Background: Hallux rigidus (HR) is a common condition with X-rays used to evaluate its pathology, grade joint changes and to inform treatment.
Method: A cross-sectional study was undertaken to evaluate radiological foot parameters in HR. In 110 subjects (180 feet) aged 18-70 years (mean 52 years) standard weight-bearing X-rays were examined using dorsal plantar and lateral views.
Results: Seventy (64%) subjects had bilateral HR and 73 (66%) were female. The mean onset of HR (denoted by first metatarsophalangeal (MTP) joint restriction/pain) was 44 (14-68 years) years and median HR duration was 6 years (1-33 years). Flat or chevron-shaped metatarsal heads presented in 131 (73%) feet and a history of first MTP joint trauma in 22% (74% of whom had unilateral HR). In 74% of feet hallux abductus interphalangeus angle (HAI degrees) was greater than normal (< or =10 degrees). Correlations between first MTP joint narrowing and sclerosis (r=0.76, p=0.01) and increased HAI degrees and first MTP joint narrowing (r=0.34, p=0.01) was found. The mean hallux equinus angle of 11 degrees was outside the normal range (16-18 degrees). Abnormal sesamoid morphology presented in 117 (65%) feet (30% irregular or hypertrophic). Proximal sesamoid displacement was greater than that seen in non-HR. Metatarsus primus elevatus was within normal range (< or =8 mm) in 160 (89%) feet. The first metatarsal was longer than the second metatarsal in 66 (37%) feet although the first metatarsal was longer than the third metatarsal in 131 (73%) feet and may be responsible for altered forefoot function in HR.
Conclusions: HR was associated with female gender, bilateral involvement, older age groups, flat or chevron-shaped metatarsal head, longer proximal phalanx, increased HAI degrees and a first metatarsal longer than the third metatarsal. For radiological parameters to be considered valid for inclusion in a classification of HR their content validity needs to be established by formal research.