The aim of this study was to radiologically evaluate the risk of reduction loss after locking plate fixation of proximal humerus fractures.

From September 2007 to April 2009, 71 patients (28 males, 43 females) with unstable proximal humeral fracture were treated with open reduction and internal fixation by locking plate. The mean follow-up time was 31.2 months (range: 26–47). The head-shaft angulation (HSA) and the humeral head height (HHH) in true anteroposterior (AP) were recorded and compared over time. All complications were noted. Shoulder function was measured by the Constant score.

Patients with ΔHSA >10° (t=2.740, P=0.008) and ΔHHH >5mm (t=2.55, P=0.019) were more likely to have impaired shoulder function. Varus collapse occurred most frequently in patients with initial reduction of HSA <125° (χ²=19.17, P<0.001, Fisher's exact test F<0.001). Patients with >5mm HHH decrease were strongly associated with loss of reduction (χ²=24.23, P<0.001, F<0.001).

Dynamic change of HSA >10° and HHH >5mm were radiological factors that indicated poor shoulder function. Intra-operative HSA >125° should be achieved to avoid reduction loss following locking plate fixation of proximal humerus fracture.

level IV.