title: Pullout of a lumbar plate with varying screw lengths.
abstract: BACKGROUND
  Screw length pertains to stability in various orthopedic fixation devices. There is little or no information on the relationship between plate pullout strength and screw length in anterior lumbar interbody fusion (ALIF) plate constructs in the literature. Such a description may prove useful, especially in the treatment of osteoporotic patients where maximizing construct stability is of utmost importance. Our purpose is to describe the influence of screw length on ALIF plate stability in severely and mildly osteoporotic bone foam models.
  
  
  METHODS
  Testing was performed on polyurethane foam blocks with densities of 0.08 g/cm(3) and 0.16 g/cm(3). Four-screw, single-level ALIF plate constructs were secured to the polyurethane foam blocks by use of sets of self-tapping cancellous bone screws that were 20, 24, 28, 32, and 36 mm in length and 6.0 mm in diameter. Plates were pulled out at 1 mm/min to failure, as defined by consistently decreasing load despite increasing displacement.
  
  
  RESULTS
  Pullout loads in 0.08-g/cm(3) foam for 20-, 24-, 28-, 32-, and 36-mm screws averaged 303, 388, 479, 586, and 708 N, respectively, increasing at a mean of 25.2 N/mm. In 0.16-g/cm(3) foam, pullout loads for 20-, 24-, 28-, 32-, and 36-mm screws averaged 1004, 1335, 1569, 1907, and 2162 N, respectively, increasing at a mean of 72.2 N/mm.
  
  
  CONCLUSIONS
  The use of longer screws in ALIF plate installation is expected to increase construct stability. Stabilization from screw length in osteoporotic patients, however, is limited.
authors.affiliation: Orthopaedic Biomechanics Laboratory, Department of Orthopaedic Surgery, Loma Linda University, Loma Linda, CA.
authors.forename: Daniel Kyle
authors.initials: DK
authors.lastname: Palmer
authors.affiliation: Orthopaedic Biomechanics Laboratory, Department of Orthopaedic Surgery, Loma Linda University, Loma Linda, CA.
authors.forename: David
authors.initials: D
authors.lastname: Rios
authors.affiliation: Orthopaedic Biomechanics Laboratory, Department of Orthopaedic Surgery, Loma Linda University, Loma Linda, CA.
authors.forename: Wyzscx Merfil
authors.initials: WM
authors.lastname: Patacxil
authors.affiliation: Orthopaedic Biomechanics Laboratory, Department of Orthopaedic Surgery, Loma Linda University, Loma Linda, CA.
authors.forename: Paul A
authors.initials: PA
authors.lastname: Williams
authors.affiliation: Orthopaedic Biomechanics Laboratory, Department of Orthopaedic Surgery, Loma Linda University, Loma Linda, CA.
authors.forename: Wayne K
authors.initials: WK
authors.lastname: Cheng
authors.affiliation: Orthopaedic Biomechanics Laboratory, Department of Orthopaedic Surgery, Loma Linda University, Loma Linda, CA.
authors.forename: Serkan
authors.initials: S
authors.lastname: İnceoğlu
keywords: ALIF; Anterior plate; Lumbar spine; Polyurethane foam; Pullout; Screw length