Geometric modification of the humeral position after total reverse shoulder arthroplasty: what is the optimal lowering of the humerus?

Abstract

Background: The main mechanical effect after reverse shoulder arthroplasty (RSA) is the lowering of the glenohumeral rotation center. The optimal value of the humeral lowering after RSA is still debated. The main objective of our study was to determine the lowering and medialization of the humerus and to correlate these parameters with short-term functional results.

Materials and methods: The study included 70 patients with complete radiographic and clinical data. A multivariate analysis was used to compare the clinical and radiographic outcomes with the humeral lowering.

Results: The mean humeral lowering was 25.4 mm (range, 6-38 mm), and the mean medialization was 9.2 mm (range, 0-20 mm). Humeral lowering significantly influenced active forward elevation and the rate of scapular notching.

Discussion: The best clinical results and the lowest incidence of scapular notching were found after a lowering of more than 24 mm in our series. We recommend humeral lengthening of at least 24 mm after implanting a total reverse shoulder prosthesis.

Keywords: Reverse shoulder arthroplasty; complications; humerus lengthening; lowering; medialization; scapular notch.