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

Abstract

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.