Objective      To explore the effect of citric acid (CA)-1-ethyl-3-(3-dimethylaminopropyl)carbodiimide (EDC)/N-hydroxysuccinimide (NHS) collagen gel on repairing annular defects.       Methods      Type I collagen was extracted from the rat tail tendon and crosslinked with CA at different mass ratios using EDC and NHS as crosslinking reagents to prepare 4 kinds of collagen gels. Forty-eight adult SD rats were divided into  sham-operation  group (n=8)

CA6 group (n=10) which was punctured and injected with CA-EDC/NHS collagen gel (CA6)

CA3 group (n=10) which was punctured and injected with CA-EDC/NHS collagen gel (CA3)

CA0 group (n=10) which was punctured and injected with EDC/NHS collagen gel (CA0)

and model group (n=10) which was punctured and untreated. X-ray filming and magnetic resonance imaging (MRI) were performed before only 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 for the morphological study.       Results      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 CA6 group indicated less degeneration tendency compared with the other 3 puncture groups at the 4th week(P0.05). The annular fibrosus was partially repaired by the collagen gels that bridged the defects.       Conclusions      CA-EDC/NHS collagen gel is capable of repairing annular defects induced by needle puncture

which may be closely related with the dose of CA.