Articular Processes Mechanism

Articular Processes Mechanism

“if the spine had all its ligaments and discs attached to it over its full length, and if the ligaments connecting it to the sacrum were also in place, then it would stand in the upright position.” [Going mental page 19] There is another ingenious mechanism in the vertebral bones themselves that contributes to this. It is a function of the articular processes, and works like this.

If you look at a full-size plastic model of the skeletal frame, you will see two wee lumps, called the superior articular processes, sticking out from the sacrum and fitting perfectly with the lower (inferior) articular processes of the 5^th and lowest lumbar vertebra.

You will also see that the 5^th lumbar vertebra has upper (superior) articular processes that fit perfectly with the inferior articular processes of the 4^th lumbar vertebra above it. This process continues up the lumbar spine through the 3^rd, 2^nd, and 1^st lumbar vertebra, where it changes slightly when the ribs come in contact with the spine.

On the sagittal plane of movement (backwards and forwards) the perfect articulation of the processes has two effects. The first is short-term and involves movement, the movement of bending your spine backwards (extension). The lateral surfaces will come into contact with each other and prevent the spine from bending too far. The second effect is long term and involves stability. It is the effect that we are more concerned with here. The same lateral surfaces will prevent the upper vertebra from sliding forwards over the one beneath it. Put more simply, in the long term the sacrum stops the 5^th lumbar vertebra from sliding forwards, the 5^th stops the 4^th, the 4^th stops the 3^rd, the 3^rd stops the 2^nd and the 2^nd stops the 1^st. But even if you look at a model, this effect is very difficult to see and even more difficult to draw. The effect is shown in the picture below.

Plan A-A

When you rotate the torso on the vertical axis, for example in dancing the Twist, the sagittal surface (running front to back) will come into contact with each other and prevent the lumbar spine from rotating too far. This effect is very easy to see on the model.

Articular processes that prevent the spine from twisting too far on the vertical axis, do not exist in the thoracic region because the ribs provide lateral stability. They do exist in the cervical spine but the mechanism is different from the lumbar spine.

This article was first published in Going Mental by Daniel McGowan. You can download the PDF of this book for free here:  FREE DOWNLOAD