Spine health terms can be confusing when you are researching a diagnosis or weighing treatment options. This glossary defines the most common terms in spine anatomy and disc conditions — from annulus fibrosus to radiculopathy — to help you have more informed conversations with your care team. Individual conditions vary; a clinical evaluation determines which terms apply to your specific situation.

Annulus Fibrosus

The annulus fibrosus is the tough, fibrous outer ring of an intervertebral disc. Composed of approximately 17 concentric layers of collagen fibers, it encases the gel-like nucleus pulposus within, providing the disc’s structural integrity and resistance to pressure. When healthy, this structure prevents inner disc material from bulging or rupturing. In patients experiencing chronic back pain, tears in the annulus fibrosus are a common contributing factor. These tears may allow inflammatory substances to leak out and irritate nearby nerves — and are a key target for treatments aimed at repairing disc integrity at the source.

Nucleus Pulposus

The nucleus pulposus is the soft, gel-like center of an intervertebral disc. Rich in water, this core acts as the primary shock absorber for the spine, distributing pressure across the vertebrae during movement and weight-bearing activities. When the outer annulus fibrosus sustains a tear, the nucleus pulposus may extrude or herniate through the opening, potentially compressing spinal nerves and causing pain, numbness, or weakness in areas such as the legs or arms. Protecting disc health involves preserving this central component from leakage.

Intervertebral Disc

Intervertebral discs are the specialized cushions located between each vertebra in your spinal column, from the neck to the lower back. They serve two primary functions: acting as shock absorbers that protect spinal bones from impact, and enabling the flexibility required for bending, twisting, and daily movement. Each disc consists of an outer annulus fibrosus and an inner nucleus pulposus. Degeneration, injury, or accumulated wear and tear to these discs are among the most common contributors to chronic back and neck pain.

Foramen

The foramen (plural: foramina) refers to the natural openings through which spinal nerves exit the spinal column and travel to different parts of the body. A pair of foramina exists between each vertebra, one on each side. When conditions such as disc bulging, disc herniation, bone spurs, or thickened ligaments develop, these openings may narrow — a condition known as foraminal stenosis. This narrowing can lead to nerve compression, causing symptoms such as pain, tingling, numbness, or weakness that may radiate into the arms, hands, legs, or feet, depending on which spinal level is affected.

Facet Joint

Facet joints are small, paired joints at the back of each vertebra, connecting adjacent spinal bones. They guide and limit spinal movement, providing stability while allowing for bending and twisting. Like other joints in the body, facet joint cartilage can wear down over time, potentially leading to arthritis. When facet joints become inflamed or arthritic, they may be a significant source of localized back or neck pain — separate from disc-related issues. A comprehensive spine assessment typically evaluates facet joint health alongside disc and nerve findings.

Vertebra

A vertebra (plural: vertebrae) is one of the individual bones that make up the spinal column. The spine consists of 33 vertebrae organized into five regions: cervical (neck), thoracic (mid-back), lumbar (lower back), sacrum, and coccyx. These bones stack on top of each other, providing structural support, protecting the spinal cord, and anchoring muscles. Between most vertebrae are intervertebral discs. Damage to a vertebra — such as a fracture or misalignment — may contribute to pain and functional limitations that require clinical evaluation to properly address.

Annular Tear

An annular tear is a rip or fissure in the annulus fibrosus, the tough outer layer of a spinal disc. These tears can result from injury, trauma, or natural degenerative changes over time. Annular tears are a common contributor to discogenic pain — where discomfort originates directly from the disc itself — due to the potential leakage of inflammatory chemicals from the nucleus pulposus that may irritate nearby nerve endings. Because the disc has a limited blood supply, annular tears often struggle to heal without targeted intervention. For patients with persistent back pain, identifying and addressing annular tears is an important diagnostic step.

Degenerative Disc Disease (DDD)

Despite its name, Degenerative Disc Disease (DDD) is more accurately described as a condition rather than a disease. It refers to the natural wear and tear that occurs in spinal discs over time — involving progressive breakdown of one or more intervertebral discs, loss of disc height, reduced hydration, and the development of tears. While many people over 50 show some degree of disc degeneration on imaging, not all experience pain. For those who do, DDD may lead to chronic back pain, stiffness, or other symptoms due to the disc’s diminished ability to absorb shock. Treatments focus on managing symptoms and, in appropriate candidates, supporting or repairing disc tissue.

