Influence of Bone Mineral Density on the Fixation of Thoracolumbar Implants A Comparative Study of Transpedicular Screws, Laminar Hooks, and Spinous Process Wires

Publisher Website
Google Scholar
Abstract
Posteriorly directed load to failure testing of four different types of spinal implants was performed in individual T5 to S1 vertebra harvested from seven fresh-frozen human cadaveric spines. The implants tested were: 1) Drum-mond spinous process wires, 2) Harrington laminar hooks, 3) Cotrel-Dubousset transpedicular screws, and 4) Steffee VSP transpedicular screws. The ultimate failure of each implant was compared with the bone mineral density of each vertebra to determine which implants, if any, were particularly advantageous in osteoporotic vertebrae. Before biomechanical testing, the spines were analyzed in vitro by dual photon absorptiometry to determine the bone mineral densities (gm/cm2) of each vertebra. The mean tensile loads to failure for each of the implants tested were as follows: Cotrel-Dubousset transpedicular screws: 345 Newtons; spinous process wire/button: 382 Newtons; Steffee transpedicular screws: 430 Newtons; and laminar hooks: 646 Newtons. The difference between the loads to failure for laminar hooks and the, other implants was significant (P < 0.05) using oneway analysis of variance. The overall correlation coefficient for bone mineral density with ultimate load to failure was 0.30 (P < 0.001). The correlation coefficients were 0.47 (P < 0.001) for spinous process wires alone; 0.096 (not significant) for laminar hooks alone; 0.37 (P < 0.001) for Cotrel-Dubousset pedicle screws; and 0.48 (P < 0.001) for Steffee pedicle screws. Of the four different implants tested, laminar hooks were most resistant to failure from posteriorly directed forces. In contrast to spinous process wires and transpedicular screws, loads to failure for laminar hooks did not correlate with bone mineral density. The increased resistance to failure from posteriorly directed forces and independence from variations in bone mineral density may indicate that laminar hooks are superior to spinous process wires and pedicle screws for spinal fixation in patients with decreased bone mineral density due to osteoporosis, osteomalacia, or other forms of metabolic bone disease.

This publication has 0 references indexed in Scilit: