Lower Back: Anatomy, Functions, Diseases
The lower back is the part of the body from the tailbone to the ribs of a person. It contains many nerve endings in the sacral region, is divided into two equal halves by the spine. The skin on the lower back can be covered with hair (in men) or rare translucent hairs (in women)
Pain in the lower back is a common ailment in people of working age. About 80% of people experience pain in this area throughout their lives, and this condition is the most significant cause of temporary disability in all professional groups. In accordance with the etiology, pain in the lumbar spine can be divided into six groups: mechanical, infectious (tuberculosis), inflammatory (ankylosing spondylitis), metabolic (osteoporosis), neoplastic (cancer) and visceral (pain caused by diseases of the internal organs).
In most people, lumbar pain is caused by mechanical causes, which include: lumbosacral sprain, degenerative diseases of the intervertebral disc, spondylolisthesis, compression and fracture of the spine.
Mechanical pain in the lower back is also called regional, and it can be local or radiating to one or both legs (sciatica). Lower back pain of mechanical etiology is usually episodic, and in most cases, the natural course of the disease has a favorable prognosis. In half of the cases of acute diseases, pain in the lumbar spine disappears after two weeks, and in 90% of the remaining patients within two months. It is believed that in every tenth case, the disease becomes chronic, and this is the group of patients that accounts for the bulk of the costs associated with diseases of the lumbar spine.
Anatomy and functions
Due to the upright posture, the anatomical structure of the lower back is different from that of most vertebrates. The vertical position increases the mechanical load on the components of the lumbosacral spine. Normally, the lumbar region consists of five vertebrae. The sacral spine is stationary, and the human coccygeal section does not carry a functional load
The vertebrae are connected to each other with the help of intervertebral discs lying between the vertebral bodies, as well as with the help of ligaments and muscles. These soft connectors provide flexibility to the spine. Two articulated vertebrae form a functional unit
The vertebral bodies and intervertebral discs are the supporting elements of the spine. An arch formed by the back of the vertebra protects the spinal cord located inside the spinal canal. The arches of the vertebrae articulate with each other through the articular surfaces of the processes of the vertebra, which determine the direction of movement. The arches of the vertebrae are also connected by numerous ligaments, which determine the degree of mobility of the spine. Muscles that straighten the body (extensors) are attached to the arches of the vertebrae. Important bone attachment sites are three bone processes of the vertebral arch (two transverse and spinous processes).
The spinal cord ends at the level of the first or second lumbar vertebrae. In the lumbar, spinal cord passes into the terminal thread, which consists of the roots of the spinal nerves. Nerve roots in pairs exit the spinal canal through the intervertebral foramen. A branch that innervates the back tissue departs from each spinal root. The muscles, ligaments and joints contain nerve endings – pain receptors. A healthy intervertebral disc has no such nerve endings, with the exception of the edge of the outer ring. However, it is believed that the disc is the most important cause of lumbar pain. The rupture of the disk ring is the most painful. As a result of degeneration of the disc, a hernia of the gelatinous nucleus (inner part) of the intervertebral disc can form, which can exit into the spinal canal and cause compression and/or inflammation of the spinal nerve with symptoms of sciatica,
Muscles provide stability and mobility of the back. The back muscles allow the body to lean back (straightening), and the abdominal muscles tilt the body forward (flexion). The accumulation of fatigue due to prolonged or repeated stress or a sharp stretching of muscles or ligaments can cause pain in the lumbar spine, although the exact origin of such pain is difficult to determine. There are conflicting data on the role of soft tissue damage in diseases of the lumbar spine.
Pain in the lower back
Throughout life, three out of four people have ever experienced lower back pain. Every fifth person suffers from pain along the sciatic nerve or lumbar pain every month, and every sixth person has a clinically confirmed lumbar pain syndrome at any time. Sciatica and herniation of the intervertebral disc are less common – 4% of the population suffers from these diseases. About half of patients with lower back pain syndrome have a dysfunction of the spine, and in 5% of cases this violation is very pronounced. Sciatica predominates among men, but other diseases of the lumbar region are equally common among men and women. Pain in the lower back is relatively rare in people under the age of 20, but with age, the prevalence of the disease gradually increases up to 65 years, after which there is a decline in the incidence.
