Comparison of glenoid screw length between 3D planned length and standard surgical measurement in reverse shoulder arthroplasty

Abstract

Background

Glenoid positioning and fixation have important implications for the outcome and survival of reverse shoulder arthroplasty. Therefore, we aim to assess new methods of assuring correct placement and fixation of the glenoid component. 3-dimensional (3D) planning can help correctly position the glenoid, however, reproducibility of the plan perioperatively is sometimes difficult. Adjustable, reusable, patient-adapted guides may be as useful and a lot more cost-reducing compared to printed models in patient-specific instrumentation.

Methods

This prospective study compared preoperatively planned screw lengths for glenoid screws and perioperatively measured screw lengths in reverse shoulder arthroplasty in 44 patients. Therefore, 3D planning to determine optimal screw length and trajectory were carried out preoperatively, while during surgery screw trajectories were measured. Statistical analysis involved analyzing the correlation between the measured screw length and the planned screw length. Our primary endpoint was to see whether preoperative 3D planning without patient-specific guides can accurately predict glenoid screw length and aid in the correct positioning and fixation of glenoid baseplates.

Results

Forty-four patients were included. Twenty five of the 44 superior screws (56.8%) were adequately predicted (r = 0.69 [P < .001]). Thirty six of 44 screws (81.8%) differed by a maximum of 1 size. Twenty two of the 44 inferior screws (50%) were adequately planned (r = 0.37 [P = .013]). Also, 36 of 44 screws (81.8%) differed by a maximum of 1 size. In 13 cases, an anterior screw was placed of which only 3 were adequately planned (23.1%) (r = 0.62 [P = .025]). A posterior screw was also used in 13 cases of which 4 were the same as planned (30.7%) (r = 0.35 [P = .245]). Of all screws per patient, 13 received the same length of screws as preoperatively planned (29%). All implants in 26 of 44 patients (59%) were adequately predicted within a maximum difference of 1 size.

Conclusion

3D planning and reusable guides can aid in the correct placement of glenoid components; however, accuracy could be improved by adding rotational control to the implantation of the glenoid and taking into account the depth of ream. A large discrepancy between planned and measured screw length offers an extra control that could trigger the surgeon’s attention in case of misplacement.