Mechanical Study of the Safe Distance Between Distal
Femoral Fracture Site and Distal Locking Screws in
Antegrade Intramedullary Nailing
Shannon B. Antekeier, MD, Robert L. Burden, Jr., MEng, Michael J. Voor, PhD,
and Craig S. Roberts, MD
To determine the safe distance for distal femoral
fractures relative to the distal locking screws in antegrade intra-
medullary femoral nailing using a currently available titanium alloy
Cyclic (fatigue) mechanical testing study.
Intramedullary nailing of left synthetic Fberglass
composite femora with type 32/33-C fractures at 1, 2, 3, and 4 cm
from the more proximal of the distal locking screws.
Main Outcome Measurement:
The number of loading cycles to
failure of the nail.
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
Under laboratory conditions, it is safe to assume that
an antegrade titanium alloy nail will survive 1 million compres-
sion/bending cycles when the fracture is
3 cm from the more
proximal of the 2 distal locking screws.
intramedullary nailing, fatigue, femur, fracture, screw
hole, mechanical study
J Orthop Trauma
ntegrade intramedullary Fxation of distal femoral frac-
tures is limited by the proximity of the fracture site to the
more proximal of the 2 distal locking screws.
analysis of clinical failures and Fnite element analysis of early
slotted and locked stainless- steel nails, Bucholz et al
a 1987 article recommended a minimum distance of 5 cm to
prevent fatigue fracture of the nail. However, newer nail designs
are no longer slotted and are made from stronger materials,
such as titanium alloy,
thus increasing their fatigue strength.
Several studies indicate that fractures can be successfully
treated when the fracture is closer to the distal screws than the
previously recommended 5 cm.
We hypothesized that current
nail designs allow closer spacing between the fracture site and
the more proximal of the distal locking screws than the 5-cm
The Frst objective of this study was to reproduce the
conditions of the study by Bucholz et al
using the same
nail design (Howmedica, Mahwah, NJ) that
was reported on in their clinical series and used in their Fnite
element analysis to establish the 5-cm recommendation. The
second objective was to apply these conditions to currently
available titanium alloy nails (TriGen
, Smith & Nephew,
Memphis, TN) to evaluate the validity of the 5-cm recom-
mendation in modern nail designs.