Research in Engineering and Aviation

A Biomechanical Study of the Comparison of Proximal Screw Configurations in a Subtrochanteric Fracture Model

June 2010

Author(s): Grisell, M., Moed, B.R., and Bledsoe, G.

Journal: Journal of Orthopaedic Trauma, 24(6):359-363. DOI: 10.1097/BOT.0b013e3181c6b17f

Abstract

Objectives: Historically, because of the magnitude of muscle forces exerted locally, as well as the commonly associated comminution, subtrochanteric fractures have been difficult to treat. Tencer et al found intramedullary nail fixation to be superior to lateral plate constructs in axial compression and combined bending. In addition, reconstruction-type intramedullary nails of more recent design have been shown to provide strength and stiffness superior to that supplied by the earlier antegrade intramedullary implants. A relatively new reconstruction nail, the DePuy VersaNail Troch Entry Nail (DePuy Orthopaedics, Inc., Warsaw, IN, USA), is unique in that it allows for two different proximal two-screw configurations: (1) the common parallel cephalomedullary arrangement and (2) a novel crossed-screw pattern. Our hypothesis was that the crossed-screw configuration would be as strong in axial loading as the cephalomedullary screw configuration.

Methods: Twenty composite femurs were instrumented using the DePuy VersaNail Troch Entry Nail in a subtrochanteric fracture model: 10 with the crossed proximal screw configuration and 10 with the traditional parallel screw configuration. These constructs were first loaded axially to calculate their stiffness and then axially loaded to failure.

Results: One specimen was rendered unusable for all calculations. Therefore, 19 constructs were evaluated: 9 parallel screw constructs, 10 crossed-screw constructs. The crossed-screw construct had a significantly higher stiffness than the parallel screw construct (347 +/- 73 N/mm and 261 +/- 42 N/mm, respectively; P = 0.01) and a significantly higher axial load to failure (2848 +/- 391 N vs. 2300 +/- 444 N; P = 0.01).

Conclusions: This study shows that axial failure loads of the crossed-screw configuration were greater than those of the parallel screw configuration. Clinically, this provides the surgeon more options for stabilizing a subtrochanteric femur fracture. This decision may be made intra-operatively if necessary, facilitating fracture fixation and providing a stable construct.

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