Extending the Indications for the Distal Chevron Osteotomy

The distal chevron osteotomy has proven to be a reliable, reproducible method of bunion repair for mild to moderate deformity. By altering the location and displacement of the osteotomy, the indications can be expanded to more complex deformities while preserving the straightforward surgical exercise.

The apex of the chevron osteotomy can be modified to a more proximal location along with a reduced angle to provide a stable healing surface that facilitates maximal lateral translation.

The proximal location of the osteotomy also reduces the risk of avascular necrosis and permits safe lateral capsule release needed for larger corrections.

This technique facilitates treatment for moderate to severe bunion deformity with a straightforward surgical method using limited, readily available internal fixation.

ANATOMY

Factors contributing to a bunion deformity vary among individuals. The diverse anatomic features require scrutiny during surgical planning.

Pertinent to the corrective factors of a translational osteotomy is the width of the distal metatarsal. The amount of correction may be limited in a small, narrow, or “hourglass”-shaped bone.

The distal metatarsal articular angle (DMAA) may be altered by varus or valgus rotation during a distal osteotomy. This additional corrective factor should be addressed during the surgical planning.

The position of the sesamoids needs to be assessed for optimal correction. Station III subluxation usually requires a lateral capsule release to restore normal joint mechanics.

Hypermobility of the first ray should be evaluated. Correction by lateral translation of the distal metatarsal may be compromised if the cuneiform–metatarsal joint is unstable.

IMAGING AND DIAGNOSTIC STUDIES

Weight-bearing anteroposterior (AP) and lateral radiographs are used to determine bone morphology, associated disease, and deformity parameters used in decision making.

The ideal correction is based on a line drawn along the first metatarsal that is parallel to the second metatarsal shaft and touches the medial base of the first metatarsal or cuneiform. This line crosses the first metatarsal shaft bisector near the ideal location for a corrective osteotomy. It also estimates the amount of translational correction needed and whether there is sufficient remaining metatarsal to receive the distal metatarsal head (FIG 1). In this example, the osteotomy could be placed slightly distal to the intersecting lines to use more cancellous bone and still have adequate bone to place the capital fragment.

The grade of sesamoid subluxation is evaluated to determine whether a lateral capsular release is indicated. The DMAA is assessed to determine any varus or valgus rotational correction needed at the time of the osteotomy.

SURGICAL MANAGEMENT

Positioning

The patient is positioned supine. When regional ankle block anesthesia is used, an ankle tourniquet is applied. Otherwise, a thigh tourniquet can be used for general or spinal anesthesia.

TECHNIQUES

Soft Tissue Preparation

When significant sesamoid subluxation is present (grade II or III), use a dorsal first web incision to expose the lateral capsule.

A Freer elevator is helpful to probe and identify the dorsal margin of the subluxed lateral sesamoid. Then incise the capsule longitudinally from the phalanx to well proximal to the lateral sesamoid. The adductor tendon is plantar to this incision and is preserved. Leave the intermetatarsal ligament intact. The purpose of this longitudinal cut is to allow medialization of the plantar sesamoid complex at the time of capsule repair from the medial side. Inspect the lateral sesamoid for wear or osteophytes that can be trimmed. Release adhesions and confirm that a freer elevator can be easily passed from proximal to distal between the metartarsal head and sesamoids.

Expose the medial joint through a longitudinal incision. Identify and protect the superficial peroneal nerve. Mobilize the tissues to expose the capsule from the medial sesamoid inferiorly to the extensor hallucis longus tendon superiorly. The medial plantar digital nerve is also at risk as the dissection nears the medial sesamoid and needs to be protected.

Cut the capsule longitudinally and slightly plantar to the center of the metatarsal. Reflect the capsule to expose the medial metatarsal eminence and the joint, avoid stripping the dorsal and plantar aspect to minimize risk of vascular insult.

Bone Preparation

Remove the medial eminence with a power saw. The amount of bone is based on radiographic interpretation. Avoid excessive removal to prevent hallux varus. Usually, the cut is 1 to 2 mm medial to the articular margin or the sagittal groove.

Determine the apex of the osteotomy and mark it with a surgical pen (TECH FIG 1). It is typically 15 to 20 mm from the articular surface. Outline the proximal limbs at an angle of about 35 to 45 degrees. If the limbs are too short, there may be instability; if they are too long, there may be difficulty translating or rotating the distal head portion.