To evaluate the nature of positional changes of humeroulnar (HU) and humeroradial (HR) joints in a cohort of 74 patients with seropositive and erosive rheumatoid arthritis (RA) followed up prospectively.
At the 15 year follow up standard anteroposterior and lateral radiographs of 148 elbow joints were evaluated. The mediolateral HU angle of the elbow was measured from anteroposterior radiographs. The proximal subluxation of the HU joint was measured from lateral radiographs as the distance between the posterior aspect of the olecranon process and the posterior surface of the humerus. The anteroposterior subluxation of the HR joint was measured from lateral radiographs as the relation of the midpoint of head of the radius to the midpoint of the capitellum of the humerus. Destruction of the elbow joints was assessed with the Larsen method on a scale of 0 to 5 and compared with the measurements.
Mean HU angle in 148 elbows of patients with RA was 11.5 degrees (SD 6.1), range -21 degrees (varus) to 34 degrees (valgus); 9.9 degrees (SD 4.3) in men and 12.0 degrees (SD 6.4) in women. The mean HU angle, 14.4 degrees (SD 6.0) of the affected joints (Larsen grades 2-4), showed more valgus than the mean 9.8 degrees (SD 2.5) of the non-affected (Larsen grades 0 to 1) joints; totally destroyed and unstable Larsen 5 joints were excluded. Mean HU and HR subluxations, 2.0 mm (SD 3.8) and 0.8 mm, of the affected joints (Larsen 2-5) were greater than the means, -1.1 mm (SD 1.5) and -0.4 mm (SD 0.9), of the non-affected joints. Both the HU proximal subluxation and the HR anterior subluxation correlated, r(s)=0.64 (95% CI 0.53 to 0.73 ) and r(s)=0.48 (95% CI 0.34 to 0.60), with the destruction of the elbow joint.
The elbow seems to turn into valgus during rheumatoid destruction and excision of the radial head may speed up this process. However, totally unstable Larsen grade 5 joints may also have varus deformity owing to mutilating bone destruction. The ulna subluxates proximally in relation to the humerus, whereas the radius moves slightly anteriorly as a consequence of elbow involvement.