title: Peri-tunnel bone loss: does it affect early tendon graft to bone tunnel healing after ACL reconstruction?
abstract: OBJECTIVE
  The clinical relevance and mechanisms of local bone loss early post-anterior cruciate ligament (ACL) reconstruction remain unclear. The early spatial and temporal changes of peri-tunnel bone, its molecular mechanisms and its relationships with graft-bone tunnel healing were investigated in a 12-week-old rat model.
  
  
  METHODS
  At various times, the reconstructed ACL complex was harvested for vivaCT imaging, biomechanical test, histology and immunohistochemical staining of CD68+ cells (a monocyte-macrophage lineage marker), MMP1 and MMP13.
  
  
  RESULTS
  The peri-tunnel bone resorbed simultaneously with improvement of graft-bone tunnel healing. There were 30.1 ± 17.4, 46.8 ± 10.5 and 81.5 ± 12.3 % loss of peri-tunnel BMD as well as 43.2 ± 21.7, 78.7 ± 8.5 and 92.4 ± 17.7 % loss of peri-tunnel bone volume/total volume (BV/TV) at week 6 at the distal femur, epiphysis and metaphysis of tibia, respectively. MMP1, MMP13 and CD68+ cells were expressed at the graft-bone tunnel interface and peri-tunnel bone and increased with time post-reconstruction at the tibia. The ultimate load and stiffness of the healing complex positively correlated with tibial tunnel bone formation and negatively correlated with tibial peri-tunnel bone. Tunnel BV/TV at the tibial metaphysis and epiphysis showed the highest correlation with ultimate load (ρ = 0.591; p = 0.001) and stiffness (ρ = 0.427; p = 0.026) of the complex, respectively.
  
  
  CONCLUSIONS
  There was time-dependent loss of peri-tunnel bone early post-reconstruction, with the greatest loss occurring at the tibial metaphysis. This was consistent with high expression of MMP1, MMP13 and CD68+ cells at the graft-bone tunnel interface and the peri-tunnel region. The significant loss of peri-tunnel bone, though not critically affecting early tunnel healing, suggested the need to protect the knee joint early post-reconstruction.
authors.forename: Pauline Po Yee
authors.initials: PP
authors.lastname: Lui
authors.forename: Yuk Wa
authors.initials: YW
authors.lastname: Lee
authors.forename: Tsui Yu
authors.initials: TY
authors.lastname: Mok
authors.forename: Yau Chuk
authors.initials: YC
authors.lastname: Cheuk
mesh_terms: D000818:Animals; D000070598:Anterior Cruciate Ligament Injuries; D059549:Anterior Cruciate Ligament Reconstruction / Q000379:methods; D015703:Antigens, CD / Q000378:metabolism; D015214:Antigens, Differentiation, Myelomonocytic / Q000378:metabolism; D015519:Bone Density; D004838:Epiphyses / Q000601:surgery; D005269:Femur / Q000000981:diagnostic imaging / Q000503:physiopathology; D007150:Immunohistochemistry; D008297:Male; D020781:Matrix Metalloproteinase 1 / Q000378:metabolism; D053509:Matrix Metalloproteinase 13 / Q000378:metabolism; D017207:Rats, Sprague-Dawley; D013710:Tendons / Q000637:transplantation*; D013977:Tibia / Q000000981:diagnostic imaging / Q000503:physiopathology; D014057:Tomography, X-Ray Computed; D014945:Wound Healing / Q000502:physiology*; D000097382:CD68 Molecule
chemical_list: D015703:Antigens, CD; D015214:Antigens, Differentiation, Myelomonocytic; D020781:Matrix Metalloproteinase 1; D053509:Matrix Metalloproteinase 13; C539355:CD68 protein, rat; D000097382:CD68 Molecule
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