Summary

When compared to standard instrumentation, the use of cost-effective, in-house 3D-printed patient-specific glenoid drill guides during anatomic TSA led to more accurate glenoid component placement.

Abstract

Traditional patient-specific instrumentation (PSI) systems for total shoulder arthroplasty (TSA) improve the accuracy of glenoid component placement but involve considerable cost and outsourcing delays. A prior cadaveric study by the senior author demonstrated that a novel, in-house 3-dimensionally (3D) printed patient-specific glenoid drill guide had improved accuracy relative to traditional, non-specific TSA instrumentation. The average production cost and time for the PSI guides from this study were $29.95 and 4 hours 40 minutes per guide, respectively. While ergonomic, these inexpensive, in-house PSI guides currently lack clinical data. Thus, the purpose of this randomized controlled trial (RCT) was to compare the accuracy of glenoid component positioning between these novel, cost-effective, 3D printed patient-specific glenoid drill guides and standard non-specific instrumentation implemented during anatomic TSA.

This single-center RCT included 28 adult patients undergoing primary anatomic TSA. Patients were blinded and randomized to either the PSI group or the standard instrumentation control group. The primary endpoint was accuracy of glenoid component placement (version and inclination), which was determined using a metal-suppression CT scan taken between 6 weeks to 1 year postoperatively. Deviation from the preoperative CT plan was calculated for each patient. Postoperative CT measurements were performed by a fellowship-trained shoulder surgeon, blinded to group allocation. The PSI group utilized a novel, cost effective patient-specific glenoid guide that is designed in-house and was previously described in detail by the senior author.1 Briefly, preoperative CT scans were reformatted using Mimics Medical Software 24.0 (Materialise, Leuven, Belgium), and a visual C++ program (Microsoft, Redmond, WA, USA) along with Rhinoceros 3D computer aided design software (Robert McNeel & Associates, Seattle, WA, USA) were utilized to construct a novel resin-based PSI guide that was designed to fit snugly against the glenoid face. The 3D-printed PSI guide contained a barrel with a 2.75 mm internal diameter that was designed to drive a pin through the center of the glenoid face at the target version/inclination. This target angle was implant and patient dependent. The control group underwent an anatomic TSA using non-specific instrumentation, which is currently the standard of care for this procedure.

Sixteen patients were randomized to the patient-specific glenoid drill guide group, and 12 were allocated to the standard instrumentation control group. Between the two groups, there were no differences in baseline age (p = 0.382), sex (p = 1.000), laterality (p = 0.698), subscapularis management (p = 1.000), Walch classification of glenoid wear (p = 1.000), glenoid inclination (p = 0.607), or glenoid version (p = 0.197). Additionally, there was no difference in the use of augmented components (p = 0.459) or the degrees of version correction (p = 0.568) between the two groups; however, the PSI group required significantly more degrees of inclination correction than the control group (p = 0.017). When examining the primary outcomes of this study, the PSI group was 2.8° more accurate than the control group for correction of version; this difference was significant (p = 0.012). For the correction of inclination, the PSI group was 2° more accurate than the control group, but this difference was not significant (p = 0.382).