Biomechanical, Radiographic, and Histological Healing Characteristics of Anterior Spinal Fusion in a Sheep Model

The healing process of anterior spinal fusion was investigated biomechanically, radiographically and histologically. Twenty-four sheep underwent anterior lumbar interbody fusion at L2-3 and L4-5 with spinal instrumentation. Four animals each were euthonized at two, four, eight, 16, 24, and 52 weeks postoperatively. Biomechanical testing demonstrated that the stiffness of the operative segment increased during first 16 weeks and the lord-sharing of the instrumentation decreased concurrently with the development of the spinal fusion. The interesting result was that fusion mass continued to mature till 52 weeks without the occurrence of device-related osteoporosis and that facet joint gradually became osteoporotic and ankylosed. These facts suggested that the anterior fusion mass gradually became to play a major role in lord-transmission resulting in the decrease of lord-sharing of both the spinal instrumentation and the posterior spinal elements. This study leads to a better understanding of anterior spinal fusion in the clinical situation.