Radiologic Comparison of Humeral Position according to the Implant Designs Following Reverse Shoulder Arthroplasty: Analysis between Medial Glenoid/Medial Humerus, Lateral Glenoid/Medial Humerus, and Medial Glenoid/Lateral Humerus Designs

Abstract

BACKGROUND: The currently available reverse shoulder arthroplasty (RSA) designs can be classified into medial glenoid/medial humerus (MGMH), lateral glenoid/medial humerus (LGMH), and medial glenoid/lateral humerus (MGLH) prosthesis designs. The purpose of this study was to radiologically analyze the effect of different RSA designs on humeral position following RSA.METHODS: A total of 50 patients who underwent primary RSA were retrospectively analyzed. Among 50 patients, 33 patients (group A: MGMH) underwent RSA with Aequalis system (Wright, Inc, Bloomington, MN, USA), 6 (group B: LGMH) with Aequalis system using bony increased offset, and 11 (group C: MGLH) with Aequalis Ascend Flex system. The acromiohumeral distance, acromioepiphyseal distance (AED), lateral humeral offset (LHO), LHO from the center of rotation (LHO(COR)), and deltoid length were radiologically measured to quantify the distalization and lateralization of the humerus.RESULTS: The increment in postoperative AED was 19.92 ± 3.93 mm in group A, 24.52 ± 5.25 mm in group B, and 25.97 ± 5.29 mm in group C, respectively (p=0.001). The increment in postoperative LHO was 0.13 ± 6.30 mm, 8.00 ± 12.14 mm, and 7.42 ± 6.88 mm, respectively (p=0.005). The increment in postoperative LHOCOR was 20.76 ± 6.06 mm, 22.04 ± 5.15 mm, and 28.11 ± 4.14 mm, respectively (p=0.002).CONCLUSIONS: The radiologic analysis of the effect of different RSA designs on humeral position following RSA showed significant differences in the increment in postoperative AED, LHO, and LHO(COR) between the 3 groups. Therefore, MGLH design seems to be more effective for humeral distalization and lateralization compared to original Grammont design.

Comparison of Lateralized Versus Medialized Reverse Total Shoulder Arthroplasty: A Systematic Review and Meta-analysis

“…Ideally, we would have liked to perform a meta-analysis of radiological measurements of lateralization, such as the acromiohumeral distance, humeral offset from the COR, or scapular neck length, to identify the relevance of more lateralized structure changes and the associated risks. 5 However, there are only a few radiological comparative studies on which to perform a meta-analysis. A future study should compare the radiological results of the 2 groups and assess the clinical outcome relationships.…”

Comparison of Clinical Performance of Inlay versus Onlay Humerus Implants in Reverse Total Shoulder Arthroplasty

“… 16) Radiographic assessment was performed to identify changes in the lateral humeral offset, which is the perpendicular distance from the COR of the glenosphere to the line that passes along the center of the proximal humerus ( Fig. 2 ); 3) the deltoid-wrapping offset, which is the perpendicular distance from the greater tuberosity to the line along the acromial undersurface; and the acromiohumeral distance, which is the perpendicular distance from the acromial undersurface to the parallel line passing the greater tuberosity ( Fig. 3 ).…”

“… 1 2) There have been many changes in the design of RTSA over the years to overcome the identified problems, with lateralization being one of the most representative changes that have been made to the implant design. 3) Lateralization can be achieved by increasing the offset intrinsic to either the glenoid or humerus. Lateralization has a reliable theoretical background of increasing the tension to the anterior and posterior muscles of both the deltoid and rotator cuffs in a manner that adds stability to the joint and benefits rotations.…”

Innovations in Shoulder Arthroplasty

“…The humeral stem onlay prosthesis was then developed with the metaphyseal tray sitting on top of the humeral cut surface. This allows for more lateralized and distalized humeral designs, preserved proximal bone stock, and the potential for stem conversion between RSA, TSA, and hemiarthroplasty [ 83 , 84 , 85 ].…”