Low Back Pain & Herniated Disc

"The lifetime prevalence of back pain in adults may reach 84%," and "In the U.S., low-back pain is the most common reason for disability." Almost all of it is ordinary: "Fewer than 5% to 10% of low back pain presentations result from specific spinal pathology, whereas 90% to 95% reflect nonspecific mechanical pain suitable for conservative management without routine imaging." NIAMS sorts it by time: "Acute back pain happens suddenly and usually lasts a few days to a few weeks." "Subacute back pain can come on suddenly or over time and lasts 4 to 12 weeks." "Chronic back pain may come on quickly or slowly and lasts longer than 12 weeks and occurs daily."

A strain is a small injury with a big reflex. "Acute episodes typically reflect sprain or strain of paraspinal musculature and supporting ligaments after a loaded segment is driven into excessive flexion, extension, or rotation." The microtears produce "edema, inflammatory mediator release, and reflex spasm that sensitize local nociceptors and restrict segmental motion." For strains, "Pain generally worsens with movement and improves with rest, and the range of motion is often restricted." Most of it resolves — "most people find relief within 6 weeks" — but "1-year recurrence rates ranging from 24% to 80%" are reported, and "Persistent peripheral nociceptive drive from these structures may, in some cases, induce central sensitization and facilitate the transition from acute to chronic pain." "Chronic, disabling back pain is more likely with prior episodes, high symptom intensity, depression, fear-avoidant behavior, or accompanying leg or widespread symptoms."

"The intervertebral discs consist of an inner nucleus pulposus (NP), outer annulus fibrosus (AF), and the cartilaginous endplates," and "The nucleus pulposus is a gel-like structure that is composed of approximately 80% water." Age dries it out: "With aging, the disc fibrochondrocytes undergo senescence and a reduction in proteoglycans production. This reduction in proteoglycans leads to dehydration and disc collapse, increasing the strain on the annulus fibrosus, resulting in tears and fissures, and consequentially facilitating the nucleus pulposus herniation." A sudden load can do it too — "axial overloading applies a large biomechanical force on the healthy disc, which may result in extrusion of disc material through a failing annulus fibrosus."

It goes backward and to the side, toward the nerve. "The annulus fibrosus is thinner on the posterolateral aspect and lacks support from the posterior longitudinal ligament, making it vulnerable to herniations. Due to the proximity of the nerve root, a posterolateral herniation is more likely to result in nerve root compression." "Approximately 95% of disc herniations in the lumbar area occur at L4-L5 or L5-S1," most often between the third and fifth decades, "with a male to female ratio of 2 to 1."

Two pains with two causes. "The pressure exerted by the herniated disc on the longitudinal ligament and the irritation caused by the local inflammation results in localized back pain. The lumbar radicular pain arises when disc material exerts pressure or contacts the thecal sac or lumbar nerve roots, resulting in nerve root ischemia and inflammation." That is why the pain runs down the leg, and why raising pressure makes it worse — "Pain exacerbation with straining, coughing, and sneezing," and "Pain intensified in a seated position, as the pressure applied to the nerve root is increased by approximately 40%." The body usually clears it: improvement is "due to phagocytosis and enzymatic resorption of extruded material," and "Over 85 to 90% of patients with an acute herniated disc experience relief of symptoms within 6 to 12 weeks without any treatments."

"Mechanical back pain comprises 90% of cases, so health providers can easily miss rare causes while focusing on common etiologies." The dangerous minority: malignancy — "a history of metastatic cancer or unexplained weight loss, with focal tenderness"; infection — "recent spinal procedures, intravenous drug use, immunosuppression, or prior lumbar surgery, especially if fever"; fracture — "significant trauma, prolonged corticosteroid use, osteoporosis, or age over 70"; and the aorta — "Acute or chronic aortic dissection can manifest as tearing back pain." No single flag is decisive — "individual red flags possess limited standalone diagnostic accuracy," while combinations of flags perform better.

Cauda equina syndrome is the one every nurse must recognise. "The cauda equina is a group of nerves and nerve roots stemming from the distal end of the spinal cord, typically levels L1 through L5, and contains axons that provide both motor and sensory innervation to the legs, bladder, anus, and perineum." "Cauda equina syndrome (CES) results from compression and disruption of the function of these nerves," and "The most common cause of compression in 45% of CES is a herniated lumbar intervertebral disc" — typically a massive midline herniation. It "occurs in 3% of all disk herniations."

"Symptoms suggestive of cauda equina syndrome require immediate recognition, as this condition constitutes a surgical emergency. New urinary retention, difficulty initiating micturition, bowel dysfunction, or sensory loss in the perineal or perianal region" — saddle anesthesia — "are key historical features." "Bilateral sciatica, rapidly escalating leg pain, or new bilateral lower-extremity weakness further heighten concern." The timing is everything: "the onset of perineal anesthesia associated with bladder dysfunction is typical of the start of CES and the time at which the clock starts on diagnosis and management," whereas "painless urinary retention often has the greatest predictive value as a stand-alone symptom, but it is unfortunately indicative of late, often irreversible CMS/CES." Surgery "within 48 hours of initial presentation" is associated with a better prognosis.