Recent studies reported the use of patient-specific guides in aim to improve accuracy in glenoid component positioning for RSA. Most of the guides assessed in the literature have shown promising results on following preoperative plans. However, there are no direct comparisons for glenoid placement and functional outcomes of a standard RSA surgery to a guided RSA surgery.

This study was designed to perform RSA surgery from a single surgeon in 20 cadaveric specimens with two methodologies for glenoid baseplate placement:

– traditional procedure in using a standard surgical instrumentation;

– assisted procedure with a specific-guide according to a preoperative plan.

The Biomet Comprehensive RSA was used. In both methods, the surgeon aimed to achieve glenoid baseplate version and tilt placement to anatomical values (0 to 5°). For the guided surgeries, a preoperative plan was performed using an interactive shoulder model (Newcastle Shoulder Model). The plan aimed to maximize impingement free range of motion (abduction, internal and external rotation). Specific guides were manufactured based on these plans by a 3D printer. Pre- and postoperative CTs were used to assess the glenoid orientation as well as the position of the baseplate. The impingement free range of motion was evaluated with a motion analysis system postoperatively.

In average both standard and guided RSA surgeries changed the postoperative glenoid version and tilt, but none of the changes were statistically significant (P>0.05). The guided surgery had a significant impact on the placement of the glenoid baseplate, which was in average 4.2mm (SD 4.0) more inferiorly compared to the standard procedure (P<0.05). This difference in baseplate placement had also an effect on the impingement results. The average inferior impingement was recorded at 10.4° (SD 4.3) and superior impingement averaged at 67.9° (SD 4.3) for the guide surgery specimens. It was better than the cadavers that received traditional procedure (average inferior and superior impingement - 29.6° (SD 13.7), 59.3° (SD 1.54), respectively, P<0.05). Rotation range of motion was 113° (SD 15.0) for the specific guide group and 63.3° (SD 27.4) for the standard guide group (P<0.05).

The specific guides allowed to achieve a more inferior glenoid placement compared to the standard instrumentation. The latter translated in a better functional outcome with a larger free impingement range of motion. The guided surgeries had no effect on the postoperative glenoid alignment but this was expected since the cadaveric specimens had no arthritis or abnormal glenoid deformities.