Second generation intramedullary nailing of subtrochanteric femur fractures: a biomechanical study of fracture site motion.
OBJECTIVE
To compare fracture site motion between different second-generation intramedullary nails used to fix subtrochanteric fractures of the proximal femur with and without femoral neck fractures.


METHODS
Nondestructive mechanical testing of four types of femoral intramedullary nails was undertaken to evaluate fracture site motion using a model that simulated single-leg and double-leg stance.


METHODS
Three types of reconstruction nails (the Russell-Taylor Delta [Smith & Nephew, Memphis, TN], the Uniflex [Biomet, Warsaw, IN], Alta CFX [Howmedica-Osteonics, Rutherford, NJ]) and the Long Gamma nail (Howmedica-Osteonics, Rutherford, NJ), each measuring 11 x 380 mm, were inserted in fiberglass composite femurs. Four fracture patterns were studied (transverse subtrochanteric, subtrochanteric with posteromedial wedge comminution, subtrochanteric with one-centimeter gap, and a one-centimeter gap with a subcapital neck fracture). Single-and double-leg stance loading was simulated using a servohydraulic load frame (MTS, Eden Prairie, MN). Two-way analysis of variance and post hoc t tests were used to determine any statistically significant differences between groups.


RESULTS
In single-leg stance there were significant differences in coronal plane rotation, shear, and axial translation across the subtrochanteric fracture site between the different nail types and the different fracture patterns (p < 0.001). In double-leg stance there were significant differences in coronal plane rotation and femoral head vertical motion between the different nail types and the different fracture patterns (p < 0.001), and there were significant differences in shear and axial translation between the different fracture patterns (p < 0.001) but not the different nail types (p > 0.05).


CONCLUSIONS
For simple, well-reduced fractures the choice of implant is not critical. As fracture severity increased (comminution, gap, and combined neck fracture), the choice of implant, particularly with reference to proximal nail dimensions and implant materials, was a significant factor in reducing fracture site motion. Therefore, our laboratory data suggest that when subtrochanteric fractures are unstable (e.g., comminution, segmental bone loss) and early weight bearing is desirable, the choice of implant is critical and should be restricted to implants that allow minimal fracture site motion (Long Gamma and Russell-Taylor).
Roberts
Craig S
CS
Department of Orthopaedic Surgery, University of Louisville, Louisville, Kentucky 40292, USA.
Nawab
Akbar
A
Wang
Mei
M
Voor
Michael J
MJ
Seligson
David
D
D001696:Biomechanical Phenomena; D001858:Bone Nails; D005264:Femoral Fractures / Q000503:physiopathology* / Q000601:surgery*; D005265:Femoral Neck Fractures / Q000503:physiopathology* / Q000601:surgery*; D005594:Fracture Fixation, Intramedullary; D006620:Hip Fractures / Q000503:physiopathology* / Q000601:surgery*; D006801:Humans; D008954:Models, Biological; D011187:Posture / Q000502:physiology; D016059:Range of Motion, Articular / Q000502:physiology*; D012399:Rotation; D013314:Stress, Mechanical; D014102:Torsion Abnormality / Q000503:physiopathology