A biomechanical model of horses back and neck based on kinematic, kinetic and EMG data

Research project P 13915 A model of the horse`s back movement Christrian PEHAM 11.10.1999 Riding horses are subject to a considerable load on the back, which leads to an increasing incidence of back disorders. Even with the use of diagnostic measures, such as radiology, scintigraphy, sonography, and hematological analysis, the precise diagnosis of back pain remains challenging and in many cases pathogenesis cannot be established. Additionally, the differentiation between primary back pain, and secondary back pain, e.g. originating in pain from a limb or an organ, is difficult. The aim of this study is to establish a biomechanical model of the equine back and neck, based on kinematic and surface electromyographic data of 15 horses without back pain. The additional influence of the rider will be assessed with a saddle pad measuring pressure distribution, and this influence will be integrated in the model. The resulting model will allow the simulation of normal back movements and restrictions thereof. Model development will start with representation of the back and neck as a simple elastic beam. Then temporary and localized changes of elasitcity will be introduced. The model will be tested against in vivo measurements of back movements of horses, and the error will be assessed. The model will then be repeatedly optimized and tested until a satisfactory simulation for the assessment of normal and pathological back movements results. From the model developed in this study, localisation of regions of increased/decreased back motion, and possible relation to external load or internal forces can be deduced. Pathological changes of the motion pattern can be assigned to regions and structures of diagnostic interest. The model will be used for enhancing the general understanding of the biomechanics of the equine back both in clinical routine and teaching.

Back pain and other diseases of the equine spine represents a significant problems in equestrian sport and veterinary medicine. Frequently they can be diagnosed only in a negative way, by excluding all other alternatives. One of the reasons lies in the inaccessibility of the equine back for suitable biomechanical studies. Existing procedures are either painful or necessitate anesthesia or are done only on isolated body parts from dead horses. Mathematical modeling however, a renowned and common medium by now to study biomechanical systems, offers an elegant way out of this dilemma. The aim of this project was to develop a biomechanical model of the equine back. In order to do derive a measure of the flexibility of the back, an essential requisite for modeling, the three-dimensional motion of the back and the activity of the long back muscle had to be studied and recorded. Out of the acquired data we designed a computer model of the back using newly derived advanced mathematical methods, in order to explore the mechanical behavior during motion with utmost realism and accuracy. The first model inspired by the concept of flexible beams was later transformed to a segmented setup, which was built closer to anatomical reality. With this model the biomechanical behavior can now be studied in dynamical simulations with realistic forces and realistic motion patterns in a totally non-invasive way. In the course of our studies we also investigated the effect of the weight of a rider as well as the influence of various saddle types. For this, we could successfully establish a very fertile cooperation not only with a private business partner (a renowned Austrian saddlery) but also with members of the Austrian Spanish Riding School. Highlights in their medical significance were the derivation and determination of a quantification of the stiffness of the back in its natural motion, the identification of locations with peak concentrations of internal stress at modified flexibility or when ridden. Worthy of note specifically for sports science, also was the surprising result that despite its asymmetrical structure when fitted properly a side saddle brings about a more uniform pressure distribution during a motion cycle than a common type saddle. The equestrian sportsman might also note that as result of this project from now on examination of saddle fits not only at stance but also in motion is offered as a regular service.