黏性補給與外生性交聯對早期退化性椎間盤的動態生物力學性質影響

Abstract

Objective: To evaluate the biodynamic properties of the mildly degenerated intervertebral disc after viscosupplementation and crosslinking. Summary of Background Data: The matrix denaturation in early degenerated intervertebral disc compromise the hydraulic retention mechanism to resist compressive loading and thus degrade disc dynamic properties. Hyaluronic acid (HA) is one of primary compositions of extracellular matrix and characterized to absorb abundant water to increase the viscosity of synovial fluid. Whether the interaction of HA and the degenerated disc matrix could resume the disc dynamic properties by similar mechanism remains unclear. The dynamic properties of the degenerated discs were partially recovered by genipin-induced crosslinking. The recovery degree may be enhanced by increasing the genipin concentration and reaction time. The recovery efficiency of HA-mediated viscosupplementation and genipin-induced crosslinking on the dynamic properties of the mildly degenerated disc has not been compared yet. Methods: A total of 36 porcine lumbar body-disc-body constructs were assigned to an “Intact disc” group (n=9) and a “Degenerated disc” group (n=27). The specimens of the “Intact disc“ were injected with 1 ml saline, while the specimens of the “Denatured disc” were injected with 1 ml 0.5% trypsin solution. After a 24 hr saline bath, an impact test was performed before and after a 30 min fatigue loading (peak to peak: 190-490 N) to obtain the dynamic properties, i.e. stiffness modulus (K, N/s) and damping coefficient (C, Ns/mm). The specimens of the “Intact disc” and 9 specimens of the “Denatured disc” were injected with 1 ml HA (“Viscosupplemented disc”), while the other 9 discs of the “Denatured disc” were injected with 1 ml 3.3% genipin solution (“Crosslinked disc”). Then the “Intact disc” and the “Viscosupplemented disc” rehydrated in saline solution for 24 hr, while the “Crosslinked disc” rehydrated for 72 hr. After that, the aforementioned protocols of rehydration, fatigue loading and the impact test were repeated to obtain the disc dynamic properties. Results: For the intact disc, the stiffness modulus was 720.2 (75.4) N/mm and the damping coefficient was 0.60 (0.06) Ns/mm. After the fatigue loading, the stiffness modulus increased to 937.7 (16.4) N/mm and the damping coefficient decreased to 0.53 (0.03) Ns/mm. HA-mediated Viscosupplementation increased the stiffness modulus and the damping coefficient, but the effect was decreased for the stiffness modulus by the fatigue loading. The disc stiffness modulus and damping coefficient were degraded by the trypsin-induced degeneration, but fully recovered by the HA-mediated viscosupplementation and genipin-induced crosslinking. However, the stiffness modulus and damping coefficient of the viscosupplemented disc were degraded by the fatigue loading, while only the stiffness modulus of the crosslinked disc degraded after the fatigue loading. Compared to the previous data, the recovery level of the genipin solution on the stiffness modulus and damping coefficient of the degenerated disc were elevated when the genipin concentration was 10 folds increased and the crosslinking time was 3 times elongated. Conclusion: The recovery efficiency of the genipin-induced crosslinking on the dynamic properties of the degenerated disc, especially on the damping coefficient, was more sustainable to the fatigue loading when compared to that of the HA-mediated viscosupplementation, and could be enhanced by increasing the genipin solution concentration and reaction time.