Ex vivo comparison of one versus two distal screws in 8 mm model 11 interlocking nails used to stabilize canine distal femoral fractures

Michael R. Reems, G. Elizabeth Pluhar, Donna L. Wheeler

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18 Scopus citations


Objective - To compare the structural properties of an 8 mm model 11 interlocking nail (IN) with 2 proximal and 2 distal screws (2/2) to 2 proximal and 1 distal screws (2/1) in an unstable canine fracture model. Study Design - Ex vivo biomechanical investigation. Sample Population - Eight pairs of adult canine femurs. Methods - A simple transverse distal metaphyseal femoral fracture with a 1 cm gap was created. The unstable fracture in 1 femur was repaired with a nail with 2 distal and 2 proximal screws and the paired femur with a nail with 1 distal and 2 proximal screws. Cyclic mechanical testing in torsion was performed to assess fatigue life, peak torque, stiffness, and mode of failure. Results - All 2/1 IN-femoral constructs, but only 2 of eight 2/2 constructs, failed before completion of 50,000 loading cycles. The 2/2 constructs had significantly greater peak torque to failure (P=.002) and longer fatigue life (P=.00003) compared with 2/1 constructs. There were no significant differences in stiffness between 2/2 and 2/1 constructs when the non-failed constructs were compared (P>.5). All constructs failed by screw deformation. Conclusions - An 8 mm model 11 IN used for fixation of unstable canine distal femoral fractures has a longer fatigue life and is stronger under torsional loads when 2 rather than 1 distal screws are placed. Clinical Relevance - When repairing unstable canine distal femoral fractures with an IN system, 2 distal screws should be inserted to avoid catastrophic implant failure before bone healing is achieved.

Original languageEnglish (US)
Pages (from-to)161-167
Number of pages7
JournalVeterinary Surgery
Issue number2
StatePublished - Feb 2006

Bibliographical note

Funding Information:
This research was supported in part by the Iowa-Veterans' Affairs Nursing Research Consortium (IVANRC).T he opinions expressed in this paper are the authors' and do not necessarily represent the opinion or policies of the Department of Veterans' Affairs or any agencyo f the U.S. government.


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