Importance of polyethylene thickness in total shoulder arthroplasty: A finite element analysis

Abstract

Background: Articular surfaces reconstruction is essential in total shoulder arthroplasty. Because of the limited glenoid bone support, thin glenoid component could improve anatomical reconstruction, but adverse mechanical effects might appear. Methods: With a numerical musculoskeletal shoulder model, we analysed and compared three values of thickness of a typical all-polyethylene glenoid component: 2, 4 (reference) and 6 mm. A loaded movement of abduction in the scapular plane was simulated. We evaluated the humeral head translation, the muscle moment arms, the joint force, the articular contact pattern, and the polyethylene and cement stress. Findings Decreasing polyethylene thickness from 6 to 2 mm slightly increased humeral head translation and muscle moment arms. This induced a small decreased of the joint reaction force, but important increase of stress within the polyethylene and the cement mantel. Interpretation The reference thickness of 4 mm seems a good compromise to avoid stress concentration and joint stuffing.

Accuracy of Humeral Articular Surface Restoration in a Novel Anatomic Shoulder Arthroplasty Technique and Design: A Cadaveric Study

“…Thicker glenoid implants are more likely to lateralize the joint line. 17 Further clinical studies are warranted to validate the findings of this study.…”

Analysis on stress and micromotion on various peg fixation at glenoid implant

“…Glenoid implant loosening is known as one of the common complications after total shoulder arthroplasty. There were various factors associated with component loosening such as high stress at the glenoid cement layer, 2, 3 glenoid mismatch, 15 glenoid malposition 16 , micromotion at bone–cement interface 3, 7 and glenoid fixation failure4, 17, 21. There were two common fixations used for glenoid component fixation, peg and keel.…”

“…The radius of curvature, R g , shape material and thickness of implant, t i , were set as 29.5 mm, pear-shape, all-polyethylene and 4 mm, 2 respectively, as shown in Fig. 2.…”

“…High rate of component loosening, up to 39%, made the loosening problem become among a common complication compared to other factors. 1 The component loosening had been related to high stress at the implant and cement, 2,3 micromotion at the bone-cement interface. 3 Currently, there were two most common glenoid fixation used for glenoid implant, which are peg and keel.…”