title: Effect of Intramedullary Rod Diameter on a String of Pearls Plate-Rod Construct in Mediolateral Bending: An In Vitro Mechanical Study.
abstract: OBJECTIVE
  To evaluate the effect of intramedullary rod (IMR) diameter on the mechanical behavior of string of pearls (SOP) plate-rod constructs.
  
  
  METHODS
  In vitro mechanical study.
  
  
  METHODS
  Synthetic bone models (n = 24).
  
  
  METHODS
  Locking 3.5 mm SOP plates were fixed to a tibial bone model with a 50 mm fracture gap. Four experimental groups (n = 4) were tested: monocortical SOP construct alone and monocortical SOP constructs augmented with a 2.4, 3.2, or 4.0 mm IMR corresponding to 24, 32, or 40% filling of the medullary cavity diameter (SOP-24, SOP-32, SOP-40). Control groups (n = 4) were stabilized with either a bicortical SOP plate (SOP-B) or a 3.5 mm limited contact dynamic compression plate (LC-DCP) with a 4.0 mm IMR filling 40% of the medullary cavity diameter (LC-DCP-40). Specimens were tested in mediolateral bending. Construct compliance (CC) and angular deformation (AD) were compared between construct types (P < .05).
  
  
  RESULTS
  CC and AD incrementally decreased with increasing IMR diameter (P < .001). There were no statistical differences between SOP-24 and SOP-B (P = .806) or between SOP-32 and LC-DCP-40 (P = .773), which was also the least compliant of all constructs (P < .001). AD followed an identical pattern of significance.
  
  
  CONCLUSIONS
  Biological osteosynthesis often relies on more compliant bridging constructs to promote beneficial micromotion at the fracture. Our study suggests use of a smaller diameter IMR (SOP-32) is comparable to a conventional plate-rod construct (LC-DCP-40). Should greater compliance be desired, an even smaller diameter IMR (SOP-24) may prove beneficial while as stable as an accepted bicortical construct (SOP-B).
authors.affiliation: Croft Veterinary Hospital, Cramlington, Northumberland, United Kingdom.
authors.forename: Scott
authors.initials: S
authors.lastname: Rutherford
authors.affiliation: Collaborative Orthopaedic Investigations Laboratory, Department of Small Animal Clinical Sciences.
authors.forename: Ryan M
authors.initials: RM
authors.lastname: Demianiuk
authors.affiliation: Collaborative Orthopaedic Investigations Laboratory, Department of Small Animal Clinical Sciences.
authors.forename: Jérôme
authors.initials: J
authors.lastname: Benamou
authors.affiliation: The Orthopaedic Biomechanics Laboratories, College of Osteopathic Medicine, Michigan State University, East Lansing, Michigan.
authors.forename: Clifford
authors.initials: C
authors.lastname: Beckett
authors.affiliation: Croft Veterinary Hospital, Cramlington, Northumberland, United Kingdom.
authors.forename: Malcolm G
authors.initials: MG
authors.lastname: Ness
authors.affiliation: Collaborative Orthopaedic Investigations Laboratory, Department of Small Animal Clinical Sciences.
authors.forename: Loïc M
authors.initials: LM
authors.lastname: Déjardin
mesh_terms: D000818:Animals; D001696:Biomechanical Phenomena; D001858:Bone Nails / Q000662:veterinary*; D001860:Bone Plates / Q000662:veterinary*; D005593:Fracture Fixation, Internal / Q000295:instrumentation*; D050723:Fractures, Bone / Q000601:surgery*; D066298:In Vitro Techniques; D008953:Models, Anatomic; D013977:Tibia / Q000473:pathology