Biomechanical evaluation of different designs of glenospheres in the SMR reverse total shoulder prosthesis: Range of motion and risk of scapular notching

• Published in: Journal of shoulder and elbow surgery Vol. 18; no. 3; pp. 354 - 359
• Main Authors: Chou, Justin, MBchB, Malak, Sharif F., ME, Anderson, Iain A., PhD, Astley, Tim, MBchB, FRACS, Poon, Peter C., MBchB, FRACS
• Format: Journal Article
• Language: English
• Published: New York, NY Mosby, Inc 01.05.2009; Elsevier
• Subjects: Analysis of Variance; Arthroplasty, Replacement - methods; Biological and medical sciences; biomechanical; Biomechanical Phenomena; Biomechanics. Biorheology; Computer Simulation; Diseases of the osteoarticular system; eccentric; Fundamental and applied biological sciences. Psychology; glenosphere; Humans; Joint Instability - prevention & control; Joint Prosthesis; Medical sciences; Orthopedics; Probability; Prosthesis Design; Range of Motion, Articular - physiology; Reverse shoulder arthroplasty; Scapula - physiopathology; scapular notching; Sensitivity and Specificity; Shoulder Impingement Syndrome - prevention & control; Shoulder Joint - physiopathology; Shoulder Joint - surgery; Stress, Mechanical; Tissues, organs and organisms biophysics; scapular notching; glenosphere; biomechanical; eccentric; Reverse shoulder arthroplasty; Biomechanics; Motion; Reverse prosthesis; Shoulder; Risk factor; Rheumatology
• ISSN: 1058-2746; 1532-6500
• DOI: 10.1016/j.jse.2009.01.015

Background Reverse total shoulder arthroplasty is a treatment option for cuff tear arthropathy. Scapular notching remains a concern. This biomechanical study compared the range-of-motion in different designs of glenospheres and hence the relative risk of scapular notching. Method A precision coordinate device was used to investigate four different designs of glenospheres (SMR prosthesis); 36mm concentric (Standard), 36 mm eccentric, 44 mm concentric, and 44 mm eccentric glenospheres. The centre of rotation in each design was first established. The position of the humeral prosthesis was recorded in the plane of the scapula to compare the degree of adduction and the total range-of-motion. Results Eccentric glenospheres were found to improve range-of-motion by allowing a higher degree of adduction. Larger diameter glenospheres were found to improve range-of-motion by increasing adduction and abduction. Compared to the 36 mm concentric (standard) glenosphere, the 36 mm eccentric glenosphere improved adduction by 14.5 degrees, the 44 mm concentric glenosphere improved adduction by 11.6 degrees, the 44 mm eccentric glenosphere improved adduction by 17.7 degrees. Conclusion Eccentric glenospheres with a center-of-rotation placed more inferiorly were shown to improve adduction. This design may reduce the clinical incidence of scapular notching. Level of evidence Basic science study.