Kinematics study of the deltoid in Reverse Shoulder Arthroplasty using Standard Pre and Post-Operative X-Rays

摘要

For patients with deficient rotator cuff Reverse Shoulder Arthroplasty, in which the centre of rotation of the glenohumeral joint is repositioned, is a popular treatment. However, for optimal restoration of motion after RSA, the correct implant selection and positioning within the bones is critical for a successful surgical outcome. This paper examines current practice of implant insertion and predicts what would be its mechanical advantage by using a developed graphical user interface importing pre and post-operative shoulder X-rays. Standardised X-rays of 8 shoulder griddle pre and post-operative were provided in the true anteroposterior (Grashey) view. Images were then calibrated and key geometrical parameters were identified in all images. A mathematical model for deltoid excursion and deltoid lever arm in full abduction was developed based on the mechanical model of the shoulder in order to investigate its performance (deltoid) in both native and reverse shoulders. Results showed that the deltoid lever arm was improved in reverse shoulders for lower abductions. In higher abductions a sudden drop in the lever arm's mechanical advantage was observed. It was also observed that more deltoid excursion occurred in full abduction of reverse shoulders compared to native shoulders.