Prosthetic humeral head center of rotation shift from ideal is associated with inferior clinical outcomes after anatomic total shoulder arthroplasty

Abstract

BackgroundCadaveric studies have demonstrated adverse biomechanical consequences to small changes in the center of rotation (COR) from ideal in anatomic total shoulder arthroplasty (TSA). The aim of the present study was to determine if there is any association between humeral COR shift from ideal in anatomic TSA and patient-reported outcomes or range of motion (ROM). MethodsA multicenter retrospective study was conducted of TSAs with minimum 2-year follow-up. Offset of the COR from ideal was measured on postoperative radiographs using a best-fit circle technique. The primary outcome was the final ASES score. A receiver operator characteristic curve was constructed to determine a significant threshold of COR change. Patient-reported outcomes and ROM for patients above and below the calculated threshold were assessed. The number of patients achieving a patient acceptable symptomatic state was also investigated. ResultsEighty-seven patients aged 65.6 ± 8.3 years, 59% male, with mean 3.2-year follow-up were included. In 64% of cases, the COR was >2 mm from ideal and in 18% of cases it was >4 mm. A significant threshold COR change of 2.7 mm was determined, which was a significant predictor of below-average ASES scores following TSA (sensitivity: 79%, specificity: 72%, P< .001). Patient acceptable symptomatic state was achieved in 100% of patients with 0-2 mm, 90% of patients with 2-4 mm, and 56% of patients with over 4 mm of COR increase. There was significantly improved final forward flexion (152 ° for COR <2.7, 139 ° for COR >2.7, P= .009) and change in active forward flexion (41° for COR < 2.7, 26 ° for COR > 2.7, P = .047) for patients with COR closer to ideal. ConclusionsAccurate restoration of ideal humeral COR during anatomic TSA is challenging and significant shifts are common. A prosthetic COR greater than 2.7 mm from ideal is associated with worse patient-reported outcomes and ROM following anatomic TSA Level of evidenceLevel III, retrospective comparative study.