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A study of debilitating orthopaedic conditions of working New Zealand Police German shepherd dogs : a thesis presented in partial fulfilment of the requirements for a doctorate degree of Veterinary Science at Massey University, Manawatu, New Zealand
This thesis explored the causes of retirement or loss from service of German shepherd
Police dogs working in New Zealand. Abnormal development of the hip joint with
subsequent development of osteoarthritis (hip dysplasia), and degeneration of the
lumbosacral junction, were identified as the leading causes of early retirement of Police
dogs due to an inability to meet the physical requirements of Police work.
Hip dysplasia is a multifactorial disease with moderate heritability and improvements in
the phenotypic selection of dogs for breeding should improve subsequent longevity in
future generations of Police dogs. Selection of dogs for breeding based on traditional
phenotypic scoring, using radiographs of the hips in extension, was shown to be
producing minimal improvement in hip status. When compared with distraction
radiography, correlation between the two methods was low and they were not
equivalent in terms of ranking dogs for susceptibility to hip dysplasia.
In the second part of the thesis, degeneration of the lumbosacral joint was reviewed
and the role of surgical management of this condition was examined. A new method of
computed tomographic volumetric analysis of the L7-S1 lateral intervertebral
neurovascular foramen was described, which can be performed on anaesthetised
dogs. This method was then tested on German shepherds, both normal and affected
by lumbosacral degeneration. The dogs were imaged in extended, neutral and flexed
positions of the lumbosacral junction. Extension results in marked narrowing of the L7-
S1 foramina. Dogs affected by degenerative disease of the lumbosacral junction had
smaller foraminal volumes than unaffected dogs, indicating that dynamic narrowing
likely contributes to clinical signs. An ex-vivo experiment demonstrated that surgical
resection of the dorsal annulus and partial L7-S1 discectomy (as commonly performed
during dorsal decompressive surgery) may lead to further narrowing of the lateral
intervertebral lumbosacral neurovascular canal. A prospective evaluation of a recently
developed surgical procedure, dorsolateral foraminotomy, confirmed effective
enlargement of the L7-S1 foraminal volume, but showed that by one year there was
bone regrowth partially attenuating the effect. Finally, a novel method of dorsal
stabilisation, which maintained the foraminal volume by fixation of the lumbosacral
junction in a favourable position, was developed through a series of pilot studies,
providing the basis for further development.