title: An internal fixator for posterior application to short segments of the thoracic, lumbar, or lumbosacral spine. Design and testing.
abstract: A new spinal implant has been designed and biomechanical testing completed, intended for application to "short-segment" spinal defects such as disc degeneration, fracture, spondylolisthesis, or tumor. Major improvements over currently available devices include: only 2-3 vertebrae are spanned, not 5-7 as with Harrington rods; true three-dimensional fixation is achieved, preventing such problems as hook or rod dislocation; three-dimensional adjustment is easily accomplished, allowing fracture or spondylolisthesis reduction to be readily performed; attachment to vertebrae is by means of transpedicular screws eliminating deliberate encroachment into the spinal canal, such as Luque wires or Harrington hooks; no special alignment between screws is needed (such as with holes or slots in a plate), allowing screw placement to fully conform to anatomic structures; and laminectomy sites and lumbosacral junction are readily instrumented. Background investigations presented here for design of this device include: CT-defined pedicle morphometry showing that screws may be larger than those currently used; effect of pitch, minor diameter, and tooth profile on screw pull-out strength; mechanical testing of a compact, three-dimensionally adjustable, strong, nonloosening articulating clamp; and establishing of the relationship between depth of penetration and strength of fixation of transpeduncular screws.
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D001863:Bone Screws; D004867:Equipment Design; D005260:Female; D006801:Humans; D008159:Lumbar Vertebrae / Q000601:surgery*; D008297:Male; D008875:Middle Aged; D009984:Orthopedic Fixation Devices; D013123:Spinal Fusion / Q000295:instrumentation / Q000379:methods; D013904:Thoracic Vertebrae / Q000601:surgery*