Anatomy and Surgery of the Intervertebral Joint

Ever wonder how your spine, which spans twenty-six bones lengthwise, is able to move without giving you pain? Or why it hurts when you do move?

The spinal column employs a number of inherent, but intricate, anatomical mechanisms in carrying out its responsibilities of supporting upright body posture and moving into different directions.

The most basic of these mechanisms is the intervertebral joint.

What Is the Intervertebral Joint?

The intervertebral joint consists of two adjacent vertebrae with a cushion in between.

These fundamental intervertebral joint elements work together as a unit, and their purpose is to facilitate a movement of the spine. Surgeons, doctors, chiropractors, and spine and biomechanics specialists refer to one intervertebral joint unit as a "motion segment."

The meeting points of the upper and lower spinal bones that comprise an intervertebral joint are the vertebral body in front and the vertebral arch in the back.

Cushioning is provided between the two bones by means of an intervertebral disc, a shock-absorbing structure that has a liquid, jelly-like substance in the center. This liquid substance, called the nucleus pulposus, is contained by tough fibers located on the outside. The tough outer fibers collectively are known as the annulus fibrosus.

In back, the movement of the motion segment is both facilitated and constrained by small facet joints, located between the vertebral arches.

The intervertebral disc is often the site of pain, and a number of conditions may prevail there. Some, like herniated disc, are generally due to injury, while others, like degenerative disc disease, tend to be related to the aging process.

Movement in all directions, which includes bending forward, arching back, tilting to the side, and/or twisting, occurs at the many intervertebral joints along the length of the spine. Ligaments made of tough fibrous bands of connective tissue help stabilize the intervertebral joints during movement as well as support the column during weight-bearing. The facet joints, which were mentioned above, are located at the back of the column and mainly contribute to spinal stabilization, i.e., limiting excess amounts of movement.

Spinal Fusion and the Intervertebral Joint

Spinal fusion surgery, as the name suggests, is a procedure that fuses two or more intervertebral joints together. Sometimes fusions are done along with a discectomy, while at other times the discectomy is given alone.

Spinal fusion is often performed on more than one motion segment; in this case, more than one intervertebral joint is fused during surgery. 

Scoliosis surgery is a good example of this, but certainly not the only example. The purpose of scoliosis surgery is to reduce the degree of rotation and/or bend in a series of adjacent vertebrae.

Among the many types of spine surgery, spinal fusion is the most common, with lumbar (low back) spinal fusion given the most often, by far and away. Lumbar spinal fusion is so prevalent, in fact, that researchers have taken up the task of evaluating its effectiveness. 

Some concerned spine specialists say that lumbar spinal fusion surgery is given when and where it is not necessary and that it does not always lead to pain relief and/or improved physical functioning in patients.

For example, Deyo, et. al. published a study in the Journal of the American Board of Family Medicine entitled "Overtreating chronic back pain: time to back off?" The researchers report on four randomized clinical trials that found spinal fusion for degenerative disc disease with no sciatica conferring relatively limited benefits to patients compared to surgery for spine fractures or deformity.

The authors comment the even though there was no real reason why more spinal fusions should be done, the use of this medical technology skyrocketed a whopping two hundred and twenty percent between the years of 1990 and 2001 in the United States. They also say this rise accelerated in 1996, when the fusion cage, which was a new type of instrumentation at that time, was approved by the FDA.

Deyo, et. al., state that this FDA approval may have contributed to the increase in the number of lumbar spinal fusion procedures given.

And finally, Deyo's team says that during that decade, Medicare claims for spinal surgery went up by forty percent. This included a seventy percent increase in overall spinal fusion surgery rates and a one hundred percent increase in the use of implants such as the fusion cage.

Protecting Your Intervertebral Discs From Injury

As with most types of back problems, engaging in regular exercise is one of the best ways to ward off potential injury and/or decrease, or delay, spinal conditions related to wear and tear.

Developing and maintaining good postural alignment is another great way to do the same.

Seeing a licensed physical therapist for a program that is tailored to your individual needs may go a long way towards keeping your spine healthy and pain-free.

And a 2018 study published in the journal Spine found that having a lumbar discectomy surgery earlier in your life may lead to the need for a lumbar fusion later. In fact, the authors say, the likelihood is about three times as much for those who had a discectomy than for those who previously had not. They warn that the rate of operation for lumbar disc herniation keeps rising, especially for those who are over the age of sixty.