Bilateral intra-annular spinal compressive stresses in vivo.

The purpose of this pilot study was to determine if compressive stresses in the annulus of the intervertebral disc vary with activity in a quadruped and are affected by treatment with an implant. Pilot in vivo tests were conducted on skeletally immature domestic pigs (approved by IACUC). One pair of sensors was implanted within the annulus of T10-11, and the second pair at T8-9. A staple was them implanted across the right side of T8-9. Wires were routed subcutaneously and exited at the dorsal cervical region. Sensor signals were acquired before and after staple implantation, post-operatively during normal activities, and biweekly under anesthesia. After 8 weeks, spines were harvested and imaged. Early results from 2 sensors during walking and sitting, post-op day 5, clearly showed cyclic stresses during gait. Stresses were attenuated at the stapled vertebra compared to the unstapled vertebra.