Understanding the terminology related to your spine health may help you engage more meaningfully with your care team and treatment options. This glossary provides patient-friendly definitions of common anatomical structures, conditions, and treatment approaches related to the spine. Because spine conditions vary widely, outcomes and appropriate treatments are always evaluated on an individual basis—what applies to one patient may not apply to another.

Spine Anatomy Terms

Annulus Fibrosus

The annulus fibrosus is the strong, multi-layered outer ring of an intervertebral disc, essential for spinal stability. Composed of roughly 17 concentric layers of collagen fibers, its primary role is to contain the nucleus pulposus (the gel-like center) and withstand the pressures placed on the spine during daily movement. When tears or fissures develop in the annulus—known as annular tears—they may compromise the disc’s structural integrity, allow inflammatory chemicals to leak out, and become a significant source of chronic back or neck pain, sometimes contributing to disc degeneration or herniation.

Nucleus Pulposus

The nucleus pulposus is the soft, gel-like core located at the center of each intervertebral disc. Rich in water, this resilient substance acts as a shock absorber, distributing pressure across the vertebrae during movement, bending, and lifting. When the annulus fibrosus is damaged, the nucleus pulposus may push through existing tears—a condition known as a herniated disc—potentially irritating or compressing nearby nerves and causing pain, numbness, or weakness in the limbs.

Intervertebral Disc

Intervertebral discs are the cushion-like structures situated between each vertebra in your spinal column, from the neck down to the lower back. These discs are critical for spinal flexibility and shock absorption. Each disc consists of a tough, fibrous outer ring (annulus fibrosus) and a soft, gel-like inner core (nucleus pulposus). Over time or due to injury, discs may degenerate, bulge, or herniate—common sources of chronic back and neck pain. For a deeper look at how these conditions develop, see our guide on 10 common lumbar spine conditions causing low back pain.

Foramen

The foramen (plural: foramina) refers to the small, bony openings on each side of the spinal column through which spinal nerves exit the spinal canal to transmit signals to the arms, legs, and organs. When discs bulge or herniate, or when bone spurs develop, these openings may narrow—a condition called foraminal stenosis. This narrowing can compress or “pinch” the exiting spinal nerves, leading to pain, numbness, tingling, or weakness in the areas supplied by the affected nerve.

Facet Joint

Facet joints are small, paired joints located at the back of each vertebra, connecting adjacent spinal levels. They provide stability while allowing controlled movements such as bending and twisting. Like other joints in the body, facet joint cartilage may wear down over time, leading to osteoarthritis or inflammation. When inflamed or damaged, facet joints can become a notable source of localized back or neck pain—often distinct from disc-related pain—and symptoms may worsen with certain movements or prolonged standing.

Vertebra

A vertebra is one of the individual bones that make up the spinal column. The spine consists of 33 vertebrae organized into regions: cervical (neck, 7 vertebrae), thoracic (mid-back, 12 vertebrae), lumbar (lower back, 5 vertebrae), sacrum (5 fused vertebrae), and coccyx (4 fused vertebrae). These bones stack upon one another, separated by intervertebral discs, to protect the spinal cord and provide structural support for the body. Damage or misalignment of vertebrae may contribute to a range of spinal conditions.

Expert Take

A thorough understanding of spinal anatomy helps patients ask more targeted questions during consultations. Our clinical team emphasizes that identifying the specific anatomical source of pain—whether a disc, nerve, facet joint, or vertebra—is a foundational step before recommending any treatment pathway. Evaluation is always individualized.

Common Disc Conditions

Annular Tear

An annular tear is a rupture or fissure in the annulus fibrosus, the strong outer ring of an intervertebral disc. These tears may occur due to aging, repetitive stress, or acute injury. Because discs have a limited blood supply, annular tears often struggle to heal on their own. They can allow inflammatory chemicals from the nucleus pulposus to leak out and irritate nearby spinal nerves, causing persistent pain, and may weaken the disc over time—making it more susceptible to bulging or herniation. Learn more about annular tears as a common culprit behind persistent back pain.

Degenerative Disc Disease (DDD)

Degenerative Disc Disease (DDD) describes the gradual wear and breakdown of one or more intervertebral discs over time. Despite its name, it is more accurately described as a condition than a disease, and it affects many people to varying degrees as they age. DDD typically involves a loss of disc hydration, height, and elasticity, often accompanied by the development of annular tears. Not everyone with disc degeneration experiences pain; for those who do, symptoms may include chronic back or neck pain, stiffness, and reduced mobility. Individual presentations vary significantly.

Herniated Disc

A herniated disc occurs when the nucleus pulposus—the soft, gel-like center of an intervertebral disc—pushes through a tear in the annulus fibrosus. The displaced disc material may then press on or irritate nearby spinal nerves, potentially causing sharp pain, numbness, tingling, or weakness in the back, buttocks, legs, or arms, depending on the location of the herniation. Also referred to as a “ruptured disc” or “slipped disc,” this condition is among the more common sources of significant spinal pain prompting patients to explore treatment options. For a broader perspective on related conditions, see our overview of annular tears and chronic back pain.

