CORR Insights®: Impact of First Metatarsal Hyperpronation on First Ray Alignment: A Study in Cadavers

Where Are We Now?

Pathologic changes of the first metatarsal play key roles in the pathogenesis of a hallux valgus deformity; two of the more important of these changes are medial deviation [2, 5, 7] and hyperpronation of the first metatarsal [3, 6]. These pathologic changes may result in or from the loss of the dynamic and static balance of the para-muscles and ligaments, which can exacerbate each other and may create vicious and self-reinforcing cycles. In addition, some intrinsic and extrinsic factors may aggravate this process. Intrinsic factors include genetic predisposition and ligamentous laxity. Extrinsic factors mainly include the chronic wearing of shoes with a narrow toe box or high heels.

Initial management is usually nonsurgical; these approaches may include adjusting shoe wear and increasing the size of the toe box to limit pain with pressure along the prominent dorsomedial eminence. For patients with hallux valgus who have severe or refractory symptoms, such as pain and difficulty with ambulation, and whose symptoms persist despite nonoperative treatments, surgical treatment can be considered. A variety of osteotomy methods serve to address pathologic changes of the first metatarsal. The osteotomy sites may be distal to the first metatarsal, in the first metatarsal shaft, in the proximal first metatarsal, or a combination of these. If a patient with hallux valgus has a distal metatarsal articular angle greater than 10°, then distal metatarsal redirectional osteotomy and metatarsal translational osteotomy are recommended. If a patient with hallux valgus has an intermetatarsal angle ≤ 13° and hallux valgus angle ≤ 40°, then distal first metatarsal osteotomy (Chevron osteotomy) is considered. If a patient has hallux valgus with an intermetatarsal angle > 13° or hallux valgus angle > 40°, then proximal first metatarsal osteotomy will be indicated. Sometimes, these procedures might be combined with distal medial closing-wedge metatarsal osteotomy.

If a patient with hallux valgus has instability of the first tarsometatarsal joint or joint hyperlaxity, then a Lapidus procedure is recommended. Ludloff osteotomy and scarf osteotomy through the diaphyseal shaft of the first metatarsal, which is an oblique osteotomy from the dorsal-proximal to the plantar-distal aspect of the first metatarsal, could be used to correct moderate to severe hallux valgus. In one study, patients who underwent scarf osteotomy had better improvements in pain, functional activities, and alignment that included the intermetatarsal angle, hallux valgus angle, distal metatarsal articular angle, and sesamoid position than those treated with Ludloff osteotomy [4].

As Lalevée et al. [1] noted in the current study in cadavers, the combination of first metatarsal intrinsic hyperpronation and first metatarsophalangeal medial soft tissue failure led to a hallux valgus deformity. The authors indicated that hallux valgus is a dynamic condition, and the deformity could be more correlated with motions during weightbearing than with plain static measurements.

Where Do We Need To Go?

It is unknown how the dynamic and static balance of the para-muscles and ligaments is lost, and how the loss of balance relates to medial deviation and hyperpronation of the first metatarsal. Do they happen simultaneously? What triggers the development of this deformity?

It will also be of interest to further evaluate how medial deviation of the first metatarsal affects the stability of the first metatarsophalangeal and metatarsosesamoid joints. Similarly, what is the effect of combined medial deviation and hyperpronation of the first metatarsal on the stability of the first metatarsophalangeal and metatarsosesamoid joints? In terms of genetics, there are still knowledge gaps regarding which genes contribute and how much. If the hallux valgus happened at birth or a very early age, or bilaterally, the patients probably had some mutated genes. Locating the causative mutation genes and related pathway warrants further investigation.

How Do We Get There?

To explore how loss of the dynamic and static balance of the para-muscles and ligaments occurs, balance could be tested using a biomechanical model. With the development of computer technology, computerized CT scanning, three-dimensional reconstruction, hallux valgus biomechanical segmentation and assignment analysis, mechanical loading, stress analysis, and displacement studies of hallux valgus biomechanics would facilitate the use of in vitro simulation in biomechanical research. The model could simulate correction procedures and test the effects of these procedures simultaneously.

To further evaluate how medial deviation and/or hyperpronation of the first metatarsal affects the stability of the first metatarsophalangeal and metatarsosesamoid joints, a cadaver model could be tested, similar to what Lalevée et al. [1] did in the current study. This also could be tested in a biomechanical model. For example, minimally invasive intermetatarsal suture button fixation between the first and second metatarsal has been used to correct medial deviation of the first metatarsal in patients with hallux valgus deformity. Another advantage is this technique also lengthens the first ray. In the next step, minimally invasive techniques could be developed to simultaneously correct medial deviation and hyperpronation of the first metatarsal. Another potential research direction is to develop a new type of shoe with a good-looking, large toe box and releasable heel height because shoes with a narrow toe box and high heels are mainly extrinsic factors for this deformity.

To identify genomic variants that are statistically associated with the risk of hallux valgus, a genome-wide association study might be performed. This method involves surveying the genomes of many people, looking for genomic variants that occur more frequently in those with hallux valgus than in those without this deformity. Understanding the genetic mechanisms behind this deformity would enable the development of early diagnostic tests and new treatments and interventions to prevent the onset of hallux valgus or minimize its severity.