The last few posts focussed on particular aspects of the spinal column and vertebrae. Today’s will review several features of the facet joints: structures which connect the vertebrae and lend both stability and flexibility to the spinal column.
Let’s first reflect briefly, though, on the fact that here we are, all of us members of a worldwide community practicing the Taoist Tai Chi™ internal arts of health, devoting time once again to the study of anatomy and physiology. Many benefits and pleasures flow, it seems to me, from this enterprise – one of the most important being that establishing connections between our art and western medicine encourages us, in a variety of ways, to persevere with our practice over the span of many years.
Some of the consequences of regular practice are local in nature and come relatively early on. A chronic discomfort somewhere in the body lessens. Motion is reestablished in a region that’s long been stiff. Stress settles and sleep seems more restorative. An area, previously weak, becomes stronger.
But there are subtler transformations that develop incrementally over many years. These changes emerge as all parts of the body work better together, as seemingly disparate regions and systems of our physiology alter their engagement with one another. The body feels stronger, more spacious and connected than it has in years – even as we age.
These shifts take considerable time and seem always to come as a surprise. They are unanticipated because we forget the body can work and feel this way.
Experiencing these changes, and then passing on their possibility to others, involves continuing our practice over a lengthy period while maintaining connection with others engaged in the same process. This persistence is not something western science can provide. But becoming familiar with western anatomy and physiology encourages us, assists us in charting our progress and in understanding the changes we note along the way.
So as we consider various aspects of anatomy, keep in mind that these are not bits of unrelated detail. Look for ways that knowledge of the parts leads to an engagement and understanding of the whole organism.
The facet joints
All joints act as a junction or pivot point between bones. Movement of the body is accomplished through the rotation of bones about the joints.
Like most of the body’s joints, the 4 facet joints built into each vertebra are synovial in type:
- cartilage lines their articulating surfaces
- synovial membrane produces a nourishing lubricant – the synovial fluid
- the joint capsule, a wrapping of connective tissue, encloses the joint
- ligaments connect the bones of the joint, preventing excessive motion
- blood vessels and sensory nerves run to the area.
Also worth noting: the hip and knee joints have precisely the same arrangement as these tiny facet joints.
Orientation of the facet joints and rotation of the spine
In the practice hall, reference is often made to rotation of the torso about the spine. So it is revealing to discover that the thoracic spine’s design allows it to turn much more freely than the lumbar region. It is the orientation of facet joint surfaces that explains this difference.
In the thoracic area, the facet joints face posteriorly, roughly parallel to the back.
This places the axis of rotation for a thoracic vertebra at the centre of both the vertebral body and disc.
Consequently, the facet joint surfaces glide on one another. The vertebral bodies and discs turn about a common axis. The intervertebral discs experience rotation-torsion but little in the way of shear. All this permits the group of 12 thoracic vertebrae to turn about 35 degrees in either direction, or 3 degrees per vertebra. Were it not constrained by its attachments to the rib cage, the thoracic spine would enjoy even greater freedom of rotation.
In the lumbar spine, however, the facet joints do not face backwards. They face each other.
Accordingly, the axis of rotation of a lumbar vertebra lies close to the base of the spinous process.
As this axis does not correspond with the centre of the disc, the disc is subjected to considerable shearing force. Disc and vertebral body must slide past one another in opposite directions. The possibility for rotation is dramatically reduced – only 5 degrees in either direction for the entire lumbar spine (5 vertebrae), or 1 degree per vertebra.
So, facet joints act like railway tracks, guiding the movements of the spine. Their orientation endows the thoracic vertebrae with three times the rotation available to the lumbar vertebrae. And the lumbar spine ends up specializing not in rotation but in forward and backward bending, movements that enable us to pick something up from the ground or reach up to retrieve an object from a high shelf.
Putting synovial joints through their normal range of motion circulates lubricating, nurturing synovial fluid. This promotes continued good health of the smooth, glistening cartilage that covers the articulating surfaces. As well, motion keeps supple the connective tissues of the muscles, tendons, ligaments and joint capsule surrounding the joint. Balanced posture and full range movement over a lifetime help prevent osteoarthritis, the wear and tear form of joint disturbance, in the facet joints. Precluding a difficulty from ever developing is known in medicine as primary prevention.
We can now appreciate how, once established, arthritis in these joints steals mobility from the spine and introduces pain to the movement that remains. Correction of faulty posture will ease some of that discomfort. And the right kind of physical training diminishes the stiffness, pain and loss of function associated with an arthritis already present. This is secondary prevention – minimizing the impact of an already established disorder on our daily lives. Like primary prevention, it forms an important part of every class in the Taoist Tai Chi™ internal arts of health.
The next post will look at the intervertebral disc, a common source of mischief in the low back.
1. Kinesiology of the Musculoskeletal System, Foundations for Rehabilitation, Second Edition, Donald A. Neumann, 2010, Mosby Elsevier, ISBN 978-0-323-03989-5
2. Atlas of Human Anatomy, 4th Edition, Frank H. Netter, 2006, Saunders Elsevier, ISBN – 13: 978-1-4160-3385-1
3. The Physiology of the Joints, Volume Three: The Spinal Column, Pelvic girdle and Head, A.I. Kapandji, 2008, Churchill Livingstone Elsevier, ISBN – 13: 9780702029592
© 2010 Taoist Tai Chi Society of Canada