What causes low back pain?

Almost everyone alive either had an episode of low back pain or will have one at some point in their life, its just that common. But why does it happen and what causes it? While some are fortunate to only have a brief “acute” episode of pain, others suffer for a long time with “chronic” lower back pain. What determines that? In this post I will address acute versus chronic lower back pain as well as the most common causes and diagnoses.

Acute or chronic and why?

Acute pain is the type of pain that has a specific cause and is expected to improve with time and healing and to resolve completely within weeks or months. Acute pain is usually due to a known cause and has an understood reason for it. It can be due to a muscle sprain or strain, a tear, or contusion. Acute pain will stop once the underlying cause resolves or the injury heals. A basic example is someone lifting and carrying a heavy box pulls a muscle in their lower back and has sudden lower back pain, after a few days of icing, stretching, and anti-inflammatory medication the pain resolves completely. Chronic pain on the other hand is pain that lasts longer than expected, has a poorly understood mechanism and lasts longer than 6 months, sometimes even years. Sometimes there is even no injury to explain or any apparent body damage. Other times chronic pain might start out as acute pain with a known specific cause or injury but can transition into chronic pain once the cause is no longer there or the injury has healed and once its been more than 6 months. An example can be someone with more than 6 months of lower back pain who has normal MRI findings, normal x-ray findings but has persisting pain despite treatment efforts. Another example could be neck or lower back pain persisting for more than 6 months with imaging studies noted for diffuse degenerative findings like degenerative discs, spinal arthritis, bulging discs, spinal stenosis , all of which may be contributing to the pain.

What are common causes of low back pain?

Causes of low back pain can be divided into the following categories: congenital (born with), sudden injuries (sprain/strains, trauma, disc herniations), degenerative injuries (wear and tear, arthritis), nerve and spinal cord related (nerve root compression, spinal cord compression), autoimmune disease (ankylosing spondylitis, rheumatoid, etc.), and non-spine causes (back pain due to sources not actually located in the back).

Congenital: This means that the cause of your low back pain has to do with something you were either born with or developed very early in life. These congenital conditions are typically a result of abnormal alignment of the spine or defects affecting the spinal cord and nerves. Examples of abnormal spinal alignment include kyphosis, lordosis, and scoliosis. In kyphosis bone deformities result in the spine bending more forward than normal. In lordosis its the opposite, the deformities results in the spine bending more backward than normal. In scoliosis the abnormalities result in the spine bending sideways.

Sudden injuries: When low back pain is due to a known sudden event, trauma, or injury like a bad fall, lifting something really heavy, car accident, repetitive bending/twisting, etc. This can result in sprain/strain injury, fracture, or disc injury. The sprains and strains or ligaments and muscles are expected to resolve quickly within a few days or weeks while fractures and disc injuries can take much longer. Types of fractures vary with severity and type and some require surgical intervention. Disc injuries can range from a mild disc bulge to a large disc herniation some of which may also require surgery.

Degenerative: Low back pain due to wear and tear and arthritis of spinal joints and discs. Those who are having lower back pain due to degenerative causes will likely have either lumbar spondylosis, degenerative disc disease, spinal stenosis, facet joint pain, or even some combination of the these.

Normal spine (below left) and Arthritic Spine (below right)

Nerve and spinal cord: Injury to the spinal cord and/or nerve roots can be a cause of lower back pain. Typically in such injuries there may also be pain that will radiate down the legs as well as numbness and tingling. Severe cases can also result in muscle weakness, loss of balance, bowel/bladder incontinence and other neurological symptoms. Spinal cord or nerve root injuries can result due to herniated discs, spinal stenosis, vertebral fractures, spondylolisthesis (when one vertebrae bone slips out of place compared to one below it), just to name some.

Autoimmune: Autoimmune disorders can cause inflammation in various parts of the body, including the spine and sacroiliac joints, leading to chronic low back pain. The most common autoimmune disorders associated with low back pain are ankylosing spondylitis, rheumatoid arthritis, psoriatic arthritis, and lupus. These disorders can have unique features that help distinguish them from other causes of low back pain. To diagnose these disorders, healthcare professionals may perform a physical exam, blood tests, and imaging studies.

Non-spinal: There are of course reasons to have back pain that are not caused by the ligaments, joints and bones of the spine and the surrounding musculature. One common culprit is the hip joint and the muscles that move the hip. One may have significant hip joint arthritis, or have a hip muscle/tendon injury yet the pain may manifest in the back or posterior to the hip itself. Sometimes the pain from the hip may radiate down the thigh and be misdiagnosed as radicular pain coming from the spine or “sciatica.” Another common diagnosis that can mimic or present like radicular pain is hip bursitis (trochanteric bursitis) which is irritation or inflammation of the hip bursa (fluid filled sac). Speaking of sciatica, the true kind is due to compression of the actual sciatic nerve and one reason this may happen is seen in Piriformis Syndrome where piriformis muscle dysfunction (contracture, spasms, etc.) results in compression of the sciatic nerve which passes through the muscle. There is also back pain due to the sacroiliac joint (SI joint) which connects the sacrum, a triangular bone at the bottom of the spine, to the pelvis. When the SI joint becomes inflamed or irritated, it can cause lower back pain, as well as pain in the buttocks, hips, and thighs. Other common non spinal causes of low back pain include fibromyalgia, a chronic pain syndrome which is characterized by widespread musculoskeletal pain, fatigue and heightened tenderness to tactile pressure, general fatigue, and sleep disturbance. Finally its crucial not to miss back pain due to some kind of organ pathology like prostatitis, pyelonephritis, urinary tract infection, aortic aneurysm, acute pancreatitis, duodenal ulcers, cholecystitis, nephrolithiasis, and cancer.