Orthopaedic Biomechanics & Sports Rehabilitation 2006

EVALUATION OF SINGLE AND MULTI JOINT MODELS OF THE ANKLE USING HYBRID EMG-DRIVEN APPROACHES

Daniel N. Bassett, Qi Shao, Daniel L. Benoit, Kurt T. Manal, and Thomas S. Buchanan

Center for Biomedical Engineering Research
University of Delaware, Newark, DE, USA
E-mail: bassett@me.udel.edu Web: http://www.cber.udel.edu/

INTRODUCTION

The evaluation of individual muscle forces is important in the study of ankle injuries or pathological gait. EMG-driven models can be very powerful tools in this regard, though they must be understood to be properly applied. In this study we compared the performance of a single-joint model of the ankle with a multi-joint model of the ankle and knee combined. Estimations of gastrocnemii muscle forces were hypothesized to be different when accounting for their contributions at the knee.

METHODS

Data were collected during the stance phase of healthy gait. EMG data were collected from the semitendinosus, biceps femoris, rectus femoris, vastus lateralis, vastus medialis about the knee (Lloyd & Besier, 2002), the tibialis anterior and soleus about the ankle, and the gastrocnemii as biarticular muscles that span both the ankle and knee. Kinematic data were used to obtain joint angles for the hip, knee, and ankle and subsequently muscle-tendon lengths and muscle moment arms using SIMM. Inverse dynamic joint moments were calculated for the knee and ankle from the kinematic data and ground reaction forces.

Our EMG-driven model is built on a forward dynamic approach using a Hill-type model (Buchanan et al., 2005). The equation relating components of our Hill-type model was integrated to calculate fiber length and tendon length ultimately giving muscle forces and joint moments (Buchanan et al., 2004).

Due to the difficulty of in vivo measurement of subject specific muscle parameters, such as tendon slack length, we used a hybrid model to tune these parameters (Goffe et al., 1994) using the inverse dynamic joint moments as the standard. The tuned models were then used to predict ankle joint moments for other walking trials.

RESULTS AND DISCUSSION

Figure 1: Ankle Joint Moment Comparison

As shown in Figure 1, the model’s ability to estimate joint moments was consistent between single and multiple joint calibrations. More importantly, however, deviations in muscle force predictions were observed in the multi-joint model. The inclusion of the knee resulted in a 15-20% increase in gastrocnemii forces (Figure 2).


Figure 2: Muscle force change between single and multi joint models throughout stance phase.

In this preliminary study, the changes in muscle forces during the latter portion of the stance phase are most likely due to the gastrocnemii being important contributors to knee flexion. The multi-joint model, which accounted for knee moments, predicted higher forces in these muscles than the single joint ankle model. Therefore, when studying ankle injuries the motion in question should be considered. Synergistic kinetic activity of the ankle and knee may need to be modeled by including both joints.

REFERENCES

Buchanan, T.S., Lloyd, D.G., Manal, K.T., Besier, T.F. (2004). J. App. Biomech, 20, 367-395.
Buchanan, T.S., Lloyd, D.G., Manal, K.T., Besier, T.F. (2005). Med Sci Sports Exerc., 1911-1916.
Goffe, W.L., Ferrier, G.D., Rogers, J. (1994). J. Econom., 60, 65-99.
Lloyd, D.G., Besier, T.F. (2002). J. Biomech., 36, 765-776.

ACKNOWLEDGEMENTS

NIH R01-HD38582 and P20-RR16458