Lumbosacral abnormalities are often associated with equine back pain and lameness. While transrectal ultrasound can image soft tissues of the thoracolumbar region and some of the sacroiliac region, the lumbosacral area is difficult to assess due to limited accessibility.
Researchers in Italy evaluated the lumbosacral junction on post-mortem exam of 51 horses that died or were euthanized for reasons unrelated to back pain.
Study Population
The authors looked for acquired pathological bony changes (APBCs) in the lumbosacral and sacroiliac regions using morphology, ultrasound, and CT scans of 42 cadaver specimens. Horses in the study were at least 4 years of age, with most middle-aged around 16 years. The authors noted their data lacked information about the presence or absence of back pain or hind-limb lameness in the living horses.
Study Findings
In their findings, APBC severity correlated with horse age. The predominant lumbosacral intervertebral disc (LS-ID) morphologies were Type 1 (normal) and Type 2, which show diffuse loss of echogenicity or dorsal thinning.
There was no correlation between the lumbosacral intervertebral disc and orientation of the L6 spinous process (SP). The researchers identified abnormal type 4-hyperechogenic material within the LS-ID due to fibrosis or mineralization associated with degenerative, age-related changes. Transrectal ultrasound attempts in living horses are likely thwarted because of the risk of rectal laceration with a linear rectal probe. Therefore, changes in LS-ID echogenicity are likely underdiagnosed.
At L6-S1, ultrasonographic abnormalities are more often identified in older horses, likely due to degenerative changes. Not all horses with an abnormality in this area demonstrate back pain. It is difficult to assess vertebral bone surfaces with an ultrasound probe in the living horse despite these bones being flatter than other lumbar vertebrae.
Ventral protrusion of the LS-ID was less than 5 millimeters in all but one horse. Previous studies indicate that LS-ID spacing of less than 5 millimeters is associated with clinical signs of LS and SI pain in some horses and no clinical signs in others. With severe LS-ID degeneration, the authors reported that ventral protrusion of the LS-ID is associated with a thin intervertebral disc and dorsal narrowing.
Abnormal echogenicity of L5-L6 was associated with type 5 LS-ID morphology, which is complete intervertebral synostosis with enthesophytes. These horses had a thicker intervertebral disc. The abnormal echogenicity of L5-L6 and LS-ID was found in conjunction with LS joint angulation or odd orientation of L6 spinal processes. The authors suggested this places abnormal stress on LS intervertebral joints. Further, the size of the L5-L6 ID and sacral promontorium indicates disc morphology is related to conformational variations rather than acquired pathology. The abnormal size of these vertebrae has the potential to induce pathological and functional changes in the LS region, said the researchers.
The research team identified lumbosacral spondylosis at L6-S1 in 24 of 42 specimens, mostly in older horses. This spondylosis was more frequent in the lumbosacral region than in the lumbar region. The lumbosacral intervertebral joint produces maximum flexion and extension along the spine.
Take-Home Message
In this study, the presence of acquired pathological bony changes of L6 and S1 correlated with age. Lumbosacral joint angulation and spondylosis correlated with irregularities of L6 and L6 spinous process as well as abnormal echogenicity of the lumbosacral intervertebral disc, localization of the sacral promontorium, and size variability of the L5-L6 intervertebral disc.
Reference
Scilimati N, Beccati F, Pepe M, et al. Post-mortem ultrasonographic and computed tomographic features of the anatomical variations and acquitted pathological bony changes of the Lumbosacroliiac region in a mixed population of horses. Equine Veterinary Journal Nov 2023; DOI: 10.1111/evj.14033
Related Reading
- Pelvic Bone Stress and Fatigue Fractures in Endurance Horses
- Horse Back Pain Rehabilitation
- Managing Lumbosacroiliac Joint Region Pain in Horses
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