Radiographic examination of bunion deformities and its angular parameters are often used as the primary considerations in choosing a corrective procedure. Unfortunately, there is a wide range of what is considered normal and the indications for certain procedures seem to change frequently as concepts and techniques evolve. Too often the findings of the clinical exam or intraoperative evaluation are cursory and almost incidental to the x-rays. Clinicians frequently make decisions based upon inspection of x-rays, experience, and “what works best in my hands.” This intuitive approach to surgery carries as many risks as perceived benefits. It becomes important to define these intangibles to lead to more consistent and successful surgical outcomes. The basis for choosing the correct procedure should begin with a careful physical examination of the foot and radiographs. Final procedural determination must be weighed against intraoperative findings.

To restore joint congruity, the intermetatarsal angle needs to be reduced. This amount of correction is based upon restoring the first metatarsal back to its normal anatomic position. Reducing to a preset angle, which is based upon measured norms of a population, is arbitrary and not necessarily anatomic. It is now accepted that the positions of the sesamoids remain constant and do not change in hallux valgus deformity. Since the hallux is intimately attached to the sesamoid apparatus, the base of the proximal phalanx remains stationary as well and does not drift laterally as the first metatarsal moves medial (1). The base of the proximal phalanx and sesamoids remain consistent and anatomic. They do not displace in hallux valgus deformity. Therefore, the primary objective of hallux valgus surgery is to place the metatarsal head back into its anatomic position over the sesamoids and behind the base of the proximal phalanx.

On the preoperative radiograph, the center of the base of the phalanx and the center of the metatarsal head are noted. The distance in mm the metatarsal head has moved medial, is the amount of correction that will be required to correct the deformity (Fig. 24.2).

A similar measurement can be obtained with the sesamoids. However to evaluate the position of the sesamoids, an axial projection must be obtained as the sesamoid station cannot be accurately assessed on the anteroposterior radiograph. The traditional method of measuring the sesamoid position is to bisect the first metatarsal and note the position of the tibial sesamoid in relation to this line. Unfortunately, the assumption that the bisection of the metatarsal overlies the crista is incorrect. There is a structural asymmetry of the metatarsal head with the medial condyle narrow and deep while the lateral one is broad and flat. The crista does bisect the head, but this does not correlate with the bisection of the shaft (Fig. 24.3).

On the axial projection, the relation of the crista to the intersesamoidal ligament can be measured. This distance is the amount the metatarsal head must move laterally to restore its position to the anatomically correct sesamoid apparatus (Fig. 24.4). This distance should closely correlate to the previously discussed distance measured on the AP x-ray. These measurements should be utilized to assess the maximum distance the metatarsal head will need to be moved. Since most bunions have a positional as well as structural component, the distance the metatarsal head must be moved is often less than measured.

Radiographic evaluation should be used as a guide, with the final position of the metatarsal determined intraoperatively. The metatarsal phalangeal articulation is congruous with the forefoot loaded, when the medial rim of the phalangeal base sits in the sagittal groove of the metatarsal head, effectively covering the articular surface (Fig. 24.5). Postosteotomy, this maneuver is performed intraoperatively and if the articular surface of the metatarsal head is exposed medially, the intermetatarsal angle has not been sufficiently corrected.