Bulging Disc

A bulging disc occurs when an intervertebral disc extends beyond its normal perimeter, though the nucleus pulposus remains contained within an intact annulus fibrosus. Unlike a herniated disc, where inner material breaks through the outer layer, a bulging disc may be thought of as a tire with low pressure—the sidewall expands outward without rupturing. A bulging disc does not always cause symptoms, but in some patients it may irritate or compress nearby nerves or spinal structures, leading to pain, numbness, or tingling. Its presence may indicate early stages of disc degeneration.

Discogenic Pain

Discogenic pain is a type of chronic spinal pain that originates directly from a damaged or degenerated intervertebral disc, rather than from nerve compression. It is typically felt in the back itself and may be described as a dull, aching, or burning sensation, often worsening with activities that load the disc—such as prolonged sitting, bending, lifting, or coughing. While MRI may reveal disc degeneration, the diagnosis of discogenic pain is often further confirmed through an annulargram, which can help identify internal annular tears as the specific source of pain. Candidates for treatment are evaluated individually.

Nerve-Related Conditions

Sciatica

Sciatica is a symptom—not a standalone condition—characterized by pain that radiates along the path of the sciatic nerve, which runs from the lower back through the hips and buttocks and down each leg. It typically affects one side of the body. Common underlying causes include a herniated disc, bone spur, or spinal stenosis compressing a portion of the sciatic nerve. Symptoms may range from a mild ache to a sharp, burning, or electric shock-like sensation, sometimes accompanied by numbness, tingling, or muscle weakness in the affected leg. For a closer look at management options, see 10 myths about sciatica and non-surgical relief.

Radiculopathy

Radiculopathy refers to a set of symptoms caused by compression or irritation of a spinal nerve root. This may occur anywhere along the spine but is most common in the cervical (neck) and lumbar (lower back) regions. Symptoms often include pain, numbness, tingling, or weakness radiating along the specific nerve pathway—lumbar radiculopathy may affect the leg, while cervical radiculopathy may affect the arm. Common underlying causes include herniated discs, bone spurs, spinal stenosis, or thickened ligaments that narrow the space around nerve roots.

Expert Take

Our clinical team notes that distinguishing true radiculopathy from referred discogenic pain is an important diagnostic step. Both conditions may produce leg or arm pain, but their underlying mechanisms—and therefore appropriate treatments—can differ considerably. A thorough evaluation, including imaging and clinical history, guides individualized treatment recommendations.

Treatment Approaches

Intra-Annular Fibrin Injection

Intra-annular fibrin injection is a minimally invasive biologic disc repair procedure aimed at treating chronic discogenic pain by addressing annular tears within damaged spinal discs. During the procedure, a biologic fibrin sealant is precisely injected into the torn annulus fibrosus under live X-ray (fluoroscopic) guidance. The fibrin may act as a natural scaffold, supporting the disc’s own regenerative processes. This approach targets the structural source of pain—the disc tear itself—and may be considered by patients seeking non-surgical options. Candidacy is determined through individual evaluation; outcomes vary by patient and condition. Learn more about annular tear repair as a non-surgical path to spine stability.

Regenerative Medicine

Regenerative medicine is a field focused on developing treatments that support the body’s natural healing capabilities to repair or restore damaged tissues. In spine care, regenerative approaches may offer non-surgical solutions that go beyond temporary symptom management. Treatments such as intra-annular fibrin injection fall within this category, aiming to restore disc integrity and function in appropriate candidates. This approach seeks to support longer-term healing by leveraging biological processes rather than relying on invasive surgery, though individual suitability and outcomes vary. For a broader overview, see 5 non-surgical disc treatments for chronic back pain.

Epidural Steroid Injection

An epidural steroid injection (ESI) is a commonly used, minimally invasive procedure intended to temporarily reduce inflammation and pain associated with irritated spinal nerves—often related to herniated discs, spinal stenosis, or degenerative disc disease. During an ESI, corticosteroid medication, sometimes combined with a local anesthetic, is injected into the epidural space surrounding the spinal cord and nerve roots. While ESIs may provide meaningful short-term relief in some patients, they do not repair underlying disc damage or annular tears. Due to potential side effects, the number of ESIs a patient may receive within a given period is typically limited, and long-term effectiveness varies.

Expert Take

Our clinical team views epidural steroid injections as one tool within a broader pain management strategy. When injections provide only temporary relief and underlying disc pathology—such as an annular tear—has been identified, patients may wish to explore whether they are candidates for a more structurally targeted approach. All treatment decisions are made through individualized evaluation.

For additional definitions and context, visit our related resource: A Glossary of Common Spine Conditions, Anatomy, and Treatments.