title: Effects of screw eccentricity on the initial stability of the acetabular cup.
abstract: One of the major failure modes of cementless acetabular components is the loosening of the acetabular cup, which is mostly attributable to insufficient initial stability. A hemispherical cup with a porous coating which is inserted with press-fit fixation and secured with several screws is one of the most widely used approaches. Many studies have found that bone screws are very helpful aids for cup fixation, but the optimal surgical technique for inserting screws has not been clearly reported. In this study, hemispherical cups were fixed into blocks of foam bone with zero to three screws. The effects of three types of screw eccentricity (a 1-mm offset and angular eccentricities of 15 degrees and 25 degrees ) on the initial stability of the acetabular cup were evaluated. The experimental results indicate that increasing the number of screws enhances the cup stability in the case of ideal screwing (i.e., with no eccentricity). An angular eccentricity of 15 degrees did not affect the cup stability for fixation with one or two screws. However, the presence of 25 degrees of angular eccentricity significantly reduced the stability of the cup, while 1 mm of offset eccentricity produced an even greater impact.
authors.affiliation: Institute of Biomedical Engineering, National Cheng Kung University, Tainan, Taiwan 701, Republic of China.
authors.forename: Jui-Ting
authors.initials: JT
authors.lastname: Hsu
authors.forename: Chih-Han
authors.initials: CH
authors.lastname: Chang
authors.forename: Kai-Nan
authors.initials: KN
authors.lastname: An
authors.forename: Mark E
authors.initials: ME
authors.lastname: Zobitz
authors.forename: Rapin
authors.initials: R
authors.lastname: Phimolsarnti
authors.forename: Ronald R
authors.initials: RR
authors.lastname: Hugate
authors.forename: Kuo-An
authors.initials: KA
authors.lastname: Lai
mesh_terms: D000077:Acetabulum / Q000601:surgery; D019644:Arthroplasty, Replacement, Hip / Q000295:instrumentation* / Q000379:methods; D001696:Biomechanical Phenomena; D001863:Bone Screws; D004868:Equipment Failure; D006801:Humans; D007593:Joint Instability / Q000209:etiology*; D008422:Materials Testing; D009984:Orthopedic Fixation Devices