title: Articular cartilage defects in a rabbit model, retention rate of periosteal flap cover.
abstract: BACKGROUND
  A periosteal flap is frequently used in procedures involving repair of articular cartilage defects. Hypertrophy of the repair tissue, probably from a retained periosteum, is a clinical problem but not much is known about this issue. The objective of the present experimental study was to investigate the retention rate of periosteal flaps with respect to various postoperative mobilization regimes and the introduction of bone marrow elements underneath the flap.
  
  
  METHODS
  We created a chondral lesion (diameter 4 mm) in both patellas of 18 New Zealand white rabbits. The subchondral bone was left intact in one knee. In the other, the bone plate was perforated, allowing bone marrow elements to enter the defect. All defects were covered with a periosteal flap, sutured and glued to the rim of the cartilage defect. Postoperatively, the rabbits were allocated to one of three groups: A. rehabilitation in cages for 4 days, then killed; B. rehabilitation in cages for 7 days, then free activity on the floor of a 10 m2 room until the end of the second week, then killed; C. rehabilitation in cages for 2 weeks, then killed.
  
  
  RESULTS
  16 of 23 periosteal flaps became detached within 2 weeks (one knee was excluded because of clinical signs of infection), with no difference in the retention rate with respect to mobilization regime or established access to bone marrow elements in the defect. The periosteum still served as a cover of the defect in 10 of 12 knees at day 4. This figure decreased to 7 of 23 knees at day 14.
  
  
  CONCLUSIONS
  Our study is the first to document the retention rate of periosteal flaps in a rabbit model. The low retention rate observed may explain why periosteal hypertrophy is not reported in experimental studies where the periosteal flap is sutured to the cartilage rim.
authors.affiliation: Institute of Surgical Research, Rikshospitalet University Hospital, Oslo, Norway. asben@online.no
authors.forename: Asbjørn
authors.initials: A
authors.lastname: Arøen
authors.forename: Stig
authors.initials: S
authors.lastname: Heir
authors.forename: Sverre
authors.initials: S
authors.lastname: Løken
authors.forename: Finn P
authors.initials: FP
authors.lastname: Reinholt
authors.forename: Lars
authors.initials: L
authors.lastname: Engebretsen
mesh_terms: D000818:Animals; D002358:Cartilage, Articular / Q000473:pathology / Q000601:surgery*; D006984:Hypertrophy; D008954:Models, Biological; D010329:Patella / Q000473:pathology / Q000601:surgery*; D010521:Periosteum / Q000473:pathology / Q000637:transplantation*; D011817:Rabbits; D013524:Surgical Flaps / Q000009:adverse effects / Q000473:pathology