Proximal Osteotomies of the First Metatarsal



Proximal Osteotomies of the First Metatarsal


Robb A. Mothershed



An increase of the first intermetatarsal angle, or metatarsus primus adductus, has long been recognized as a major contributing factor in the deformity of hallux abducto valgus.

This component of hallux abducto valgus has been addressed by proximal osteotomies for decades. A transverse plane osteotomy of the first metatarsal base for the repair of hallux abducto valgus deformity was first described in 1901 by Loison (1), and it was performed in 1903 by Balacescu (2). After a number of modifications, the procedure became more favorable in the late 1960s and early 1970s. The procedure began to lose its popularity over the last 15 years because of certain complications that were believed to be inherent to the procedure, including first metatarsal elevatus, shortening of the metatarsal, failure of the fixation, and delayed union. Subsequently, surgeons began to appreciate that most of these deficiencies resulted from surgical technique, inadequate fixation, and an insufficient period of non-weightbearing postoperatively. The perceived complications associated with the closing base wedge osteotomy also led surgeons to consider other forms of proximal osteotomies such as the crescentic and chevron. The favorability of the crescentic and chevron osteotomies has been replaced by the opening wedge osteotomy because of the advancement of fixation devices. Other surgeons have expanded the limitations of more distal procedures such as the Austin osteotomy because the distal procedures are technically easier to perform and the patient can remain weightbearing during the postoperative period. However, the proximal osteotomies still are effective, particularly in patients with severe deformities and in patients with high intermetatarsal angles. The technical advances in surgical technique, rigid internal fixation, and the institution of a non-weight-bearing interval in the postoperative recovery have demonstrated that these procedures can provide consistently good results.






ANATOMIC CONSIDERATIONS

The most effective incision is placed from the first metatarsal-cuneiform joint to the proximal phalanx of the hallux. The initial incision is placed at the level of the first metatarsophalangeal joint (MTPJ) and then extended proximally to the first metatarsal-cuneiform joint, after the first MTPJ is released and the medial eminence excised (Fig. 28.1). The single incision approach has been performed for decades without any sequalae. After completion of the proximal portion of the incision, dissection is carried through the relatively thin subcutaneous tissues. The previously defined tissue planes at the first MTPJ may be followed into the proximal portion of the first metatarsal. Often times a branch of the medial dorsal cutaneous nerve is identified at the proximal aspect of the incision.

The nerve branch can easily be retracted into the medial subcutaneous tissues. After clearance of the superficial fascia from the deeper structures, the deep fascia can be incised medial to the extensor hallucis longus tendon, being careful to maintain enough of a margin for closure of the fascia. Once the deep fascia is reflected, the extensor hallucis longus tendon can be retracted laterally, allowing for better exposure of the periosteum over the base and shaft of the metatarsal. The periosteum is incised from the proximal and medial extent of the first metatarsal base and is extended laterally and dorsally on the first metatarsal shaft and then medially and distally toward the previous periosteal incision at the first metatarsal head (Fig. 28.2A). The periosteum is reflected from the first metatarsal with a Freer elevator, allowing exposure of the medial and lateral aspects of the metatarsal base (Fig. 28.2B and C). It is important not to free the periosteum from the area adjacent to the proposed apex of the osteotomy; otherwise, the stability of the osteotomy may be compromised. The periosteum should be handled with care and reapproximated at closure, because it does provide blood supply to the healing osteotomy. The
anatomical layers are reapproximated in a stepwise fashion at the completion of the procedure. Good anatomical dissection is essential to facilitate closure of the tissue planes.






Figure 28.2 A: A periosteal incision is placed from the proximal shaft of the metatarsal and extended distally to the initial periosteal incision over the first MTPJ. B: A Freer elevator is used to free the periosteum from the metatarsal. C: The Freer is placed at a 45 degree angle along the lateral side of the metatarsal to efficiently free the periosteum.






Figure 28.3 A: The traditional axis of a base wedge osteotomy. If the osteotomy is made perpendicular to the metatarsal, then subsequent lateral displacement of the distal metatarsal will result in sagittal plane dorsiflexion. B: If the osteotomy is made perpendicular to the weight-bearing surface, then lateral displacement of the distal metatarsal will not dorsiflex or plantarflex the metatarsal head, and it should remain parallel with the weight-bearing surface.


TECHNIQUES


CLOSING BASE WEDGE OSTEOTOMY

The modern version of the oblique osteotomy of the first metatarsal base was created at the Podiatry Institute in 1977 (9). The osteotomy can better accommodate the use of two points of fixation and it allows the surgeon to place the apex of the osteotomy more proximally, thus providing a longer radius arm for correction. The use of an axis guide can facilitate the performance of the osteotomy. The axis guide provides an accurate means of assessing and implementing concomitant dorsiflexion or plantarflexion of the distal portion of the metatarsal with closure of the osteotomy. It is important to understand the hinge-axis concept when performing the osteotomy to facilitate its performance. An intact cortical hinge can act as an axis of rotation for the base wedge osteotomy. The traditionally perceived axis for a hinged osteotomy of the first metatarsal was perpendicular to the long axis of the bone (Fig. 28.3A). As a result of the anatomic declination of the first metatarsal in the human foot, rotation of the distal segment of the first metatarsal around this axis after a closing base wedge osteotomy would tend to create elevation of the metatarsal head from the weightbearing surface. If the osteotomy is designed so the axis is perpendicular to the weight-bearing surface, then full rotation of the distal segment of the metatarsal can occur without elevating or plantarflexing the metatarsal head in relation to the weightbearing plane (Fig. 28.3B).

The sagittal plane orientation of the axis must be maintained to prevent elevation of the metatarsal head; however, the frontal plane orientation can be manipulated to influence the ultimate position of the metatarsal head in the weight-bearing plane. Manipulation of the axis in the frontal plane is based on the presumption that the axis remains perpendicular to the weight-bearing surface in the sagittal plane (Fig. 28.4A).

If the axis is maintained perpendicular to the weight-bearing surface in the frontal plane, then the lateral rotation of the distal metatarsal segment maintains the metatarsal head on the weight-bearing surface. The manipulation of the superior pole of the axis laterally creates a dorsomedial hinge, and plantarflexion of the distal segment of the metatarsal occurs with lateral rotation or closing of the base wedge osteotomy (Fig. 28.4B). Conversely, when the superior pole of the axis is tilted medially, a plantar medial hinge is created, and dorsiflexion of the distal segment occurs with closing of the base wedge osteotomy (Fig. 28.4C). In the patient with normal alignment and length of the metatarsal, it is important to plantarflex the distal segment to offset the degree of shortening and subsequent elevation of the metatarsal, which could occur with straight translocation of the metatarsal.

The hinge-axis concept is essential to the execution of the proximal closing wedge osteotomy of the first metatarsal. The width of the first metatarsal determines whether a 0.035- or 0.045-inch Kirschner wire (K-wire) is used as an axis guide and is drilled through the base of the first metatarsal to represent the proposed hinge site of the osteotomy. The K-wire should be inserted dorsally and medially in the metatarsal just distal to the intended apex of the osteotomy to allow reciprocal planing of the osteotomy. The surgeon must be mindful of the growth plate in juvenile patients. The wire is then drilled into the metatarsal perpendicular to the weight-bearing surface at the appropriate angle in the frontal plane to effect the desired manipulation of the distal aspect of the metatarsal that is necessary for each individual patient (Fig. 28.5A).

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Jul 26, 2016 | Posted by in MUSCULOSKELETAL MEDICINE | Comments Off on Proximal Osteotomies of the First Metatarsal
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