Vertebral column

Biomechanics of vertebral joints

1. Vertebral Column Dr. Chandan Verma (PT ) ( BPT,MPT,YICC,PhD pursuing) Assistant pofessor (Mahatma Gandhi Physiotherapy College, Jaipur )

2. INTRODUCTION GENERAL STRUCTURE The vertebral column resembles a curved rod, composed of 33 vertebrae and 23 intervertebral discs. The vertebral column is divided into the following five regions Twenty-four of the vertebrae in adults : C-7, T-12, L-5 & Five of the remaining nine vertebrae are fused to form the sacrum, and the remaining four constitute the coccygeal vertebrae.

3. Spinal curve primary curves :- the original posterior convexity throughout life are called primary curves The two curves (thoracic and sacral) that retain The secondary or lordotic curves develop as a result of the accommodation of the skeleton to the upright posture. the two curves (cervical and lumbar) that show a reversal of the original posterior convexity are called secondary curves primary curves secondary curves

4. A Typical Vertebra The anterior portion of a vertebra is called the vertebral body. The posterior portion of a vertebra is called the vertebral or neural arch. The neural arch is further divided into the pedicles and the posterior elements

5. Components of a Typical Vertebra

6. Vertebral bone trabecular systems Vertebral bone trabecular systems that develop in response to the stresses placed on the vertebral bodies and the neural arch are found within the spongy bone . The vertical systems within the vertebral bodies help support the body’s weight and resist compression forces There are also fan-shaped trabeculae introduced into the vertebral body at the area of the pedicle in response to bending and shearing forces transmitted through this region.

7. The Intervertebral Disc The intervertebral discs are composed of three parts: (1) the nucleus pulposus -(gelatinous mass found in the center) (2) the anulus fibrosus - (fibrous outer ring) (3) the vertebral end plate -(cartilaginous layer covering covering the superior and inferior surfaces of the disc, separating it from the cancellous bone of the vertebral bodies above and below) composed of water, collagen, and proteoglycans

8. Compression of an intervertebral disc Compression of an intervertebral disc A. In this schematic representation of a disc, the nucleus pulposus is shown as a round ball in the middle of the anulus fibrosus . B. Under compressive loading, pressure is exerted in all directions as the nucleus pulposus attempts to expand. Tension in the anulus fibrosus rises as a result of the nuclear pressure. C. A force equal in magnitude but opposite in direction is exerted by the anulus fibrosus on the nucleus pulposus , which restrains radial expansion of the nucleus pulposus and establishes equilibrium. The nuclear pressure is transmitted by the anulus fibrosus to the end plates.

9. Articulations Two main types of articulations Interbody or cartilaginous joints- interbetween vertebral body and disc Diarthrodial or synovial:- joints between the zygapophyseal facets located on the superior articular processes of one vertebra and the zygapophyseal facets on the inferior articular processes of an adjacent vertebra above Interbody and zygapophyseal joints.

10. Interbody Joints motion Translations and rotations of one vertebra in relation to an adjacent vertebra. A. Side-to-side translation (gliding) occurs in the frontal plane. B. Superior and inferior translation (axial distraction and compression ) occur vertically. C. Anteroposterior translation occurs in the sagittal plane. D. Side-to-side rotation (tilting) in a frontal plane occurs around an anteroposterior axis. E. Rotation occurs in the transverse plane around a vertical axis. F. Anteroposterior rotation (tilting) occurs in the sagittal plane around a frontal axis.

11. The Intervertebral Disc intresting facts two principle functions;-increasing available motion, and to transmit load from one vertebral body to the next vertebra The intervertebral discs, which make up about 20% to 33% of the length of the vertebral column, increase in size from the cervical to the lumbar regions. The disc thickness varies from approximately 3 mm in the cervical region, where the weight-bearing loads are the lowest, to about 9 mm in the lumbar region where the weight-bearing loads are the highest. the discs are smallest in the cervical region and largest in the lumbar region the ratio between disc thickness and vertebral body height that determines the available motion.1 The greater the ratio, the greater the mobility. The ratio is greatest in the cervical region, followed by the lumbar region, and the ratio is smallest in the thoracic region. This reflects the greater functional needs for mobility in the cervical and lumbar regions and for stability in the thoracic region

12. Ligaments and Joint Capsules Six main ligamen ts are associated with the intervertebral and zygapophyseal joints. They are the anterior and posterior longitudinal ligaments, the ligamentum flavum , and the interspinous , supraspinous , and intertransverse ligaments

13. Anterior longitudinal ligament (ALL). Anterior longitudinal ligament (ALL). The ALL is slack and may be compressed in forward flexion of the vertebral column. B. The ALL is stretched in extension of the vertebral column Posterior longitudinal ligament (PLL). The PLL is stretched during forward flexion of the vertebral column. B. The ligament is slack and may be compressed during extension

14. Major Ligaments of the Vertebral Column

15. Function Kinematics Coupling is defined as the consistent association of one motion about an axis with another motion around a different axis. The most predominant motions that exhibit coupled behaviors are lateral flexion and rotation. It appears that pure lateral flexion and pure rotation do not occur in any region of the spine The motions of flexion and extension occur as a result of the tilting and gliding of a superior vertebra over the inferior vertebra. As the superior vertebra moves through a range of motion, it follows a series of different arcs, each of which has a different instantaneous axis of rotation.37,38 The nucleus pulposus acts like a pivot but is able to undergo greater distortion than a ball is because it behaves as a fluid.

16. Flexion and Extension The intervertebral disc allows the vertebra to tilt, which dramatically increases ROM at the interbody joint. Without an intervertebral disc, only translatory motions could occur.

17. Lateral Flexion & Rotation Lateral flexion and rotation of the vertebra are limited by tension in the intertransverse ligament on the convexity of the curve. The superior vertebra tilts laterally and rotates over the adjacent vertebra below during lateral flexion

18. Kinetics Axial Compression:- Axial compression (force acting through the long axis of the spine at right angles to the discs) occurs as a result of the force of gravity, ground reaction forces, and forces produced by the ligaments and muscular contractions. The discs and vertebral bodies resist most of the compressive force, but the neural arches and zygapophyseal joints share some of the load in certain postures and during specific motions. The compressive load is transmitted from the superior end plate to the inferior end plate through the trabecular bone of the vertebral body and the cortical shell.

19. Kinetics con.. Bending Bending causes both compression and tension on the structures of the spine. In forward flexion, the anterior structures (anterior portion of the disc, anterior ligaments, and muscles) are subjected to compression; the posterior structures are subjected to tension Torsion Torsional forces are created during axial rotation that occurs as a part of the coupled motions that take place in the spine. The torsional stiffness in flexion and lateral bending of the upper thoracic region from T1 to T6 is similar, but torsional stiffness increases from T7/T8 to L3/L4. Torsional stiffness is provided by the outer layers of both the vertebral bodies and intervertebral discs and by the orientation of the facets

20. Kinetics con.. Shear Shear forces act on the midplane of the disc and tend to cause each vertebra to undergo translation (move anteriorly , posteriorly , or from side to side in relation to the inferior vertebra). In the lumbar spine, the zygapophyseal joints resist some of the shear force and the discs resist the remainder.

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