Thumb boutonnière deformity without rheumatoid arthritis or trauma.

Boutonniere deformity of the thumb without rheumatoid arthritis or trauma is not widely recognised. This study aimed to investigate its prevalence, relation to sex and age, and identifying factors associated with the extensor mechanism using ultrasonography. We examined 248 thumbs from 127 participants who were asymptomatic for hand disorders and had no history of hand injury. Boutonniere deformity was identified in 20 thumbs of 17 participants and was significantly more prevalent among elderly participants than among young participants. No significant differences in sex or hand dominance were noted. The deformity had a significant effect on range of motion and grip and pinch strengths. The extensor pollicis brevis (EPB) tendon was significantly narrower in affected thumbs than in non-affected thumbs. The prevalence of boutonniere deformity without rheumatoid arthritis or trauma was 13%, and the deformity was associated with advanced age and a narrow EPB tendon. Level of evidence: III