Back Pain Causes: Unpacking the Differences Between Herniated Discs, Bulging Discs, and Pinched Nerves

Before we dive into defining each of these common causes of back pain, let’s review a bit of spinal anatomy.

The spinal column is made up of twenty-four vertebrae, each separated from the next by an intervertebral disc. The spinal cord runs down an opening in the middle of the vertebrae and the discs called the spinal canal. Spinal nerves, also called nerve roots, originate from the spinal cord and exit the spinal column on both sides of each pair of adjacent vertebrae, through a gap known as the intervertebral foramen. The nerves traverse our arms and legs, providing the ability to control muscle movements and respond to sensory stimuli (e.g., touch).

Pinched nerves, disc bulges, and herniations all arise from issues that develop in the spinal discs and neighboring nerves. Before diving into each of these three conditions, let's dig just a little further into the structure of the spinal discs. Spinal discs provide shock absorption and stabilize the spinal column during load-bearing activities (1, 2). Each spinal disc is composed of a nucleus pulposus and an annulus fibrosis (1, 2). The nucleus pulposus is the inner part of the disc and consists of a toothpaste-like substance made of water and collagen (1). The annulus fibrosis is the outer part of the disc and features collagen fibers arranged in concentric rings, a formation that provides tensile strength (1). The annulus fibrosis is thicker in the front of the spinal column than in the back, making the backside of the disc more susceptible to deformations (1).  Most commonly, a herniation occurs on the backside of the disc and out to the side, bringing it in direct contact with the spinal nerve (2). This is called a posterolateral herniation (2).

With age, the nucleus pulposus dehydrates and its internal fluid pressure decreases (1). This amplifies the stress placed on the annulus fibrosis (1). Over time, the increased stress reduces the height of the disc, weakens the annulus fibrosis, and raises the risk of deformation (1, 2).

With this background in mind, a “disc herniation” refers to the displacement of disc material beyond the intervertebral disc space (2, 3). This occurs when there is a tear in the outer annulus fibrosis and the inner nucleus pulposus leaks or protrudes through. When this happens, the leaking disc material can pinch the spinal cord or spinal nerves, causing pain and dysfunction. Herniated discs are sometimes called slipped discs or ruptured discs.

On the other hand, bulging discs result from disc dehydration, causing the outer wall of the disc to weaken and bulge outwards and sag downwards as a result (4, 5). Disc dehydration is often the result of age-related degenerative changes. In a bulging disc, there isn't a tear in the outer annulus fibrosis. However, a bulging disc is at a higher risk of herniation than a healthy disc due to its dehydrated state. A bulging disc may cause low-level chronic pain due to impingement on the spinal cord or spinal nerves, which is usually not as severe as with a herniated disc due to its gradual onset.

A pinched nerve arises when a nerve is compressed by a surrounding structure, disrupting its conduction of electrical signals. A nerve can be compressed anywhere along its length, from its origin (brain or spinal cord) to the peripheral structure it communicates with (i. e., muscle) (6). So, pinched nerves can occur anywhere throughout the body and not only in the back. Disc herniations and disc bulges in the lower back can result in compression of the lower back nerves, which results in back pain.

Herniated discs and pinched nerves can arise from acute causes, such as trauma or injury, or from age-related degeneration. By contrast, a bulging disc is almost always the result of age-related degenerative changes in the body.

Poor posture and mechanics can significantly increase the chance of disc herniation. Examples of posture shortcomings which can impact spinal discs include improper lifting technique, repetitive strain on the spine through bending or twisting motions, and excessive sitting, such as while driving or working at a desk. Lifting with your back (bending at your spine) instead of your legs (bending at your knees and hips) can also increase the likelihood of disc herniation. Muscle weakness is another key factor in disc herniation. Weak abdominals and back muscles (“core muscles”) may also increase the risk of disc herniation due to poor stabilization of the spine during physical activity.

Age-related disc dehydration can also cause disc herniation. Some studies have also shown that smoking can increase the likelihood of the development of lumbar disc herniation (7).

Bulging discs almost always arise because of the degeneration that comes along with aging. Bulges tend to develop gradually and often simultaneously arise in different discs. In addition to contributing to complications like future herniation, bulging discs can also cause spinal stenosis, or a narrowing of the spinal canal, which is where the spinal cord runs (8). Spinal stenosis can be the result of multiple discs bulging into the spinal canal and compressing the spinal cord, disrupting the flow of electrical signals (8).

Pinched nerves can be caused by a number of underlying issues, including poor posture, poor body mechanics, repetitive movements, prolonged positions, soft tissue (muscle, tendon, ligament, fascia) tightness, or inflammation due to injury. Complications from surgery can also cause pinched nerves. A pinched nerve can have a sudden, acute onset such as with surgery or injury, or can present as a chronic issue, such as with poor posture or body mechanics that gradually cause nerve compression over time. Although they can occur anywhere in the body pinched nerves are especially common in the wrist (carpal tunnel syndrome), shoulder region (thoracic outlet syndrome), and lower back (sciatica).

Pinched nerves are often associated with other pathologies; as we discussed, they can directly result from disc herniations and bulges, among other conditions.

