Mechanical study of the safe distance between distal femoral fracture site and distal locking screws in antegrade intramedullary nailing.
OBJECTIVE
To determine the safe distance for distal femoral fractures relative to the distal locking screws in antegrade intramedullary femoral nailing using a currently available titanium alloy nail design.


METHODS
Cyclic (fatigue) mechanical testing study.


METHODS
Biomechanics laboratory.


METHODS
Intramedullary nailing of left synthetic fiberglass composite femora with type 32/33-C fractures at 1, 2, 3, and 4 cm from the more proximal of the distal locking screws.


METHODS
The number of loading cycles to failure of the nail.


RESULTS
A load level of 700 N through the femoral mechanical axis was validated as adequate to cause fatigue failure within 200,000 cycles in slotted stainless- steel nails. In the nonslotted titanium alloy nails, this load level caused failure in only 1 of 3 nails with a fracture at 2 cm from the more proximal of the 2 distal locking screws and in 2 of 3 nails with a fracture at 1 cm from the more proximal of the 2 distal locking screws. All of the other nails did not fail >1 million cycles.


CONCLUSIONS
Under laboratory conditions, it is safe to assume that an antegrade titanium alloy nail will survive 1 million compression/bending cycles when the fracture is > or = 3 cm from the more proximal of the 2 distal locking screws.
Antekeier
Shannon B
SB
Orthopaedic Bioengineering Laboratory, Department of Orthopaedic Surgery, University of Louisville, Louisville, KY 40202, USA.
Burden
Robert L
RL
Voor
Michael J
MJ
Roberts
Craig S
CS
D001696:Biomechanical Phenomena / Q000379:methods; D001858:Bone Nails; D001863:Bone Screws; D019245:Compressive Strength; D004548:Elasticity; D004867:Equipment Design; D019544:Equipment Failure Analysis; D005264:Femoral Fractures / Q000503:physiopathology* / Q000601:surgery*; D005593:Fracture Fixation, Internal / Q000295:instrumentation* / Q000379:methods*; D006801:Humans; D011475:Prosthesis Failure; D019919:Prosthesis Implantation / Q000379:methods*; D013718:Tensile Strength; D016896:Treatment Outcome