Can a force driven harmonic oscillator model be clinically applied to ACL reconstructed patients?

The purpose of this study was to determine whether anterior cruciate ligament (ACL) reconstructed patients select a preferred stride period during walking that was consistent with the resonant period of their legs modeled as force driven harmonic oscillators (FDHO). Thirty-four ACL reconstructed patients, 6 weeks after surgery, performed treadmill walking at a self-selected speed. The FDHO model with different gravitational factors of n=1.5, 2 and 2.5 was used to determine the best-fit prediction of the patients preferred stride period. In addition, the elastic component of the model was empirically derived to determine its relationship with the models prediction accuracy. A gravitational factor of 1.5 applied to the resonance formula was found to be the best prediction of the patient's preferred stride period. The elastic component demonstrated a negative, linear relationship with the model's prediction error of the preferred stride period with a gravitational factor of 2. The results were interpreted to indicate that an adaptation in the elastic component represented a reduction in the global stiffness of the leg caused by a net reduction in active muscle tension. The FDHO model may have the clinical potential for determining the baseline and recovery status of ACL reconstructed patients.