Optimization of spinal instrumentation stiffness and its effect on interbody fusion

Abstract

We further tested the effect of spinal instrumentation stiffness in vivo in the goat cervical spine following anterior cervical discectomy and fusion. In vivo results showed that instrumentation with plates of two different stiffnesses resulted in two distinct magnitudes of load-sharing during repeatable activities. In animals instrumented with stiff fusion plates, force maxima were observed when animals were in extension and minima were found when animals were in flexion; the opposite trend was observed in animals instrumented with compliant fusion plates. During the course of fusion, we measured a decrease in interbody load for five weeks following surgery, after which interbody loading remained similar over the remaining weeks of the study. After explanting tissues, histological examination of instrumented motion segments demonstrated that levels instrumented with more stiff plates tended to exhibit new bone formation but lower rates of bridging fusion. Animals instrumented with a more compliant fusion plate were also found to exhibit new bone formation with increased rates of fusion compared to the animals treated with the stiff plates.