Repairing the ruptured annular fibrosus by using type I collagen combined with citric acid, EDC and NHS: an in vivo study.

To explore the effect of citric acid (CA)-1-ethyl-3-(3-dimethylaminopropyl)carbodiimide (EDC)/N-hydroxysuccinimide (NHS) collagen gel on repairing annular defects.

Type I collagen was extracted from the rat-tail tendon and crosslinked with CA at different mass ratio using EDC and NHS as crosslinking reagents to prepare four kinds of collagen gels. Forty-eight adult SD rats were divided into first sham group (n = 8), second group (n = 10) which was punctured and injected with CA-EDC/NHS collagen gel, third group (n = 10) which was punctured and injected with CA-EDC/NHS collagen gel, fourth group (n = 10) which was punctured and injected with EDC/NHS collagen gel, and fifth group (n = 10) which was punctured and untreated. X-ray images and magnetic resonance imaging images were obtained before puncture and at the 1st, 2nd, and 4th week after puncture. At each time point, disc height index (%DHI), voxel count and modified MRI Pfirrmann grading were collected and analyzed. All animals were killed at the 4th week to study the morphology.

The discs in the second group showed only slight degeneration compared with the healthy discs, and the results of %DHI (average 79%), voxel count (average 126.9), Pfirrmann grading (average grade 1.3) and morphology in the second group indicated less degeneration tendency compared with the other three puncture groups at the 4th week (P < 0.05). The annular fibrosus was partially repaired by the collagen gels that bridged the defects.

CA-EDC/NHS collagen gel is capable of repairing annular defects induced by needle puncture, which may be closely related to the dose of CA.