title: In vitro biomechanical analysis of a new lumbar low-profile locking screw-plate construct versus a standard top-loading cantilevered pedicle screw-rod construct: technical report.
abstract: OBJECTIVE
  A standard top-loading lumbar pedicle screw-rod system is compared with a pedicle screw-plate system with smaller-diameter screws, more medial entry, and lower profile to assess the relative stability, strength, and resistance to fatigue of the 2 systems.
  
  
  METHODS
  Seven human cadaveric specimens were studied with each surgical construct. Nondestructive, nonconstraining pure moments were applied to specimens to induce flexion, extension, lateral bending, and axial rotation while recording L5-S1 motion optoelectronically. After initial tests, specimens were fatigued for 10,000 cycles and retested to assess early postoperative loosening. Specimens were then loaded to failure in hyperextension.
  
  
  RESULTS
  The standard screw-rod construct reduced range of motion to a mean of 20% of normal, whereas the screw-plate construct reduced range of motion to 13% of normal. Differences between systems were not significant in any loading mode (P > 0.06). The 14% loosening of the screw-rod system with fatigue was not significantly different from the 10% loosening observed with the screw-plate system (P > 0.15). Mean failure loads of 30 Nm for screw-rod and 37 Nm for screw-plate were also not significantly different (P = 0.38).
  
  
  CONCLUSIONS
  Posterior fixation at L5-S1 using the low-profile screw-plate system offers stability, resistance to fatigue, and resistance to failure equivalent to fixation using a standard cantilevered pedicle screw-rod system.
authors.affiliation: Spinal Biomechanics Laboratory, Division of Neurological Surgery, Barrow Neurological Institute, St. Joseph's Hospital and Medical Center, Phoenix, Arizona 85013, USA.
authors.forename: Neil R
authors.initials: NR
authors.lastname: Crawford
authors.forename: Seref
authors.initials: S
authors.lastname: Doğan
authors.forename: K Zafer
authors.initials: KZ
authors.lastname: Yüksel
authors.forename: Octavio
authors.initials: O
authors.lastname: Villasana-Ramos
authors.forename: Julio C
authors.initials: JC
authors.lastname: Soto-Barraza
authors.forename: Anna G U
authors.initials: AG
authors.lastname: Sawa
authors.forename: Randall W
authors.initials: RW
authors.lastname: Porter
authors.forename: Frederick F
authors.initials: FF
authors.lastname: Marciano
authors.forename: Nicholas
authors.initials: N
authors.lastname: Theodore
mesh_terms: D000328:Adult; D000368:Aged; D001696:Biomechanical Phenomena; D001860:Bone Plates; D001863:Bone Screws; D002102:Cadaver; D005260:Female; D006801:Humans; D066298:In Vitro Techniques; D016268:Internal Fixators; D008159:Lumbar Vertebrae / Q000601:surgery*; D008297:Male; D008875:Middle Aged