Arthrodesis of the ankle was performed on eight fresh-frozen human
specimens, and four external fixator configurations were applied: a
unilateral external fixator, a Calandruccio clamp alone, a Calandruccio
clamp with two anterior struts, and a Calandruccio clamp with four struts
(two anterior and two posterior). Each specimen was subjected to 4.0
newton-meters of internal-external tibial torque and 4.0 newton-meters of
plantar flexion-dorsiflexion bending moment. The unilateral frame permitted
the least tibiotalar motion during plantar flexion-dorsiflexion testing.
The Calandruccio clamp allowed more than twice the motion allowed by the
unilateral fixator in this testing mode, but the rigidity of the fixation
with the Calandruccio clamp was improved with the addition of two
interlocking struts, which connected fixator pins proximal and distal to
the site of the arthrodesis. The addition of two more struts, to make a
four-strut construct, resulted in a small (0.8-degree) additional decrease
in the mean tibiotalar motion. There were no detectable differences in the
mean tibiotalar motion due to torsional loading between the four fixation
configurations.