Reply re: Vertically Oriented Femoral Neck Fractures

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Excerpt

In response:
We appreciate the letter that was written in response to our article “Vertically oriented femoral neck fractures: a biomechanical comparison of 3 fixation constructs.” In reviewing the paper referred to in the letter “The effect of moment arm length on high angled femoral neck fractures (Pauwels' JII)” by Matthew S. Lepine, BS; William R. Barfield, PhD; John Desjardins, PhD; and Langdon A. Hartsock, MD published in the Journal of Biomedical Science and Engineering (JBiSE), Volume 3, 448–453, 2010, we did note several key similarities, crucial differences, and important findings. In the work by Lepine et al, the authors elegantly investigated the biomechanical stability of 5 fixation constructs for the treatment of femoral neck fractures with 3 different lever arms (subcapital, transcervical, and basicervical). They were only able to find statistically significant differences in their basicervical group, showing that in this group, an inverted triangle–cannulated screw construct was inferior to all 4 fixed angle constructs (DHS with and without derotational screws and DCS with and DHHS with and without derotational screws).
Our study looks specifically at high-angle Pauwels' III transcervical femoral neck fractures, and interestingly we were able to find significant differences with regards to cycles to failure, axial stiffness, and load to failure between our CHS and cannulated screw groups. Our ability to detect these differences may have been because of the use of fourth generation sawbones, which have been shown to closer approximate the structural characteristics of proximal femoral bone. In addition, we were able to use a larger number of samples per group (especially during cycles to failure) than were used by Lepine et al, which may have allowed us to better detect differences between groups. Also, we looked at cycles to failure, allowing another data point to show differences between these groups, and a different loading structure that may have been able to detect more subtle differences.
Also, in our study we compared both CHS and inverted triangle groups to a different screw formation, the “CS” or cross screw group. This group did not show any difference with the inverted triangle group, and was inferior to the CHS group as well. It is interesting to note that in both studies, the CHS and inverted triangle–cannulated screw groups had very similar loads to failure, validating the methods of both studies. In addition, both studies arrived at the same recommendations for the use of fixed angle constructs whenever possible in the treatment of high-angle femoral neck fractures in young populations. Given the statistically similar findings between cannulated screw groups in our study, we could not recommend either the inverted triangle or cross screw group over the other.
We commend the authors of “The effect of moment arm length on high angled femoral neck fractures (Pauwels' III)” for their outstanding work and hope that both studies validate the biomechanical superiority of fixed angle constructs for fixation of these fractures. We believe that both papers provide important contributions to the body of work regarding the optimal management of a very challenging injury.

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