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Table of contents
Nuckley, Paula M. Hallux valgus is a progressive foot deformity characterized by a lateral deviation of the hallux with corresponding medial deviation of the first metatarsal. Late-stage changes may render the hallux painful and without functional utility, leading to impaired gait. Various environmental, genetic, and anatomical predispositions have been suggested, but the exact cause of hallux valgus is unknown.
Evidence indicates that conservative intervention for hallux valgus provides relief from symptoms but does not reverse deformity. Part 1 of this perspective article reviews the literature describing the anatomy, pathomechanics, and etiology of hallux valgus. Part 2 expands on the biomechanical initiators of hallux valgus attributed to the first metatarsal. Theory is advanced that collapse of the arch with vertical orientation tilt of the first metatarsal axis initiates deformity.
To counteract the progression of hallux valgus, we use theory to discuss a possible mechanism by which foot orthoses can bolster the arch and reorient the first metatarsal axis horizontally. Hallux valgus Fig. Deformity disrupts the normal straight alignment of the first metatarsophalangeal MTP joint.
When hallux valgus is severe, the first MTP joint may dislocate, leading to impaired gait. Hallux valgus disrupts normal alignment of the metatarsophalangeal joint. Arrows indicate the direction of joint member deformity displacements. The hallux abducts while the first metatarsocuneiform segments adduct. The severity of the hallux-metatarsal deformity is measured by A hallux valgus angle and B intermetatarsal 1—2 angle. To reduce discomfort, individuals having hallux valgus are advised to avoid wearing high-heeled, pointed-toed shoes.
Shoes made from soft leather that are flat in style work best and if necessary, the toe box can be stretched to accommodate for bunion enlargement. Therapy for hallux valgus aims to correct the forces acting on the first MTP joint. Suggestions for care include foot exercise to rebalance muscle strength force-generating capacity , 7 and the use of toe spacers and splinting to stretch tissue tightness.
Part 1 of this perspective reviews the anatomy, pathomechanics, and the etiology of hallux valgus. This review suggests a characteristic or behavior of the first metatarsal may initiate hallux valgus or contribute to its recurrence following surgery. The kinetic and kinematic behaviors of the first metatarsal arch segment are further evaluated in part 2, wherein a theoretical perspective on the genesis of hallux valgus is presented. The purpose of the article is to develop a biomechanically derived perspective on hallux valgus and suggest indications for conservative orthotic treatment strategies.
The hallux has a distal phalanx and proximal phalanx Fig. The proximal phalanx articulates with the first metatarsal. The MTP joint is a biaxial condylar articulation that relies on a synovial capsule, collateral ligaments, and a fibrous plantar plate to maintain joint stability. The Lisfranc ligament connects the first and second metatarsals. The first metatarsal in connection with the medial cuneiform is called the first ray. The first metatarsal and cuneiform bones move together as a single, unified arch segment but separately from the second metatarsal. Bone segments rotate around joint axis systems.
A joint axis can be thought of as a line that varies in 3-dimensional position and orientation about which a segment rotates in a perpendicular plane. In the foot, sagittal-plane dorsiflexion and plantar flexion occur about a mediolaterally directed joint axis, transverse-plane adduction and abduction occur about a vertical axis, and frontal-plane inversion and eversion occur about a longitudinal axis. Because joints do not truly align perpendicular to the cardinal planes, 16 , 17 rotations of the hallux and first metatarsal segments occur in some proportion across each of the cardinal planes.
The progression of hallux valgus, although not well understood, is predictable. This gives rise to hypertrophy, resulting in the cosmetic feature most commonly associated with hallux valgus. Hallux valgus alters bony contact pressures across the first MTP joint members. Eventually, the cartilage erodes and changes the shape of the first metatarsal head Fig. Scranton and Rutkowski 23 qualitatively evaluated the extent of cartilage and subchondral bone damage in 35 cadavers having hallux valgus.
Erosion of the plantar surface of the metatarsal head was present in every specimen having completely dislocated sesamoids.
