A comparison of onlay versus inlay glenoid component loosening in total shoulder arthroplasty.

BACKGROUND: Glenoid component loosening is common in total shoulder arthroplasty (TSA), often resulting from the mechanical interaction of glenohumeral components. This cadaveric study was performed to evaluate and to compare commercially available onlay and inlay glenoid prosthetic designs with respect to loading characteristics and loosening. METHODS: Sixteen prescreened cadaveric shoulders (8 matched pairs) underwent either onlay or inlay TSA. We created a custom glenohumeral loading model and used cycles of 5 mm anterior-posterior humeral translation to simulate a rocking-horse loosening mechanism for all testing. Articular TekScan measurements were performed with 9.1 kg (88.9 N) of glenohumeral compression before and after TSA. Fatigue testing was performed with 34.0 kg (333.6 N) of glenohumeral compression using high-definition video to document gross glenoid loosening. Testing ended with gross loosening or a maximum of 4000 cycles. Mean contact area, pressure, and joint reaction force were used to compare the 2 glenoid designs. RESULTS: In both implant types, contact area decreased and pressure increased after TSA (P < .0001). Force increased at the onlay component edge only (P = .0012) compared with native glenoid testing. Force was greater in the onlay vs. the inlay implants (P < .0001). During fatigue testing, all onlay glenoid components exhibited gross loosening at a mean of 1126 cycles (range, 749-1838), whereas none of the inlay glenoid components exhibited gross loosening (P < .0001). CONCLUSION: The inlay glenoid implant exhibited biomechanical characteristics favoring stability and decreased loosening compared with the onlay glenoid implant in this cadaveric model.

Anatomic total shoulder arthroplasty with inlay glenoid component: A systematic review.

Background: A total shoulder arthroplasty (TSA) system utilizing an inlay glenoid component has been proposed as a means of reducing glenoid component loosening while still providing patients with desirable functional and clinical outcomes. The purpose of this study was to systematically review current outcomes literature on TSA using an inlay glenoid component. Methods: A literature search was conducted using PubMed/MEDLINE, Cochrane Database of Systematic Reviews, and Web of Science databases. Studies comparing pre- and postoperative functional and clinical outcomes were included. Results: Five studies with 148 shoulders (133 patients) were included. Patient-reported outcomes improved, including the American Shoulder and Elbow Surgeons score (mean change 34.1 to 80.6), Penn Shoulder Score (mean change 43.3 to 85.5), Single Assessment Numeric Evaluation score (mean change 34.1 to 80.6), and visual analog scale-pain (mean change 6.9 to 1.6). Range of motion improved for forward elevation (mean change 109.6 to 156.2) and external rotation (mean change 21.5 to 50.8). Glenoid component loosening occurred in one shoulder (0.68%). Two revision surgeries (1.35%) were performed. Discussion: The use of an inlay glenoid component is associated with improvements in postoperative pain, function, and satisfaction while minimizing rates of glenoid component loosening and the need for revision surgery over short-term follow-up. Level of evidence: systematic review, level IV.