Understanding Your Intervertebral Discs: Anatomy and Healing

Intervertebral discs connect the bones of the spine and distribute the load as you move. They allow two adjacent vertebrae to move relative to one another and help absorb shock.¹ Changes may appear on imaging as you age, even in people who aren’t experiencing pain. Your healthcare provider will therefore interpret these findings in light of your symptoms and the results of your physical exam.

What is an intervertebral disc and what is its main role?

An intervertebral disc connects two vertebral bodies—the thick parts of the bones in the spine—and distributes weight while allowing movement. Its gel-like center is surrounded by a ring of strong fibers. Two thin layers of cartilage, called articular surfaces, connect it to the vertebrae above and below.²

Intervertebral discs are the natural cushions of your spine. They are located between almost all the vertebrae of your spine, from the top of the neck to the sacrum, the bone at the base of the spine. An adult spine has 23 of them: the first is located between the second and third cervical vertebrae, and the last is between the fifth lumbar vertebra and the sacrum. There is no disc between the first two cervical vertebrae.² Together, the discs account for about one-quarter to one-third of the spine’s length.²

The discs work together with the vertebrae—the small joints at the back of the spine—and the ligaments, which are strong bands that connect the bones. Together, these structures support the back and guide its movements. Our comprehensive guide to low back pain explains this type of pain and the other structures in this region.

The discs help maintain the space between the vertebrae. Nerves exit the spine through openings called intervertebral foramina. An experiment involving six sets comprising the last lumbar vertebra and the sacrum, harvested postmortem, simulated slippage between these bones. In this model, a decrease in disc height reduced the size of the openings. The presence of symptoms also depends on other structures and the clinical examination.³

How is a healthy intervertebral disc structured?

A healthy disc consists of a gel-like core, a fibrous ring, and two cartilage endplates. The core, called the nucleus pulposus, contains a lot of water. The ring, called the annulus fibrosus, contains layers of collagen—fibers that resist traction, that is, a force that stretches them. The endplates connect the disc to the vertebrae. This structure combines flexibility and strength.²

The nucleus contains proteoglycans, large negatively charged molecules that promote water retention. Water moves in response to the concentration of dissolved substances, including salts; this phenomenon is called osmosis.⁵ The pressure thus created balances out the forces exerted by the body’s weight, muscles, and ligaments.⁶ This balance helps maintain the disc’s height and distribute loads.

The fibrous ring surrounds and contains the nucleus. It’s like the tough layers of an onion. The collagen fibers are angled, and their direction alternates from one layer to the next. Within a single layer, all the fibers point in the same direction, and the orientation changes by about 60 degrees from one layer to the next, so that every other layer is parallel.² The crisscrossing of the fibers contributes to the ring’s strength when it is stretched. This structure allows the disc to combine strength and flexibility.

How do intervertebral discs function during movement?

The discs change shape and redistribute the load when you bend, turn, or stand up straight. Their nucleus can also shift within the annulus. The extent and direction of this shift vary depending on the condition of the disc and the movement.^{1, 7}

The classic model predicts that the spine shifts backward when you lean forward, and forward when you arch your back. A meta-analysis of 14 studies published in 2025 found a response consistent with this model in 85.4% of measurements among people without pain. However, results vary widely, and the quality of the studies is low. Data on herniated discs are very limited.⁷

In some people, repeated movements cause leg pain to shift toward the back. This response is called centralization. A physical therapist can assess it using the McKenzie approach to guide exercises. A 2018 review links this response to a generally more favorable outcome. It does not find this response in everyone and finds no evidence that it predicts which treatment will be more effective.⁸ Centralization describes the progression of symptoms; it does not directly show what is happening within the disc nucleus.

During your daily activities, the discs undergo cycles of compression and decompression. When you are standing or sitting, your body weight and muscle tension compress the discs. This compression forces fluid out into the surrounding tissues: over a 24-hour cycle, the disc loses and then regains about 25% of its fluid.⁹ When you lie down at night, the disc rehydrates. That’s why you’re slightly taller in the morning than at the end of the day: in eight pain-free volunteers aged 22 to 29 who were monitored using magnetic resonance imaging (MRI), disc height decreased between morning and evening, and this decrease contributed to the loss in height measured throughout the day.¹⁰

The cells of the disc receive oxygen and glucose primarily by diffusion—that is, as these substances pass through the tissues from areas where they are more concentrated. The movement of fluid during loading contributes very little to the direct transport of these small molecules.¹¹ Our comprehensive guide to back pain offers general advice on physical activity.

