Bunion (Hallux Valgus)

Descriptive text is not available for this image BASICS

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
  • Progressive subluxation of the 1st MTP joint in later stages

EPIDEMIOLOGY

  • More common in adults; female:male ratio: 15:1
  • More common in shoe-wearing populations especially constrictive footwear between the age of 20 and 39 years
  • More commonly observed in those with connective tissue disorders including Marfan syndrome, Ehlers-Danlos syndrome, and Down syndrome

Prevalence

  • Adults (aged 18 to 65 years): estimated prevalence of 23% (1)
  • Elderly (>65 years): estimated prevalence of 36% (1)
  • 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:

  • The 1st metatarsal, proximal phalanx, and distal phalanx form the anatomy of the hallux with two sesamoid bones (medial and lateral) contributing to the 1st MTP joint. The sesamoid bones are embedded in the flexor hallucis brevis tendon and articulation allows for force generation.
  • The hallux valgus angle is formed by the intersection of the longitudinal axes of the proximal phalanx and the 1st metatarsal. Normal is <15 degrees, ≥20 degrees is pathologic, and 45 to 50 degrees is classified as severe.
  • 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 possible following an autosomal dominant pattern with incomplete penetrance.
  • 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, contracture of Achilles tendon, 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, restrictive footwear)
  • No association with obesity or occupation (except for ballet dancing)

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

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