The Effect of Lateralization on Clinical Outcomes after Anatomic Total Shoulder Arthroplasty

Background: Lateralization has been previously studied for reverse shoulder arthroplasty, but there is little clinical research investigating the independent effect of medialization or lateralization of the joint line, nor global medialization or lateralization for anatomic total shoulder arthroplasty (TSA). The goal of this study was to assess the impact of lateralization on clinical outcomes after anatomic TSA.

Methods: A retrospective review of a multi-institutional registry was performed. All anatomic TSAs with postoperative radiographs and minimum 2-year clinical outcomes were included. Six measurements were made on postoperative radiographs: (1) humeral COR shift from ideal, (2) acromion to glenoid distance (A-G), (3) glenoid to greater tuberosity distance (GT-G), (4) acromion to greater tuberosity distance (A-GT), (5) lateralization shoulder angle (LSA) and (6) critical shoulder angle (CSA). Linear regression analyses were performed to evaluate any associations between radiographic measures and PROs, range of motion (ROM) and strength.

Results: 357 patients were included, mean age 65 years and 61% male. For PROs, the COR (p =0.002) was significantly associated with the ASES score. Additionally, COR was significantly associated with the WOOS score. For ROM, COR shift was the only radiographic measure with a significant association with forward flexion (p =0.002). Other significant associations with ROM in the regressions were: use of CT based preoperative planning (FF) and preoperative ROM. The A-G distance (p =0.008) and GT-G distance (p =0.002) were both significantly associated with external rotation strength.

Conclusions: Increasing humeral COR shift negatively impacts PROs and ROM after anatomic TSA regardless of the joint line position. Increased glenoid lateralization and increased global lateralization were associated with increased ER strength.