The dose response relationship between intervertebral disc flexion-extension neutral zone metrics and injected genipin concentration.

PURPOSE: Quantify changes in the flexion--extension neutral zone of the intervertebral disc with injections of increasing genipin concentration. METHODS: Bovine motion segments were treated with varying concentrations of genipin using bilateral injections of constant volume. After overnight static compression loading of the treated segments, anterior-posterior offset loading was used to simulate flexion-extension motion. Range of motion, neutral zone length, neutral zone stiffness, and an instability score were measured. RESULTS: Injection of the disc annulus with increasing concentrations of genipin resulted in corresponding changes in flexion-extension neutral zone. A minimum concentration of 40 mM was needed to observe a significant change. The largest changes were observed with the 400 mM injection. Netural zone stability was the most sensitive of the metrics with a percent change of 48% at 40 mM and over 200% at 400 mM. CONCLUSION: This study establishes the efficacy of using injection delivery to affect disc joint mechanics and quantifies the dose response between injected genipin and the flexion-extension stability of the disc.

Optimization of protein crosslinking formulations for the treatment of degenerative disc disease.

STUDY DESIGN: Biochemical studies aimed at optimization of protein crosslinking formulations for the treatment of degenerative disc disease and subsequent biomechanical testing of tissues treated with these formulations. OBJECTIVE: To optimize protein crosslinking formulations for treatment of degenerating spinal discs. SUMMARY OF BACKGROUND DATA: Nonsurgical exogenous crosslinking therapy is a potential new, noninvasive technology for the treatment of degenerative disc disease. The technology is based on the injection of protein crosslinking reagents into the pathologic disc to restore its mechanical properties and also to potentially increase the permeability of the tissue and so facilitate the exchange of waste products and nutrients. METHODS: Diffusion of genipin (GP) was monitored following injection into spinal discs and the effects of surfactants on diffusion studied. Formulations for GP and methylglyoxal (MG) were biochemically optimized and used to treat bovine spinal discs. Their effects on bovine anulus tissue were evaluated using a circumferential tensile test, while the GP formulation was also tested with respect to its ability to reduce disc bulge under load. RESULTS: GP exhibited a distinct time-dependent diffusion and sodium-dodecyl-sulfate, but not Tween-20, enhanced diffusion by 30%. Two crosslinkers, GP and MG, were inhibited by amines but enhanced by phosphate ions. Both formulations could enhance a number of physical parameters of bovine anulus tissue, while the GP formulation could reduce disc bulge following injections into spinal discs. CONCLUSION: Formulations lacking amines and containing phosphate ions appear to be promising candidates for clinical use of the crosslinkers GP and MG.