Patient-Specific Instrumentation Reduces Deviations Between Planned and Post-Osteotomy Humeral Retrotorsion and Height in Shoulder Arthroplasty.

BACKGROUND Patient-specific instrumentation (PSI) may potentially improve humeral osteotomy in shoulder arthroplasty. The purpose of this study was to compare the deviation between planned and post-osteotomy humeral inclination, retrotorsion and height in shoulder arthroplasty, using PSI versus standard cutting guides (SCG). METHODS Twenty fresh-frozen cadaveric specimens were allocated to undergo humeral osteotomy using either PSI or SCG, such that the two groups have similar age, gender and side. Pre-osteotomy computed tomography (CT) scan was performed and used for the three-dimensional (3D) planning. The osteotomy procedure was performed using a PSI designed for each specimen or a SCG depending on the group. A post-osteotomy CT scan was performed. The pre-osteotomy and post-osteotomy 3D CT scan reconstructions were superimposed to calculate the deviation between planned and post-osteotomy inclination, retrotorsion and height. Outliers were defined as cases with one or more of the following deviations: >5° inclination, >10° retrotorsion, and >3 mm height. The deviation and outliers in inclination, retrotorsion and height were compared between the two groups. RESULTS The deviations between planned and post-osteotomy parameters were similar among the PSI and SCG groups for inclination (p=0.260), while they were significantly greater in the SCG group for retrotorsion (p<0.001) and height (p=0.003). There were 8 outliers in the SCG group, compared to only 1 outlier in the PSI group (p=0.005). Most outliers in the SCG group were due to deviation >10° in retrotorsion. CONCLUSION After 3D planning PSI compared to SCG reduces the deviation between planned and post humeral osteotomy retrotorsion and height.