ABSTRACT
Objective:To compare the effects of glenosphere offset positions on the impingement-free range of motion (ROM) in reverse total shoulder arthroplasty (RTSA).Methods:Shoulder joint models were reconstructed using shoulder CT scans of 6 patients with primary osteoarthritis. RTSA was performed virtually according to standard surgical procedures, and shoulder movements were simulated. Reverse shoulder models were constructed with 2 lateral offsets (0 and 4 mm) and 6 positional offsets (center, inferior, posterior, anterior, anterior-inferior, and posterior-inferior). The impingement-free ROM and impingement sites for abduction-adduction, flexion-extension, total rotation (sum of internal and external rotation), and total ROM (sum of ROM in all movement modes) were evaluated.Results:All the 12 combinations of different glenosphere offsets achieved 50% of the original shoulder ROM in all movements. In the abduction-adduction motion with 0 and 4 mm lateral offsets, the anterior-inferior offset provided the largest ROM (94.4°±8.7° and 105.3°±6.9°, respectively), but there was no significant difference between the positions ( P>0.05). In the flexion-extension motion with 0 and 4 mm lateral offsets, the posterior-inferior offset showed the largest ROM (194.1°±6.9° and 196.9°±9.7°, respectively), but there was no significant difference between the positions ( P>0.05). In the total rotation motion with 0 and 4 mm lateral offsets, the anterior-inferior offset had the largest ROM (141.5°±5.9° and 160.6°±8.5°, respectively), showing significant advantages over the center, anterior, and posterior offsets ( P<0.05), but insignificant advantages over the inferior and posterior-inferior offsets ( P>0.05). In total ROM, the anterior-inferior offset provided the largest ROM. When the lateral offset was 0 mm, the anterior-inferior offset provided a ROM of 421.8°±16.4°, showing significant advantages over the center and posterior offsets ( P<0.05). Compared with the lateral glenosphere offset of 0 mm, the lateral glenosphere offset of 4 mm significantly improved total shoulder ROM (122.8°±10.6° versus 145.8°±4.8°) and total ROM (390.9°±11.6° versus 428.4°±19.8°) ( P<0.05). Conclusions:The anterior-inferior, inferior, and posterior-inferior glenosphere offsets can improve ROM in all movement patterns. The position and lateral offset of the glenosphere significantly affect the total rotation and total ROM of the shoulder joint. Specifically, the anterior-inferior and inferior offsets show significant advantages over the center position in total rotation and total ROM of the shoulder joint.