Biomechanical evaluation of the less invasive stabilization system, angled blade plate, and retrograde intramedullary nail for the internal fixation of distal femur fractures.
OBJECTIVE
To evaluate the stability of the retrograde intramedullary nail (IMN), angled blade plate (ABP), and a locked internal fixator (Less Invasive Stabilization System [LISS], Synthes, Paoli, PA) for internal fixation of distal femur fractures.


METHODS
Destructive biomechanical testing of matched pairs of fresh-frozen human cadaveric bone-implant constructs.


METHODS
Biomechanical laboratory.


METHODS
A fracture model was created to simulate an AO/OTA33-A3 fracture. Forty-eight matched pairs of specimens were used. Six groups of 8 pairs each were tested to failure: LISS versus ABP and LISS versus IMN (axial, torsional, and cyclical axial).


METHODS
Load to failure, mode of failure, energy to failure, displacement at the load to failure, and stiffness.


RESULTS
Fixation strength (load/moment to failure) of the LISS constructs was 34% greater in axial loading (P = 0.01) and 32% less in torsional loading (P = 0.05) compared with ABP constructs and 13% greater in axial loading (P = 0.35) and 45% less in torsional loading (P < 0.01) compared with IMN constructs. Loss of distal fixation in axial loading occurred in 1 of 16 cases with the LISS, in 3 of 8 cases with the ABP, and in 8 of 8 cases with the IMN. Cyclical axial loading demonstrated significantly less plastic deformation for the LISS construct compared with ABP constructs (P < 0.01) and similar plastic deformation compared with IMN constructs (P = 0.98).


CONCLUSIONS
All 3 fixation devices (LISS, ABP, and IMN) offer sufficient torsional stability and sufficient proximal fixation that withstands axial loading without failing. The LISS provides improved distal fixation, especially in osteoporotic bone, at the expense of more displacement at the fracture site.
Department of Orthopedic Surgery, University of Minnesota, Regions Hospital, St. Paul, MN, USA.
Michael
M
Zlowodzki
Scott
S
Williamson
Peter A
PA
Cole
Lyle D
LD
Zardiackas
Philip J
PJ
Kregor
D000368:Aged; D001696:Biomechanical Phenomena; D015519:Bone Density; D005264:Femoral Fractures / Q000601:surgery*; D005594:Fracture Fixation, Intramedullary / Q000295:instrumentation / Q000379:methods*; D006801:Humans; D019060:Minimally Invasive Surgical Procedures / Q000295:instrumentation / Q000379:methods; D008954:Models, Biological