Bunion (Hallux Valgus)
- 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
- Predominant age: more common in adults
- Gender difference: Female > male by ~2:1
- More common in shoe-wearing populations
- Commonly bilateral
Unknown and difficult to assess
- 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.
- Cohort and twin studies suggest heritability.
- Genome-wide association studies suggest sex-specific differences in genetic mechanisms.
- 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)
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
- 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
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