A Look at the Outliers: Optimal Placement for Reverse Total Shoulder Arthroplasty

Background Recent publications describe recommended ranges for post-operative radiographic measurements, such as the lateralization shoulder angle (LSA) and distalization shoulder angle (DSA), to optimize patient outcomes. However, no consensus exists on optimal implant positioning for reverse total shoulder arthroplasty (rTSA). The purpose of this study was to identify pre- and post-operative radiographic measurements in patients who achieved excellent range of motion to optimize implant positioning in patients undergoing rTSA. We hypothesized that restoring the lateral humeral offset to closely align with the patient’s pre-operative anatomy, along with achieving optimal lateralization and distalization shoulder angles as outlined in the literature, would correlate with excellent clinical outcomes. Methods A total of 425 patients with end-stage glenohumeral arthritis or irreparable rotator cuff arthropathy underwent rTSA from January 2021 to January 2023 at an outpatient orthopedic surgery center. Of these patients, 33 were identified as achieving excellent range of motion 6 months post-operatively, defined as exceeding active forward flexion ≥ 170º and active external rotation > 60º. Exclusions included prior shoulder surgery (n=2), revision from anatomic total shoulder arthroplasty to rTSA (n=2), pre-operative fracture (n=1), and bilateral procedures (n=1), leaving 27 patients. Both medialized (Zimmer TM rTSA) and lateralized (Tornier Perform) devices were used during the study. Radiographic measurements of the patients’ pre- and post-operative shoulder anatomy were recorded from two independent reviewers. Measurements were reported as the mean ± standard deviation and the inter-observer correlation assessed using the intra-class correlation coefficient. Results Patients were 51.9% female, with a mean age of 68.2 years at operation. 13 patients received the medialized inlay and 14 received the lateralized inlay rTSA. The average post-operative lateralization shoulder angle (LSA) and distalization shoulder angle (DSA) were 90º and 43º, respectively. The acromiohumeral interval (AHI) distalized an average of 22 mm, from a mean pre-operative length of 7 mm to a mean post-operative length of 29 mm (p < .001). The post-operative lateral humeral offset (LHO) on average was within 3.1 ± 4.4 mm of the patients’ pre-operative anatomy (p < .001). The medialized inlay did not significantly differ from the lateralized inlay in any radiographic measurements except in LHO. The post-operative LHO of the medialized inlay was 55 mm and the lateralized inlay was 66 mm (p < .001). Conclusion In patients who achieved excellent range of motion following rTSA, the lateral humeral offset was restored very closely to pre-operative anatomy, the lateralization and distalization shoulder angles were also restored within optimal ranges defined in the literature, and the acromiohumeral interval was distalized by an average of 22 mm. This study demonstrates that post-operative restoration of lateral humeral offset to pre-operative measurements is correlated with excellent post-operative outcomes. Level of Evidence Treatment Study – Level IV