A preliminary musculoskeletal model of the German Shepherd lumbosacral spine : a thesis presented in partial fulfilment of the requirements for the degree of Master of Science in Animal Science at Massey University, Manawatū, New Zealand

Abstract

German shepherd dogs (GSD) are commonly utilised in police and military forces, where they undertake physically demanding working roles. These duties, combined with the typical GSD musculoskeletal conformation, consequently result in a high incidence of degenerative lumbo-sacral stenosis in this breed. This debilitating condition compromises the welfare of the animal and often results in premature loss from service. A preliminary mathematical musculoskeletal model was developed in the AnyBody Modelling System software platform from computed tomography imagery and muscle dissection. Positions of hard and soft tissue elements were recorded from the specimen to construct this patient-specific model. Inverse dynamics simulations were run with incremental alterations of two muscle input parameters: muscle fibre length and sarcomere length. The effect of these parameters was found to be extremely sensitive on the model output values, with minor input variations resulting in major output variations. Histology data was obtained from muscle excised in the dissection, and indicated variability in muscle sarcomere length up to 0.681 μm within the muscle and an average of 0.389 μm between GSD muscles. The sensitivity analysis indicated a 0.1 μm variation in sarcomere length exceeded the set threshold of ± 2.5 % from the measured sarcomere length output value of strength for the muscle sacrocaudalis dorsalis medialis. Muscle length sensitivity indicated a 1 mm input variation remained within the strength output threshold, while a 2 mm variation exceeded the threshold. This research resulted in the development of a preliminary and functional biomechanical model of the GSD lumbo-sacral spine capable of simulation studies. The results of the inverse dynamics sensitivity analysis identified the critical effect of variation of muscle fibre length and sarcomere length as muscle input parameters, and emphasised the requirement of precise muscle measurement, specific to each individual muscle.