Veterinary Clinical Sciences - Theses

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    Influence of retractor type and position on thoracoscopic-assisted pulmonary surgery in dogs
    Chambers, Brenton Andrew ( 2018)
    Thoracotomy is performed frequently in dogs for the purposes of exploration of the thorax, lung lobectomy, correction of vascular ring anomalies and patent ductus arteriosus, pericardiectomy, thoracic duct ligation, biopsy and resection of mediastinal and pleural masses and removal of foreign bodies from within the pleural space, intrathoracic oesophagus and the lower respiratory tract. Persistent post-thoracotomy pain is reported frequently by human patients characterised by discomfort and altered sensation in the skin adjacent to the surgical site. Multiple surgical techniques have been developed in an attempt to reduce the morbidity of these procedures. Minimally invasive surgical techniques have been a significant step towards this goal. A significant limitation of minimally invasive surgery is the loss of tactile feedback and video-assisted techniques which utilise smaller incision, permitting the introduction of the surgeon’s hand or fingers to the thorax have been developed to overcome these limitations. These techniques have recently been introduced for veterinary patients (Chambers and others 2012, Gower and Mayhew 2011a, Laksito and others 2010b, 2011, Wormser and others 2014). Both traditional and video or thoracoscopic-assisted techniques require the use of tissue retractors, typically placed in an intercostal position. Access is afforded by the forceful retraction of soft tissues such as the intercostal muscles and ribs. Studies in both animals and humans have demonstrated detrimental soft tissue changes associated with such retraction including direct and ischaemic damage to the soft tissues adjacent to the retraction device. The present study examines several aspects of thoracoscopic-assisted pulmonary surgery in dogs including the effect on blood flow in the intercostal musculature and nerve conduction in the intercostal nerves associated with two different retraction modalities. Additionally, the influence of assisted port location and thoracic conformation on access to and delivery of pulmonary tissues for the purposes of complete or partial lung lobectomy was assessed. Force, contact area and pressure were compared and related to intramuscular pressure, perfusion, oxygen indices, nerve conduction and histologic change in dogs undergoing simultaneous controlled thoracotomy incisions. The novel retractor resulted in lower pressure and improved oxygenation in adjacent tissues compared to mechanical retraction which may translate clinically into reduced post-operative morbidity. For all lobes except the accessory lung lobe, the exposure provided by the reported thoracoscopic-assisted approach was considered adequate for complete or partial lung lobectomy. The cranial and caudal portions of the left cranial lung lobe and the right middle lung lobe were best exposed with the assisted portal in the middle dorso-ventral third of the thoracic wall at the fourth intercostal space of the ipsilateral side in both breeds. The right cranial lung lobe was best exposed with the assisted portal positioned in the middle third of the fourth intercostal space in kelpies but the sixth intercostal space in greyhounds. The right caudal lung lobe was best exposed when the assisted portal was positioned in the ventral third of the fourth intercostal space in the kelpie but in the middle third of the sixth intercostal space in the greyhound. The described thoracoscopic-assisted technique is a practical method for exposure of the lobes of the lung, other than the accessory lobe, for partial lung lobectomy in the dog. The portals described also allow the introduction of a linear stapler for the purpose of complete lung lobectomy.
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    Metal endoprostheses for limb salvage surgery in dogs with distal radial osteosarcoma: evaluation of first and second generation metal endoprostheses and investigation of a novel endoprosthesis
    Mitchell, Katherine Elizabeth ( 2017)
    Osteosarcoma (OSA) is the most commonly diagnosed primary bone tumour in dogs, usually affecting middle-aged, large breed dogs. The standard of care surgical treatment for local tumour control in dogs with osteosarcoma is limb amputation; however limb-sparing surgery is gaining wider acceptance as an alternative surgical treatment. All limb sparing techniques show high complication rates, including infection, construct failure or fracture and local recurrence. Metal endoprosthesis (EN) limb-sparing surgery was developed to overcome limitations of other techniques, including access to specialised equipment and facilities such as radiation therapy or bone bank facilities. The first generation of metal EN (GEN1) was shown to be biomechanically superior, but not clinically different to the cortical allograft. A second generation metal EN (GEN2) was developed but biomechanical studies and clinical outcomes have not been reported other than in single case reports. The first component of this thesis is a multi-institutional retrospective case series that evaluated surgical and oncologic outcomes for dogs treated with GEN1 or GEN2 for OSA of the distal radius. Records from 45 dogs with distal radial OSA were examined; 28 dogs received GEN1 and 17 dogs received GEN2. One or multiple complications occurred in 43 dogs (96%, 14 minor, 29 major) including 35 with infection (78%), 16 with implant-related complication (36%) and 11 with local recurrence (24%). This study showed no significant difference in case (surgical or oncologic) outcomes between dogs receiving GEN1 and GEN2 endoprosthesis for limb-sparing surgery of the distal radius. The frequency of complications, including infection and those implant-related, remains unacceptably high for both generations of endoprosthesis. Further refinement of the endoprosthesis or re-evaluation of the surgical technique for implantation of the endoprosthesis is indicated. A finite element (FE) model of the canine forelimb has been designed by a multi-disciplinary team from Colorado State University. Evaluation of GEN2 in the FE model predicted stresses in the proximal radius that exceeded the fatigue limit and yield stress of 316L stainless steel; the predicted stresses of GEN2 are too high for sustained performance. An engineering specific approach was taken to design a novel EN and evaluation in the FE model resulted in 50% reduction in peak stresses in the radial screws compared to GEN2 in the FE model. The second component of this thesis is evaluation of the suitability of the novel EN for clinical use. The novel EN prototypes were manufactured using three-dimensional printing (3DP) in plastic and stainless steel. Three size variations of the novel EN were designed using a computer-aided design (CAD) program and implanted into large breed cadaver radii. There was a large variation in radius morphology between and within large breeds; making the novel EN unlikely to be suitable as an off the shelf implant. The most appropriate application of the novel EN would be via rapid prototyping based on an individual’s computed tomography scan. This thesis highlights the difficulties associated with limb sparing surgery in veterinary surgery. The currently available procedures provide an alternative for pet-owners that are averse to amputation. However, pet-owners must be aware of the high complication frequencies associated with the techniques. Once refined; the novel EN has potential to decrease implant-related complication rates, however the infection rates are likely to remain high.