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
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.