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Abstract
In the treatment of either acute severe open tibial fractures or their sequelae, a
convenient external fixator is desirable. The conventional transosseous fixation with
pins entering the medullary cavity is associated with problems such as pin loosening
and pin track infection. Due to the bacterial contamination of the medullary space
via the pin track the change of treatment from primary external fixation to secondary
medullary nailing is an infection risk. In order to minimize these problems an external
clamp fixator, the Pinless, was created. Medullary penetration is avoided by substitution
of the conventional pins with clamps. The latter are inserted by hand (removable handles)
and anchored only in the bone cortex. The medullary cavity stays intact. But is this
clamp fixation stable enough for clinical use?
Material and Methods: On paired human cadaver tibiae, we compared the mechanical properties of the experimental
Pinless, the conventional AO-tubular fixator and the Ultra-X fixator. Clamps differing
in size (small/large) and material (steel/titanium) were used and compared to Schanz
screws (steel, 5.0 mm diameter).
We measured the stiffness of comparable configurations (1 or 2 bars) under axial compression,
four-point-bending in two planes, and torsion. The pull-out force of the different
clamps in relation to the bone diameter and number of rocking movements during insertion
was also determined.
Results: The Pinless configurations with small clamps and 1 bar showed stiffness values as
follows (as a percentage of the corresponding AO-tubular fixator): ![Math Eq]()
% (steel/titanium clamp) axial stiffness, ![Math Eq]()
% bending stiffness perpendicular to the reference plane, ![Math Eq]()
% bending stiffness parallel to the reference plane, and ![Math Eq]()
% torsional stiffness. The corresponding Ultra-X device was not as stiff as the Pinless.
The use of two longitudinal rods increased the relative stiffness only under axial
compression. The mean pull-out force on the proximal tibia was 1011 N for the small
steel clamp, 717 N for the large steel clamp, 681 N for the small and 777 N for the
large titanium clamp. At the lowest tibial diameter the values were reduced by 10
to 43 %. The rocking movements doubled the pull-out force, e.g. there was a pull-out
force for the large clamp of 600 N with five rocking movements compared to 310 N without.
% (steel/titanium clamp) axial stiffness, 
% bending stiffness perpendicular to the reference plane, 
% bending stiffness parallel to the reference plane, and 
% torsional stiffness. The corresponding Ultra-X device was not as stiff as the Pinless.
The use of two longitudinal rods increased the relative stiffness only under axial
compression. The mean pull-out force on the proximal tibia was 1011 N for the small
steel clamp, 717 N for the large steel clamp, 681 N for the small and 777 N for the
large titanium clamp. At the lowest tibial diameter the values were reduced by 10
to 43 %. The rocking movements doubled the pull-out force, e.g. there was a pull-out
force for the large clamp of 600 N with five rocking movements compared to 310 N without.Discussion: The Pinless was not as stiff as the conventional AO-tubular device but suffer than
the clinically used Ultra-X, especially in sagittal bending, the main load on a tibial
fracture in the first weeks after trauma. A certain number of rocking movements improve
the anchorage of the clamps in the cortex tremendously. In clinical trials the Finless
appeared to be mechanically sufficient for temporary tibial fracture stabilisation
in patients not bearing weight and for support of the lower leg during management
of soft tissue traumata (burn injury, compartment syndrome, soft tissue reconstruction).
Furthermore, the clamp proved ideal as a traction device.
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© 1992 Published by Elsevier Inc.
