title: Characterization of subchondral bone repair for marrow-stimulated chondral defects and its relationship to articular cartilage resurfacing.
abstract: BACKGROUND
  Microfracture and drilling are bone marrow-stimulation techniques that initiate cartilage repair by providing access to cell populations in subchondral bone marrow. This study examined the effect of hole depth and of microfracture versus drilling on subchondral bone repair and cartilage repair in full-thickness chondral defects.
  
  
  OBJECTIVE
  Repaired subchondral bone does not reconstitute its native structure and exhibits atypical morphologic features. Drilling deeper induces greater bone remodeling and is related to improved cartilage repair.
  
  
  METHODS
  Controlled laboratory study.
  
  
  METHODS
  Trochlear cartilage defects debrided of the calcified layer were prepared bilaterally in 16 skeletally mature rabbits. Drill holes were made to a depth of 2 mm or 6 mm and microfracture holes to 2 mm. Animals were sacrificed 3 months postoperatively, and joints were scanned by micro-computed tomography before histoprocessing. Bone repair was assessed with a novel scoring system and by 3-dimentional micro-computed tomography and compared with intact controls. Correlation of subchondral bone features to cartilage repair outcome was performed.
  
  
  RESULTS
  Although surgical holes were partly repaired with mineralized tissue, atypical features such as residual holes, cysts, and bony overgrowth were frequently observed. For all treatment groups, repair led to an average bone volume density similar to that of the controls but the repair bone was more porous and branched as shown by significantly higher bone surface area density and connectivity density. Deeper versus shallower drilling induced a larger region of repairing and remodeling subchondral bone that positively correlated with improved cartilage repair.
  
  
  CONCLUSIONS
  Incomplete reconstitution of normal bone structure and continued remodeling occurred in chondral defects 3 months after bone marrow stimulation. Deep drilling induced a larger volume of repairing and remodeling bone, which appeared beneficial for chondral repair.
  
  
  CONCLUSIONS
  Bone marrow stimulation does not reconstitute normal bone structure. Strategies that increase subchondral bone involvement in marrow stimulation could further benefit cartilage repair.
authors.affiliation: Chemical Engineering, Ecole Polytechnique, Montreal, Quebec, Canada.
authors.forename: Hongmei
authors.initials: H
authors.lastname: Chen
authors.forename: Anik
authors.initials: A
authors.lastname: Chevrier
authors.forename: Caroline D
authors.initials: CD
authors.lastname: Hoemann
authors.forename: Jun
authors.initials: J
authors.lastname: Sun
authors.forename: Wei
authors.initials: W
authors.lastname: Ouyang
authors.forename: Michael D
authors.initials: MD
authors.lastname: Buschmann
mesh_terms: D000818:Animals; D054544:Arthroplasty, Subchondral / Q000379:methods*; D001861:Bone Regeneration; D002358:Cartilage, Articular / Q000502:physiology* / Q000601:surgery*; D005260:Female; D007867:Leg Bones / Q000000981:diagnostic imaging; D011817:Rabbits; D011897:Random Allocation; D055114:X-Ray Microtomography