With age, the prevalence of degenerative changes in the lumbar spine also increases. Half of the 35-44-year-old men and nine out of every ten men 65 years of age and older showed signs of disc degeneration in the lumbar spine radiographically. Signs of severe degeneration of the lumbar spine were noted in 5% and 38% of men of these age groups, respectively. Degenerative changes are slightly more common in men than in women. People with degenerative disc changes in the lumbar spine suffer from lower back pain more often than those who do not have such changes, but degenerative disc changes are also often observed in people who do not have symptoms of the disease. With NMR imaging, disc degeneration was detected in 6% of women aged 20 years or younger, who had no symptoms of the disease, and 79% of women aged 60 years or older.
In general, pain in the lumbar spine is more common in people whose work is associated with physical activity. In the United States, the highest level of compensated back injuries is found among manual workers, nurses, and truck drivers.
Workplace risk factors
Epidemiological studies have shown quite naturally that lumbar pain, sciatica, herniated disc and degenerative changes in the lumbar spine are associated with hard physical work. However, the limits of the permissible physical load on this part of the spine are little known.
Lower back pain occurs more often in those categories of workers whose work is associated with lifting, carrying or moving (pushing, pulling) weights. Muscles and ligaments are subjected to strong stretching, and bones and articular surfaces are subjected to strong pressure. Such an effect can cause mechanical damage to the vertebral bodies, intervertebral discs, ligaments and processes of the vertebrae. The cause of injury may be sudden overstrain or fatigue due to prolonged physical activity. It is believed that the cause of degeneration of the lumbar spine discs may be repeated microtraumas, which symptomatically may not manifest in any way.
Low back pain is also associated with frequent or prolonged bends, bends, or other atypical body positions. To feed the intervertebral disc, movement is necessary since constant static stress can interfere with the supply of nutrients to the disc. In other soft tissues, fatigue can develop for the same reason. The risk of pain in the lumbar increases with prolonged sitting in the same position, for example, a seamstress or minder.
Continued driving has been shown to increase the risk of developing lumbar pain, sciatica, or herniated disc. The driver’s body undergoes general vibration, which adversely affects the power of the drives. The risk of lumbar pain also increases with unexpected jolts on rough roads, a tense posture, and physical work performed by professional drivers.
The obvious cause of spinal injuries is injury due to an accident, such as falling or slipping. Traumatic injuries of the spine, in addition to the acute manifestation of trauma, also significantly affect the development of chronic pain of the lumbar spine.
The development of lower back pain is also associated with various psycho-social factors in the workplace, such as monotonous work and work in time-constrained conditions, insufficient public support from employees or management. It is believed that psychosocial factors affect the onset and cure of lumbar pain but there are conflicting opinions on the etiological role of these factors.
Individual risk factors
- Hight and overweight. Data on the relationship of pain in the lumbar with physique and overweight are contradictory. However, there is quite convincing data on the relationship between the development of sciatica or hernia of the intervertebral disc with the hight. High people may not have enough disk power due to its large volume, and workers with high growth may also experience ergonomic problems in the workplace;
- Physical development: The results of a study of the relationship between physical development and lumbar pain are contradictory. Lumbar pain is more common among people who are physically weaker than their work requires. According to some studies, the respiratory capacity of the lungs does not predict the occurrence of lumbar pain or the risk of injury. The least physically fit people may have an increased risk of back injuries, but the most physically developed people may get the most severe injuries. One study showed that well-developed back muscles prevented primary lumbar pain;
- The mobility of the lumbar spine varies greatly in different people. In people with acute or chronic lumbar pain, mobility is reduced, but in long-term studies, good mobility did not predict the occurrence of pain in the lumbar spine;
- Smoking. Several studies have shown that smoking is associated with an increased risk of developing lumbar pain and herniated disc. Smoking probably also enhances disc degeneration. In experimental studies, it was found that smoking disrupts the nutrition of the intervertebral discs;
- Anatomical features of the structure. Congenital defects of the vertebrae, different lengths of the legs, can cause an altered load on the spine. Such factors, however, are not considered decisive in the occurrence of lower back pain. A narrow spinal canal is a risk factor for squeezing nerve roots and developing sciatica;
- Psychological factors. Chronic pain in the lumbar region is associated with psychological factors (e.g., depression), but not all people with chronic lower back pain have psychological problems. In order to distinguish between lower back pain caused by psychological and physical factors, various methods are used, but the results are contradictory. Symptoms of psychological stress are more often observed in people with pain in the lumbar spine than in people without pain symptom, and perhaps psychological stress even allows predicting the occurrence of lumbar pain in the future.