title: Effects of small incongruities in a sheep model of osteochondral autografting.
abstract: BACKGROUND
  Exact reconstruction of an osteochondral defect by autogenous transplantation (mosaicplasty) is difficult given the variation in joint surface contour. Clinical and experimental studies do not show the extent to which incongruity can be tolerated in autografting.
  
  
  OBJECTIVE
  Grafted articular cartilage will hypertrophy to correct the incongruity created by recession of the transplanted surface.
  
  
  METHODS
  Controlled laboratory study.
  
  
  METHODS
  To test the response of grafts to incongruities, osteochondral autografts were transplanted from the trochlea to the femoral condyle in adult male sheep stifle joints. In groups of 6 animals, graft surfaces were placed flush, countersunk 1 mm or countersunk 2 mm, then histologically analyzed 6 weeks after surgery. Cartilage thickness, condition of the articular surfaces, and preservation of hyaline characteristics were the primary features compared.
  
  
  RESULTS
  Bony union, vascularization, and new bone formation were present in all grafts. Cartilage-to-cartilage healing did not occur. In flush specimens, cartilage changed minimally in thickness and histologic architecture. The specimens countersunk 1 mm demonstrated significant cartilage thickening (54.7% increase, P <.05). Chondrocyte hyperplasia, tidemark advancement, and vascular invasion occurred at the chondroosseous junction, and the surface remained smooth. Cartilage necrosis and fibrous overgrowth were observed in all grafts countersunk 2 mm.
  
  
  CONCLUSIONS
  Minimally countersunk autografts possess a capacity for remodeling that can correct initial incongruities while preserving hyaline characteristics. Grafts placed deeper do not restore the contour or composition of the original articular surface.
  
  
  CONCLUSIONS
  If preservation of normal hyaline cartilage is the objective, thin grafted articular cartilage can remodel, but the tolerance for incongruity is limited and probably less than that reported for an intra-articular fracture.
authors.affiliation: Valley Orthopaedic Associates, Renton, Washington, USA.
authors.forename: Fred S
authors.initials: FS
authors.lastname: Huang
authors.forename: Peter T
authors.initials: PT
authors.lastname: Simonian
authors.forename: Anthony G
authors.initials: AG
authors.lastname: Norman
authors.forename: John M
authors.initials: JM
authors.lastname: Clark
mesh_terms: D000818:Animals; D016723:Bone Remodeling; D016025:Bone Transplantation / Q000379:methods*; D002358:Cartilage, Articular / Q000473:pathology / Q000637:transplantation*; D005269:Femur / Q000601:surgery / Q000637:transplantation*; D005355:Fibrosis; D006965:Hyperplasia; D008297:Male; D023421:Models, Animal; D010011:Osteocytes / Q000473:pathology; D012756:Sheep; D013264:Stifle / Q000473:pathology; D014182:Transplantation, Autologous; D014945:Wound Healing