Description

• Lateral deviation of the great toe (“Hallux abducto valgus” derives from the Latin for “big toe askew.”)
• Associated medial deviation of the 1st metatarsal, leading to a medial prominence of the 1st metatarsophalangeal (MTP) joint (also known as “bunion”)
• Progressive subluxation of the 1st MTP joint in later stages
• System(s) affected: musculoskeletal/skin

Epidemiology

• Predominant age: more common in adults
• Gender difference: Female > male by ~2:1
• More common in shoe-wearing populations
• Commonly bilateral

Incidence
Unknown and difficult to assess

Prevalence

• Prevalence increases with age, particularly in females.
• Adults (aged 18 to 65 years): estimated prevalence of 23%
• Elderly (>65 years) adults: estimated prevalence of 36%
• Juvenile hallux valgus: more common in girls (>80% of cases)

Etiology and Pathophysiology

Multifactorial and controversial. Contributing factors may include underlying anatomy and repetitive external forces:

• Absence of muscles that directly stabilize the 1st MTP allows relatively unopposed forces to influence lateral deviation of the proximal phalanx and medial deviation of the 1st metatarsal head.
• Medial MTP joint capsule and medial collateral ligament are chronically stretched and may eventually rupture, decreasing stability and causing progressive subluxation of the 1st MTP joint.
• Lateral joint capsule and collateral ligaments also contract
• Lateral and plantar migration of abductor hallucis muscle moves the great toe into plantar flexion and lateral pronation.

Genetics

• Cohort and twin studies suggest heritability.
• Genome-wide association studies suggest sex-specific differences in genetic mechanisms.

Risk Factors

• Genetic predisposition
• Abnormal biomechanics (i.e., flexible flat feet)
• Foot deformities: joint laxity, hindfoot pronation, Achilles tendon tightness, pes planus (fallen arches), metatarsus primus varus
• Amputation of 2nd toe
• Inflammatory joint disease
• Neuromuscular disorders (cerebral palsy, stroke)
• Improper footwear (high heels; narrow toe box)

General Prevention

Proper footwear may decrease the progression of the disease.

Commonly Associated Conditions

• Medial bursitis of the 1st MTP joint (most common)
• Hammertoe deformity of the 2nd phalanx
• Plantar callus
• Metatarsalgia
• Degeneration of cartilage covering the 1st metatarsal head and sesamoids
• Pronated feet; ankle equinus
• Onychocryptosis (ingrown toenail)
• Entrapment of the medial dorsal cutaneous nerve
• Synovitis of the MTP joint