Temporal and spatial modulation of chondrogenic foci in subchondral microdrill holes by chitosan-glycerol phosphate/blood implants.
OBJECTIVE
Subchondral drilling initiates a cartilage repair response involving formation of chondrogenic foci in the subchondral compartment. The purpose of this study was to structurally characterize these sites of chondrogenesis and to investigate the effects of chitosan-glycerol phosphate (GP)/blood implants on their formation.


METHODS
Thirty-two New Zealand White rabbits received bilateral cartilage defects bearing four subchondral drill holes. One knee per rabbit was treated by solidifying a chitosan-GP/blood implant over the defect. After 1-56 days of repair, chondrogenic foci were characterized by histostaining and immunostaining. Collagen fiber orientation was characterized by polarized light microscopy.


RESULTS
Glycosaminoglycan and collagen type II were present throughout the foci while the upper zone expressed collagen type I and the lower zone collagen type X. Large chondrogenic foci had a stratified structure with flatter cells closer to the articular surface, and round or hypertrophic chondrocytes deeper in the drill holes that showed signs of calcification after 3 weeks of repair in control defects. Markers for pre-hypertrophic chondrocytes (Patched) and for proliferation (Ki-67) were detected within foci. Some cells displayed a columnar arrangement where collagen was vertically oriented. For treated defects, chondrogenic foci appeared 1-3 weeks later, foci were nascent and mature rather than resorbing, and foci developed closer to the articular surface.


CONCLUSIONS
Chondrogenic foci bear some similarities to growth cartilage and can give rise to a repair tissue that has similar zonal stratification as articular cartilage. The temporal and spatial formation of chondrogenic foci can be modulated by cartilage repair therapies.
Department of Chemical Engineering, Ecole Polytechnique de Montreal, PO Box 6079, Succ Centre-Ville, Montreal, Quebec, Canada.
A
A
Chevrier
C D
CD
Hoemann
J
J
Sun
M D
MD
Buschmann
D000818:Animals; D015415:Biomarkers / Q000032:analysis; D002357:Cartilage Diseases / Q000188:drug therapy* / Q000378:metabolism / Q000473:pathology; D049109:Cell Proliferation / Q000187:drug effects; D048271:Chitosan / Q000494:pharmacology* / Q000627:therapeutic use; D020219:Chondrogenesis / Q000187:drug effects*; D003029:Coagulants / Q000494:pharmacology* / Q000627:therapeutic use; D003094:Collagen / Q000648:ultrastructure; D024043:Collagen Type II / Q000378:metabolism; D004195:Disease Models, Animal; D005990:Glycerol / Q000494:pharmacology / Q000627:therapeutic use; D006025:Glycosaminoglycans / Q000378:metabolism; D010710:Phosphates / Q000494:pharmacology / Q000627:therapeutic use; D011817:Rabbits
D015415:Biomarkers; D003029:Coagulants; D024043:Collagen Type II; D006025:Glycosaminoglycans; D010710:Phosphates; D003094:Collagen; D048271:Chitosan; D005990:Glycerol