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In a different study, Roukis et al 24 mapped articular wear patterns in feet undergoing hallux valgus surgery. All patients older than 50 years showed erosive damage involving nearly half of the combined MTP joint surface area. Such late-stage changes in joint structure may render the hallux painful and without functional utility. Deformity remains and worsens due to the unbalance of moments acting on the hallux during gait. The magnitude of this medial force component equals the GRF acting on the hallux multiplied by the tangent of the angle approximating the hallux valgus angle. Added to this is the misdirected moment action of FHL muscle.
In response to developing deformity, the resultant pull of the FHL shifts from a plantar direction to a lateral direction, changing the joint moment action from the sagittal plane to the transverse plane. The cause of hallux valgus is unknown. Deformity also may develop in childhood. Premised on the belief that structure influences function, research has investigated length of the first metatarsal as a separate factor in hallux valgus.
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Both relative long 2 , 46 , 47 and short 48 — 50 first metatarsals have been reported as associated with deformity progression. These opposing results suggest that length of the first metatarsal may be incidental to the development of deformity, or that length effects are significant only when combined with other precursor traits.
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Shape of the first metatarsal head also has been explored as a potential predisposition of hallux valgus. The finding, 47 however, may be questioned because the contribution of joint erosion was not considered in the visual analysis used in classifying shape of the metatarsal head. Other studies 3 , 51 , 52 that also reviewed radiographs in patients with hallux valgus showed no trends in data to support the notion that roundness of the metatarsal head leads to deformity.
Even though the shape and geometry of the first metatarsal head exhibit little correlation with the development of hallux valgus, variation in first MC joint osteology is thought to precipitate first MTP joint malalignment. Measurements made on the bone images showed the connecting facets of the MC joint in women were shaped to permit the first metatarsal to translate medially into adduction. Ferrari et al 53 discussed this difference in joint structure between sexes to explain why hallux valgus develops most often in women. These results, although interesting, cannot be easily incorporated into treatment.
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The predisposition most often identified with hallux valgus is collapse of the medial arch, especially as it relates to instability of the first metatarsal. Part 2 of this perspective article explores the codependent kinetic and kinematic behaviors of the arch and first metatarsal. We advance a theory that collapse of the arch with vertical orientation of the first metatarsal axis initiates hallux valgus. Consistent with the research reviewed, we discuss a novel mechanism by which orthoses used to bolster the arch might counteract deformity progression.
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More than 40 years ago, Ebisui suggested the first metatarsal axis could precipitate hallux valgus and issued the following challenge to understanding and treatment: Whether the first ray axis is intimately related to hallux valgus is a matter of conjecture. Further investigation will be necessary before any definitive conclusion can be made.
It is hoped that this study will stimulate others to investigate the fundamental mechanics of hallux valgus. It is our contention that more emphasis should be placed upon the cause and prevention of deformity rather than on the many variations of surgical procedures for its correction. Part 2 of this perspective article gives a response to this challenge wherein the first metatarsal axis and its predisposition to hallux valgus are described. The literature and theory are predicated upon 3 major tenets: 1 the first metatarsal rotates about its own axis; 2 collapse of the arch orients tilts of the first metatarsal axis toward vertical, which allows the first metatarsal to adduct with less anatomical resistance; and 3 instability of the first metatarsal arch segment is a related factor of hallux valgus.
These tenets of first metatarsal biomechanics support our theory for hallux valgus that collapse of the arch with vertical orientation of the first metatarsal axis initiates deformity. Part 2 concludes with a discussion using this theoretical perspective to advocate for orthoses-based treatment strategies. Studies on cadavers provide the only primary source research describing the first metatarsal axis.
He located the axis by observing the trajectory of an external jig fastened to bone while imposing an external load to move the first metatarsal. The observed motion of the first metatarsal in relation to the navicular coupled dorsiflexion with inversion DF-IN and plantar flexion with eversion PF-EV. Data confirmed the metatarsal moved independent of the foot in the pattern of motion Hicks 16 had described.
Kelso et al 65 expressed reservations that non—weight-bearing measurements may not capture the kinematics of foot function. Some studies 67 , 68 support this concern, noting that weight-bearing and non—weight-bearing measurements differ. The first metatarsal axis represented in 3 different foot postures: A pronation, B neutral, and C supination. Orientation of the axis changes as a function of arch height. Position and orientation are physical traits of a joint axis. An axis defines a location in 3-dimensional space about which neighboring segments displace.