Parr TE, Anderson JK, Marionneaux AM, Tokish JM, Tolan SJ, Hawkins RJ, Kissenberth MJ, DesJardins JD. Assessment of glenoid baseplate initial micromotion and fixation strength in reverse total shoulder arthroplasty designs using a direct shear force methodology.
Shoulder Elbow 2022;
14:606-614. [PMID:
36479005 PMCID:
PMC9720869 DOI:
10.1177/17585732211032945]
[Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/22/2021] [Accepted: 06/24/2021] [Indexed: 11/17/2022]
Abstract
Background
In a reverse total shoulder arthroplasty, the altered glenohumeral joint center of rotation subjects the glenoid baseplate to increased shear forces and potential loosening.
Methods
This study examined glenoid baseplate micromotion and initial fixation strength with the application of direct shear force in a Sawbone model. The reverse total shoulder arthroplasty systems examined were the DJO Reverse® Shoulder Prosthesis, the Exactech Equinoxe® Reverse System, and the Tornier AequalisTM Reverse Shoulder Prosthesis. Specimens were cyclically tested with increasing shear loads until 150 µm of displacement between the implant and glenoid was achieved, and subsequently until failure, classified as either 1 cm of implant/glenoid displacement or fracture.
Results
The average load withstood for the 150 µm threshold for DJO, Tornier, and Exactech was 460 ± 88 N, 525 ± 100 N, and 585 ± 160 N, respectively. The average total load at device failure for DJO, Tornier, and Exactech was 980 ± 260 N, 1260 ± 120 N, and 1350 ± 230 N, respectively.
Discussion
The Exactech implant design trended toward requiring more load to induce micromotion at each threshold and to induce device failure, most commonly seen as inferior screw pull out. This study proposes design features that may enhance fixation and suggests little risk of initial micromotion or failure during initial post-operative recovery.
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