Stereological analysis of subchondral angiogenesis induced by chitosan and coagulation factors in microdrilled articular cartilage defects

Abstract

Objective: Cartilage repair elicited by bone marrow stimulation can be enhanced by a chitosan-glycerol phosphate (GP)/blood implant, through mechanisms involving therapeutic inflammatory angiogenesis. The implant is formed by in situ coagulation, which can be accelerated by adding coagulation factors. We hypothesized that coagulation factors enhance acute subchondral angiogenesis in repairing drilled defects.

Design: Full-thickness cartilage defects were created bilaterally in 12 skeletally mature rabbit knee trochlea, microdrilled, then allowed to bleed as a control (N = 6) or treated with chitosan-GP/blood implant (N = 6), or implant solidified with thrombin (IIa), tissue factor (TF) with recombinant human factor VIIa (rhFVIIa), or rhFVIIa alone (N = 4 each condition). At 3 weeks post-operative, quantitative stereology was used to obtain blood vessel length (L(V)), surface (S(V)), and volume (V(V)) density at systematic depths in two microdrill holes per defect. Collagen type I, type II and glycosaminoglycan (GAG) percent stain in non-mineralized repair tissue were analysed by histomorphometry.

Results: All drill holes were healing, and showed a depth-dependent increase in granulation tissue blood vessel density (Lv, Sv, and Vv, P < 0.005). Residual chitosan implant locally suppressed blood vessel ingrowth into the granulation tissue, whereas holes completely cleared of chitosan amplified angiogenesis vs microdrill-only (P = 0.049), an effect enhanced by IIa. Chitosan implant suppressed strong Col-I, Col-II, and GAG accumulation that occurred spontaneously in drill-only bone defects (P < 0.005) and coagulation factors did not alter this effect.

Conclusions: Subchondral angiogenesis is promoted by chitosan implant clearance. Chitosan implant treatment suppresses fibrocartilage scar tissue formation, and promotes bone remodeling, which allows more blood vessel migration and woven bone repair towards the cartilage lesion area.