title: Locking plate fixation of humeral head fractures with a telescoping screw. A comparative biomechanical study versus a standard plate.
abstract: OBJECTIVE
  Locking plate fixation of humeral head fractures bares the risk of glenohumeral screw penetration. In order to circumvent this problem it is recommended to insert shorter locking screws having at least a 6mm distance to the humeral head cortex. This in turn may reduce fixation stability and may lead to early varus displacement. One second frequent failure mechanism is cranial displacement of the greater tubercle. The study evaluates the biomechanical properties of a locking plate employing an additional telescoping screw that may enhance resistance to varus displacement. Screw in screw fixation of the greater tubercle may reduce the rate of cranial displacement.
  
  
  METHODS
  In four paired fresh-frozen human cadaver humeri (age>70 years) a Neer IV/3 fracture was created with a 5mm osteotomy gap simulating metaphyseal comminution. Limbs were randomly assigned to receive plate fixation with an additional telescoping screw (Humerus Tele Screw: HTS) and on the contralateral limb Philos plate fixation before biomechanical evaluation (MTS-Bionix 858.2). Standard locking screws were placed in both groups 6mm below the radiological head circumference; the telescoping screw was placed in the subchondral layer. The greater tubercle was fixed with an additional screw in both techniques, in the HTS group the screw was anchored in the sleeve of the telescrew (screw in screw fixation).
  
  
  RESULTS
  Fixation stability with a mean stiffness of 300.9±28.8 N/mm in the HTS plate group proved to be significantly higher than in the Philos plate group (184.2±23.4 N/mm; p=0.006). The HTS plate also resisted higher loads in terms of fixation failure with loss of reduction at 290±58.6 N in comparison to 205±8.6 N for the Philos plate (p=0.2). Displacement of the greater tubercle occurred in no case of the HTS plate group and in two out of four cases in the Philos plate group.
  
  
  CONCLUSIONS
  The HTS plate provides high fixation stability in an in vitro humeral head fracture model and securely prevents displacement of the greater tubercle.
authors.affiliation: Department for Trauma Surgery, University of Aachen, Germany. georg.gradl@med.uni-rostock.de
authors.forename: Gertraud
authors.initials: G
authors.lastname: Gradl
authors.forename: Hans-Werner
authors.initials: HW
authors.lastname: Stedtfeld
authors.forename: Michael
authors.initials: M
authors.lastname: Morlock
authors.forename: Kay
authors.initials: K
authors.lastname: Sellenschloh
authors.forename: Klaus
authors.initials: K
authors.lastname: Püschel
authors.forename: Thomas
authors.initials: T
authors.lastname: Mittlmeier
authors.forename: Georg
authors.initials: G
authors.lastname: Gradl
mesh_terms: D000368:Aged; D001696:Biomechanical Phenomena; D001860:Bone Plates; D001863:Bone Screws; D002102:Cadaver; D004868:Equipment Failure; D005260:Female; D005593:Fracture Fixation, Internal / Q000379:methods*; D006801:Humans; D006810:Humeral Fractures / Q000601:surgery*; D058430:Humeral Head / Q000473:pathology / Q000601:surgery*; D008297:Male; D008953:Models, Anatomic