Overview
This lecture reviews key anatomical differences between thoracic and lumbar vertebrae, their clinical implications, and common spinal pathologies such as spondylolysis, spondylolisthesis, and herniated intervertebral discs.
Thoracic Vertebrae Features
- Thoracic vertebrae have limited movement, mostly rotation, around an axis through vertebral body centers.
- Articular facets in upper and mid thoracic vertebrae are in the coronal plane to permit slight rotation.
- The T12 vertebra is unique: its superior articular facet is in the coronal plane (for T11), while its inferior facet is sagittal (for L1).
Lumbar Vertebrae Features
- Lumbar vertebrae (e.g., L1) have both superior and inferior articular facets in the sagittal plane, allowing flexion and extension.
- L5 vertebra articulates with S1; the space between articular processes is called the pars interarticularis.
Transitional Vertebra: T12
- T12 vertebra transitions between thoracic (coronal facets, rotation) and lumbar (sagittal facets, flexion/extension) types.
- T12 is subjected to maximal mechanical stress and strain.
Clinical Significance: Spondylolysis and Spondylolisthesis
- Spondylolysis is a fracture of the pars interarticularis, seen as a "Scottie dog" sign on oblique lumbar X-rays.
- Bilateral spondylolysis can cause spondylolisthesis, where the vertebral body (often L5) slips forward over S1.
Herniated Intervertebral Discs (Herniated Nucleus Pulposus)
- Disc herniation usually occurs in the lower lumbar or cervical regions after sudden spine flexion.
- The nucleus pulposus herniates posterolaterally as the annulus fibrosus ruptures, compressing the emerging spinal nerve.
- Compression of L5 nerve at L4-L5 disc causes dorsiflexion weakness; S1 involvement affects plantarflexion.
Key Terms & Definitions
- Articular facet â Joint surface on a vertebra for articulation with adjacent vertebrae.
- Coronal plane â Vertical plane that divides the body into anterior and posterior sections.
- Sagittal plane â Vertical plane that divides the body into left and right sections.
- Pars interarticularis â The segment of bone between the superior and inferior articular processes of a vertebra.
- Spondylolysis â Stress fracture of the pars interarticularis.
- Spondylolisthesis â Forward slipping of one vertebra over another, usually due to spondylolysis.
- Nucleus pulposus â Gel-like center of an intervertebral disc.
- Annulus fibrosus â Tough outer layer of an intervertebral disc.
Action Items / Next Steps
- Review anatomical features of vertebral articular facets and their planes.
- Study radiological signs (Scottie dog) for spondylolysis and spondylolisthesis.
- Understand clinical implications of disc herniation at different spinal levels.