How does the center of the disc get nourishment without blood vessels?

The center of the disc receives oxygen and nutrients from the small surrounding blood vessels as they pass through the tissue. This transport, called diffusion, allows the cells to survive despite the absence of blood vessels in the nucleus.⁴

The pulpy core remains blood vessel-free throughout life. The fibrous ring and the plateaus receive more blood early in life, and this blood flow decreases with age. New blood vessels may also form in these regions when the tissue is damaged.¹²

Oxygen and glucose enter primarily through the vertebral endplates (the thin layer of cartilage that separates the disc from the vertebral bone, just above and just below it). They travel to the center of the disc. Waste products produced by the cells, such as lactic acid, follow the reverse path. For each substance, the difference in concentration drives its movement toward the region where it is less concentrated.⁴

A decrease in nutrient supply can harm the cells of the disc. Blood flow around the disc, the passage of nutrients through the endplates, and the cells’ nutritional needs all influence this supply.¹¹Muscle-strengthening exercises are designed to improve your physical abilities and help you resume the activities you want to do. Your physical therapist will tailor these exercises to your symptoms.

Recommendations regarding lower back pain and sciatica—pain that radiates down the leg—encourage people to continue their normal activities as their abilities allow.¹³ Our exercise progression guide offers ways to gradually adjust your activity level based on your symptoms and goals.

What happens during a disc herniation?

A herniated disc is a localized protrusion of disc material beyond its normal space. It can take the form of a protrusion or an extrusion; a completely detached fragment is called a sequestration. Bulging is more extensive and constitutes a separate category, which is not classified as a herniation under this nomenclature.¹⁴ A herniation may compress a nerve without the imaging findings alone being sufficient to explain the symptoms. Some herniations resolve over time, but their course alone does not determine the treatment.

The term "herniated disc" describes a finding seen on imaging. In this condition, disc material protrudes beyond its normal boundaries. The image does not allow us to determine exactly when this change occurred or to attribute its presence to a specific movement or exertion.

These findings highlight a crucial point: The presence of a disc abnormality on imaging does not necessarily mean that it is causing your pain. In a study of 98 people without lower back pain, 27% had at least one disc protrusion visible on an MRI, and the authors concluded that these bulges and protrusions could be incidental findings—that is, images observed incidentally that are unrelated to any symptoms.¹⁵ If you have an MRI, don’t be discouraged by the results: these findings must be interpreted within the full clinical context. An image must be compared to your symptoms. Signs of degeneration are common in people without pain and increase with age¹⁷, and in a study of people with sciatica—pain that radiates down the leg—followed for one year, the MRI could not distinguish between those who were doing well and those who were doing less well.¹⁸ Check out our article on medical imaging to understand why images alone don’t tell the whole story and how your physical therapist incorporates these results into the overall evaluation. To understand in detail when a lumbar disc herniation actually causes symptoms and to discover evidence-based treatment options, see our comprehensive guide to lumbar disc herniation.

Disc abnormalities are common in people without pain: in a study of 36 volunteers with no lower back pain or sciatica, 81% had disc bulging and 56% had at least one annular tear.¹⁹ The sample size is small, so these percentages describe this specific group and cannot be directly applied to the general population.

When a herniated disc compresses a nerve root, it can cause symptoms related to that nerve, such as pain radiating down the leg. However, even this compression does not always cause symptoms. A systematic review on how to grade herniations and nerve root compression on MRI emphasizes this point: the imaging findings must be interpreted in conjunction with the clinical presentation and symptoms before determining a course of treatment.²⁰ When compression causes symptoms, many people gradually improve without surgery.²¹

In a study involving a single patient examined at ten centers, MRI reports differed from one center to another: the ten scans of the same person yielded 49 distinct findings, none of which appeared in all ten reports, and overall agreement among the centers was low.²² This case illustrates potential variability without assessing the overall reliability of any lumbar MRI interpretation.

Can herniated discs heal on their own?

