Cet article a été publié dans un numéro de la revue, cliquez ici pour y accéder
Background and purpose
To minimize notching problem associated with reversed prostheses, inferior positioning of base plate is recommended. This reduces the risk of notching, but does not eliminate it completely. Both polyethylene/PE-induced osteolysis and implant-to-bone or implant-to-implant contact may still occur, contributing to the risk of screw-breakage and resulting long-term failure. Therefore, the stability and integration of a newly developed base plate without inferior screw and inversion of bearing materials was investigated.
Patients and methods
Biomechanical assessment of primary stability of the two types of glenoid baseplate (1- and 2-pegged) was carried out according to ASTM F-2028-02 (American Society for Testing and Materials). Patients with a follow-up period of at least 2 years were clinically (n=78) and for most of them radiologically (n=61) examined. The X-rays were evaluated for loosening and scapular notching.
The mean values of micromotions after 100,000 cycles showed no relevant differences between the 2-peg and the 1-peg base plates (47μm for the 2-peg design and 43μm for the 1-peg design), i.e. both were below the borderline for secure Osseointegration of 150μm. Radiologically, no signs of loosening or radiolucent lines/RLL were found for both base plates. The mean incidence of inferior scapular notching was 23.6% (42mm glenoid sphere: 15.8%). Only grade 1 and grade 2 notching was observed. Additionally as result of absence of PE-induced osteolysis shape, size, borderline and location of notching differed from those observed with conventional reverse total shoulder arthroplasty bearing materials.
In combination with modified inferior operating technique, the newly designed implant has the potential to reduce the incidence of scapular notching and to avoid both PE-induced osteolysis and metal-screw contact. The new design did not compromise stability of the base plate in any way during the investigation period, as demonstrated both by the data from the biomechanical investigation and also by the radiological follow-up.
Level of evidence
Level III, case-control study.Le texte complet de cet article est disponible en PDF.
Keywords : Reverse prosthesis, Inversed shoulder prostheses, Micromotion, Scapular notching