An Attempt to Assess the Indications for Reverse Total Shoulder Arthroplasty Based on Biomechanical Analysis.

Background: Starting from the 1950s, shoulder arthroplasty has been developing, one consequence of which has been the concept of reverse shoulder arthroplasty (RSA). Initially, it was supposed to be used only in patients with irreversible rotator cuff damage, but it quickly gained more and more indications for use. The aim of the present study was to assess biomechanical, objective indications for RSA in patients with shoulder osteoarthritis (OA) based on an inertial measurement system with electromyography.

Material and methods: 20 patients were qualified to this prospective study, 10 each in a control and experimental group. The study was conducted between August 2020 and October 2021. The experimental group consisted of 9 women and 1 man aged 55 to 85 years old, with osteoarthritis of the shoulder associated with rotator cuff damage. The study utilised the myoMotion inertial sensor system (Noraxon, USA) synchronized with the surface electromyography system Myotrace 400 (Noraxon, USA).

Results: Movement phase diagrams were used to assess the movement patterns. To examine the movement pattern in the shoulder, three motor tests can be proposed: flexion-extension, flexion in the scapular plane and abduction-adduction. The observation of trends for the operated limb showed the highest absolute improvement in the group with the greatest impairment of the movement pattern in the initial test. However, on final evaluation, these results were still twice as low as those obtained in the group with the least impairment.

Conclusions: 1. Early qualification of patients with shoulder OA for RSA could mean a greater likelihood of functional and quality-of-life improvement. 2. Movement patterns after RSA may improve, but will probably not return to physiological values.