Overview
The dog has seven lumbar vertebrae; the first (L1) is described on its own. From L2 to L7 the bodies are long and increase slightly in length up to about L6, while L7 is shorter. This segment carries the large epaxial and sublumbar muscles and transmits the thrust of the pelvic limbs to the trunk.
Key features
- Body: long and slightly flattened dorsoventrally.
- Transverse processes: long, flat plates directed cranioventrally and laterally, longest in the middle of the series. They give attachment to the sublumbar muscles and the thoracolumbar fascia.
- Spinous processes: shorter and broader than in the thoracic region, inclined cranially.
- Articular processes: the cranial processes carry a mammillary process (processus mamillaris); small accessory processes project caudally. The articular surfaces are curved and nearly sagittal, which limits rotation.
- Vertebral canal: the spinal cord ends around L6–L7 in most dogs; caudal to it the canal contains the cauda equina.
Clinical relevance
- Thoracolumbar disc disease (T11–L2 and the cranial lumbar discs) is the most common cause of acute paraparesis in chondrodystrophic dogs.
- Lumbosacral stenosis (L7–S1) compresses the cauda equina and causes lumbar pain and pelvic limb lameness, mainly in large working breeds.
- Spondylosis deformans: ventral osteophytes bridging the lumbar discs; common and often incidental in older dogs.
- Transitional lumbosacral vertebrae (L7 with sacral features) predispose to lumbosacral disease.
- Cerebrospinal fluid can be collected by lumbar puncture, usually at L5–L6.
In this model L2–L7 are reconstructed by deforming the scanned first lumbar vertebra; their outline and proportions are approximate.