Description

• Hammer toes include three distinct types of deformity.
  • Hammer toe (as defined) involves a plantar flexion deformity of the proximal interphalangeal (PIP) joint with varying degrees of hyperextension of the metatarsophalangeal (MTP) and distal interphalangeal (DIP) joint, primarily in sagittal plane (1).
  • Claw toe involves a plantar flexion deformity of the PIP and DIP joint with varying degrees of hyperextension of the MTP.
  • Mallet toe involves a plantar flexion deformity of the DIP joint only.
• Each can be flexible, semirigid, or fixed.
  • Flexible: passively correctable to neutral position
  • Semirigid: partially correctable to neutral position
  • Fixed: not correctable to neutral position without intervention

Epidemiology

Most common deformity of lesser digits, typically affecting only one or two toes:

• Second toe is the most commonly involved.
• Hallux malleus is term used when the great toe (hallux) is involved.

Incidence

• Undefined
• Increases with age, duration of deformity (from flexible to rigid)

Prevalence

• Predominant sex: female > male (2)
  • Female predominance from 2.5:1 to 9:1, depending on age group
• Can range from 1% to 20% of population studied
• Blacks are more often affected than whites (2).

Etiology and Pathophysiology

• Can be congenital or acquired
• Three categories of acquired hammer toes:
  • Flexor stabilization (most common cause and occurs in pronated foot/foot with pes planus). The flexor digitorum longus (FDL) muscle remains overactive, overusing the toes to assist in relative foot instability.
  • Extensor substitution (most common with pes cavus)—occurs during the swing phase of gait. The extensor digitorum longus (EDL) muscle remains overactive, substituting for dysfunctional hip and ankle extensors.
  • Flexor substitution—the least common cause and seen commonly with pes cavus. The FDL muscle remains overactive with relative weakness/dysfunction to the Achilles and flexor hallucis longus (FHL), which are the main plantar flexors of the foot.
• Biomechanical dysfunction results in muscle/tendon imbalance between the EDL tendon at the PIP joint and the FDL tendon at the MTP joint; the imbalance at the MTP joint level leads to the altering of the stabilizing force of the intrinsic muscles inserting into the extensor sling and wing apparatus of the MTP joint. In the case of classic hammer toes, the toe(s) sublux dorsally as the MTP hyperextends. This results in plantar flexion of the PIP joint and hyperextension of the MTP joint (2).
• Specific pathomechanics vary by etiology:
  • Toe length discrepancy or narrow footwear toe box induces PIP joint flexion by forcing digit to accommodate shoe.
    • May also lead to MTP joint synovitis secondary to overuse, with elongation of plantar plate and MTP joint hyperextension
    • 4th and 5th toes commonly assume an adductovarus attitude, which can make the toes appear to sit on their side and in advanced cases can cause one toe to sit directly under another toe.
  • Rheumatoid arthritis (RA) causes MTP joint destruction and resultant subluxation.
  • Any condition that compromises intra-articular and periarticular tissues, first ray instability with or without a bunion deformity, an anatomically long 2nd metatarsal, inflammatory joint disease, neuromuscular conditions, improper-fitting shoes, and trauma
  • Damage to joint capsule, collateral ligaments, or synovia leads to unstable PIP joint or MTP joint.

Genetics

• Significant heritability rates of 49–90%
• Specific genetic markers are not identified.

Risk Factors

• Pes cavus, pes planus
• Hallux valgus
• Metatarsus adductus
• Ankle equinus
• Neuromuscular disease (rare)
• Trauma; improperly fitted shoes (narrow toe box) and/or tight hosiery
• Abnormal metatarsal and/or digit length
• Inflammatory joint disease (e.g., RA)
• Connective tissue disease
• Diabetes mellitus

General Prevention

• Proper fitting of shoes. Use of pressure-dispersive footwear, shoes with soft uppers, and extra-depth toe boxes can help reduce pain and irritation from rubbing.
• Foot orthoses modulate biomechanical dysfunction and muscular imbalance, preventing progression (2).
• Limiting use of shoes in the growing foot. Use of zero drop shoes when necessary. Traditional shoes have an elevated heel relative to the ball of the foot (MTP joints). Therefore, at rest, the toes are positioned in dorsal subluxation at the MTP joints and forced to be contracted (termed toe spring).
• Perform toe strengthening exercises, which will help with prevention of imbalance between the extrinsic muscles of the calf and the intrinsic muscles of the foot.
• Control of predisposing factors (e.g., inflammatory joint disease) may also slow progression.

Commonly Associated Conditions

• Hallux valgus
• Cavus foot (pes cavus)
• Flat foot (pes planus)
• Metatarsus adductus
• Dorsal callus