Postoperative assessment of the individualized humeral component retroversion in reverse total shoulder arthroplasty: a novel method applying computed tomography scans without an elbow.

Background: Humeral component retroversion (HcRV) can be customized to match native humeral retroversion (RV) during reverse total shoulder arthroplasty. However, assessing postoperative individualized HcRV using computed tomography (CT) scans without an elbow can be challenging. Therefore, we developed a new method to obtain the HcRV and evaluated its reliability.

Methods: A total of 106 patients underwent reverse total shoulder arthroplasty using a single implant, in which the humeral component was implanted based on the preoperative humeral RV (Pre_HRV) using a bilateral CT scan of the elbow. Intraoperatively, a RV guide with version hole at 10° intervals was used; Pre_HRV was converted to 5° increments and applied for humeral component implantation. The axis of intertubercular sulcus (ITS) was defined as the line perpendicular to the intertubercular line, and the angle between the axis of ITS and the transepicondylar axis was defined as the bicipital groove rotation (BGR). ITS orientation was defined as the angle between the axis of ITS and the central axis of the humeral head. Since the BGR does not change, the postoperatively implanted HcRV (Post_HcRV)f is calculated as the BGR minus the value of the postoperative ITS orientation. An agreement analysis was performed between Post_HcRV and both the intraoperatively applied humeral RV and Pre_HRV, as well as between the preoperative and postoperative ITS orientations. The humeral component's insertional errors were also evaluated.

Results: All radiologic measurements exhibited excellent interobserver and intraobserver reliabilities. The reliabilities between Post_HcRV and both intraoperatively applied humeral RV and Pre_HRV, as well as between preoperative and postoperative ITS orientations, showed excellent agreement (intraclass correlation coefficients: 0.953, 0.952, and 0.873, respectively). The humeral component was inserted within 5° in 86.8% of the planned humeral RV cases.

Conclusions: The HcRV measured using the BGR and ITS orientations achieved good accuracy for restoring the planned humeral RV using a RV guide with the forearm axis. Therefore, this new radiological measurement method can aid orthopedic surgeons in confirming Post_HcRV on CT scans without an elbow.