Effect of hind limb position on the craniocaudal length of the lumbosacral space in anesthetized dogs.

OBJECTIVE To investigate whether rostral extension of the hind limbs increases the cranio-caudal dorsal interlaminar distance between the seventh lumbar vertebra and the sacral bone (LS distance) in sternally recumbent anesthetized dogs. STUDY DESIGN Prospective clinical study. ANIMALS Eighteen dogs (eight neutered males, three intact males, six spayed females, one intact female) of various breeds, weighing 4-34 kg and ranging in age from 1 to 13 years. METHODS Each dog was grouped by size: small (≤ 10 kg), medium (15-20 kg) or large (≥ 25 kg). Each dog was anesthetized and positioned in sternal recumbency. Computed tomography (CT) of the lumbosacral area was performed with the hind limbs resting on the stifle and the feet extended posteriorly, and then with the hind limbs extended rostrally. LS distance, craniocaudal dorsal interlaminar distance between sixth and seventh lumbar vertebra (L6-L7 distance), length of L7 vertebral body and lumbosacral angle (LS angle) were measured on a reconstructed mid-sagittal CT image from the two hind limb positions. The measurements from the two hind limb positions for the whole dog population and by size were compared using Student's T tests. Diagnostic interpretation of the CT images was performed. RESULTS The length of L7 was taken as the reference value as it was not affected by hind limb position. LS distance, L6-L7 distance and LS angle were significantly higher when the hind limbs were extended rostrally in all three size groups. The CT images of ten dogs showed clinically undetected osteoarthrosis of the ileo- and lumbosacral area. CONCLUSIONS AND CLINICAL RELEVANCE Rostral extension of the hind limbs significantly increases LS and L6-L7 distance and LS angle even in dogs with clinically undetected osteoarthrosis of the ileo- and lumbosacral area, and may enhance the ease of lumbosacral epidural injection in sternally recumbent anesthetized dogs.