An internal fixator for posterior application to short segments of the thoracic, lumbar, or lumbosacral spine. Design and testing

• Published in: Clinical orthopaedics and related research no. 203; p. 75
• Main Authors: Krag, M H, Beynnon, B D, Pope, M H, Frymoyer, J W, Haugh, L D, Weaver, D L
• Format: Journal Article
• Language: English
• Published: United States 01.02.1986
• Subjects: Adolescent; Adult; Aged; Bone Screws; Equipment Design; Female; Humans; Lumbar Vertebrae - surgery; Male; Middle Aged; Orthopedic Fixation Devices; Spinal Fusion - instrumentation; Spinal Fusion - methods; Thoracic Vertebrae - surgery
• ISSN: 0009-921X; 1528-1132
• DOI: 10.1097/00003086-198602000-00011

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.