Date of Award
Master of Science (MS)
Glenoid deformity remains one of the most difficult challenges facing reverse total shoulder arthroplasty (RTSA) surgeons today as approximately 42,000 cases are performed in the United States each year (Schairer et al., 2015; Day et al., 2010). While RTSA aids in reducing pain and improving function in patients suffering from shoulder pathologic processes, high complication rates, ranging from 14-75%, and revision rates, ranging from 4-40%, have been reported (Sershon et al., 2014; Zumstein et al., 2011). More importantly, glenoid baseplate loosening remains a huge concern for surgeons as it is remains the number one cause for revision surgery (Tashjian et al., 2015). When taking a biconcave, or B2, glenoid into account, higher complication rates have been reported in comparison to lesser severe glenoid deformities (Mizuno et al., 2013). In an attempt to help enhance RTSA clinical outcomes, the purpose of this study was to compare micromotion in a validated model, using Arthrex’s Virtual Implant Positioning™ (VIP) System, between RTSA glenoid components placed in Malpositioning versus Optimal Clinical Positioning in the simulated B2 glenoid.
Twenty Arthrex Univers Revers™ implants were implanted into B2 scapula sawbones, with 10 implants being placed in Malpositioning while the other 10 were placed in Optimal Clinical Positioning. The Malpositioning group was defined according to an Iannotti et al. (2014) study and represented the worst case implantation scenario while the Optimal Clinical Positioning group optimized baseplate positioning according to idealized VIP plans generated by Arthrex VIP engineers. Cyclic displacement and failure tests were performed using the Instron and Linear Variable Differential Transformer (LVDT), which measured and recorded baseplate micromotion. Each cyclic displacement test ran for 30 cycles at 1 Hz, with Instron load being applied in the inferior to superior direction. After 150 μm of baseplate micromotion was reached, each specimen was tested to failure by causing either a displacement of 1 cm or scapula fracture, whichever occurred first. After both tests were completed, data was collected and analyzed in order to compare baseplate loading and micromotion, for both cyclic and failure testing, between implantation groups with t-tests being run at α=0.05 for statistical significance.
The Optimal Clinical Positioning specimen withstood higher loading forces versus the Malpositioning specimen at 150 µm of baseplate micromotion, which could contribute to better clinical outcomes and reduced complication rates. Variability amongst specimen in each implantation group existed, which could be a direct result of baseplate angulation, variations in baseplate alignment, or baseplate implantation depth. No significant differences in maximum failure loads or micromotion were found between the two implantation groups, which could be a result of other dominating factors including screw fixation strength or baseplate design parameters that aid in enhancing fixation. Results suggest that the VIPTM System can deal with significant variations in implantation technique and still lead to similar clinical outcomes by optimizing baseplate positioning. In conclusion, this study is the first to show that a RTSA implant can provide adequate fixation despite challenging B2 glenoid pathology, which makes fixation strength and stability challenging.
Hall, Shannon, "Micromotion and Strength of the Glenoid Component in Reverse Total Shoulder Arthroplasty: The Effect of Malpositioning Versus Optimal Clinical Positioning in the Simulated B2 Glenoid" (2018). All Theses. 3242.