The effect of kyphosis on the mechanical strength of a long-segment posterior construct Using a synthetic model

• Published in: Spine (Philadelphia, Pa. 1976) Pa. 1976), 2000-07, Vol.25 (13), p.1644-1648
• Main Authors: ORCHOWSKI, J, POLLY, D. W, KLEMME, W. R, ODA, I, CUNNINGHAM, B
• Format: Article
• Language: English
• Subjects: Biological and medical sciences; Bone Nails; Compressive Strength - physiology; Humans; Kyphosis - physiopathology; Kyphosis - surgery; Medical sciences; Models, Anatomic; Spinal Fusion; Spine - physiopathology; Spine - surgery; Surgery (general aspects). Transplantations, organ and tissue grafts. Graft diseases; Technology. Biomaterials. Equipments
• ISSN: 0362-2436; 1528-1159
• DOI: 10.1097/00007632-200007010-00007

This experimental study used synthetic spine models to compare the effect of the angle of kyphosis, rod diameter, and hook number on the biomechanical stiffness of a long-segment posterior spinal construct. To examine the biomechanical effects of incremental kyphosis on variously instrumented long-segment posterior spinal constructs. Euler's formula for loading of curved long columns would suggest that kyphosis has a profound impact on the biomechanical behavior of long-segment posterior spinal constructs. The effects of sagittal contour on the mechanical properties of long-segment posterior spinal constructs have not been well documented. Kyphotic and straight synthetic spine models were used to test long-segment posterior instrumentation constructs biomechanically while varying rod diameter and the number of hook sites. The synthetic spines, composed of polypropylene vertebral blocks and isoprene elastomer intervertebral spacers, were fabricated with either 0 degrees, 27 degrees, or 53 degrees of sagittal contour. The models were instrumented with 5.5- or 6.35-mm titanium rods, and with either 8 or 12 hooks. The models were loaded from 0 to 300 N in a cyclical ramp fashion using an MTS 858 Bionix testing device testing device. Construct stiffness (force and displacement) during axial compression was determined. Straight model: Changing the hook number from 8 to 12 caused a 32% increase in construct stiffness with the 5.5-mm rod. Changing the rod diameter from 5.5 to 6.35 mm caused a 36% increase in construct stiffness with the 8-hook pattern. Changing both the rods and hooks caused the stiffness to increase 44%. 27 degrees Changing the hook number from 8 to 12 caused a 20% increase in construct stiffness with the 6.5-mm rod. Changing the rod diameter from 5.5 to 6.35 mm caused a 29% increase in construct stiffness with the 12-hook pattern. Changing both the rods and hooks caused the construct stiffness to increase 26%. 53 degrees Changing the hook number from 8 to 12 caused a 14% increase in construct stiffness with the 6.35-mm rod. Changing the rod diameter from 5.5 to 6.35 mm caused a 17% (P