title: A comparative anatomical study of the human knee and six animal species.
abstract: OBJECTIVE
  Animal models are an indispensable tool for developing and testing new clinical applications regarding the treatment of acute injuries and chronic diseases of the knee joint. Therefore, the purpose of this study was to compare the anatomy of the intra-articular structures of the human knee to species commonly used in large animal research studies.
  
  
  METHODS
  Fresh frozen cow (n=4), sheep (n=3), goat (n=4), dog (n=4), pig (n=5), rabbit (n=5), and human (n=4) cadaveric knees were used. Passive range of motion and intra-articular structure sizes of the knees were measured, the structure sizes normalized to the tibial plateau, and compared among the species.
  
  
  RESULTS
  Statistically significant differences in the range of motion and intra-articular structure sizes were found among all the species. Only the human knee was able to attain full extension. After normalization, only the pig ACL was significantly longer than the human counterpart. The tibial insertion site of the ACL was split by the anterior lateral meniscus attachment in the cow, sheep, and pig knees. The sheep PCL had two distinct tibial insertion sites, while all the other knees had only one. Furthermore, only in human knees, both lateral meniscal attachments were located more centrally than the medial meniscal attachments.
  
  
  CONCLUSIONS
  Despite the relatively preserved dimensions of the cruciate ligaments, menisci, and intercondylar notch amongst human and animals, structural differences in the cruciate ligament attachment sites and morphology of the menisci between humans and animals are important to consider when selecting an animal model.
authors.affiliation: Department of Orthopaedic Surgery, Children's Hospital of Boston, Harvard Medical School, 300 Longwood Ave, Boston, MA 02115, USA. Benedikt.Proffen@childrens.harvard.edu
authors.forename: Benedikt L
authors.initials: BL
authors.lastname: Proffen
authors.forename: Megan
authors.initials: M
authors.lastname: McElfresh
authors.forename: Braden C
authors.initials: BC
authors.lastname: Fleming
authors.forename: Martha M
authors.initials: MM
authors.lastname: Murray
mesh_terms: D000818:Animals; D002417:Cattle; D004285:Dogs; D005260:Female; D006041:Goats; D006614:Hindlimb / Q000033:anatomy & histology*; D006801:Humans; D007719:Knee Joint / Q000033:anatomy & histology* / Q000502:physiology; D008023:Ligaments, Articular / Q000033:anatomy & histology; D008297:Male; D008592:Menisci, Tibial / Q000033:anatomy & histology; D023421:Models, Animal; D011817:Rabbits; D016059:Range of Motion, Articular; D012756:Sheep; D013045:Species Specificity; D013552:Swine