title: A model of soft-tissue graft anterior cruciate ligament reconstruction in sheep.
abstract: BACKGROUND
  Since there is to our knowledge no clinically valid and reproducible animal model of soft-tissue anterior cruciate ligament (ACL) reconstruction currently available, we developed one in sheep, in terms of graft suitability, postsurgical recovery, and knee stability.
  
  
  METHODS
  To find a suitable graft, anatomical dissections of the hind limbs of 7 sheep were performed. After a pilot study in 3 sheep, we reconstructed the ACL with an ipsilateral, longitudinally split, superficial digital flexor tendon autograft and anatomic graft fixation in 42 sheep (study 1) and with a full, superficial digital flexor tendon autograft and extracortical graft fixation in 48 sheep (study 2). Follow-up examinations ranged from 6 to 104 weeks (study 1) and 3 to 24 weeks (study 2).
  
  
  RESULTS
  All animals tolerated the graft harvest well and returned to physiological movement after about 4 weeks. Only 1 out of 93 ACL reconstructions failed. At final follow-up, the anteroposterior (AP) drawer displacement in both studies had almost regained the value of the intact contralateral knee. Maximum load-to-failure improved over time in both studies but was significantly lower at all time points compared with the intact ACL and the graft tissues. Tensile stress was significantly lower at final follow-up in both studies compared with the intact ACL and graft tissues. It attained 43.3% of the intact ACL and 58.3% of the graft tissue in study 1 and 28.9% and 22.8% in study 2, respectively.
  
  
  CONCLUSIONS
  The flexor tendon is suitable, and sheep appear to be an appropriate animal model for soft-tissue graft ACL reconstruction. They tolerate the graft harvest well and quickly return to full weight-bearing and physiological movement. Their knees become stable without showing signs of macroscopically evident osteoarthritis.
authors.affiliation: Sports Traumatology and Arthroscopy Service, Trauma & Reconstructive Surgery, Charité, Campus Virchow Clinic, Humboldt University, Berlin, Germany.
authors.forename: Patrick
authors.initials: P
authors.lastname: Hunt
authors.forename: Sven U
authors.initials: SU
authors.lastname: Scheffler
authors.forename: Frank N
authors.initials: FN
authors.lastname: Unterhauser
authors.forename: Andreas
authors.initials: A
authors.lastname: Weiler
mesh_terms: D000818:Animals; D016118:Anterior Cruciate Ligament / Q000503:physiopathology / Q000601:surgery*; D000070598:Anterior Cruciate Ligament Injuries; D001863:Bone Screws; D005260:Female; D005269:Femur / Q000601:surgery; D005500:Follow-Up Studies; D023421:Models, Animal; D010865:Pilot Projects; D020127:Recovery of Function / Q000502:physiology; D012756:Sheep; D013710:Tendons / Q000637:transplantation*; D013718:Tensile Strength / Q000502:physiology; D013977:Tibia / Q000601:surgery; D013997:Time Factors; D014182:Transplantation, Autologous; D016474:Weight-Bearing / Q000502:physiology