INTERNAL LOAD ESTIMATION FOR CLINICAL PROGNOSIS

Abstract

Introduction: In therapy and rehabilitation it is important to know the ranges of the expected loads in the human body resulting from different movements. Because of the difficulty of measuring experimental dynamic loads (hip loads, Bergmann, Taylor), the loads created under these dynamic conditions are estimated by theoretical models and computer simulation. The method will be presented considering a squat jump. Methods: A squat jump performed with both legs, maximum strength and without counter-movement was modeled by a two-dimensional multi-body system with four segments. The movement-generating muscles were implemented taking into account the muscle insertions and paths, as well as Hill’s force-velocity-relation. The data were extracted from MR images and the literature. The muscles were excited by Hatze’s stimulation model. To obtain maximal jump height, the muscles were excited coordinately by optimization algorithms. Results: In the case of a vertical jump, the loads reached maximum values of 4250 N, 4750 N and 4800 N in hip, knee and ankle joints, respectively. The mean values of the hip, knee and ankle joint loads were 3100 N, 3650 N and 2600 N, respectively. Comparing the calculated values with those of Bassey et al. (1997), who measured the hip load during a fast jump, a good agreement of the load values was found. Conclusion: With this vertical jump it was proved that an estimation of joint loads is possible. A multitude of movements can be examined with this model in order to compile data for a joint load database which can be used for clinical prognosis. References: Bassey, E.J., Littlewood, J.J., Taylor, S.J.G. (1997). Relations Between Compressive Axial Forces in an Instrumented Massive Femoral Implant, Ground Reaction Forces, and Integrated Electromyographs From Vastus Lateralis During Various Ostogenic Exercies. J. Biomechanics 30, 213-223. Bergmann, G., Graichen, F., Rohlmann, A. (1993). Hip Joint Loading During Walking and Running, Measured in Two Patients. J. Biomechanics 26, 969-990.