Notes on Anatomy and Physiology: Facet Joints of the Spine

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.

Fig 1 The elements associated with all synovial joints: articular cartilage, synovial membrane and fluid, joint capsule, ligaments, blood vessels and nerves. Neumann, 2010, page 30

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.

Fig 2 The facet joints of the thoracic vertebrae face the back. Netter, 2006, Plate 154

This places the axis of rotation for a thoracic vertebra at the centre of both the vertebral body and disc.

Fig 3 Because the thoracic facet joints face back- wards, the axis of rotation for the thoracic vertebra runs through the centre of the vertebral body. Kapandji, 2008, page 149

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.

Fig 4 The orientation of the facet joints of the 2nd lumbar vertebra. Netter, 2006, Plate 155

Accordingly, the axis of rotation of a lumbar vertebra lies close to the base of the spinous process.

Fig 5 Rotation of the lumbar vertebrae quickly produces shearing forces on the intervening discs. Kapandji, 2008, page 95

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

Bruce McFarlane, MD

© 2010 Taoist Tai Chi Society of Canada

3 Comments

Filed under Anatomy and Physiology, Health Watch

3 responses to “Notes on Anatomy and Physiology: Facet Joints of the Spine

  1. i have yet to read this….and then digest it…..and then learn it…..my 111 move……..for now…….i can tell you my spine is tingling….as is the rest of my being……..having this wonderfull resourse……keep on keeping on with this blog…..and many thank you’s

  2. David Kemp

    According to Chinese medicine, the health of the joints (including these joints in the spine) can be pathologically affected in several ways. Pathogenic factors that affect the normal flow of Qi that nourishes and maintains the joints can arise either from outside or inside the body; externally arising factors include Cold, Heat or Damp (visible as inflammation or swellings) and are thought to be related to the external climate. Living and working in an environment that is consistantly cold or damp allows these factors to enter the body and lodge in the joints where the Qi flow becomes restricted, allowing pain to arise as a result. Not everyone is affected in the same way by the same things; it is thought that there needs to be some underlying weakness or deficiency in the body, possibly related to overworking (which depletes defensive Qi) or some constitutional tendency that allows the invasion of the body to take place.

    Internal sources of pathology relate primarily to the emotional or mental state of the person, and can affect the way the internal organs are able to assimilate Qi from food and air, and circulate the resulting products (being Qi and Blood) to the tissues. The digestive function is thought to be mainly affected by “Overthinking”, essentially meaning worry or brooding, which causes the digestive process to fail to fully separate foodstuffs into useful and non-useful parts. When this occurs the muscles that are responsible for movement become “undernourished” by Qi and Blood, and may become weak and easily tired. The organ responsible for this transformation of food was thought to be the “Spleen”, equating roughly to the pancreas in modern-day thinking. When the Spleen function becomes weakened, either through Overthinking or through an inappropriate diet, not only do the muscles lack energy, but Dampness can arise from inside, which can go on to lodge in the tissues forming edema or swellings in the joints, blocking the channels and restricting Qi flow.

    Joint health also relies on the condition of the tendons, ligaments and connective tissues. Chinese medicine theorises that the tendons require nourishment by Qi and Blood to maintain strength and flexibility, and disruption to the smooth flow of these substances results in tendons that become stiff and rigid. The Liver is the organ that is thought to regulate this smooth flow of Qi and Blood, and should it become affected by certain emotions then the smoothing action becomes choppy and erratic. This is thought to relate directly to “Anger”, meaning frustration and rage at one end of the scale, and resentment or bitterness at the other. Over exposure to these emotions “tightens up” the inside of the body, restricting the flow of Qi not only to the tendons, but the rest of the tissues as well.

    Chinese medicine asserts that there is always a circular relationship between the tissues, organs
    and emotions; when we exercise the tissues we create a positive affect on the organs and help to relieve the effects of negative emotions on the body. Maybe this explains why Taoist Tai Chi seems to work so well on relieving the affects of stress on the body; by stretching the tendons we reduce the affects of Anger, and by working the muscles we can reduce the affects of Worry. It seems that when our instructors say “relax- don’t worry”, or “stretch more, but stay relaxed” that we’re given a way to affect both Body and Mind that directly taps into an old and wise tradition of self care passed on by Mr Moy.

  3. Nick Della Volpe

    Dr. McFarlane,
    Thanks for sharing your special knowledge of the body with society members. We are all students of the body at some level, as we practice our tai chi and delve into Master Moi’s frequent question of “how does it feel?” as we explore that mind – body connection. Your spinal notes help us to visualize and better understand the mechanics underlying the subtle benefits of the moves in the set and the jongs.
    A grateful “up down same time to you”
    Nick

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