title: Inferior tendon graft to bone tunnel healing at the tibia compared to that at the femur after anterior cruciate ligament reconstruction.
abstract: BACKGROUND
  Tunnel widening after anterior cruciate ligament (ACL) reconstruction (ACLR) is commonly reported without a clear understanding of the mechanism. This study aimed to quantify the spatiotemporal change of the newly formed bone mass, bone tunnel diameter, and area along both bone tunnels using micro-computed tomography (microCT) and correlated the result with histology.
  
  
  METHODS
  ACLR was performed in 24 rabbits. At baseline and weeks 2, 6, and 12, the juxta-articular, middle, and exit segments of both tunnels were harvested for microCT and histological evaluation.
  
  
  RESULTS
  microCT and histology revealed significant bone tunnel and graft-bone tunnel healing, respectively, only at week 6 after reconstruction. Despite this, the mean tunnel diameter and area remained relatively unchanged with time. The newly formed bone mass [new bone volume/total bone volume (BV/TV) ratio] and its bone mineral density (BMD) were both higher, whereas the mean tunnel diameter and area were significantly smaller at the femoral tunnel compared to those at the tibial tunnel at weeks 6 and 12 and at week 12, respectively. These were consistent with histological findings, which showed inferior graft remodeling and integration at the tibial tunnel at weeks 6 and 12. The BV/TV increased, whereas the mean tunnel diameter and area decreased toward the exit segment of both tunnels. However, whereas better histological healing occurred at the femoral exit segment, poorer graft remodeling and Sharpey's fiber formation occurred at the tibial exit segment.
  
  
  CONCLUSIONS
  Poor healing was observed during the initial 6 weeks, particularly that of the tibia, after ACLR. Bone resorption was rapid during healing, resulting in unchanged tunnel diameter and area with time.
authors.affiliation: Department of Orthopaedics and Traumatology, The Chinese University of Hong Kong, Prince of Wales Hospital, Shatin, NT, Hong Kong SAR, China.
authors.forename: Pauline Po Yee
authors.initials: PP
authors.lastname: Lui
authors.forename: Grace
authors.initials: G
authors.lastname: Ho
authors.forename: Wai Ting
authors.initials: WT
authors.lastname: Shum
authors.forename: Yuk Wa
authors.initials: YW
authors.lastname: Lee
authors.forename: Po Yan
authors.initials: PY
authors.lastname: Ho
authors.forename: Wing Nin
authors.initials: WN
authors.lastname: Lo
authors.forename: Chun Kwong
authors.initials: CK
authors.lastname: Lo
mesh_terms: D000818:Animals; D016118:Anterior Cruciate Ligament / Q000601:surgery*; D000070598:Anterior Cruciate Ligament Injuries; D015519:Bone Density; D001861:Bone Regeneration / Q000502:physiology*; D001862:Bone Resorption / Q000503:physiopathology*; D050376:Bone-Patellar Tendon-Bone Grafting / Q000009:adverse effects*; D005260:Female; D005269:Femur / Q000473:pathology; D011817:Rabbits; D013977:Tibia / Q000473:pathology*; D014057:Tomography, X-Ray Computed / Q000379:methods; D014945:Wound Healing / Q000502:physiology*