title: 2D motion analysis of rabbits after Achilles tendon rupture repair and histological analysis of extracted tendons: can the number of animals be reduced by operating both hind legs simultaneously?
abstract: BACKGROUND
  Considering the 3Rs principle in animal experiments, there is a demand to perform research experiments with the fewest number of animals possible while warranting the welfare of the animals. Orthopaedic experimental studies involving operations on the hind legs of rabbits are either performed on one hind leg with the second hind leg serving as control or on both hind legs simultaneously (control: rabbits with no operations at all).
  
  
  METHODS
  The Achilles tendon of rabbits was transected and sutured, and the two-dimensional motion pattern of animals having only one leg operated was compared to rabbits having both hind legs operated (control: non-treated animals). Step length, maximum ankle angle, minimum ankle angle and the resulting range of motion of both hind legs were determined weekly over a time span from 3 weeks to 12 weeks post-operation. The results were fitted by a linear mixed effects model including time dependency. Moreover, all tendon specimen were analysed histologically. Tenocyte and tenoblast density, tenocyte and tenoblast nuclei width, inflammation level and collagen fibre alignment were determined.
  
  
  RESULTS
  Statistically significant differences in the motion pattern were found when one-leg treated and two-leg treated animals were compared. However, the absolute differences were on average less than 20%. Histologically, 1-leg treated animals had tendon tissue with higher cell density, but lower inflammation and less ondulated collagen fibres compared to 2-leg treated animals; the nuclei width was the same for both groups. With regard to welfare, all animals were fine during the experiments.
  
  
  CONCLUSIONS
  While comparative studies should be performed with one-leg treated animals due to interaction effects, for proof-of-principle studies, operating two legs per animal may be justified as the welfare of the animals is warranted. This is a great benefit in the sense of the 3Rs because up to 50% of animals can be spared.
authors.affiliation: Division of Plastic and Reconstructive Surgery, University Hospital Zurich, Sternwartstrasse 14, 8091 Zurich, Switzerland. johanna.buschmann@usz.ch
authors.forename: Johanna
authors.initials: J
authors.lastname: Buschmann
authors.forename: Angela
authors.initials: A
authors.lastname: Müller
authors.forename: Flora
authors.initials: F
authors.lastname: Nicholls
authors.forename: Rita
authors.initials: R
authors.lastname: Achermann
authors.forename: Gabriella Meier
authors.initials: GM
authors.lastname: Bürgisser
authors.forename: Walter
authors.initials: W
authors.lastname: Baumgartner
authors.forename: Maurizio
authors.initials: M
authors.lastname: Calcagni
authors.forename: Pietro
authors.initials: P
authors.lastname: Giovanoli
mesh_terms: D000125:Achilles Tendon / Q000293:injuries* / Q000473:pathology / Q000601:surgery*; D032761:Animal Experimentation / Q000941:ethics*; D000818:Animals; D000843:Ankle Joint / Q000502:physiology; D005260:Female; D011817:Rabbits; D016059:Range of Motion, Articular; D012421:Rupture / Q000473:pathology / Q000534:rehabilitation; D013708:Tendon Injuries / Q000473:pathology / Q000601:surgery*; D014945:Wound Healing / Q000502:physiology
keywords: 3Rs; Achilles tendon rupture; Motion analysis; Rabbit; Study design