title: The preclinical sheep model of high tibial osteotomy relating basic science to the clinics: standards, techniques and pitfalls.
abstract: OBJECTIVE
  To develop a preclinical large animal model of high tibial osteotomy to study the effect of axial alignment on the lower extremity on specific issues of the knee joint, such as in articular cartilage repair, development of osteoarthritis and meniscal lesions. Preoperative planning, surgical procedure and postoperative care known from humans were adapted to develop a HTO model in the adult sheep.
  
  
  METHODS
  Thirty-five healthy, skeletally mature, female Merino sheep between 2 and 4 years of age underwent a HTO of their right tibia in a medial open-wedge technique inducing a normal (group 1) and an excessive valgus alignment (group 2) and a closed-wedge technique (group 3) inducing a varus alignment with the aim of elucidating the effect of limb alignment on cartilage repair in vivo. Animals were followed up for 6 months.
  
  
  RESULTS
  Solid bone healing and maintenance of correction are most likely if the following surgical principles are respected: (1) medial and longitudinal approach to the proximal tibia; (2) biplanar osteotomy to increase initial rotatory stability regardless of the direction of correction; (3) small, narrow but long implant with locking screws; (4) posterior plate placement to avoid slope changes; (5) use of bicortical screws to account for the brittle bone of the tibial head and to avoid tibial head displacement.
  
  
  CONCLUSIONS
  Although successful high tibial osteotomy in sheep is complex, the sheep may--because of its similarities with humans--serve as an elegant model to induce axial malalignment in a clinically relevant environment, and osteotomy healing under challenging mechanical conditions.
authors: Department of Orthopaedic Surgery, Centre Hospitalier de Luxembourg, 1460, Luxembourg, Luxembourg. dietrichpape@yahoo.de
authors: Dietrich
authors: D
authors: Pape
authors: Henning
authors: H
authors: Madry
mesh_terms: D000818:Animals; D001861:Bone Regeneration; D002358:Cartilage, Articular / Q000502:physiology; D005260:Female; D005500:Follow-Up Studies; D056304:Genu Valgum / Q000209:etiology; D056305:Genu Varum / Q000209:etiology; D023421:Models, Animal; D010027:Osteotomy / Q000295:instrumentation / Q000379:methods*; D034561:Sheep, Domestic / Q000502:physiology / Q000601:surgery*; D013264:Stifle / Q000502:physiology / Q000601:surgery*; D013977:Tibia / Q000502:physiology / Q000601:surgery*; D014945:Wound Healing