Metatarsal Lengthening in Revision Hallux Valgus Surgery

Shortening of the first metatarsal may occur after first metatarsal osteotomies for hallux valgus correction.^1–3

If the first metatarsal is considerably shortened, the patient may develop painful transfer metatarsalgia of the lesser toes.⁷

ANATOMY

The physiologically normal first metatarsal is generally of similar length to or slightly shorter than the neighboring second metatarsal.

This length relationship between the first metatarsal and the lesser metatarsals allows for a smooth, progressive weight transfer and optimizes the windlass mechanism during gait.

The relative plantar position of the first metatarsal head (and sesamoids) also makes the windlass mechanism more effective in transferring weight to the lesser toes and may compensate for a physiologically shorter first metatarsal.

PATHOGENESIS

Some metatarsal shortening occurs with the majority of all first metatarsal osteotomies performed during hallux valgus correction.⁶

An iatrogenically shortened first metatarsal can disrupt the normal forefoot weight transfer mechanism and cause a pathologic overload of the adjacent metatarsals.

Relative dorsiflexion of the metatarsal head can also occur after hallux valgus correction with metatarsal osteotomy, exacerbating the mechanical disadvantage of the shortened metatarsal and further contributing to transfer metatarsalgia.

NATURAL HISTORY

Transfer metatarsalgia generally does not resolve spontaneously, particularly if coupled with a concomitant forefoot fat pad atrophy.

Mild transfer metatarsalgia is generally well tolerated, as the patient is able to modify gait, stance, and activity to compensate.

However, the problem may progress, with painful callus formation developing under the lesser metatarsal heads. Severe, recalcitrant transfer metatarsalgia may cause debilitating forefoot pain that often persists until normal forefoot biomechanics are restored or reasonable footwear accommodation is used.

PATIENT HISTORY AND PHYSICAL FINDINGS

The great toe usually, but not always, appears shorter than the adjacent metatarsal, especially when compared to the contralateral foot (FIG 1).

The plantar surface of the forefoot usually, but not always, has calluses under the lesser metatarsal heads.

The lesser metatarsal heads are tender.

When examined simultaneously, the first metatarsal head (and sesamoids) may appear elevated and more proximal relative to the second metatarsal head, particularly when compared to the contralateral foot.

The medial forefoot incisions from prior forefoot surgery must be noted in anticipation of potential revision surgery.

Hallux metatarsophalangeal (MTP) joint alignment must be examined. A recurrence of hallux valgus deformity after prior surgery will need to be corrected in conjunction with metatarsal lengthening.

Hallux MTP joint motion must be determined. Stiffness and crepitance may suggest arthrosis that may favor first MTP joint arthrodesis over first metatarsal lengthening (FIG 2).

IMAGING AND OTHER DIAGNOSTIC STUDIES

Weight-bearing plain radiographs are mandatory; we recommend bilateral radiographs to include the contralateral foot for comparison.

Anteroposterior (AP) radiographs of the symptomatic foot indicate the amount of first metatarsal shortening, the presence of residual deformity (particularly the first metatarsal head–sesamoid relationship), the nature of the prior hallux valgus surgery, and the integrity of the first MTP joint (FIG 3A).

Lateral radiographs suggest the degree of concomitant elevation of the first metatarsal (FIG 3B).

Contralateral foot radiographs provide some indication of the required lengthening, which is useful in surgical planning.

DIFFERENTIAL DIAGNOSIS

Recurrence of hallux valgus

First metatarsal head avascular necrosis

Dorsiflexed malunion of first metatarsal

NONOPERATIVE MANAGEMENT

Oral anti-inflammatory medication

Shoe wear modification (ie, greater stiffness in combination with a rocker sole to unload the forefoot)

Orthotics with medial posting for the first metatarsal and metatarsal support for the lesser metatarsals

SURGICAL MANAGEMENT

Surgical management is indicated when nonoperative treatments have failed and other causes are not responsible for the forefoot pain and transfer metatarsalgia.

Two broad categories may be considered in the surgical management of transfer metatarsalgia secondary to a short first metatarsal: shortening of the lesser metatarsals and lengthening of the first metatarsal.^4,5,8,9

With severe first metatarsal shortening, a combination of these two approaches may need to be considered.

First metatarsal lengthening affords the advantage of correcting the problem at its source in lieu of performing surgery on lesser metatarsals that are physiologically normal but subject to an overload phenomenon.

Preoperative Planning

Weight-bearing plain radiographs are essential to plan the desired lengthening and potential realignment of the metatarsal and MTP joint, determine the need for hardware removal from previous surgery, and identify potential arthritis in the MTP joint.

The contralateral first metatarsal, if not previously operated, serves as an ideal template to determine how a more physiologic first metatarsal anatomy may be restored.

To account for magnification, relative lengths of the first and second metatarsals may be used as a reference.

Once the patient is deemed appropriate for metatarsal lengthening, the appropriate position for the external fixator half-pins and corticotomy should be planned radiographically.

Positioning

The patient should be placed in the supine position on the operating table.

A bump should not be placed under the ipsilateral hip to allow external rotation of the leg and better access to the medial side of the foot.

Approach

A four-pin single-plane external fixator will be placed along the medial border of the first metatarsal, and a short, longitudinal dorsal approach to the metatarsal is needed to perform the metatarsal osteotomy (FIG 4).