Intradiscal Delivery of Anabolic Growth Factors and a Metalloproteinase Inhibitor in a Rabbit Acute Lumbar Disc Injury Model

BACKGROUND

The purpose of our study was to examine the effect of controlled delivery of TGF-β₃, BMP-4, and TIMP-2 with a biocompatible biopolymer, chitosan, on an acutely injured intervertebral disc (IVD) in a rabbit model.

METHODS

After conducting an in vitro analysis of the chondrogenic capacity of the biomolecule cocktail use (ie, TGF-β₃, BMP-4, and TIMP-2) and confirming stem cell viability in chitosan hydrogel, 15 New Zealand white rabbits underwent a lateral approach of the L1 to L4 IVDs. In each rabbit, the L2 to L3 IVD was left pristine, whereas the L1 to L2 and the L3 to L4 IVDs in each rabbit underwent nucleotomy via a 25-G needle, and the animal was subsequently randomized to no further treatment (defect only), chitosan alone, Chitosan + TGF-β₃ + BMP-4, or chitosan + TGF-β₃ + BMP-4 + TIMP-2. At 6 weeks after injury and intervention, the rabbits were killed and spines harvested to undergo quantitative T2 magnetic resonance imaging (MRI) and subsequent histologic analysis.

RESULTS

In the in vitro analysis, cells treated with experimental media containing TGF-β₃, BMP-4, and TIMP-2 exhibited staining indicative of GAG production and began to exhibit a chondrocytic morphology. Quantitative T2 MRI mapping demonstrates that discs treated with chitosan, chitosan containing TGF-β₃ and BMP-4, or chitosan containing TGF-β₃, BMP-4, and TIMP-2 had consistently higher T2 relaxation times compared with defect-only discs. When the T2 relaxation times of each treatment group and defect-only discs were normalized to the healthy control disc, it was found that the T2 relaxation time of discs treated with chitosan containing TGF-β₃ and BMP-4 and discs treated with chitosan containing TGF-β₃, BMP-4, and TIMP-2 were significantly greater compared with defect-only discs (P = .048 and P = .013, respectively). Histologically, animals that received chitosan only, or chitosan with TGF-β₃ and BMP-4, showed a significantly higher intensity of Safranin-O staining (P = .016 and P = .02, respectively) compared with control discs, whereas the difference in staining intensity in animals that received chitosan loaded with TGF-β₃, BMP-4, and TIMP-2 failed to achieve significance (P = .161).

CONCLUSIONS

A combination of chitosan, TGF-β₃, and BMP-4 was effective at promoting regeneration in an acute disc injury rabbit model, whereas TIMP-2 did not have a significant effect.

Predisposing factors for dural tear in patients undergoing lumbar spine surgery

OBJECT The purpose of this prospective cohort study was to identify risk factors for incidental durotomies in lumbar spine surgery. The authors hypothesized that the incidence of durotomy would be higher in cases involving multiple operations. METHODS The authors prospectively evaluated 523 patients who underwent lumbar and thoracolumbar spine surgery. They compared data on patients in whom a dural tear occurred and those in whom a dural tear did not occur. Data from patients in whom a dural tear occurred were compared with data from patients who did not experience durotomy. The data included basic demographic information, intraoperative data, and clinical information from a medical record review. RESULTS One hundred thirty-one patients underwent discectomy and 392 patients underwent laminectomy. Among the 131 patients who underwent discectomy 6 patients had a dural tear. Among the 392 patients who underwent discectomy 49 patients had dural tear. Patients with incidental durotomy were older (mean 65 ± 13 vs 60 ± 14 years of age; p = 0.044, t-test), and had longer surgery (146 ± 59 vs 110 ± 54 minutes; p = 0.025, t-test), compared with the patients without dural tear. The incidence of dural tear was more common in patients with a history of previous spine surgery (p < 0.001). CONCLUSIONS In patients who underwent lumbar and thoracolumbar spine surgery for degenerative problems, previous surgery and older age were found to be predisposing factors for dural tear.