ANATOMY AND BIOMECHANICS OF SPINE

In the previous blog i gave you all a brief idea about how physiotherapy plays an important role in our day-to-day life. In this post I'll be discussing about anatomy and biomechanics of our vertebral column and the concept of anatomy and biomechanics goes hand in hand. So let's start!

ANATOMY OF VERTEBRAL COLUMN: Our vertebral column is composed of 26 vertebrae divided into 5 major parts - 1. Cervical (7) 2. Thoracic (12) 3. Lumbar (5) 4. Sacrum (5, fused) 5. Coccyx(4, fused). 

It transmits body weight in walking and standing which plays a major role in normal walking pattern of people (GAIT CYCLE in medical term). It has two types of curves - KYPHOTIC and LORDOTIC.

The kyphotic curve is present at the thoracic and sacrococcygeal part and the lordotic curve is present at the cervicolumbar part. A new born has only kyphotic curve present in its vertebrae. These curves are important to resist high compressive loads.

Not going very deep into anatomy, I'll just let you know how a typical vertebrae looks like:

So now we'll talk about the biomechanics of vertebral column which is the root of physiotherapy.

Before starting let me make you familiar with few terms : Flexion- Moving the body forwards , Extension- Moving the body backwards, Abduction- Moving the limb or other part away from the body, Adduction- Moving the limb or other part towards the body.

KINEMATICS : It is the study of motion of objects without considering the factors that cause or affect the motion.

The vertebral column has the following movements: Flexion and Extension, Lateral flexion and Rotation. These motions appear to occur independently of each other but at the level of individual motion segment, these motions are often COUPLED.

So, what is coupling? It is the consistent association of one motion with another motion around different axis. The motions lateral flexion and rotation exhibit coupled motion. The most consistent pattern of coupled motion is seen at the cervical spine (lower cervical spine, i.e., C3- C7).

KINETICS : It is the branch of classics mechanics that concerns the effect of forces and torques on the motion of bodies.

Okay, so basically the vertebral column's ability to resist the forces depends on various factors as the individual's age, posture, type and duration of loading, and mainly the condition and properties of the muscles, joint capsules, ligaments, etc. Here I'll give you a picture which will make you clear about how the forces work on vertebral column : 

AXIAL COMPRESSION: It is a force acting through the long axis of the spine as you can see in B part of the picture and this compression occurs as a result of force of gravity, forces produced by ligaments and muscular contraction. 

BENDING: It causes both compression and tension on the structure of spine. In forward flexion, the anterior structures are subjected to compression and posterior structure are subjected to tension. In extension, posterior structures are generally unloaded or subjected to compression while the anterior structures are subjected to tension.

TORSION: These forces are created during axial rotation that occurs as a part of coupled motion that takes place in the spine. There is a risk of rupture of disc fibres is increased when there is combination of torsion, heavy axial compression and forward bending.

SHEAR: It occurs parallel to disc and tend to cause each vertebrae to slide on the one below. 

Here was some of the basics you need to know about vertebral column in order to understand and get more clear image of deformities occuring in the spine which I'll be dicussing in my next post. THANKYOU!