Abstract
INTRODUCTION
Preoperative planning software for reverse total shoulder arthroplasty (RTSA) allows surgeons to virtually perform a reconstruction based off 3D models generated from CT scans of the glenohumeral joint. While anatomical studies have defined the range of normal values for glenoid version and inclination, there is no clear consensus on glenoid component selection and position for RTSA. The purpose of this study was to examine the distribution of chosen glenoid implant as a function of glenoid wear severity, and to evaluate the inter-surgeon variability of optimal glenoid component placement in RTSA.
METHODS
CT scans from 45 patients with glenohumeral arthritis were planned by 8 fellowship trained shoulder arthroplasty specialists using a 3D preoperative planning software, planning each case for optimal implant selection and placement. The software provided four glenoid baseplate implant types: a standard non-augmented component, an 8° posterior augment wedged component, a 10° superior augment wedged component, and a combined 8° posterior and 10° superior wedged augment component. The software interface allowed the surgeons to control version, inclination, rotation, depth, anterior-posterior and superior-inferior position of the glenoid components in 1mm and 1° increments, which were recorded and compared for final implant position in each case.
RESULTS
Two cases were excluded due to extreme deformity and consensus that a feasible RTSA may not be possible. For resultant implant version, a bimodal distribution was observed with a local maxima occurring at 0°, and a bell-shaped distribution at −5° of version. Upon individual surgeon analysis, it was revealed that certain surgeons had a preference to correct to 0 degrees, whereas others were more accepting of residual version. As well, the surgeons accepting residual retroversion removed less bone on average per implant type than the surgeons who aimed to correct to 0°. For resultant implant inclination, surgeons consistently tried to plan for 0 degrees of inclination.
CONCLUSION
This study indicates that while there was limited consensus on the optimal reconstruction in any one case, there appear to be thresholds of retroversion and inclination that favor the use of augmented glenoid components based on frequency of selection. Our results indicate a wide variability in terms of what experienced shoulder surgeons consider to be an optimal reconstruction despite the common goal of attempting to restore anatomy, maximize implant fixation in bone and minimize bone removal. High frequency of augmented glenoid component use raises questions about how much retroversion and inclination is optimal and whether this technology allows surgeons to potentially focus more on a quantitative reconstruction relative to the Friedman axis versus a qualitative implant placement relative to what may be normal anatomy for a patient.
