title: Screw-hole clusters in acetabular cups: a morphological study of optimal positioning of screw-holes.
abstract: BACKGROUND
  Rigid and safe transacetabular screw fixation in total hip arthroplasty (THA) is achieved by pursuing deeper bone stock and avoiding injuries to the neurovascular structures, but these efforts can be restricted by the distribution of screw-holes on cups by the manufacturer. We therefore tried to determine: (i) optimal screw-hole positions on cups to allow anatomical placement of screws; (ii) rationality of the basic 3-screw-hole cluster on commercial cups; and (iii) the optimum method for placing commercial cups in accordance with acetabular anatomy.
  
  
  METHODS
  Periacetabular osseous structure of 64 hips and arterial structures of 50 hips were three-dimensionally reconstructed. Simulated transacetabular screw fixation during THA was performed in these hips with 3 different screw lengths (15, 25, and 35 mm) to define deeper and safer screw trajectories. Screw-hole locations of 7 commercially available cups were measured and matched with the periacetabular anatomy.
  
  
  RESULTS
  When the cup was placed into the acetabulum at 45° of abduction and 20° of anteversion, the optimal locations of 2 screw-holes on the cups were at 30° and 64° of latitude, with a 35° separation angle. The inversetriangle distribution pattern was safer than the triangle pattern in basic 3-screw-hole-cluster cups. When placing the commercial cups, 5°-10° of anterior rotation can be added to allow better screw trajectories.
  
  
  CONCLUSIONS
  Our study determined optimal screw-hole positions and their distribution pattern on cups. We describe methods to place the commercial cups that are not designed according to acetabular anatomy.
authors.affiliation: Department of Orthopaedics, Beijing Jishuitan Hospital, Beijing - China.
authors.forename: Xinghua
authors.initials: X
authors.lastname: Yin
authors.affiliation: Department of Orthopaedics, Beijing Jishuitan Hospital, Beijing - China.
authors.forename: Yixin
authors.initials: Y
authors.lastname: Zhou
authors.affiliation: Department of Orthopaedics, Beijing Jishuitan Hospital, Beijing - China.
authors.forename: Qiheng
authors.initials: Q
authors.lastname: Tang
authors.affiliation: Department of Orthopaedics, Beijing Jishuitan Hospital, Beijing - China.
authors.forename: Dejin
authors.initials: D
authors.lastname: Yang
authors.affiliation: Department of Orthopaedics, Beijing Jishuitan Hospital, Beijing - China.
authors.forename: Hao
authors.initials: H
authors.lastname: Tang
authors.affiliation: Department of Orthopaedics, Beijing Jishuitan Hospital, Beijing - China.
authors.forename: Xingjian
authors.initials: X
authors.lastname: Huang
mesh_terms: D000077:Acetabulum / Q000000981:diagnostic imaging / Q000601:surgery; D019644:Arthroplasty, Replacement, Hip / Q000379:methods*; D001863:Bone Screws; D003198:Computer Simulation; D006801:Humans; D021621:Imaging, Three-Dimensional; D011474:Prosthesis Design / Q000379:methods*; D017755:Prosthesis Fitting; D012680:Sensitivity and Specificity