title: Fracture of the outer metallic head of the bipolar hip prosthesis: an unusual bearing surface failure.
abstract: Fracture of the bearing surface is an infrequent cause of failure of a hip arthroplasty. Although well documented with ceramic heads, fracture of the metallic head is much rarer. We report a case of a fracture of the outer metallic head of a modular cemented bipolar hemiarthroplasty 2 years after the index procedure. Over time, the outer head lost its intended motion and assumed a vertical position. We hypothesized that this position caused asymmetrical loading with stress concentration at the poles, compounded by repeated impingement between the skirted inner cobalt-chromium (Cr-Co) head and the outer stainless steel head of this particular prosthesis. These were supported by the finite element studies. In addition, scanning electron microscopy and energy dispersive x-ray studies showed metallurgical defects that seemed to have initiated and/or accelerated the fracture. Although rare, this mode of failure calls for increased awareness, periodic follow-up, and quality control.
authors.affiliation: Department of Orthopaedics, SUNY Downstate Medical Center, Brooklyn, New York 11203, USA.
authors.forename: Aditya V
authors.initials: AV
authors.lastname: Maheshwari
authors.forename: Anoop
authors.initials: A
authors.lastname: Chawla
authors.forename: Obi U
authors.initials: OU
authors.lastname: Osuji
authors.forename: Rajesh
authors.initials: R
authors.lastname: Malhotra
authors.forename: Yash P
authors.initials: YP
authors.lastname: Gulati
mesh_terms: D000368:Aged; D019644:Arthroplasty, Replacement, Hip / Q000295:instrumentation* / Q000379:methods; D002858:Chromium Alloys; D019544:Equipment Failure Analysis; D005260:Female; D005265:Femoral Neck Fractures / Q000601:surgery*; D006621:Hip Joint / Q000000981:diagnostic imaging / Q000601:surgery; D006622:Hip Prosthesis; D006801:Humans; D011474:Prosthesis Design; D011475:Prosthesis Failure; D011859:Radiography
chemical_list: D002858:Chromium Alloys