Needle puncture injury affects intervertebral disc mechanics and biology in an organ culture model

Study Design. A bovine intervertebral disc organ culture model was used to study the effect of needle puncture injury on short-term disc mechanics and biology. Objective. To test the hypothesis that significant changes in intervertebral disc structure, mechanics, and cellular response would be present within 1 week of needle puncture injury with a large-gauge needle but not with a small-gauge needle. Summary of Background Data. Defects in anulus fibrosus induced by needle puncture injury can compromise mechanical integrity of the disc and lead to degeneration in animal models. The immediate and short-term mechanical and biologic response to anulus injury through needle puncture in a large animal model is not known. Methods. Bovine caudal intervertebral discs were harvested, punctured posterolaterally using 25G and 14G needles, and placed in organ culture for 6 days. Discs underwent a daily dynamic compression loading protocol for 5 days from 0.2 to 1 MPa at 1 Hz for 1 hour. Disc structure and function were assessed with measurements of dynamic modulus, creep, height loss, water content, proteoglycan loss to the culture medium, cell viability, and histology. Results. Needle puncture injury caused a rapid decrease in dynamic modulus and increase in creep during 1-hour loading, although no changes were detected in water content, disc height, or proteoglycan lost to the media. Cell viability was maintained except for localized cell death at the needle insertion site. An increase in cell number and possible remodeling response was seen in the insertion site in the nucleus pulposus. Conclusion. Relatively minor disruption in the disc from needle puncture injury had immediate and progressive mechanical and biologic consequences with important implications for the use of discography, and repair-regeneration techniques. Results also suggest diagnostic techniques sensitive to mechanical changes in the disc may be important for early detection of degenerative changes in response to anulus injury.