Mathys Affinis® Inverse

Abstract

The Affinis Inverse was developed to reduce implant-specific complications and problems of the Grammont prosthesis such as humeral and glenoid loosening, component disconnections, and periprosthetic humeral fractures. The main problem—the glenoid component fixation and positioning in combination with the notching phenomenon—was the initial challenge for the development. The neck-shaft inclination, the center of rotation at the glenoid bone–prosthesis interface, and the inlay cup depth were assessed as sensitive concerning instabilities and glenoid loosening. Therefore, these design features were kept according to Grammont’s concept. The main modifications are a new 2-peg baseplate fixation without an inferior screw and the inversion of the bearing materials. In a prospective multicenter study in six European centers (88 cases, mean follow-up time 49.0 months), the concept has proven an optimized fixation, no component disassembly, and a new type of a simple mechanical notching on the scapular neck. No progressive notching caused by polyethylene abrasion was observed at this stage. A considerably reduced complication rate of 4.5 %, revision rate of 3.4 %, and a clinical outcome comparable to common RTSA systems confirm these optimizations in the early course. The placement of the baseplate, the three glenosphere sizes (36; 39; 42) for better soft tissue balancing, and the resulting inferior overhang of the glenosphere were confirmed as efficient to reduce scapular notching. The introduction of optimized bearing materials (HXLPE and ceramic) will reduce the gravimetric wear significant. The clinical relevance has to be proven in the long-term.