Causes / typical injury mechanism: Hallux rigidus is the most common arthritic condition of the foot. It is more common for patients to present with the condition bilaterally than unilaterally.

The condition arises due to osteoarthritis of the first metatarsophalangeal (MTP) joint and metatarsosesamoidal joint. It leads to dorsal osteophyte formation and the classic decreased motion of the great toe at the MTP joint.

Classic history and presentation: Patients with hallux rigidus will typically present with localized pain of the first MTP joint that is worsened with movement. The condition also presents as stiffness in the first digit, specifically with decreased range of motion (ROM) in the sagittal plane. This may affect the patient's ability to walk and can lead to altered gait. The first MTP joint is typically swollen or enlarged due to deformity, which can result from dorsal osteophyte formation. This can make certain shoe types uncomfortable or even cause neurogenic pain from nerve compression.

Prevalence:

• Age – This condition affects 2.5% of people older than 50 years of age. It can occur in younger age groups but will typically be less advanced with milder symptoms. When it presents in a more advanced state at a younger age, it may be due to prior trauma.
• Sex / gender – This condition is more common in women.

Risk factors: Risk factors include prior orthopedic conditions of the hallux, such as trauma or repetitive stress, gout, rheumatoid arthritis, hallux limitus, or osteochondritis dissecans. The anatomical structure of the foot, such as long first metatarsal, metatarsus elevatus, metatarsus adductus, pes planus, and irregular first MTP joint morphology, can also predispose patients to hallux rigidus. The condition has been linked to patients with a family history of hallux rigidus. It has also been linked to frequent wearing of ill-fitting footwear.

Pathophysiology: The pathophysiology of hallux rigidus is debated, although the condition is often linked to trauma, including an isolated fracture or recurrent microtrauma.

Grade / classification system: Hallux rigidus is based on a 4-point grading scale –

• Grade 0
  • No radiographic abnormalities
  • Examination shows no pain, but some stiffness and decreased ROM
• Grade 1
  • Radiography shows minimal dorsal osteophytes with minimal joint-space narrowing, periarticular sclerosis, and flattening of metatarsal head
  • Examination shows mild pain worsened at extremes of dorsiflexion and plantarflexion, and stiffness
• Grade 2
  • Radiography shows dorsal, lateral, and medial osteophytes with flattening of metatarsal head involving no more than 25% of joint space on lateral radiograph, intermediate joint-space narrowing, and sclerosis, without sesamoid involvement
  • Examination shows at least moderate pain, which is worsened before the extremes of dorsiflexion and plantarflexion, and stiffness
• Grade 3
  • Radiography shows substantial joint space narrowing with possible periarticular cystic changes, more than 25% of joint space involvement on lateral radiograph, and sesamoid enlargement, in addition to findings from Grade 2
  • Examination shows constant pain and significant stiffness at the extremes of dorsiflexion and plantarflexion, but not at mid-range
• Grade 4
  • Same radiography as Grade 3
  • Examination is same as Grade 3 in addition to pain at mid-range of passive motion