The effect of lateralization on clinical outcomes after anatomic total shoulder arthroplasty

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.

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 center of rotation (COR) shift from ideal, (2) acromion to glenoid distance, (3) glenoid to greater tuberosity distance, (4) acromion to greater tuberosity distance, (5) lateralization shoulder angle, and (6) critical shoulder angle. Linear regression analyses were performed to evaluate any associations between radiographic measures and patient reported outcomes, range of motion (ROM), and strength.

A total of 357 patients were included, of which mean age was 65 years and 61% were male. For PROs, the COR (P = .002) was significantly associated with the American Shoulder and Elbow Surgeons score. Additionally, COR was significantly associated with the Western Ontario Osteoarthritis of the Shoulder score. For ROM, COR shift was the only radiographic measure with a significant association with forward flexion (P = .002). Other significant associations with ROM in the regressions were: use of computed tomography based preoperative planning (forward flexion) and preoperative ROM. The acromion to glenoid distance distance (P = .008) and glenoid to greater tuberosity distance (P = .002) were both significantly associated with external rotation strength.

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.