The acromion plate angle: a simple measurement to predict clinical outcomes after plate removal in proximal humerus fractures

Abstract

Background

One-third of patients who undergo open reduction and internal fixation of proximal humerus fractures require subsequent plate removal (PR). It is currently unclear which patients will benefit most from this procedure. Therefore, to support preoperative decision-making we sought to identify predictive factors of the clinical benefits of PR.

Materials and methods

All patients with open reduction and internal fixation for proximal humerus fractures from 2014 to 2020 were recorded prospectively in an institutional register. All those with a 1-year follow-up were included in the study. The clinical and radiographic follow-ups after 12 months, and before and after PR were evaluated. The radiographic analysis included measuring known parameters (acromion tuberosity index, lateral acromion angle, critical shoulder angle) and a new measurement: the acromion plate angle (APA).

Results

We included 91 patients of whom 31 had undergone later PR. A significant difference between the group without and with PR was only seen in the age (P ≤ .001). Significant improvement in the absolute Constant score (CS) (+12.6), relative CS (+16.6), elevation (+29.5°), abduction (+32.6°), and external rotation (+18.1°) (P values <.001) was observed following PR. The regression analysis revealed that older age and low APA were significant predictors of clinically relevant improvement of the absolute CS. Optimal cut-off values for age (>55 years) and APA (<36°), corresponding to a minimal increase of 10 points in the absolute CS, were also identified.

Conclusion

Significant improvements in absolute CS and range of motion were achieved in all patients after PR. Even though it was performed more frequently in younger patients, patients >55 years profited the most. An APA of <36° was found to be a positive predictor for significant and relevant functional improvement after PR. Its easy use on ap radiographs allows uncomplicated integration into the clinical decision-making process and helps inform the patients in terms of what to expect after the intervention.