title: Is distal locking necessary? A biomechanical investigation of intramedullary nailing constructs for intertrochanteric fractures.
abstract: OBJECTIVE
  Unstable intertrochanteric fractures in the elderly occur frequently. Several studies have evaluated the biomechanical impact of distally locking long cephalomedullary nails under axial loading; however, the impact of torsional loading has not been investigated. The purpose of this study is to determine the rotational load to failure of unstable intertrochanteric fractures treated with long cephalomedullary nails, with and without distal interlocking.
  
  
  METHODS
  Eleven paired cadaveric femora treated with long cephalomedullary nails were randomized into 2 groups. Group 1 was left unlocked, whereas group 2 was distally locked. Osteotomies were completed to create unstable 4-part fractures. The femora were anatomically fixed proximally and distally and secured to the biomechanical testing machine to undergo internal rotation. Torque and rotational angle were measured until failure.
  
  
  RESULTS
  The locked group had a mean maximal torsional load of 57.9 ± 19.0 N·m and a mean rotational stiffness of 119.4 ± 35.7 N·m/rad. The femora treated with unlocked nails had a mean maximal torsional load of 29.1 ± 12.2 N·m and a mean rotational stiffness of 77.2 ± 31.3 N·m/rad. Distal locking resulted in a significant increase in maximal rotational load (P = 0.001) and rotational stiffness (P = 0.004) before failure. No significant difference was found in mean rotational angle at failure between groups (26.0 ± 9.6 degrees, P = 0.263).
  
  
  CONCLUSIONS
  Maximal torsional load to failure for the unlocked group is within the functional range of rotational loads experienced at the hip for an average adult. The results show that distal locking significantly increases rotational load to failure. The authors highly recommend routine use of distal interlocking screws during cephalomedullary nail placement in unstable intertrochanteric fractures.
authors.affiliation: Department of Orthopaedic Surgery and Rehabilitation Medicine, SUNY Downstate Medical Center, Brooklyn, NY, USA.
authors.forename: David
authors.initials: D
authors.lastname: Gallagher
authors.forename: Brock
authors.initials: B
authors.lastname: Adams
authors.forename: Hebah
authors.initials: H
authors.lastname: El-Gendi
authors.forename: Ashish
authors.initials: A
authors.lastname: Patel
authors.forename: Lauren
authors.initials: L
authors.lastname: Grossman
authors.forename: Jay
authors.initials: J
authors.lastname: Berdia
authors.forename: Yevgeniy
authors.initials: Y
authors.lastname: Korshunov
authors.forename: Ariel
authors.initials: A
authors.lastname: Goldman
mesh_terms: D001858:Bone Nails; D002102:Cadaver; D005264:Femoral Fractures / Q000150:complications / Q000503:physiopathology* / Q000601:surgery*; D005594:Fracture Fixation, Intramedullary / Q000295:instrumentation* / Q000379:methods*; D017276:Friction; D006801:Humans; D007593:Joint Instability / Q000209:etiology / Q000503:physiopathology* / Q000601:surgery*; D016059:Range of Motion, Articular; D019415:Torque; D016474:Weight-Bearing