Spinal Neuronavigation for Lumbar Plate Fixation in Miniature Breed Dogs.

OBJECTIVE: The main aim of this pilot study was to assess the feasibility of spinal neuronavigation for plate fixation of lumbar vertebrae in miniature breed dogs using a surgical navigation system in combination with a custom-made reference array. STUDY DESIGN: This was an experimental cadaveric study in five miniature breed dogs. METHODS: A 4-hole locking plate with four 2.0-mm locking screws was placed on two adjacent lumbar vertebrae using a neuronavigation system consisting of a mobile cone beam computed tomography linked to a navigation system. The procedure was performed by a novice surgeon. The plate and screw positions were assessed for surgical safety using predefined criteria. Surgical accuracy was determined by the deviation of entry and exit points between pre- and postoperative images. RESULTS: A total of five plates and 20 screws were placed. In 85% (17/20), screws were placed appropriately. The median entry point deviation was 1.8 mm (range: 0.3-3.7) and the median exit point deviation was 1.6 mm (range: 0.6-5). CONCLUSION: Achievement of surgical accuracy in the placement of screws for fixation of lumbar vertebral plates in small breed dogs using neuronavigation with a custom-made reference array by a novice surgeon resulted in surgical safe plate placement in four of the five cadavers. Therefore, we judge the method as promising, however, further studies are necessary to allow the transfer of image-guided navigation for lumbar plate fixation into the clinic.

Determination of cutoff values on computed tomography and magnetic resonance images for the diagnosis of atlantoaxial instability in small-breed dogs.

OBJECTIVE: To determine cutoff values for the diagnosis of atlantoaxial instability (AAI) based on cross-sectional imaging in small-breed dogs. STUDY DESIGN: Retrospective multicenter study. SAMPLE POPULATION: Client-owned dogs (n = 123) and 28 cadavers. METHODS: Dogs were assigned to three groups: a control group, a "potentially unstable" group, and an AAI-affected group, according to imaging findings and clinical signs. The ventral compression index (VCI), cranial translation ratio (CTR), C1-C2 overlap, C1-C2 angle, atlantoaxial distance, basion-dens interval, dens-to-axis length ratio (DALR), power ratio, and clivus canal angles were measured on CT or T2-weighted magnetic resonance (MR) images. Receiver operating characteristic (ROC) analysis was performed to define cutoff values in flexed (≥25°) and extended (<25°) head positions. RESULTS: Cutoff values for the VCI of ≥0.16 in extended and ≥0.2 in flexed head positions were diagnostic for AAI (sensitivity of 100% and 100%, specificity of 94.54% and 96.67%, respectively). Cutoff values for the other measurements were defined with a lower sensitivity (75%-96%) and specificity (70%-97%). A combination of the measurements did not increase the sensitivity and specificity compared with the VCI as single measurement. CONCLUSION: Cutoff values for several imaging measurements were established with good sensitivity and specificity. The VCI, defined as the ratio between the ventral and dorsal atlantodental interval, had the highest sensitivity and specificity in both head positions. CLINICAL SIGNIFICANCE: The use of defined cutoff values allows an objective diagnosis of AAI in small-breed dogs. The decision for surgical intervention, however, should remain based on a combination of clinical and imaging findings.

Influence of the Head Neck Position on Imaging Measurements Used to Assess the Craniovertebral Junction in Small Breed Dogs: A Cadaveric Study.

OBJECTIVE: The study aimed to determine the influence of head neck position on imaging measurements used to assess the craniovertebral junction (CVJ) and to recommend the most appropriate position for the evaluation of the CVJ. STUDY DESIGN: A cross-sectional sample of adult dogs' cadavers was subjected to a computed tomography scan of the cranium and the cranial cervical region in three standardized head positions. Imaging measurements often used to assess the CVJ were measured. The influence of the head neck position, breed, weight and gender on imaging measurements was tested using repeated measures analysis of variance. RESULTS: Twenty-eight cadavers of small breed dogs were enrolled in the study. All cadavers examined had occipital dysplasia. All transarticular imaging measurements were dependent on the head neck position. In addition, the breed, weight and gender had an influence on several measurements. CONCLUSION: We recommend a standardized head neck position of 50 degrees flexion if quantitative imaging measurements of the CVJ are used to diagnose pathologies in this region. Future studies should focus on the definition of cut-off values for quantitative imaging measurements of the CVJ to differentiate between healthy and diseased small breed dogs. Regarding atlantoaxial instability, a combination of six parameters (C1-C2 angle, C1-C2 overlap, atlantoaxial distance, dens-to-axis length ratio, ventral compression index and clivus canal angle) is promising for its diagnosis.

Morphometric and functional study of the canine atlantoaxial joint.

The atlantoaxial joint can be affected by instability, in most cases a congenital pathology in young small breed dogs. Causes of atlantoaxial instability (AAI) are variable but are usually attributed to a lack of ligamentous support. The purpose of the present study was to specify the role of the ligamentous structures in the stabilisation of the atlantoaxial joint and to find possible adaptations of the ligaments' internal structure to their specific function. Five Beagle cadavers were included in this study. Each dog was subjected to a computed tomography (CT) and a magnetic resonance imaging (MRI) examination of the upper cervical region. This region was then dissected and the ligamentous structures stabilising the atlantoaxial joint were measured and removed for histological analysis. A ligament to dens ratio (LDR) was established in order to provide a basis for comparison with the measurements taken in other dog breeds. MRI and gross anatomical measurements were very similar, confirming the validity of the results. MRI thus seems reliable for evaluating the ligamentous structures of the canine occipitoatlantoaxial region. The movement exerting the greatest stress on the atlantoaxial ligaments and inducing the greatest distension of the alar ligaments was a head flexion combined with a rotation. A clear adaptation of the ligamentous shape and internal structure to their specific function was observed. Histologically, alar ligaments consisted of wavy collagen fibres and a high proportion of elastic fibres, providing them with a remarkable elasticity compared to the transverse ligament structure which was much more rigid.