It’s important to note that many people have bulging and herniated discs and are asymptomatic. Therefore, you and your doctor should always rely heavily on your history and clinical examination, and less on imaging results (i.e., X-ray, MRI, CT scan) when developing your care plan.

Herniated discs are most prevalent in people aged 30 to 50 years. Men are two times more likely to suffer from a herniated disc than women (2, 3). Each year, up to 2% of adults will develop a new herniation (2). Typically, herniations in older adults result from degenerative changes, while herniations in young adults result from acute injury (5).

Disc herniations most commonly occur in the lumbar spine (low back), followed by the cervical spine (neck) (2). The most prevalent herniation sites are the L4/L5 and L5/S1 levels, which are the bottom two levels of the lumbar spine (9). The lumbar and cervical spines are the most mobile parts of the spine, making them more susceptible to injury. Herniation is uncommon in the thoracic spine (mid-back) because it’s hypomobile, or stiff (2).

There are few studies on the prevalence of bulging discs, as they’re much more likely to be asymptomatic than herniated discs. One study found that in asymptomatic people ages 20-60, about 20% had bulging discs, and the likelihood of having one increased with age (9).

Pinched nerves are also extremely common. Sometimes the symptoms of a pinched nerve merely last seconds, such as when a hand or foot “falls asleep” (10). However, more chronic nerve compressions can cause irreversible damage if untreated, so you should seek care promptly if you suspect a nerve-related origin for your back pain and the pain persists (10).

As with herniations, nerve compressions in the back most commonly arise in the cervical and lumbar regions.

Disc issues and nerve compressions often result in back pain or neck pain. Radiating arm or leg pain also commonly co-occurs with back pain owing to a disc or nerve issue.

Pain from disc pathology can result from the inflammatory response directly related to the pathological disc. The inflammatory component of pain is often localized and less likely to radiate outwards.

Muscle weakness and sensory disturbances (numbness, tingling, diminished reflexes) generally only result from nerve compression, not directly from a disc issue. Pinched nerves can also commonly cause radiating symptoms, felt in the arms or legs, that stem directly from the pathology in the spine. A pinched nerve can cause mild pain and tingling, or if left untreated, permanent nerve dysfunction and even nerve death (11).

The location of the herniation or bulge within the disc will determine if it affects the spinal cord or the spinal nerve (2). When the herniation is in the middle of the disc, it will compress the spinal cord. When it’s in the posterolateral part of the disc, it will affect the spinal nerve.

Trauma-related herniations result in acute pain onset. When pain arises abruptly, it’s more likely due to a herniation than a bulge.

Both herniated and bulging discs gradually worsen over time as a result of chronic, degenerative changes in the spine. With age-related changes, disc pathology may occur at multiple spinal levels. If a bulging disc is near herniation, you may start to experience a sudden increase in pain that is moderate to severe.

When a herniation or bulge arises in the cervical spine, as opposed to the lumbar spine, you may experience:

• Intermittent or continuous neck pain
• Radiating pain in your upper back, shoulder, arm, hand, or fingers (2, 5)
• Numbness or tingling down your arm (i.e., paresthesia) (2, 5)
• Weakness in the shoulder, arm, wrist, or hand muscles (2, 5)
• Diminished reflexes in the arm (2)

On the other hand, disc pathologies in the lumbar spine are characterized by the following symptoms:

• Intermittent or continuous back pain which may be made worse with sneezing, coughing, or standing for long periods of time (5)
• Radiating pain in your buttock, groin, hip, leg, foot, or toes (i.e., sciatica) (2, 5)
• Numbness or tingling down your leg (i.e., paresthesia) (2, 5)
• Weakness in the hip, leg, ankle, or foot muscles (2, 5)
• Spasm of back muscles (5)
• Diminished reflexes in the leg (2, 5)
• Bowel and bladder control issues (5)
• Difficulty walking or incoordination (5)

When a spinal nerve is involved in pain onset, symptoms typically arise on one side of the body and the location of the symptoms corresponds to the specific spinal level that is affected (i.e., C5, L4, L5, etc).

However, when the spinal cord is compressed, it’s possible to have symptoms on both sides of the body. In general, you may experience symptoms in parts of the body below the compression. For example, if the spinal cord is compressed by a herniated disc in the neck, you may experience symptoms in your neck and arms and all the way down to your legs (5). Any spinal cord compression could also cause bowel and bladder control issues (5).

Bulging discs, herniated discs, and pinched nerves are different conditions that can all result in lower back pain. The first two are specific, distinct issues with unique pathologies, while the third is a collective term for a common issue that can arise anywhere in the body.

If you’re experiencing pain, tingling, weakness, or numbness in your neck, back, or limbs, either with an acute or gradual onset, talk to a healthcare provider about whether your pain may be the result of any of these issues. Your healthcare provider will conduct a thorough exam, possibly including imaging, to determine the cause of your pain and dysfunction.

Care for low back pain resulting from any of these three conditions is almost always conservative care, which includes physical therapy for 8-12 weeks (2). Surgery should be saved as a last resort as it has mixed outcomes, unless the pain is the result of trauma or the patient has severe neurological compromise (2).

If you suffer from any of these conditions, participating in regular exercise, maintaining a healthy body weight, and implementing lifestyle modifications, such as improving posture and body mechanics, will help to minimize pain and improve function (2).