Mukherjee M, Jones J, Childs K.
Introduction/Purpose: Spinal disease is one of the major causes of disability and early retirement in working dogs. Lumbosacral stenosis (LSS) is a common spinal disease in these dogs and is defined as an abnormal narrowing of the spinal canal in the lower back region. Labrador retrievers are one of the most commonly used working breeds and are predisposed to LSS for reasons that are not completely understood. Previous studies in humans disagree on the quantitative phenotypic characteristics of lumbar spinal stenosis. There are no published studies on quantitative characteristics of LSS in dogs. The purpose of this retrospective study was to describe the range of numerical measures that can be expected in the lumbar spinal canal of this breed.
Methods: Computed tomography (CT) archives at the Holland Military Working Dog Hospital and the Virginia Tech Veterinary Teaching Hospital were searched for CT scans of Labrador retrievers that included the lumbosacral spine. Scans with evidence of previous surgery, neoplasia, fractures or infection were excluded. The remaining scans were transferred to image analysis workstations (Apple Inc. Cupertino, CAl for analysis using CT image analysis freeware (OsiriX DICOM Viewer, Version 4.2). A single observer made measurements unaware of clinical findings. Quantitative variables recorded for each dog were spinal canal area, canal fat area, canal density and vertebral body area. Each variable was measured in triplicate and at each of 5 vertebral locations (caudal L5, cranial L6, caudal L6, cranial L7 and caudal L7). All area measurements were in crrr’ and densities in Hounsfield units (HU). Means for triplicate measures and canal/vertebral body area ratios were calculated for each dog and each location. Quantitative variable means and ranges for all dogs were graphed and described.
Results: A total of 23 dogs met inclusion criteria. Across all 5 locations in all dogs, mean canal areas ranged from 0.56 to 1.74; mean canal/vertebral body area ratios ranged from 0.21 to 0.79; mean canal fat areas ranged from 0.00 to 1.12; and mean canal densities ranged from -48.67 to 157.02. Spinal canal, canal fat, and vertebral body area measurements had higher intra-reader repeatability than canal density measurements.
Discussion/Conclusion: Findings indicated that quantitative CT phenotypic characteristics of the lumbar spinal canal vary widely within the Labrador retriever breed. Follow-up studies are in progress to describe qualitative phenotypic characteristics of the lumbar spinal canal for this breed.