Perforation tolerance of glenoid implants to abnormal glenoid retroversion, anteversion, and medialization.

BACKGROUND: Loosening of the glenoid implant is a common complication of total shoulder arthroplasty. To prevent this, we need to ensure the glenoid vault is not perforated during insertion of the glenoid implant to allow for cement containment and maximum pressurization. Factors affecting perforation potential include glenoid implant design and alignment. This study looks at the perforation tolerance of 15 commercially available glenoid implants to increased retroversion, increased anteversion, and medialization. MATERIALS AND METHODS: Accurate 3-dimensional models of the 15 glenoid implants were created from exact dimensions obtained from the manufacturers and virtually implanted into 3-dimensional reconstructed models of 40 nonarthritic scapulae. Perforation tolerances of each implant to increased retroversion, increased anteversion, and medialization were determined through computer simulation to represent asymmetrical arthritic posterior wear, anterior wear, and eccentric corrective reaming, respectively. RESULTS: In all 15 glenoid implants, the overall mean increased retroversion tolerated before perforation was 19°, increased anteversion was 16°, and abnormal version fully corrected by eccentric reaming was 17°. Each glenoid implant was evaluated individually to allow for direct comparison and, finally, size-matched and downsized glenoid implants in relation to the size of the humeral head. CONCLUSION: The results from this study help surgeons, when faced with a severely arthritic glenoid, to choose the appropriate glenoid implant to minimize perforation potential, and provide guidance on how much abnormal version and how much corrective reaming can be tolerated before perforation occurs and fixation is compromised. These results can also help with future implant designs.

A 2-dimensional glenoid vault method for measuring glenoid version on computed tomography.

BACKGROUND: Accurate placement of the glenoid prosthesis in shoulder arthroplasty is critical; precise glenoid prosthesis alignment being a key element to avoid poor fixation and early loosening. The current recognized 2-dimensional (2-D) method for measuring glenoid version may be irrelevant to the above, as it does not take into account the complex and variable relationship of the scapular body in relation to the glenoid. On the contrary, a 3-dimensional (3-D) method, which focuses solely on the glenoid, is superior but not readily accessible. We have, therefore, developed a new 2-D method based solely on the glenoid vault which is readily accessible. MATERIALS AND METHODS: To determine normal version using our method, computer tomography (CT) scans of 107 normal shoulders were assessed as the control group. We then assessed 63 arthritic shoulders to establish any significant difference. Inter- and intraobserver reliability were assessed using 4 observers who independently reviewed 50 blinded CT images 3 weeks apart. For comparison, the currently recognized method, as described by Friedman et al, was also utilized in this study. RESULTS: Using our new method, the mean glenoid version in the control group was 19 ± 3° of retroversion; and in the arthritic group, 25 ± 6° of retroversion. Intra- and interobserver reliability were very high. CONCLUSION: Our new 2-D glenoid vault method is relevant, as it focuses solely on the glenoid vault, is precise with a low standard deviation, and is reliably reproducible as shown by the intra- and interobserver reliability data, all while remaining readily accessible.