Radiographic study of the distal ulna in rheumatoid arthritis with extensor digitorum communis ruptures

Objectives: Extensor digitorum communis (EDC) rupture of the wrist often occurs in patients with rheumatoid arthritis (RA). Early operation is desirable for patients with a high risk of rupture; therefore, rheumatologists should diagnose it during daily examinations. This study aimed to clarify radiographic changes in the distal ulna and related factors associated with EDC rupture in patients with RA.

Methods: We analysed plain radiographs of 40 patients with RA associated with EDC rupture and 62 healthy controls. We investigated the deformation of the distal ulna, Larsen grades, and radiological parameters such as ulnar variance (UV), ulnar bowing angle, dorsal protrusion (DP), and dorsal bowing angle.

Results: The ratios of the ulna head deformation, Larsen grades, UV, DP, and dorsal bowing angle were significantly larger in the ruptured group than in the control group. Multiple logistic regression analysis revealed that DP and Larsen grades were significantly associated with EDC rupture.

Conclusions: Deformity of the distal ulna is evident in patients with an EDC rupture. Ulnar head deformation, high Larsen grades, and large DP are the potential risk factors for EDC rupture.