Most Common Causes of Sciatica
A variety of lower back conditions may lead to sciatica. Most commonly, a lumbar herniated disc will cause sciatic nerve pain. The most common causes of sciatic pain include:
Lumbar Herniated Disc
A herniated disc occurs when the soft inner core of the disc (nucleus pulposus) leaks out, or herniates, through the fibrous outer core (annulus) and irritates the nerve root from pressing against it.
A herniated disc is sometimes referred to as a slipped disc, ruptured disc, bulging disc, protruding disc, or a pinched nerve. Sciatica is the most common symptom of a lumbar herniated disc.
Many factors increase the risk for disc herniation:
- Lifestyle choices such as tobacco use, lack of regular exercise, and inadequate nutrition substantially contribute to poor disc health.
- As the body ages, natural body changes cause discs to gradually dry out. This can affect disc strength and resilience. The aging process can make your discs less capable of absorbing the shock from your movements.
- Poor posture combined with the habitual use of incorrect body mechanics stresses the lumbar spine and affects its normal ability to carry the bulk of the body's weight.
Combine these factors with the effects from daily wear and tear, injury, incorrect lifting, or twisting and it is easy to understand why a disc may herniate.
Degenerative Disc Disease
While disc degeneration is a natural process that occurs with aging, for some people one or more degenerated discs in the lower back can also irritate a nerve root from pressing against it and cause sciatica.
Degenerative disc disease is not really a disease. A diagnosis of degenerative disc disease is alarming to many because it sounds like a progressive disease. For most people the term degenerative understandably implies that the symptoms will get worse with age. However, the term does not apply to the symptoms. It only describes the process of the disc degenerating over time. Degenerative discs are often referred to as narrowing of the disc space or loss of disc height.
Several factors can cause discs to degenerate, including age. Specific factors include:
- The drying out of the disc. As we age, the disc dries out and doesn't absorb shocks as well
- Daily activities and sports can cause tears in the outer core of the disc
- Injuries can cause swelling, soreness and instability
Unlike other tissues of the body, there is very little blood supply to the disc, so once a disc is injured, it cannot repair itself, and the discs can start to deteriorate.
Degenerative spondylolisthesis occurs due to the aging process along with the development of marked facet joint arthritis with rotatory vertebral slip. Degenerative spondylolisthesis occurs most often at the L4-L5 lumbar vertebrae level. Its isthmic counterpart, most often occurs at the L5-S1 lumbosacral level.
Degenerative changes in the spine are often referred to those that cause the loss of normal structure and/or function. Degenerative spondylolisthesis (DS) is a disorder that causes the forward motion (slip) of one vertebral body over the one below.
A lumbar spinal condition in which a fracture of the isthmus causes one vertebral body to slip forward on top of the vertebral body below it. The isthmus is a small, thin segment of bone that connects the facet joints at the back of the spine.
With a combination of disc space collapse, the fracture, and the vertebral body slipping forward, the nerve can get pinched and cause sciatica.
Lumbar spinal stenosis This condition commonly causes sciatica due to a narrowing of the spinal canal. This usually happens when bone and/or tissue grow in the openings in the spinal bones which can press against the nerves branching out from the spinal cord. The result can be pain, numbness, or weakness, most often in the legs, feet, and buttocks.
Lumbar spinal stenosis is related to natural aging in the spine and is relatively common in adults over age 60. It's most often caused by changes that can happen as people age. For example:
- Connective tissues called ligaments get thicker.
- Arthritis can lead to the growth of bony spurs that push on the nerves that branch out from the spinal cord.
- Discs between the bones may be pushed backward into the spinal canal.
The sciatic nerve can get irritated as it runs under the piriformis muscle in the buttock. If the piriformis muscle irritates or pinches a nerve root that comprises the sciatic nerve, it can cause sciatica-type pain.
Piriformis syndrome is an uncommon neuromuscular disorder that is caused when the piriformis muscle compresses the sciatic nerve. The piriformis muscle is a flat, band-like muscle located in the buttocks near the top of the hip joint. This muscle is important in lower body movement because it stabilizes the hip joint and lifts and rotates the thigh away from the body. This enables us to walk, shift our weight from one foot to another, and maintain balance. It is also used in sports that involve lifting and rotating the thighs -- in short, in almost every motion of the hips and legs.
The sciatic nerve passes alongside, or with some people, through the piriformis muscle, down the back of the leg, and eventually branches off into smaller nerves that end in the feet. Nerve compression can be caused by spasm of the piriformis muscle.
This is not a true radiculopathy (the clinical definition of sciatica). The leg pain can feel the same as sciatica caused by a nerve irritation. A careful diagnosis is necessary to determine the actual cause of the person's pain.
Sacroiliac Joint Dysfunction
There are two sacroiliac joints (often referred to as the SI joints) in your lower back, and they sit on each side of your spine. Their main job is to carry the weight of your upper body when you stand or walk and shift that load to your legs. The SI joints are a shock absorber for your spine and provide stability for your body. The SI joints usually don’t move more than 2 – 4 millimeters themselves. But each one contains many nerve endings that can cause significant pain if the joint is damaged or loses its ability to move properly. Everyday wear and tear, arthritis, or a single injury can damage these joints, changing their normal movement and creating chronic and sometimes debilitating SI joint pain that often, generally feels like low back pain.
Irritation of the sacroiliac joint—located at the bottom of the spine—can also irritate the L5 nerve, which lies on top of the sacroiliac joint, causing sciatica-type pain. The leg pain can feel the same as sciatica caused by a nerve irritation.
Major reasons for pain around the SIJ include:
- Muscle tightness
- Pregnancy: the pelvis widens to prepare for birth, stretching the ligaments. These are strong, flexible tissue that connects bone to bone
- Different types of arthritis
- Difference in leg lengths
- Wearing away of the cartilage (cushion) between the bones
- Trauma from impact, such as landing hard on buttocks
- History of pelvic fractures or injuries