Radiographic findings are one objective component for determining whether phalangeal osteotomy will be needed for correction of the hallux valgus deformity. Evaluation of the proximal phalanx in relation to the first ray and distal phalanx has been established through plain film radiographs particularly in the anterior-posterior view. The intermetatarsal angle (IMA) is commonly measured and has been associated with the severity of the deformity with normal values variably reported but commonly said to be less than 8° [3]. The issues surrounding radiographic evaluation are discussed in Chap. 5. As an accepted rule, proximal phalangeal osteotomies are not appropriate sole procedures to correct hallux valgus. The higher the intermetatarsal angle, the greater the need for correction of the bunion by a first metatarsal procedure. The relationship of the long axis of the proximal phalanx to that of the first metatarsal has been identified as the hallux abductus angle (HAA) with generally accepted normal value of 15° [4]. The hallux interphalangeal angle (HIA) is established between the long axis of the proximal phalanx in relation to that of the distal phalanx and is found to be 10° abducted in the normal presentation [4] (Fig. 8.3). The distal articular set angle (DASA) is the angular relationship of the articular surface of the base of the proximal phalanx to the long axis of phalanx and is normally established to be 7.5° [4] (Fig. 8.4). DASA correlates with a proximal deformity in the phalanx. An increase in the HIA can represent an intraosseous deformity of the proximal phalanx which would not be corrected without a phalangeal osteotomy. Rettedal et al. suggested another way to assess for an intraosseous proximal phalanx deformity by radiographically measuring the length of the medial and lateral cortices of the phalanx. If there is a longer medial side, a proximal phalanx osteotomy may be necessary to fully reduce the bunion deformity and produce a rectus toe [5]. However, it is imperative to note that as the hallux valgus angle increases, the hallux rotates in a valgus direction which can skew measurements [5].

Indications for a proximal phalangeal osteotomy should be considered specific to correct proximal phalanx incongruities versus bunion correction. After the metatarsophalangeal joint has been corrected and is congruent, the toe should be examined. An increase in DASA represents an incongruity of the cartilage of the base of the phalanx and would be better corrected with a proximal osteotomy. If the deformity exists in the hallux interphalangeal joint, the deformity is likely to be intraosseous, and correction should occur distally in the phalanx [5].

If the proximal phalanx osteotomy is being performed along with a metatarsophalangeal joint dissection, the incision is usually elongated to provide adequate exposure of the phalanx. This can be performed in either a dorsal medial or direct medial approach (Fig. 8.5). Care is taken to avoid the dorsal medial and plantar cutaneous nerves (Fig. 8.6). For a proximal correction, a proximal medial closing wedge is usually performed in the metaphyseal bone anywhere from 5 to 10 mm away from the articular surface [3] (Fig. 8.7). Care must be taken to avoid penetration into the articular surface of the base of the proximal phalanx. The thickness of the wedge depends on the amount of correction needed. The saw blade is generally accepted to take 1 mm of bone with each cut, and this should be considered in the size of the wedge. The distal cut is made perpendicular to the long axis of the phalanx, and proximal cut should be made parallel with the articular surface. Using this methodology, no calculations for wedge size are needed, and the deformity is corrected relative to adjacent structures. Shannak et al. performed a study to determine the width of the base wedge needed for specific angular corrections. They suggested for an approximate 10° correction, a wedge with a base of 3 mm of bone in men and 2.5 mm in women should be removed [6]. It should be noted that radiographic findings are two dimensional and may not represent the true 3D deformity ; therefore the technique using adjacent structure landmarks may be more reliable . The wedge is removed, and the lateral cortex is gently feathered to allow the osseous gap to be reduced with gentle compression (Fig. 8.8). The axis guide of the cut should remain perpendicular with the weight-bearing surface to prevent dorsiflexion or plantarflexion translation when the wedge is closed [3]. Fixation is then employed per surgeon preference. Often, a medially placed staple is used to secure stability (Figs. 8.9 and 8.10).