Some hernias shrink on their own, and many people get better without surgery. However, a reduction visible on imaging and the resolution of symptoms are two different outcomes. A review of eleven studies found a reduction in herniated tissue in about 67% of people followed without surgery.²³ Another review, covering 38 studies and 2,219 people, estimates this proportion at 63%, with wide variations depending on the methods used.²⁴ These percentages do not indicate a specific timeframe or a guaranteed outcome for any individual.

Regression refers to a reduction in the amount of material protruding from the disc; resorption refers to its gradual elimination by the body. These terms describe the progression of a herniated disc. They do not mean that the entire disc returns exactly to its original structure.

A herniated disc does not always require surgery. In a study of people treated for sciatica, 85% of those whose herniated disc was still visible after one year reported a complete or nearly complete resolution of symptoms, compared with 83% of those whose herniated disc was no longer visible.¹⁸ This group included both people who underwent surgery early on and those who were monitored for a longer period without surgery; therefore, the figure reflects a trend rather than the effect of a specific treatment.

In a 2015 systematic review, radiographic regression was observed in 96% of impactions, 70% of extrusions, 41% of protrusions, and 13% of bulges.¹⁶ A 2024 statistical synthesis, known as a meta-analysis, covering 31 studies and 2,233 individuals treated without surgery, yielded slightly lower estimates for the first three types: 87.8%, 66.9%, and 37.5%, with 13.3% for bulges.²⁵ These proportions do not describe either the rate of healing or clinical recovery.

In a Danish study, 106 adults from the general population underwent MRI scans at ages 41, 45, and 49. Of the 140 herniated discs studied, 65% remained stable, 17.5% decreased in size, 12.5% increased in size, and 5% fluctuated from one scan to the next.²⁶

Defense cells likely play a role in resorption. Macrophages—cells capable of removing debris—are present in herniated tissues. Laboratory experiments on human tissues also show increased production of enzymes that break down tissue.²⁷ Laboratory experiments on mouse tissue support the role of interactions between these immune cells and the cells of the disc.²⁸ This research explains part of the process; it does not predict how long it will take for an individual to recover.

The type of hernia is associated with the likelihood of its resolution. In the cited reviews, herniated fragments and extrusions resolve more often than protrusions. This association does not guarantee a faster recovery or a more complete resolution of pain.

In a follow-up study on sciatica, at the one-year mark, the continued presence of a herniated disc on an MRI scan did not allow researchers to determine who was doing well and who was doing less well.¹⁸

Non-surgical treatments may include education, temporary adjustments to your activities, and progressive exercises. Physical therapy supports the resumption of movement and activities based on your symptoms and evaluation. Our movement rehabilitation program tailors the exercises to the activities you wish to resume. You do not need to wait for the hernia to disappear on imaging to see an improvement in your functional abilities.¹⁸

What does disc degeneration mean?

Disc degeneration refers to changes in the intervertebral discs that become more common with age, though they are not always painful. A review of 33 studies involving 3,110 pain-free individuals found that approximately 68% of people aged 40 had disc degeneration. This estimate ranges from 37% at age 20 to 96% at age 80.¹⁷ The healthcare professional therefore interprets the imaging findings in conjunction with the patient’s symptoms, the results of the physical examination, and the patient’s limited activities.

A person may experience these changes and continue their activities without pain.¹⁷ In a study of 3,369 people with and without back pain, the links between MRI changes and pain intensity were generally modest. Some associations existed, but the imaging did not directly measure symptom intensity.²⁹ The imaging report is part of the evaluation, not a complete diagnosis of your pain.

The evaluation takes into account what triggers the symptoms, the range of motion, strength, and sensations in the legs. These factors help determine whether a visible change might be related to your problem.²⁰

The characteristic changes include several factors. The water content of the disc nucleus decreases as the disc degenerates with age. There is also a reduction in the concentration of proteoglycans (the molecules that retain water), fissures in the annulus, and a decrease in disc height. Scientific journals describe degeneration as a combination of changes in proteoglycans, a loss of the water they retain, and a decrease in the disc’s internal pressure, which alters its mechanical properties.^{5, 30} These changes alter the way the disc distributes loads.

Core and back exercises can improve your functional abilities even if the condition of the disc does not change. They are selected based on your strength, your tolerance for movement, and the activities you wish to perform. Our exercises for the stabilizing muscles, which help control core movements, are tailored to your assessment and your response.

