Medial Cuneiform Osteotomy

Forefoot varus is a component of the multiplanar pes planovalgus deformity that occurs as a result of posterior tibial tendon insufficiency.

In addition to being a component of adult acquired flatfoot deformity, forefoot varus is also present in some cases of congenital pes planus and posttraumatic deformities of the first tarsometatarsal joint.

In 1936, Cotton³ described an adjunctive procedure for the operative treatment of flatfoot deformity using an opening wedge plantarflexion medial cuneiform osteotomy to restore what he termed the triangle of support of the static foot.

ANATOMY

Forefoot varus deformity may occur through a dorsiflexion angulation or rotation at the talonavicular, naviculocuneiform, or tarsometatarsal joints.

These joints are supported by the spring ligament and the plantar intertarsal ligaments, including the long plantar ligament.

In addition, the naviculocuneiform and tarsometatarsal joints are supported by their relatively constrained joint architecture, which in the normal state allows only a few degrees of motion in the sagittal plane.

Medial displacement calcaneal osteotomy, lateral column lengthening, and subtalar fusion all provide correction of heel valgus; lateral column lengthening will correct forefoot abduction, but none of these procedures adequately addresses the fixed forefoot varus component of the pes planovalgus deformity.

PATHOGENESIS

The pathogenesis of forefoot varus in association with an adult acquired flatfoot deformity secondary to posterior tibial tendon insufficiency is not well understood.

Forefoot varus is presumed to develop when the posterior tibialis tendon can no longer provide dynamic support to the medial column of the midfoot. In the absence of the posterior tibialis tendon acting as a dynamic stabilizer, the static ligamentous stabilizers (spring ligament complex and the plantar supporting intertarsal ligaments) stretch out due to the repetitive dorsally directed weight-bearing forces on the medial column of the foot.

Several patterns of medial column “sag” have been described; although the understanding of why some patients have dorsal instability at the first tarsometatarsal joint, the naviculocuneiform joint or the talonavicular joint is not well understood. The differences in the magnitude and location of the dorsal sag may be related to bony anatomy, generalized ligamentous laxity, the presence or absence of gastrocnemius–soleus contracture, and the existence of an underlying congenital pes planovalgus deformity.

NATURAL HISTORY

The natural history of forefoot varus associated with an acquired adult flatfoot deformity has not been studied. It is presumed that the severity of the forefoot varus deformity progresses as the underlying pes planovalgus deformity progresses. Long-standing instability and subluxation at the first tarsometatarsal joint or naviculocuneiform joint may result in localized osteoarthritis of these joints.

Some acquired adult flatfeet develop a fixed forefoot varus without osteoarthritis when the deformity has been long-standing and capsular stiffness holds the joint in the deformed position.

PATIENT HISTORY AND PHYSICAL FINDINGS

Forefoot varus is one of the components of a pes planovalgus deformity that is determined primarily by radiographic and physical examination findings.

In the patient history, there may be complaints of localized pain to the dorsal medial column of the midfoot, either the tarsometatarsal joint or the naviculocuneiform joint.

Patients may complain of pressure-related discomfort beneath the base of the first metatarsal or cuneiform due to excessive weight bearing at the apex of the plantar medial column sag.

The presence and the magnitude of forefoot varus are determined on physical examination by placing the hindfoot into the “subtalar neutral” position with the patient seated (FIG 1).

With the hindfoot held in neutral and with the talonavicular joint congruent, a dorsally directed force is applied to the fourth and fifth metatarsal heads until the ankle is dorsiflexed to the neutral position. If the first metatarsal head rests above the transverse plane of the fifth metatarsal, then forefoot varus is present.

Forefoot varus is quantified clinically by the degree to which the first metatarsal rests above the transverse plane of the forefoot as a mild, moderate, or severe deformity.

The deformity is also qualified by whether the forefoot varus deformity is passively correctable by manual pressure to bring the first ray back down to the level of the other metatarsals or whether it is fixed in this position.

IMAGING AND OTHER DIAGNOSTIC STUDIES

Standing anteroposterior (AP) and lateral radiographs with a medial oblique view of the involved foot will determine the presence of subluxation or osteoarthritis at the first tarsometatarsal or naviculocuneiform joint.

The lateral standing radiograph will quantify the amount of dorsiflexion based on the measurement of the lateral talo–first metatarsal angle.

The apex of the deformity may be at the talonavicular joint, the naviculocuneiform joint, or the first tarsometatarsal joint.

In the case of an acquired flatfoot deformity superimposed on a congenital pes planovalgus deformity, comparison measurements of the opposite foot standing radiograph may help determine what amount of deformity is a result of posterior tibial tendon insufficiency.

A weight-bearing AP radiograph of the involved ankle will determine the presence of a valgus tilt of the talus within the ankle joint mortise secondary to deltoid insufficiency.

Additional procedures to address medial ankle instability due to deltoid ligament insufficiency may be needed to fully correct the valgus hindfoot deformity.

DIFFERENTIAL DIAGNOSIS

Forefoot varus secondary to instability or osteoarthritis at the first tarsometatarsal joint

Global forefoot varus associated with supination of the first, second, and third metatarsals

NONOPERATIVE MANAGEMENT

If the deformity is passively correctable, a custom-molded total contact foot orthosis is fabricated with posting under the medial aspect of the hindfoot and midfoot to correct heel valgus and additional posting placed under the lateral aspect of the forefoot to promote plantarflexion of the first ray with weight bearing.

If the forefoot varus is fixed, an accommodative total contact foot orthosis would be fabricated with medial posting under the entire hindfoot and midfoot or a medial wedge could be added to the sole of the shoe.

If pain symptoms are not controlled with foot orthoses alone, a custom-made leather and polypropylene-molded gauntlet-style brace or a polypropylene custom-molded short articulated ankle–foot orthosis would be indicated.^1,2

Because forefoot varus is only one component of a complex multiplanar pes planovalgus deformity, decision making about conservative versus operative treatment will most likely depend on the characteristics of the hindfoot valgus deformity rather than solely on the forefoot varus component alone.

SURGICAL MANAGEMENT

The plantarflexion opening wedge medial cuneiform osteotomy for correction of fixed forefoot varus associated with a flatfoot deformity is rarely performed in isolation and typically is performed as a component of multiple procedures to correct a given flatfoot deformity.

Typically, the surgeon begins with bony correction of the foot, followed by soft tissue reconstruction and tendon transfers.

The reconstructive procedure begins in the proximal aspect of the foot and ankle and proceeds distally because each level of correction is determined by aligning it to the next most proximal segment. Therefore, the forefoot varus is often the last portion of the bony deformity to be corrected during the realignment portion of the procedure.

Occasionally, once the hindfoot deformity correction has been performed, the apparent forefoot varus that was present preoperatively has been improved sufficiently that osteotomy of the first cuneiform is not required.

Preoperative Planning

This opening wedge osteotomy requires interposition of some type of bone graft material. Therefore, the surgeon should be prepared to harvest a bone graft or have allograft or synthetic bone graft material available.

We have used exclusively frozen tricortical iliac crest allograft bone for this interposition osteotomy without complication.

Positioning

The patient is positioned supine with a small pad placed under the ipsilateral buttock to internally rotate the foot to the neutral position.

Approach

The osteotomy opens dorsally; therefore, the approach is over the dorsal aspect of the first cuneiform.

If procedures are performed on the medial side of the midfoot, the incisions should be kept at least 3 cm apart to minimize undermining.

Performing this osteotomy through a medial approach would significantly increase the difficulty, would require significant additional soft tissue dissection, and would require retraction of the anterior tibialis tendon near its insertion.