PERFORMANCE EVALUATION OF THE TRABECULAR METAL GLENOID Matthew L. Mroczkowski M.S. Total shoulder arthroplasty is successful in relieving pain and restoring function to the joint, but chronic loosening of the glenoid implant remains a common complication. The Zimmer® Trabecular Metal™ Glenoid is an implant that is designed to achieve long-term fixation with biological ingrowth. The purpose of this paper is to describe the testing and analyses that were conducted to assess the performance of the implant under expected in vivo conditions. The Trabecular Metal Glenoid is a monoblock implant for reconstructive total shoulder arthroplasty. It consists of a Trabecular Metal base with a fully integrated, compression molded ultra-high molecular weight polyethylene (UHMWPE) articular surface. The base of the implant has five posts that provide fixation. The five post configuration provides initial fixation using a press-fit between the implant and the bone. Long-term fixation is provided by biological ingrowth into the Trabecular Metal material. The implant strength was evaluated using a novel fatigue test and subsequent static test method. Initial fixation of the implant was evaluated using the ASTM F 2028-05 standard. Initial fixation tests were performed on a cemented UHMWPE design for comparison. Finite element analyses were conducted to compare the contact stresses in the UHMWPE relative to a solid metal-backed design. The Trabecular Metal Glenoid successfully met the performance requirement. Displacement measurements from the initial fixation test were reduced (i.e. indicated less motion) compared to a cemented UHMWPE design. The contact stresses in the UHMWPE were reduced compared to a metal-backed design for functionally important loading conditions in which there is translation of the humeral head. Through experimental and analytical testing, the Trabecular Metal Glenoid has been shown to withstand repetitive eccentric loading, provide initial fixation superior to a cemented UHMWPE design, and reduce the contact stresses in the UHMWPE compared to a metal-backed design. The most common complication in total shoulder arthroplasty is failure of the glenoid component. Failure of the glenoid component has been attributed to several different causative factors1 including: , • Inadequate initial fixation • Inability to fully seat the implant • Inability to handle eccentric loading • Poor quality bone stock Figure 1 – The Trabecular Metal Glenoid This paper is intended to describe the performance evaluation (strength and initial fixation testing) that was conducted in the development of the Trabecular Metal Glenoid. Due to its large range of motion, the loads occurring at the glenohumeral joint are multi-directional and activitydependent. The Trabecular Metal Glenoid base was engineered to withstand these loads while conserving as much bone as possible. The configuration of the posts provides support in the anterior, posterior, superior and inferior quadrants of the glenoid. Anterior Figure 2 – The base of the Trabecular M

The strength of the Trabecular Metal Glenoid was evaluated through mechanical testing, which consisted of the following steps: 1. Specimen preparation (Figure 3) – Blocks of rigid polyurethane foam were prepared to simulate a situation in which the glenoid implant is not fully seated, and a gap is present around the perimeter of the articular surface. The keel portion of the glenoid test specimens was rigidly fixed by PMMA bone cement in a cavity inside the foam block. 2. Fatigue testing – A dynamic test was performed, in which load was applied repeatedly to determine the implant’s resistance...

The results from the dynamic loosening test are shown in Figure 7. A comparison of the Trabecular Metal Glenoid with the Bigliani/Flatow keeled glenoid is summarized in Table 1. The results are expressed as a percentage of the motion measured for the cemented Bigliani/Flatow keeled glenoid (e.g. the long-term results of the backside cemented application reveal a reduction of 29.2%). Joint Kinematics Restoration of normal joint motion is one of the key goals in total shoulder arthroplasty. The Trabecular Metal Glenoid is designed to achieve this using the same articular surface as the Bigliani/Flatow...

Axial Compression A-P Translation90° AbductionSolid metal-backed (Ti) design Trabecular Metal Glenoid design (.PRESS GLEB _S/HEAD. Figure 8 - Finite element analysis results Conclusions Through experimental and analytical testing, the Trabecular Metal Glenoid has been shown to: • Withstand repetitive eccentric loading • Provide initial fixation superior to a cemented polyethylene design • Restore more normal glenohumeral joint kinematics and contact area patterns • Reduce contact stresses in the UHMWPE compared to a metal-backed design References 1. Matsen FA, et al. Glenoid component failure...