A disc change seen on imaging alone does not determine whether it explains the symptoms or requires treatment. Our comprehensive guide to lumbar osteoarthritis also explains why imaging findings must be interpreted in conjunction with the clinical picture.

What myths about intervertebral discs need to be debunked?

Intervertebral discs can withstand everyday stresses; a herniated disc does not always require surgery; and an abnormal imaging finding does not necessarily indicate the cause of pain. Believing otherwise can lead to unnecessarily avoiding certain activities or misinterpreting test results. The table distinguishes these beliefs from the actual observed findings.

Tolerance for a particular activity varies depending on the person and the situation. You can adjust the duration, frequency, or intensity of the activity, and then progress based on how you respond. Persistent worsening of symptoms, new weakness, or other concerning signs require a reevaluation.

For a lumbar hernia, non-surgical treatment and surgery may be discussed when symptoms persist despite initial treatment. A review of randomized controlled trials notes that, among individuals with an indication for surgery, surgery provides greater relief from leg pain in the short term, though the difference becomes small in the short- to medium-term and negligible after 12 months, and that the certainty of these results is low or very low.³¹ The decision is therefore made in consultation with the patient, based on the desired speed of relief, the risks, and the patient’s preferences. The decision takes into account any loss of strength or sensation, the intensity and progression of symptoms, as well as the patient’s goals and preferences. Signs of cauda equina syndrome require urgent medical evaluation.

A disc image alone cannot explain the intensity or progression of pain. Our comprehensive guide to chronic pain outlines other factors to consider. Our program for persistent pain tailors exercises and advice to your specific situation. For lower back pain that lasts more than three months without a specific cause, exercise programs are likely to slightly reduce pain and difficulties with daily activities compared to no intervention.³² This finding applies to the programs studied; it does not prove that exercise can make a herniated disc go away.

The professional can explain what the imaging report shows and what it does not allow us to conclude. You can then discuss which movements to resume, possible adjustments, and symptoms that warrant a follow-up visit.

When should you seek help for an intervertebral disc problem?

Pain that radiates down the leg, accompanied by persistent numbness or progressive weakness, requires prompt medical attention. New-onset difficulty urinating, loss of bladder or bowel control, numbness around the genitals, or significant weakness in both legs requires immediate evaluation in the emergency room.

The course of the condition depends on the symptoms and the results of the examination. When a lumbar herniated disc irritates or compresses a nerve, many people gradually improve without surgery. However, certain signs require prompt evaluation.²¹

• Nerve-related pain: Pain that radiates down the leg—especially when accompanied by numbness, tingling, or weakness—should be evaluated. A treatment plan may include a gradual return to activities and, depending on the response, exercises that gently mobilize the nerves relative to the surrounding tissues.
• Changes in sensation: Persistent numbness, tingling, or burning sensations in the leg or foot. These symptoms warrant an evaluation to investigate their possible causes and determine the next steps.
• Progressive Muscle Weakness: Difficulty standing on your toes, walking on your heels, or weakness during specific movements. This is a more concerning sign that requires a prompt assessment.

Go to the emergency room immediately if you experience a new difficulty urinating, loss of bladder or bowel control, new numbness around the genitals, or significant or rapidly progressive weakness in your legs. These signs may indicate severe nerve compression in the lower back, known as cauda equina syndrome.³³ The other signs listed below also require prompt evaluation.

• Cauda equina syndrome: new difficulty urinating, loss of bladder or bowel control, numbness around the genitals, or severe weakness in both legs (a medical emergency that may require surgery)
• Back pain accompanied by fever, chills, or unexplained weight loss should be evaluated promptly
• Intense nighttime pain that persists despite a change in position; this should be noted during a rapid assessment

If there are no urgent symptoms, non-surgical treatment options can be discussed. These may include education, temporary adjustments to daily activities, and progressive exercises. For a lumbar herniated disc, surgery also remains an option depending on the degree of weakness or loss of sensation, symptoms, progression, and patient preferences. Our guide on physical therapy for lower back pain describes an example of a treatment plan. A physical therapy evaluation can identify restricted movements, strength, and sensation to guide treatment.

If you are experiencing symptoms related to a disc problem, our back pain page allows you to quickly book an appointment with a qualified physiotherapist.

References

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