title: Incidence and natural course of initial polar gaps in Birmingham Hip Resurfacing cups.
abstract: The purpose of this study was to retrospectively investigate the incidence of initial polar gaps and their effect on clinical results in Birmingham Hip Resurfacing cups. A total of 151 hips in 134 patients who underwent hip resurfacing at a mean age of 50 years were examined. The mean follow-up period was 7 years. A polar gap was identified in 47 hips (31%) with a mean width of 2.1 mm. Gaps of 2 mm or more were identified in 21 hips, 6 of which showed reductions in cup inclination during the initial 3 months. After 3 months, no progressive cup migration was observed. There was no cup revision. All gaps were filled with bone within 2 years of surgery. The initial polar gaps had no significant influence on the stability of hydroxyapatite-coated Porocast cobalt-chromium hemispherical monoblock cups (Midland Medical Technologies Ltd, Birmingham, UK), although gaps of 2 mm or more had a higher risk of early migration.
authors.affiliation: Department of Orthopaedic Surgery, Osaka University Graduate School of Medicine, Osaka, Japan.
authors.forename: Satoshi
authors.initials: S
authors.lastname: Nakasone
authors.forename: Masaki
authors.initials: M
authors.lastname: Takao
authors.forename: Takashi
authors.initials: T
authors.lastname: Nishii
authors.forename: Takashi
authors.initials: T
authors.lastname: Sakai
authors.forename: Nobuhiko
authors.initials: N
authors.lastname: Sugano
mesh_terms: D000077:Acetabulum / Q000000981:diagnostic imaging / Q000601:surgery*; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D019644:Arthroplasty, Replacement, Hip / Q000295:instrumentation*; D002857:Chromium; D003035:Cobalt; D017886:Durapatite; D005260:Female; D005548:Foreign-Body Migration / Q000453:epidemiology; D006622:Hip Prosthesis; D006801:Humans; D015994:Incidence; D008297:Male; D008875:Middle Aged; D010012:Osteogenesis; D011474:Prosthesis Design; D011475:Prosthesis Failure; D011859:Radiography; D012189:Retrospective Studies; D013499:Surface Properties
chemical_list: D002857:Chromium; D003035:Cobalt; D017886:Durapatite