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

ABSTRACT

BACKGROUND: Humeral component retroversion (HcRV) can be customized to match native humeral retroversion (RV) during reverse total shoulder arthroplasty (RTSA). 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 RTSA 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 retroversion 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 trans-epicondylar 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 postoperative 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 (I_HRV) and Pre_HRV, as well as between the pre- and postoperative ITS orientations. The humeral component's insertional errors were also evaluated. RESULTS: All radiologic measurements exhibited excellent inter- and intra-observer reliabilities. The reliabilities between Post_HcRV and both I_HRV and Pre_HRV, as well as between pre- 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 retroversion 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.