Abstract
Introduction and Aims: Clinical studies report successful treatment of hangman’s fractures by direct screw repair followed by a collar post-operatively. However, to date there has not been a biomechanical analysis of failure strength of direct lag screw fixation of hangman’s fracture, relative to the strength of the intact specimens.
Method: This repeated measures biomechanical study evaluates the tensile force required to cause bipedicular (hangman’s) fractures in isolated porcine C2 specimens, and the subsequent force to failure after direct fracture repair with bipedicular lag screws. Of 60 mounted porcine C2 specimens subjected to tensile antero-posterior force, hangman’s fracture occurred in 15 cases, 12 of which were fixed with bipedicular 4.0 mm lag screws. These fixed specimens were re-tested to failure in the same manner.
Results: Most specimens had laminar fractures after application of tensile force, with 15 of 60 (25.0%) exhibiting bipedicular fractures. The force to bipedicular failure was 3259.1 + 148.5 N (mean + SEM). After screw fixation, the force to failure of the same specimens was 882.0 + 108.5 N (mean + SEM), or 27.3% of the intact bone.
Conclusion: The pullout strength was substantial (882 N), although the relative strength of fixation was only 27.3% of the fracture strength exhibited by the intact specimens. We discuss the findings in relation to previous studies. This is the first study to examine screw pull-out forces after direct repair of hangman’s fracture. One or more of the authors are receiving or have received material benefits or support from a commercial source.
These abstracts were prepared by Editorial Secretary, George Sikorski. Correspondence should be addressed to Australian Orthopaedic Association, Ground Floor, The William Bland Centre, 229 Macquarie Street, Sydney, NSW 2000, Australia.
