The in vivo impact of computer navigation on screw number and length in reverse total shoulder arthroplasty

Abstract

Little information exists regarding the benefit of computer navigation in shoulder arthroplasty in the clinical setting. This study aims to quantify how computer navigation affects the number and length of screws used during in vivo reverse total shoulder arthroplasty (RSA) placement. A retrospective review of a research database was performed from 1/1/2015 to 12/31/2019 to identify patients who underwent primary RSA before and after the use of computer navigation. One-hundred consecutive RSAs were selected from the computer navigation implantation date; then, 100 consecutive sex-matched RSAs were chosen prior to navigation implantation in reverse chronological order. Baseplate augments were chosen based on surgeon discretion, with the goal of restoring version to within 10 degrees of neutral and inclination to neutral or slightly inferior with removal of the smallest amount of subchondral bone possible. Screws were placed with the goal of at least 3 screws with good purchase and added as needed, with up to 5 screws utilized. We compared demographic factors, comorbidities, preoperative diagnosis, number of screws, screw length, number of wasted screws, and number of cases with bone graft used behind the baseplate between the 2 groups. Chi-squared test was used for bivariate analysis and student t-test was used for continuous variables. A total of 200 RSAs were included, with 100 primary RSAs (mean age, 69.3 years) performed prior to computer navigation compared to 100 primary RSAs (mean age, 69.7 years) performed using computer navigation. The total number of screws used in RSAs without computer navigation was 414 screws; the total used in the computer navigation cases was 344. RSAs placed with computer navigation used significantly fewer screws per case (3.4 vs. 4.1 screws; p<0.001) and had a significantly longer average screw length (35.0mm vs. 32.6mm; p<0.001). Three screws were implanted in 61% of computer navigation cases compared to 1% of cases without computer navigation (p<0.001). Screws 30mm in length or longer were more commonly used in patients undergoing RSA using computer navigation (84.6% vs. 73.7%; p<0.001). This study shows that computer navigation in RSA leads to longer and fewer glenoid baseplate screws being implanted. Computer navigation appears to assist with better screw placement, which may have similar clinical benefits of better glenoid fixation. Additionally, using fewer screws can save glenoid bone stock, avoid added glenoid stress risers, and decrease operative time.