title: Setscrew distal locking for intramedullary nails: a biomechanical study.
abstract: OBJECTIVE
  This biomechanical study was undertaken to examine the effectiveness of setscrew distal locking in a static intramedullary (IM) femoral nail on the stability of fixation of femoral shaft fractures.
  
  
  METHODS
  Fifteen fresh-frozen cadeveric femora were randomly separated into three groups of five bones and transversely sectioned immediately distal to the isthmus. After the insertion of the large-diameter nails, distal locking was obtained by conventional method in the first group. In the second group, set-screw design was used in which two transverse screws penetrated only the lateral cortex of the femur and compressed the nail in the intramedullary canal. No distal locking was used in the third group.
  
  
  METHODS
  All instrumented femurs were mounted on a servohydraulic testing machine and tested in both rotations (20 degrees) and axial compression (amplitude: 1,000 Newton).
  
  
  METHODS
  Loading-versus-displacement data, acquired at a ten-Hertz sampling rate, were calibrated and used to calculate maximum torque, stiffness, and energy capacity to failure. Maximum displacement and axial stiffness also were determined.
  
  
  RESULTS
  Mean maximum torque at 10 degrees for each group were 15.3+/-4.8 newton-meters for the interlocking group, 8.5 +/-1.2 newton-meters for the setscrew group, and 3.6+/-2.7 newton-meters for the nonlocked femora. At 20 degrees of rotational displacement, the torque measured 37.4+/-2.6 newton-meters; 15.0+/-4.0 newton-meters; and 5.3+/-3.1 newton-meters, respectively (p < 0.05). Mean torsional stiffness was 1.17+/-0.76 newton-meters per degree for the setscrew group and 1.34+/-0.83 newton-meters per degree for the interlocking group (p > 0.05). The setscrew design provided 87 percent of the torsional rigidity of the interlocking group. In the axial compression test, mean maximum shortening was 1.1+/-0.3 millimeters in the interlocking group and 1.4+/-0.6 millimeters in the setscrew group (p > 0.05). The mean stiffness on longitudinal compression provided by the interlocking screws and the setscrews was 918 and 860 newton-meters per millimeter, respectively.
  
  
  CONCLUSIONS
  The distal setscrew design provides adequate distal fixation of intramedullary nail for patients in the postoperative rehabilitation period of the femoral shaft fractures treated with intramedullary nailing.
authors.affiliation: Department of Orthopedics and Traumatology, Osmangazi University, Meŝelik, Eskiŝehir, Turkey.
authors.forename: N
authors.initials: N
authors.lastname: Köse
authors.forename: I
authors.initials: I
authors.lastname: Günal
authors.forename: X
authors.initials: X
authors.lastname: Wang
authors.forename: K A
authors.initials: KA
authors.lastname: Athanasiou
authors.forename: C M
authors.initials: CM
authors.lastname: Agrawal
authors.forename: J D
authors.initials: JD
authors.lastname: Mabrey
mesh_terms: D000328:Adult; D001696:Biomechanical Phenomena; D001858:Bone Nails / Q000592:standards*; D001863:Bone Screws / Q000592:standards*; D002102:Cadaver; D019245:Compressive Strength; D004548:Elasticity; D004867:Equipment Design; D005264:Femoral Fractures / Q000000981:diagnostic imaging / Q000601:surgery*; D005594:Fracture Fixation, Intramedullary / Q000295:instrumentation*; D006801:Humans; D008297:Male; D008422:Materials Testing; D008875:Middle Aged; D011859:Radiography; D012399:Rotation; D013718:Tensile Strength; D019415:Torque; D014102:Torsion Abnormality