title: Relationship between pull-out strength and oscillation angle in bipolar cups: an in vitro study.
abstract: To compare the past and present bipolar hip arthroplasty (BHA) models in terms of balance between pull-out strength and oscillation angle (OA).
  
  
  
  The pull-out strength and OA of 8 BHA models were compared: UPF-II, IBC, and Tandem XLPE (Smith & Nephew); Ringloc x (Biomet); J-FX (DePuy); Bipolar (Nakashima Medical); Multipolar (Zimmer); and Centrax (Stryker).
  
  
  
  Respectively for the UPF-II, IBC, Tandem, Ringloc, J-FX, Nakashima Bipolar, Multipolar, and Centrax, the mean pull-out strength was 2219 N, 3303 N, 1503 N, 951 N, 1453 N, 1856 N, 1536 N, and 753 N, whereas the mean OA was 54.2°, 53.8°, 64.0°, 73.2°, 63.0°, 65.4°, 55.6°, and 75.4°. The OA was lower in the integrated types. For pull-out strength of the locking mechanism, the integrated type (IBC and Nakashima) was stronger than the metal or polyethylene ring-lock type (all others). The pull-out strength and OA were negatively correlated (r= -0.881, p=0.007), and the balance between the 2 varied for different models.
  
  
  
  There is a trade-off between the pullout strength and OA; optimal balance between the 2 should be based on each patient's need.
authors: Department of Orthopaedic Surgery, Faculty of Medicine, Oita University, Yufu City, Oita, Japan.
authors: N
authors: N
authors: Kaku
authors: T
authors: T
authors: Tabata
authors: H
authors: H
authors: Tsumura
mesh_terms: D019644:Arthroplasty, Replacement, Hip / Q000295:instrumentation*; D001696:Biomechanical Phenomena; D006622:Hip Prosthesis; D006801:Humans; D008953:Models, Anatomic; D011474:Prosthesis Design; D013718:Tensile Strength
keywords: hemiarthroplasty; osteonecrosis; prostheses and implants