Most commonly, mechanical issues and soft-tissue injuries are the cause of low back pain. These injuries can include damage to the intervertebral discs, compression of nerve roots, and improper movement of the spinal joints.
The single most common cause of lower back pain is a torn or pulled muscle and/or ligament.
Muscle Strain and Ligament Sprain
A low back sprain or strain can happen suddenly, or can develop slowly over time from repetitive movements.
- Strains occur when a muscle is stretched too far and tears, damaging the muscle itself.
- Sprains happen when over-stretching and tearing affects ligaments, which connect the bones together.
For practical purposes, it does not matter whether the muscle or ligament is damaged, as the symptoms and treatment are the same.
Common causes of sprain and strain include:
- Lifting a heavy object, or twisting the spine while lifting
- Sudden movements that place too much stress on the low back, such as a fall
- Poor posture over time
- Sports injuries, especially in sports that involve twisting or large forces of impact
While sprains and strains do not sound serious and do not typically cause long-lasting pain, the acute pain can be quite severe.
Causes of Chronic Lower Back Pain
Pain is considered chronic once it lasts for more than three months and exceeds the body’s natural healing process. Chronic pain in the low back often involves a disc problem, a joint problem, and/or an irritated nerve root. Common causes include:
Lumbar herniated disc. The jelly-like center of a lumbar disc can break through the tough outer layer and irritate a nearby nerve root. The herniated portion of the disc is full of proteins that cause inflammation when they reach a nerve root, and inflammation, as well as nerve compression, cause nerve root pain. The disc wall is also richly supplied by nerve fibers, and a tear through the wall can cause severe pain.
Degenerative disc disease. At birth, intervertebral discs are full of water and at their healthiest. As people age over time, discs lose hydration and wear down. As the disc loses hydration, it cannot resist forces as well, and transfers force to the disc wall that may develop tears and cause pain or weakening that can lead to a herniation. The disc can also collapse and contribute to stenosis.
Facet joint dysfunction. There are two facet joints behind each disc at each motion segment in the lumbar spine. These joints have cartilage between the bones and are surrounded by a capsular ligament, which is richly innervated by nerves. These joints can be painful by themselves, or in conjunction with disc pain.
Sacroiliac joint dysfunction. The sacroiliac joint connects the sacrum at the bottom of the spine to each side of the pelvis. It is a strong, low-motion joint that primarily absorbs shock and tension between the upper body and the lower body. The sacroiliac joint can become painful if it becomes inflamed (sacroiliitis) or if there is too much or too little motion of the joint.
Spinal stenosis. This condition causes pain through narrowing of the spinal canal where the nerve roots are located. The narrowing can be central, forminal, or both, and can be at a single level or multiple levels in the lower back.
Spondylolisthesis. This condition occurs when one vertebra slips over the adjacent one. There are 5 types of spondylolisthesis but the most common are secondary to a defect or fracture of the pars (between the facet joints) or mechanical instability of the facet joints (degenerative). The pain can be caused by instability (back) or compression of the nerves (leg).
Osteoarthritis. This condition results from wear and tear of the disc and facet joints. It causes pain, inflammation, instability, and stenosis to a variable degree, and can occur at a single level or multiple levels of the lower spine. Spinal osteoarthritis is associated with aging and is slowly progressive. It is also referred to as spondylosis or degenerative joint disease.
Deformity. Curvature of the spine can include scoliosis or kyphosis. The deformity may be associated with lower back pain if it leads to the breakdown of the discs, facet joints, sacroiliac joints or stenosis.
Trauma. Acute fractures or dislocations of the spine can lead to pain. Lower back pain that develops after a trauma, such as a motor vehicle accident or a fall, should be medically evaluated.
Compression fracture. A fracture that occurs in the cylindrical vertebra, in which the bone essentially caves in on itself, can cause sudden pain. This type of fracture is most common due to weak bones, such as from osteoporosis, and is more common in older people.
It is important to note that the presence of one or more of these conditions does not necessarily mean that is the cause of pain. For example, osteoarthritis or degenerative disc disease could appear on an imaging study but the person may not report pain.
Less Common Causes of Low Back Pain
While considerably less common, low back pain may also be caused by:
Infection. Also called osteomyelitis, a spinal infection is rare but can cause severe pain and is life threatening if untreated. It can be caused by surgical procedures, injections, or spread through the blood stream. Patients with a compromised immune system are more susceptible to developing an infection in the spine.
Tumor. Most spinal tumors start in another part of the body and metastasize to the spine. The most common tumors that spread to the spine start from cancer in the breast, prostate, kidney, thyroid, or lung. Any new symptoms of back pain in a patient with a known diagnosis of cancer should be evaluated for possible spinal metastasis.
Autoimmune disease. Back pain is a possible symptom associated with autoimmune conditions, such as ankylosing spondylitis, rheumatoid arthritis, lupus, crohn’s disease, fibromyalgia, and others.
This list includes the more common causes of back pain, but there are many more. Finding the optimal treatment for low back pain usually depends on obtaining a correct clinical diagnosis that identifies the underlying cause of the patient’s symptoms.