OTA 2006 Posters

Scientific Poster #76 Basic Science

· Comparison of a Three-Screw Proximally Configured Femoral Intramedullary Nail with a Reconstruction Nail in a Subtrochanteric Fracture Model
Brian Fissel, MD (a-Depuy); Berton R. Moed, MD (a-Depuy); J. Gary Bledsoe, PhD (a-Depuy);
Saint Louis University School of Medicine, St. Louis, Missouri, USA

Purpose: Many options exist in the treatment of subtrochanteric femur fractures, including intramedullary (IM) nailing. A trochanteric reconstruction nail is often the implant of choice, but there can be difficulty placing two parallel screws in a narrow femoral neck. The purpose of this study was to biomechanically evaluate a piriformis fossa entry IM nail having two new transverse proximal screw configurations compared to a trochanteric reconstruction nail in an unstable subtrochanteric femur fracture model.

Methods: Synthetic composite femurs were mounted on a Material Testing System and loaded in compression to obtain baseline values. The femurs were then instrumented with one of three IM nail proximal screw configurations: (1) a 3-screw configured piriformis fossa entry nail with two transverse screws and a screw angled into the femoral neck, (2) a similar nail with two screws, having a single transverse screw and a single screw angled into the femoral neck, or (3) a trochanteric entry nail with the standard two parallel screws angled into the femoral neck. An unstable fracture was created and these constructs were tested in compression as before. Each construct was then tested to ultimate load to failure in compression.

Results: The stiffness in the unstable subtrochanteric femur fracture model for the 3-screw construct was 214 N/mm, the 2-screw construct 123 N/mm, and the reconstruction nail construct 127 N/mm. The 3-screw construct was significantly stiffer in compression than either the 2-screw construct or the trochanteric reconstruction nail (P = 0.013 and 0.012 respectively). Load to failure was similar for all three screw/nail configurations with the 3-screw construct failing at a mean of 2230 N, the 2-screw construct failing at a mean of 2283 N, and the reconstruction nail failing at a mean of 2121 N (P = 1.0)

Conclusions/Significance: The proximal 3-screw configuration provided greater stiffness and similar load to failure compared to the 2-screw configuration and trochanteric reconstruction nail. The piriformis entry transverse proximal screw constructs offer added flexibility and options for screw placement in subtrochanteric femur fractures. These alternatives may prove very helpful for situations in which the insertion of two parallel screws into the femoral neck would prove difficult or impossible.

If noted, the author indicates something of value received. The codes are identified as a-research or institutional support; b-miscellaneous funding; c-royalties; d-stock options; e-consultant or employee; n-no conflicts disclosed, and *disclosure not available at time of printing.
· The FDA has not cleared this drug and/or medical device for the use described in this presentation (i.e., the drug or medical device is being discussed for an "off label" use). · · FDA information not available at time of printing.