Herniated Disc

A herniated disc occurs when the soft, gel-like nucleus pulposus pushes through a tear in the annulus fibrosus — the disc’s tougher outer layer. When the herniated material presses on nearby spinal nerves, it may cause sharp pain, numbness, tingling, or weakness that radiates into the arms or legs, often far from the actual disc site. Patients often refer to this as a “slipped disc” or “ruptured disc.” Identifying a herniated disc is a key diagnostic step for developing treatment strategies aimed at relieving nerve compression and supporting the healing process. See also: Bulging Disc vs. Herniated Disc: Understanding Your Pain.

Bulging Disc

A bulging disc occurs when an intervertebral disc extends beyond its normal perimeter, but the outer annulus fibrosus remains intact — unlike a herniated disc, where the nucleus pulposus breaks through entirely. The disc’s circumference may appear to swell outward. While structurally less severe than a herniation, a bulging disc may still cause significant pain if the expanded disc material presses on nearby spinal nerves or other structures within the spinal canal. Distinguishing between a bulging and a herniated disc helps guide treatment decisions, as both may produce similar radicular symptoms through different underlying mechanisms.

Sciatica

Sciatica describes pain that radiates along the path of the sciatic nerve — the longest nerve in the body. This pain typically originates in the lower back, travels through the buttock, and extends down the back of one leg. Symptoms may range from a mild ache to a sharp or burning sensation, and may include numbness, tingling, or weakness in the affected limb. Sciatica is most often associated with a herniated disc or bone spur in the lower spine that compresses a portion of the sciatic nerve. Addressing the underlying nerve compression is central to relieving these symptoms for appropriate candidates. For more, see: 10 Myths About Sciatica and Non-Surgical Relief.

Radiculopathy

Radiculopathy describes a condition in which a nerve root in the spine becomes compressed or irritated, producing symptoms that radiate along that nerve’s pathway. These symptoms may include pain, numbness, tingling, or weakness in the arms (cervical radiculopathy) or legs (lumbar radiculopathy). Common causes include herniated discs, spinal stenosis, bone spurs, or inflammation. While symptoms are felt in the extremities, the underlying issue resides in the spine. Treatment focuses on decompressing or calming the irritated nerve root to reduce radiating discomfort and restore function where possible.

Discogenic Pain

Discogenic pain refers to chronic back or neck pain that originates directly from a damaged or degenerated intervertebral disc, rather than from nerve compression. This type of pain is often a deep, aching discomfort in the spine itself that may worsen with activities that load the disc — such as sitting, bending forward, or lifting. It may be caused by annular tears that allow inflammatory chemicals to escape, or by a disc that has lost its ability to absorb shock effectively. Accurately diagnosing discogenic pain matters because treatments such as intra-annular fibrin injection are specifically designed to target damaged disc tissue at the source of the problem.

Expert Take

Discogenic pain is frequently underdiagnosed because imaging alone does not always reveal the degree of disc-level inflammation or the presence of small annular tears. Our clinical team uses a combination of advanced imaging interpretation and detailed functional history to identify discogenic contributors — so that candidates for biologic disc repair are evaluated on findings that reflect their actual pain source, not just structural changes visible on MRI. Each case is assessed individually before any treatment pathway is recommended.

Fibrin

Fibrin is a naturally occurring protein in the human body that plays a central role in blood clotting and wound healing. When an injury occurs, fibrin molecules polymerize to form a mesh-like scaffold that helps stop bleeding and provides a framework for new tissue growth. In the context of regenerative spine care, purified fibrin is precisely delivered into damaged spinal discs during the intra-annular fibrin injection procedure. Here, it acts as a biologic sealant for annular tears and provides natural scaffolding that may support the body’s own healing mechanisms. Individual responses vary and are evaluated on a case-by-case basis.

Intra-annular Fibrin Injection

Intra-annular fibrin injection is a biologic disc repair procedure for appropriate candidates with chronic discogenic back or neck pain caused by annular tears. This minimally invasive approach involves injecting a concentrated fibrin solution directly into the tears of the annulus fibrosus — the outer ring of the spinal disc. The fibrin acts as a natural sealant and provides a scaffold that may support the body’s own regenerative processes and encourage disc tissue repair. The goal is to restore disc structural integrity, reduce leakage of inflammatory chemicals, and address the underlying source of pain as a non-surgical alternative. Candidacy is determined through individual evaluation; outcomes and recovery timelines vary by patient.

If you would like to read more, we recommend this article: Spine Anatomy and Disc Conditions Explained