Document Type


Publication Date



Background. The reasons behind the development of future pathology in individuals with anterior cruciate ligament deficiency are unknown. This is due to the lack of appropriate methods to assess functional dynamic knee stability. In this study, we investigated the effect of walking speed on the functional dynamic stability of the anterior cruciate ligament deficient knee. We defined functional dynamic stability as local stability or the sensitivity of the knee to small perturbations. The natural stride-to-stride variations that exist during locomotion reflect exactly the presence of these perturbations. We hypothesized that speed will affect local stability in the deficient knee, especially when compared with the contralateral intact.

Methods. Ten subjects with unilateral deficiency walked on a treadmill at their self-selected speed, 20% faster, and 20% slower, while kinematic data were collected (50 Hz) for 100 consecutive footfalls for each condition. The largest Lyapunov Exponent of the resulted knee joint flexion–extension time series was calculated to quantify local stability.

Findings. The deficient knee was significantly more locally unstable than the contralateral knee. Furthermore, increases in walking speed did not affect local stability for our subject population.

Interpretations. The altered local stability may render the deficient knee less adaptable to the ever-changing environmental demands. This may explain the increased future pathology found in these knees. However, future efforts should attempt to evaluate this speculation using longitudinal studies. We also propose that the tools utilized in this study can be used eventually to assess functional dynamic knee stability in clinical gait analysis.


NOTICE: this is the author’s version of a work that was accepted for publication in Clinical Biomechanics. Changes resulting from the publishing process, such as peer review, editing, corrections, structural formatting, and other quality control mechanisms may not be reflected in this document. Changes may have been made to this work since it was submitted for publication. A definitive version was subsequently published in Clinical Biomechanics, Vol. 19, Issue 9 (November 2004) DOI: 10.1016/j.clinbiomech.2004.06.008.

Journal Title

Clinical Biomechanics





First Page


Last Page


Included in

Biomechanics Commons