eminence is resected orthogonally to the
PASA deviation with preservation of all effective articular cartilage (Fig. 29.4E-H). This is important, along with minimal initial resection of the eminence, to avoid scalloping of the medial metatarsal contour once the PASA swivel is accomplished. Even in severe hallux valgus deformity, the eminence resection is often minimal, which has prompted some surgeons to forgo opening the medial capsular structures in shaft osteotomies that address PASA correction, thus reducing capsular adhesions. A 0.045-inch Kirschner wire (K-wire) is positioned at the anticipated apex of the offset-V osteotomy as an axis guide and is oriented to accomplish the desired displacement plane of the distal fragment (Fig. 29.4I). It is important to recognize that an axis guide pin that is directed plantarly as it passes from medial to lateral creates some plantarflexion of the capital fragment with IM correction; however, this will result in some elevatus of the capital fragment as the PASA is swiveled out. Factors that influence pin orientation include relative length of the first metatarsal, metatarsus primus elevatus, sub-second and third metatarsalgia, and PASA deviation. Occasionally, a Cotton open wedge medial cuneiform osteotomy can be added as an adjunctive procedure to help depress the first metatarsal and restore length when required.

The geometry of the offset-V osteotomy varies depending on the size and shape of the metatarsal and the magnitude of the deformity. The typical divergence of the wings of the osteotomy is 40 to 45 degrees. The length of the dorsal wing depends on the overall length and width of the metatarsal and the degree of PASA to be addressed, but it usually extends 50% to 75% of the length of the bone. Significant PASA swivel of the capital fragment requires a shorter dorsal cut to prevent the juxtaposition of the proximal wing against the second metatarsal (Fig. 29.5).