Lateralization in Reverse Shoulder Arthroplasty

Abstract

Indications for Reverse Shoulder Arthroplasty (RSA) have been extended over the last 25 years, and RSA has become the most frequently implanted shoulder arthroplasty worldwide. The initial Grammont design with medialization of the joint center of rotation (JCOR), placement of the JCOR at the bone-implant interface, distalization and semi-constrained configuration has been associated with drawbacks such as reduced rotation and range of motion (ROM), notching, instability and loss of shoulder contour. This review summarizes new strategies to overcome these drawbacks and analyzes the use of glenoid-sided, humeral-sided or global bipolar lateralization, which are applied differently by surgeons and current implant manufacturers. Advantages and drawbacks are discussed. There is evidence that lateralization addresses the initial drawbacks of the Grammont design, improving stability, rates of notching, ROM and shoulder contour, but the ideal extent of lateralization of the glenoid and humerus remains unclear, as well as the maximal acceptable joint reaction force after reduction. Overstuffing and spine of scapula fractures are potential risks. CT-based 3D planning as well as artificial intelligence will help surgeons with planning and execution of appropriate lateralization in RSA. Long-term follow-up of lateralization with new implant designs and implantation strategies is needed.

Keywords: BIO-RSA; ROM; Reverse Shoulder Arthroplasty (RSA); bipolar lateralization; lateralization; notching; shoulder prosthesis.

Figure 1

Deltoid wrapping. (a) Poor deltoid wrapping due to medialization. (b) Improved deltoid wrapping due to humeral lateralization (c) Improved deltoid wrapping due to glenoid lateralization. (d) Further increase in deltoid wrapping due to combined bipolar lateralization.

Figure 2

Sirveaux classification of notching [15]. Grade 1, inferior pillar of the scapular neck. Grade 2, the notch is in contact with the lower screw as a result of erosion of the scapular neck to the level of the screw. Grade 3, the notch extends over the lower screw. Grade 4, the notch extends under the baseplate.

Figure 3

Baseline (red) representing Delta III glenoid-sided lateralization as a reference (* Stemless). Yellow: Maximal additional offset as a result of GS size/other parameters. Figure consistent with Werthel’s data [7].

Figure 4

Lateralized RSA after ORIF (Open Reduction Internal Fixation)/osteonecrosis in a young patient after a fracture dislocation and plating. The revision required humeral canal opening with a burr. Outstanding ROM. Radiograph: Combined humeral and glenoid lateralization (Bipolar lateralization; 145° stem, forced varus implantation as a result of sclerosis/insufficient bone stock). Yellow line: Augmented distance from the insert to the lateral scapular margin.

Figure 5

AP radiographs with increased glenoid-sided offset: (a) Bony, (b) Metal. Minor valgus implantation of stems.

Figure 6

Scapular orientation according to thoracic kyphosis. (A) Normal position. (B) Mild kyphosis altering scapular orientation. (C) Severe kyphosis with pronounced scapular internal rotation.

Figure 7

Influence of the humeral implant’s orientation on the ROM. (a) Perfect opposition, (b) Not enough retrotorsion, (c) Too much retrotorsion.

Figure 8

Use of software allowing planning of rigid body motion (Blueprint software, Imascap, Plouzané, France).

Figure 9

Gap space requirement for reduction of a standard 36 mm GS with a standard insert (+6 mm) and tray (+0 mm). Baseplate/GS distance of approximately 18.9 mm and insert/tray jump distance of 20 mm.