Changes in knee kinematics after application of an articulated external fixator in normal and posterior cruciate ligament-deficient knees.

ABSTRACT

We studied how the location of an articulated external fixator, the EBI-Orthofix (EBI Corp, Persippany, NJ), affects the kinematics of the posterior cruciate ligament (PCL)-deficient knee. Ten unembalmed cadaver whole lower limbs were randomly divided into two groups of five limbs each (1) fixator hinge located near the average knee flexion axis (the anatomic position group); and (2) fixator hinge located distal to the joint line and posterior to the flexion axis (the fibular styloid position group). Three loading conditions, passive flexion/extension, flexion/extension with anterior force of 100 N, and flexion/extension with posterior force of 100 N were used for each knee with the PCL intact and with the PCL cut. With the fixator located in the anatomic position, and after cutting of the PCL, posterior translation was reduced to normal limits only at flexion angles < or = 15 degrees. In this configuration, the fixator was ineffective at minimizing posterior translation at flexion angles > or = 30 degrees. With the fixator located at the fibular styloid position, however, posterior translation of the tibia in the PCL deficient knees was reduced to near normal limits at all flexion angles. These results were statistically different than the anatomic position group at all flexion angles > or = 30 degrees (P < .01). The external fixator appears to allow normal range of motion while effectively shielding the PCL graft from stress caused by posterior translational forces. Issues related to the potential complications and patient acceptance must be addressed thoroughly before this technique is applied in clinical practice.