Acquired triplane deformity of the first metatarsophalangeal joint in which the hallux is abducted in the transverse plane, dorsiflexed in the sagittal plane and everted in the frontal plane
True descriptive terminology is hallux abducto valgus (HAV), but a lot of literature uses the term ‘hallux valgus’. ‘Bunion’ usually refers to the exostosis associated with the HAV deformity - also the common lay term for HAV.
A hallux valgus may occur at the interphalangeal joint.
Prevalence unknown - one of the more common lower extremity deformities. Incidence increases with age and females appear to have a 3 times greater prevalence than males. Lower incidence in non-shoe wearing populations.
Abnormal biomechanics of the first ray and the first metatarsophalangeal joint is the primary aetiological factor in hallux abducto-valgus (these include abnormal subtalar and midtarsal joint pronation and its resultant unstable first ray, a dorsiflexed first ray, a long first metatarsal).
While the definitive aetiology is not known, generally accepted risk factors include:
• Hereditary factors (many are considered to have hereditary influences, but the HAV is probably not hereditary – more likely that other causal/risk factors are inherited)
• Age (more common in older age groups)
• Gender (more common in females)
• Footwear (traditionally accepted that narrow shoes cause HAV)
• Inflammatory joint conditions (joint space destruction; muscle wasting; inflammation displaces tendons – eg gout; rheumatoid arthritis)
• Muscle imbalance
• Metatarsus primus varus (more appropriately called metatarsus primus adductus)
• Metatarsus adductus
• Long first metatarsal
• Hypermobile first metatarsal
• Post surgical (altered muscle pull from tibial sesamoid removal; second toe amputation)
• Excessive rearfoot pronation
These will vary depending on the stage and amount of deformity, but will consist of varying amounts of:
• Abduction and valgus of the hallux
• Medial exostosis
• Central toes abducted and clawed
• Lesions sub second metatarsal head, medial side hallux IPJ, dorsal second digit, fifth digit
• Osteoarthritic symptoms
Several descriptions of the of the sequence of pathomechanical events in HAV have been published with Root et al (1977) being the most widely accepted.
Root et al (1977):
Order of events of the development of HAV:
The hypermobile first metatarsal head inverts relative to the hallux
A valgus subluxation occurs at the first metatarsophalangeal joint
The base of the proximal phalanx of subluxes laterally upon the first metatarsal head
The hallux abducts upon the first metatarsal head and presses the second toes
The first ray subluxes at its base
• The first metatarsal adducts to increase the metatarsal angle.
Roukis et al (1996):
These authors propose that the decrease of first metatarsophalangeal dorsiflexion that results from dorsiflexion of the first ray is the predominant factor in the development of HAV. When the first metatarsal dorsiflexes, it decreases the range of motion available at the first metatarsophalangeal joint. The pathology that follow this event is determined by the how much the first ray dorsiflexes before it reaches its end range of motion. As the first ray dorsiflexes it also inverts – the amount of inversion is proportional o the amount of dorsiflexion. As a result of these authors propose that over time, those individuals with a large first ray range of motion, a hallux abducto valgus deformity will result. Those with a smaller range of dorsiflexion are considered to develop a functional hallux limitus.
Factors that are considered to influence the rate of development of HAV:
• the extent of abnormal subtalar joint pronation during propulsion
• the size of the angle of forefoot adductus
• the extent of calcaneal eversion which is caused by abnormal pronation of the foot
• the extent of subtalar and midtarsal joint subluxation
• the extent of chronic inflammation of the first metatarsophalangeal joint
• the inclination of the subtalar joint axis
• the angle and base of gait
• the diminution or absence of the propulsive period during gait
The hypothetical pathomechanics of HAV has been described into four clinical stages by Root et al (1977)
This stage is characterised by lateral displacement of the proximal phalanx relative to the first metatarsal head.
Stage 2 in the progression of HAV deformity is clinically characterised by the appearance of hallux abductus deformity. The hallux becomes abnormally abducted and presses against the second toe. The time interval between stage 1 and 2 development is usually indicative of the eventually severity of the HAV deformity. Ie a long time interval suggest a mild eventual deformity
The third stage of HAV is characterised by an increase in the angular value between the longitudinal axis of the first and second metatarsals. The first subluxes away from the second ray into an adductus deformity.
This is a transverse plane deformity, so the term ‘metatarsus primus adductus’ is preferably to the term used in some literature – ‘metatarsus primus varus’.
The fourth stage of the HAV deformity is that in which the hallux becomes partially or completely dislocated upon the first metatarsal head. This deformity develops only when the second toe loses all of its buttressing effect against abduction.
Role of Footwear
The role of footwear in the aetiology of HAV is unclear. Some authors are adamant it is the cause, whereas other believe it play a minor role. HAV is more common in shoe wearing populations, but it does occur in non-shoe wearing populations. Not all those who wear ill fitting footwear develop HAV.
At the least it can be assumed that footwear plays the following role:
• It brings the deformity on at a younger age
• It speeds the progression of the deformity
• It makes the prognosis worse
• It provides the resistance for symptoms to develop
The presence of other risk factors are needed for the footwear to have these effects.
The first step in the evaluating HAV for treatment is to establish the aims of the patient – are they pain relief? deformity reduction?; increased function? etc.
Specific interventions include:
• Palliation of lesions
• Pain relief
• Footwear modification
• Mobilisation and/or manipulation
• Physical therapy – ICE, heat, mobilisations
• Mechanical control of excessive subtalar joint pronation
• Padding and strapping
• Orthoses for accommodation
• Education – aetiology, exacerbating factors, lifestyle changes, footwear, activities
Over 150 surgical procedures have been described in the literature. The basic procedures include:
• Capsule-tendon balancing procedure
• Arthroplastic procedures
• Osteotomies of the distal metatarsal
• Osteotomies of the proximal metatarsal
• Osteotomies of the base of the proximal phalanx
Very little prospective research is available on the options available for HAV management. One prospective study using night splints for juvenile HAV showed improvement in the hallux abductus angle (add ref).