What Is the Cause of Sciatica Pain?

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Lower back pain associated with sciatica is a very common, self-limiting condition. It can reduce quality of life associated with activities of daily living in a significant proportion. In USA only more than 6 million people per year suffer from sciatica and cost billions of USD for the health economy.

Life time prevalence of sciatica and lower back pain is about 60 – 75% and it equally affects men and women. Sciatica usually affects humans in their 4th or 5th decades of life. Sciatica correction surgeries are common among the people in their 4th decade of life. See also How to Relieve Sciatic Nerve Pain? for more information.


Lower back pain affects the back between the chest cavity and butt. It often radiated to the thighs in posterior aspects. Sciatica is the back pain which involves the distribution of a lumbar nerve root. It is often associated with abnormal sensory and motor deficits. Pain can be exacerbated by walking and other movements.

Risk factors

  • Family history of Lower back pain associated with sciatica
  • Occupations which involves frequent bending forward and backwards
  • Occupations involving frequent weight lifting
  • Osteoporosis
  • Congenital lordosis and scoliosis of the spine

Practical Anatomy

Anatomy in the lumbosacral and sacroiliac region is very complex. It consists of various bones, ligaments, joints and other soft tissues. Each of these can contribute to sciatica pain and there can be combinations of different pathological processes for sciatica. There are mainly two theories for the pathophysiology of sciatica:

  1. Referred pain theory
  2. Compression theory

First one is referred pain. Pain may arise in any muscle, joint, bone or other soft tissue and can refer to the nerve. Second one is compression or irritation of the sciatic nerve root by any internal or external factor.

Spinal cord is the continuation of the brain stem which runs through the spinal canal of the spine. It runs and gives branches along its course. Spine consists of several vertebras and in between vertebra there is a gap (Intervertebral foramina) which allows the nerve to come out. Usually there is a ganglion which comprises of nerve fibers and it helps the nerve to transmit signals effectively.

The nerve may be larger than the gap due to various reasons which make it to compress. The intervertebral joint has a capsule which encloses the nerve and ganglion and if there is any swelling or other inflammation in the joint capsule, it may compress the nerve and cause pain.

There are few ligaments which binds vertebrae together such as supraspinus, infraspinous and longitudinal ligaments. They enclose the vertebra. If there is any disease in the ligaments it can entrap and compress the nerves emerging and cause sciatica.

The intervertebral joint is made of two vertebrae and an intervertebral disc. Vertebra is hard bones and intervertebral disc is soft jelly like material which lubricates the surfaces of hard vertebrae. When there is pressure from above or below the vertebra the intervertebral disc tends to herniate. Like s slice of meat in between the sandwich bread slices. The herniated disc can press on the nerve. The pressing irritates the nerve and causes the nerve to stimulate causing the sciatica pain. In long-term this pressing may cause physical damage and cause the nerve to be damaged permanently which would result in permanent sciatica which is a very painful condition. It is also known as chronic sciatica.

Chronic diseases

In patients with chronic conditions like diabetes mellitus, amyloidosis, hypothyroidism the bony surfaces of the intervertebral joint is thickened. This thickening is caused by the deposition of various materials from the blood. Thickened surfaces exert more pressure on the nerves causing them to stimulate. These stimulated nerves cause the sciatica pain.

Malignant conditions affecting the bones and other soft tissues such as ligaments may also thicken the bony surfaces thus compressing the nerves. Classical examples are various connective tissue tumors and bone cancers such as multiple myeloma, Osteomas, osteosarcomas.

The intervertebral disc can be affected by cancers of connective tissue origin. Mainly costochondromas, costochondrosarcoms are the classic examples.

Bones are prone to degenerative a change which is known as osteoporosis. These degenerative changes typically affect the spine as spine is like a tall building compromise of many floors. Floors are like vertebras. When a vertebra is affected by osteoporosis it can collapse causing the vertebral body to disintegrate. Adjacent vertebras can be affected. Thus the nerve which comes out in between the two vertebras gets compressed and cause sciatica.

Osteoporosis is one of the most common mechanisms of sciatica in very old population but may be a cause of sciatica in patients with nutritional deficiencies such as calcium and vitamin D. There can be in born errors of vitamin D deficiency which can cause osteoporosis and in return can cause sciatica.


Spinal trauma is a common scenario in RTA. Due to advances in modern medicine the healing of injuries is a common scenario. When bones are fractured the healing can be disorganized. Same applies to vertebras. When the vertebral fractures heal it can compress the nerves and cause sciatica.


Lower back pain associated with Sciatica is a common condition in many people. Many factors contribute to the development of sciatica and lower back pain. In modern medicine various treatments strategies are invented for the treatment of sciatica.

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