title: Evaluation of a new baseplate in reverse total shoulder arthroplasty - comparison of biomechanical testing of stability with roentgenological follow up criteria.
abstract: OBJECTIVE
  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.
  
  
  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.
  
  
  RESULTS
  The mean values of micromotions after 100,000 cycles showed no relevant differences between the 2-peg and the 1-peg base plates (47 μm for the 2-peg design and 43 μm for the 1-peg design), i.e. both were below the borderline for secure Osseointegration of 150 μm. 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% (42 mm 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.
  
  
  CONCLUSIONS
  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.
  
  
  METHODS
  Level III, case-control study.
authors.affiliation: Sports Clinic Erfurt, Am Urbicher Kreuz 7, 99099 Erfurt, Germany. Electronic address: prof.irlenbusch@sportklinik-erfurt.de.
authors.forename: U
authors.initials: U
authors.lastname: Irlenbusch
authors.affiliation: Hòpital cantonal Fribourg, Fribourg, Switzerland.
authors.forename: G
authors.initials: G
authors.lastname: Kohut
mesh_terms: D000368:Aged; D019643:Arthroplasty, Replacement / Q000295:instrumentation*; D001696:Biomechanical Phenomena; D001860:Bone Plates; D001863:Bone Screws; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D007593:Joint Instability / Q000000981:diagnostic imaging / Q000503:physiopathology / Q000601:surgery*; D008297:Male; D008422:Materials Testing / Q000379:methods*; D011446:Prospective Studies; D011474:Prosthesis Design; D011859:Radiography; D012785:Shoulder Joint / Q000000981:diagnostic imaging / Q000503:physiopathology / Q000601:surgery*; D013997:Time Factors; D016896:Treatment Outcome
keywords: Inversed shoulder prostheses; Micromotion; Reverse prosthesis; Scapular notching