title: In vitro biomechanical testing of a micro external skeletal fixator.
abstract: OBJECTIVE
  To biomechanically test the properties of three different Universal Micro External Fixator (UMEX™) configurations with regard to their use in very small animals (<5kg) and compare the UMEX system to the widely used IMEX External Skeletal Fixation (SK™) system in terms of stiffness, space needed for pin placement and weight.
  
  
  METHODS
  Three different UMEX configurations (type Ia, type Ib, and type II modified) and one SK configuration type Ia were used to stabilize Delrin plastic rods in a 1 cm fracture gap model. These constructs were tested in axial compression, craniocaudal bending, mediolateral bending, and torsion. Testing was conducted within the elastic range and mean stiffness in each mode was determined from the slope of the linear portion of the load-deformation curve. A Kruskal Wallis one-way analysis of variance on ranks test was utilized to assess differences between constructs (p <0.05).
  
  
  RESULTS
  The UMEX type II modified configuration was significantly stiffer than the other UMEX configurations and the SK type Ia, except in craniocaudal bending, where the SK type Ia configuration was stiffer than all UMEX constructs. The UMEX type Ia configuration was significantly the weakest of those frames. The UMEX constructs were lighter and smaller than the SK, thus facilitating closer pin placement.
  
  
  CONCLUSIONS
  Results supported previous reports concerning the superiority of more complex constructs regarding stiffness. The UMEX system appears to be a valid alternative for the treatment of long-bone fractures in very small animals.
authors.affiliation: Dr. med. vet. Ramona Deiss, Bahnhofstrasse 56, 3127 Mühlethurnen, Switzerland, Phone: +41 79 786 86 32, E-mail: ramona.deiss@me.com.
authors.forename: R
authors.initials: R
authors.lastname: Deiss
authors.forename: M S
authors.initials: MS
authors.lastname: Bali
authors.forename: M
authors.initials: M
authors.lastname: Doherr
authors.forename: D
authors.initials: D
authors.lastname: Spreng
authors.forename: U
authors.initials: U
authors.lastname: Rytz
authors.forename: S J
authors.initials: SJ
authors.lastname: Ferguson
mesh_terms: D000818:Animals; D001696:Biomechanical Phenomena; D049628:Body Size; D004868:Equipment Failure; D016267:External Fixators / Q000662:veterinary*; D008422:Materials Testing / Q000662:veterinary*
keywords: External skeletal fixation; cats; close pin placement; frame configuration; miniature dogs