In recent years, many scholars have conducted in-depth studies on the neuroanatomy, biochemistry, and biomechanics of the intervertebral disc before and after degeneration or injury, and it has been gradually recognized that lesions occurring within the intervertebral disc can also cause lower back pain in the absence of disc herniation – discogenic lower back pain.
Pathologic changes of structural damage to the intervertebral disc
These pathological changes, known as intra-disc disorders (IDD), occur in approximately 40% of patients with chronic lower back pain.
Pathogenesis of discogenic lower back pain
1, the stimulation of chemical substances in the intervertebral disc
In recent years, many studies have shown that the process of intervertebral disc degeneration or injury can produce a large number of inflammatory mediators or degeneration products, and the stimulation of these chemicals on peripheral nerve fibers can make the nerve tissue in a hypersensitive state, which can cause pain under slight external stimulation.
2, the emergence of the posterior intervertebral disc fissure fiber ring
The appearance of a fissure from the nucleus pulposus to the outer layer of the annulus fibrosus is accompanied by the invasion of granulation tissue and the exudation of inflammatory cells to form a band of inflammatory granulation tissue in the posterior part of the intervertebral disc to produce growth factors related to healing and growth.
Under the action of these factors, degeneration and inflammation of the intervertebral disc occur, thus causing lower back pain.
3.Change of mechanical pressure in the intervertebral disc
It is currently believed that because the content of inflammatory mediators in the degenerated intervertebral disc is very high, under the action of inflammatory mediators, the injury receptors at the sinus nerve terminals are in a hypersensitive state, thus the pain threshold to mechanical pressure decreases, and nerve impulses can be generated under slight mechanical pressure stimulation.
The diagnosis of discogenic lower back pain is clinically extremely common and multifactorial, and is a loss-of-function lower back pain caused by stimulation of pain receptors within the disc by various intravertebral disorders (e.g., degeneration, endplate injury, etc.), without neurogenic symptoms, without radiographic evidence of ganglion or segmental hyperactivity, and can be described as chemically mediated discogenic pain.
The clinical presentation is often highly variable and the diagnosis of discogenic lower back pain can only be made when the clinical presentation, MRI, and discography are combined and other known causes of chronic lower back pain are excluded.
Clinical features
(1) The most important clinical feature is the decreased tolerance to sitting, and the pain often increases in sitting position. The reason for this is that the pressure in the intervertebral disc is highest in the sitting position, especially in the sitting forward position.
(2) The pain is mainly located in the lower back, sometimes it can also radiate to the lower extremities, and 65% of them are accompanied by pain below the knee of the lower extremities, which can be unilateral. The most common aggravating factor is after exertion, and painful symptoms are heavier in sitting than in standing or walking.
Imaging characteristics
(1) X-ray manifestations.
Conventional X-ray examination is mostly negative, and sometimes a slightly narrowed intervertebral space, bone formation or intervertebral instability is seen.
(2) T2-weighted MRI.
The images show low-signal changes in the diseased discs (black disc sign) and high-signal areas posterior to the annulus fibrosus. This is considered to be a sensitive manifestation of IDD.
Diagnostic criteria; there is no gold standard for diagnosis, but it is generally accepted that the following conditions must be met.
(1) Recurrent lower back pain symptoms lasting >6 months.
(2) Persistent lower back pain aggravated in sitting position without radicular symptoms.
(3) Positive discography or MR manifestation of typical single-segment disc hyposignal and high-signal areas in the posterior part of the fibrous ring.
Positive discogram- induced, replicated lower back pain during discogram and discogram showing tear of the fibrous annulus.