Three-Dimensional Analysis of Bone Morphology of the Rheumatoid Arthritis Elbow.

Introduction: Accurate treatment of elbow rheumatoid arthritis (RA) requires understanding the joint destruction pattern. However, comprehensive bone-deformation patterns remain unclear. Thus, we aimed to quantitatively evaluate three-dimensional (3D) deformity in RA elbows compared with normal elbows.

Methods: The authors created 3D CT models of the distal humerus, proximal ulna, and radial head for 26 elbows with RA (Larsen classification IV) and 26 normal elbows. These models were superimposed onto one reference bone, selected from normal elbows. The intermodel distance was measured at categorized anatomical regions of the individual bones, and the measurements were compared between the RA and normal elbows. Correlation between clinical outcomes, including range of motion and 3D deformities, were also assessed in the RA group.

Results: RA elbows exhibited notable bone destruction in both the anterior-inferior region of the distal humerus (7.9 to 9.9 mm vs. 9.5 to 12.6 mm) and the trochlear notch (16.7 to 20.1 mm vs. 11.3 to 15.4 mm) compared with normal elbows, with all differences being statistically significant (P < 0.05). The radial head in RA elbow was shortened (2.24 ± 1.97 mm vs. -0.18 ± 0.59 mm; P < 0.05), with osteophyte formation, particularly on the lateral side (P < 0.05). Humeroulnar joint deformity correlated with flexion-extension limitation (R = 0.42 to 0.74), and the radial head correlated with forearm supination limitation (R = 0.57 to 0.58).

Conclusion: Bone destruction was shown in the anterior-inferior region of the distal humerus and trochlear notch, and the radial head was shortened with osteophyte formation, resulting in a proximal shift of the forearm bones and impaired motion. This provides valuable insights into RA elbow pathology and contributes to advancements in treatment.