Preoperative radius head dislocation affects forearm rotation after mobilization of congenital radioulnar synostosis

The present study was carried out to answer three questions: 1) How much forearm rotation can be expected after mobilization of congenital radioulnar synostosis (CRUS)? 2) Does preoperative radius head dislocation affect forearm rotation after mobilization? 3) What factors other than radius head dislocation affect postoperative forearm rotation?We performed mobilization of CRUS with a free vascularized fascio-fat graft and a radius osteotomy (Kanaya's procedure) on 26 forearms of 25 patients. The age at the surgery ranged from 5.3 to 13.4 years. The follow-up duration ranged 24-111 months. We classified CRUS into 3 groups according to the dislocation of the radius head: posterior dislocation (N = 13), anterior dislocation (N = 9) and no dislocation (N = 4). Since major complaints of patients and parents were poor forearm rotation and lack of supination, they were evaluated separately.Mean preoperative forearm ankylosis angle was 34.8° (range; neutral to 90° pronation). Preoperative pronation ankylosis angle was higher in the posterior dislocation group (mean 55.3°) than the anterior dislocation (mean 11.6°) and no dislocation groups (mean 5.0°). There was no re-ankylosis after mobilization and the mean postoperative active range of motion (ROM) was 86.5°. The mean active ROM was 75.7° in the posterior dislocation group, 96.1° in anterior dislocation group and 100.0° in no dislocation group. The mean active supination was 6.9, 33.9 and 47.5° respectively. The posterior dislocation group showed less ROM and less supination than other groups. Preoperative pronation ankylosis angle showed negative correlation with postoperative ROM (ρ = - 0.59) and postoperative supination (ρ = - 0.73).The mean postoperative active ROM of this mobilization was 86.5°. Posterior dislocation group showed higher pronation ankylosis angle preoperatively, and less postoperative ROM and less supination than anterior and no dislocation groups. Preoperative pronation ankylosis angle showed negative correlation with postoperative ROM and supination.