title: Value of washers in internal fixation of femoral neck fractures with cancellous screws: a biomechanical evaluation.
abstract: OBJECTIVE
  The purpose of this study was to evaluate the maximum insertion torque of cancellous bone screws in osteoporotic proximal femurs with and without the use of washers.
  
  
  METHODS
  Eight matched pairs of osteoporotic fresh-frozen human cadaveric femurs (age >70 years, all female) were used. Two screws were inserted in each femur either with or without a washer, and maximum insertion torque was measured using a 50 N·m torque transducer. The testing was performed using a customized device, which allowed the torque transducer to apply a constant axial force and rate of rotation to the screws.
  
  
  RESULTS
  In 14 of 16 paired trials, the maximum screw insertion torque was higher when a washer was used. The average maximum torque with a washer was 5.1 N·m compared with 3.1 N·m without a washer (P < 0.01).
  
  
  CONCLUSIONS
  The addition of washers increased the maximum insertion torque of cancellous screws in the proximal femur by 65% in this study. Washers prevent the screw heads from penetrating the lateral cortex at low insertion torque loads, and thereby provide for an improved purchase of the screws in the femoral head with a higher maximum insertion torque. We advocate for routine washer use and encourage future clinical studies to further understand the correlation between their use and improved outcomes in this patient population.
authors: *IU Health Physicians, Ortho Sports Medicine, Indiana University, Indianapolis, IN; †Department of Medicial Engineering, Steadman Philippon Research Institute,Vail, CO; ‡Orthopaedic Surgery Department, The Queen's Medical Center, University of Hawaii, Honolulu, HI; and §Department of Orthopaedic Surgery, Regions Hospital, University of Minnesota, St. Paul, MN.
authors: Michael P
authors: MP
authors: Zlowodzki
authors: Coen A
authors: CA
authors: Wijdicks
authors: Bryan M
authors: BM
authors: Armitage
authors: Peter A
authors: PA
authors: Cole
mesh_terms: D000368:Aged; D001696:Biomechanical Phenomena; D001863:Bone Screws; D002102:Cadaver; D005260:Female; D005265:Femoral Neck Fractures / Q000601:surgery; D005269:Femur / Q000503:physiopathology / Q000601:surgery*; D005593:Fracture Fixation, Internal / Q000295:instrumentation; D006801:Humans; D016268:Internal Fixators; D010024:Osteoporosis / Q000503:physiopathology / Q000601:surgery*; D019415:Torque