Influence of the Valgus Force During Knee Flexion in Neutral Rotation

Purpose: The pivot shift test is generally accepted to be a clinically useful tool. In the current study, the authors aimed to determine the minimum amount of valgus force required to elicit a positive pivot shift test utilizing a mechanized pivot shifter device in ACL-deficient knees. The authors proposed that increasing the applied force from a minimum critical value would lead to greater magnitudes of femoro-tibial translation.

Materials And Methods: Six fresh-frozen pelvis-to-toes specimens were used in this cadaveric study. Tracking and recording of tibiofemoral kinematics during throughout testing was achieved by an image-free surgical navigation system with dedicated ACL software. A load cell was attached to the mechanized pivot shifter through a three-degree-of-freedom arm. Valgus force magnitudes of 0-5 kg were then sequentially applied, and knee flexion in neutral rotation was performed on the ACL-deficient knees. A total of two trials were performed for each force.

Results: The greatest difference in lateral and medial compartment translation, during the pivot shift test, utilizing a mechanized pivot shifter in an ACL-deficient knee, was measured between an applied valgus force of 0 and 1 kg. The mean difference between 4 and 5 kg was 0.2 mm (CI = -11.29 to 10.89) for the lateral compartment, and there was no difference in translation for the medial compartment (CI = -17.43 to 17.43).

Conclusions: The principal finding of the current study was that a greater force does not produce a greater magnitude of femoro-tibial translation during knee flexion in neutral rotation, contrary to the initial hypothesis.