BIOMECHANICS OF THE THORACIC SPINE . pptx

Biomechanics of thoracic spine

1. BIOMECHANICS OF THORACIC SPINE Presented by- Shakti Swarupa Bhanja Satarupa Nanda Final Year BPO

2. INTRODUCTION We need a better understanding of biomechanics of thoracic spine because- Better breathing mechanics Improved posture correction Aided diagnosis and treatment of spinal deformities Enchanced athletic performance and injury prevention

3. BONY ANATOMY 12 vertebrae Ventral curve Anterior bodies are load bearing Posterior arches resist tension Anterior – Posterior diameter increases T1-T12 Transverse width decreases from T1-T3 then increases to T3-T12 Anterior height of vertebral bodies 2-3mm less anteriorly vs.posteriorly

4. ANATOMY OF THORACIC SPINE Typical thoracic vertebral structure- BODY- The transverse and A-P diameters of the bodies are equal. The anterior height is less than the posterior height. Two demifacets for articulation with the ribs are located on the posterolateral corners of the vertebral plateaus. ARCHES- Pedicles- Variable in shape and orientation Laminae - Short, thick, and broad Superior zygapophyseal facets- Thin and flat; face posteriorly , superiorly, and laterally Inferior zygapophyseal facets- Face anteriorly , inferiorly, and medially Transverse processes- Large, with thickened ends. Possess paired oval facets for articulations with the ribs. Show a caudal decrease in length. Spinous processes- T1 to T10 slope inferiorly. T11 and T12 have a triangular shape. Vertebral foramen- Small and circular

5. Atypical thoracic vertebral structure- The 1 st and 12 th thoracic vertebrae are transitional vertebrae, possessing characteristics of the cervical and lumbar vertebrae, respectively. The 1 st thoracic vertebra has a typical cervical-shaped body with the transverse diameter of the body nearly twice the A-P diameter. The spinous process of T1 is particularly long and prominent. The 12 th thoracic vertebra has thoracic-like superior zygapophyseal articular facets that face posterolaterally . The inferior zygapophyseal facets, however, are more lumbar-like and have convex surfaces that face anterolaterally to articulate with the vertical, concave, posteromedially facing superior zygapophyseal facets of L1 vertebra. T1, T11 and T12 possess full costal facets instead of demifacets to articulate corresponding vertebral bodies.

6. INTERVERTEBRAL DISCS- Thoracic intervertebral discs are thinner than those in other regions, especially in the upper thoracic segments. The ratio of disc size to the vertebral body size is smallest in the thoracic region, resulting in less mobility and greater stability for this region. The endplates show a gradual increase in transverse and A-P diameters from T1 to T12. The thoracic region is less flexible and more stable than the cervical region because of the limitations imposed by structural elements such as rib cage, spinous processes, taut zygapophyseal joint capsules, the thicker ligamentum flavum , and the dimensions of the discs and the vertebral bodies.

7. LIGAMENTS(unique to thoracic spine)- Radiate ligament of head of rib- head of rib to the bodies of 2 vertebrae and intervertebral disc. Costotransverse ligament- neck of the rib to transverse process. Lateral costotransverse ligament- transverse process to tubercle of the rib. Superior costotransverse ligament- upper border of the neck of the rib to the transverse process of the vertebrae superior to it.

8. MUSCLES -

9. ARTICULATIONS- Each thoracic vertebra articulates with a set of paired ribs by way of two joints- Costovertebral joints Costotransverse joints INTERBODY JOINTS- It involves flat vertebral surfaces that allow for translations in each direction to occur. The discs allow for tilting of the vertebral bodies. ZYGAPOPHYSEAL JOINTS- These are plane synovial joints with fibro-adipose meniscoids present.

10. BIOMECHANICS KINETICS The thoracic region is subjected to increased compression forces in comparison with the cervical region because of the greater amount of body weight that needs to be supported and the region’s kyphotic shape.

11. The LOG falls anterior to the thoracic spine. This produces a flexion moment on the thoracic spine that is counteracted by the posterior ligaments and the spinal extensors. The greatest flexion moment is at the peak of the kyphotic curvature as a result of the increased moment arm of the LOG.

12. KINEMATICS Osteokinematics – The zygapophyseal joints lie approximately 20 degrees off the frontal plane from T1 to T6 and therefore allows greater ROM into lateral flexion and rotation and less ROM into flexion and extension. The facet joints in lower thoracic region(T9 to T12) are oriented more in sagittal plane and therefore permit somewhat more flexion and extension. The ROM in lateral flexion is coupled with some axial rotation, which decreases in the lower part of thoracic region due to its sagittal orientation. The direction of coupled rotation varies widely among individuals.

13. The ribs and costal joints restrict lateral flexion in the upper and middle thoracic segments, lateral flexion and rotation are relatively free because these segments are not limited by the ribs.

14. Arthrokinematics - Thoracic motion-

15. Rotation and gliding motions occur between the ribs and the vertebral bodies at the costovertebral joints.

16. BIOMECHANICS OF THORACO-LUMBAR REGION T11 and T12 have free floating ribs whoose costo -vertebral joints directly oppose the vertebral body The transverse processes of T11 and T12 do not articulate with their respective ribs. This transition between a rigid T-spine and a mobile L-spine provides a fulcrum for flexion-extension. T-spine kyphosis meets L-spine lordosis also includes additional load at the T-L junction as force is through the T spine to the T-L junction. Upto 75% of the thoracic and lumbar spinal fractures occur between T12-L2.

17. Holdsworth expressed the view that the rotational fracture dislocation occurs only at the thoracolumbar junction and in the lumbar spine and is the most unstable of all vertebral injuries; the cord and roots are in grave danger. He states that 95% of all paraplegias at the thoracolumbar level have this rotational fracture dislocation.

18. REFERENCES Joint Structure and Function, a comprehensive analysis (6 th edition)-Pamela K.Levangie , Cynthia C. Norkin , Michael D.Lewek Atlas of Orthoses and Assistive Devices(3 rd edition) Clinical Biomechanics of the Spine(2 nd edition)- Augustus A. White III, Manohar M. Panjabi

19. THANK YOU