Lumbosacral Discogenic Pain Syndrome

Spinal abnormalities are more common in athletes than in non-athletes in the general population. Any spinal injury pattern can be observed in athletes who are subjected to trauma. Athletes are susceptible to degenerative disc changes at an early age because of the repetitive loading activities involved in sports.

Back pain is second only to the common cold as a cause of lost time from work and results in more lost productivity than any other medical condition. It has been estimated to result in 175.8 million days of restricted activity annually in the United States, and at any given time, 2.4 million Americans are disabled secondary to low back pain. Of these 2.4 million Americans, one half are chronically disabled. Data from the National Ambulatory Medical Care Survey from 1989-1990 revealed that there were almost 15 million office visits for low back pain, ranking this as the fifth reason for all physician visits.

In most industrialized nations, the lifetime prevalence of back pain exceeds 70%, and in the United States, a 15-20% 1-year prevalence rate has been estimated. ^[1] In 1990, 400,000 industrial low back injuries resulting in disability occurred in the United States. In 1985, a prospective Swedish study of adults aged 20-65 years conducted over an 18-month period reported over 7,500 work absences related to acute low back pain. Of these episodes, 57% of workers recovered within 1 week, 90% in 6 weeks, and 95% after 12 weeks. In 1987, Deyo reported a slower recovery rate in the United States, with only 33.2% of patients recovering in less than 1 month, 33% recovering in 1-5 months, and 32.7% taking longer than 6 months to recover. Finally, recurrence rates from 60-85% have been reported during the first 2 years following an acute back injury.

Frymoyer reported that 40% of patients experience leg pain in association with back pain; a much lower percentage reported numbness and weakness; and only 1% of adult respondents in the United States reported symptoms indicative of true sciatica. Herniated discs occur primarily in the second through the fifth decades of life and have a slight male preponderance. The L4-5 disc has been shown to be the most commonly herniated disc, resulting an L5 radiculopathy. The L5-S1 disc is a close second in frequency of herniation. Translating the frequency of back pain into economic terms emphasizes the magnitude of the problem. Lower back injuries account for approximately 22% of compensable workplace injuries, but they account for 31% of compensation payments. In the United States, the direct costs of spinal disorders were estimated to be in excess of $23 billion during 1990.This represented an increase of nearly 47% over the estimated costs in 1984.

United States statistics

Overall, imaging signs of degeneration of the lumbosacral discs correlate closely with age. Approximately 20% of teens aged 11-16 years will begin to have mild signs, whereas 10% of 50-year-olds and 60% of 70-year-olds will have signs of severe degeneration. ^[2]

Thoracolumbar spinal abnormalities are more common in athletes than in nonathletes in the general population. Studies investigating spinal injuries in athletes are largely limited to those injuries that are severe enough to limit participation. Many athletes report injuries that allow for continued competition, and they participate with chronic low back pain.

Nearly 50% of college football linemen experience low back pain during a typical season, while 10-27% of all college football players experience lumbar spinal symptoms.

Among elite athletes, the 1-year prevalence of low back pain ranges from 18% to 65% across various Olympic sports. The lowest prevalence of low back pain is among basketball players and the highest prevalence is among rowers. ^[3]

The rate of lumbar spinal injury in gymnasts has been directly related to the level of competition. Evidence from magnetic resonance imaging (MRI) scans that support this relationship is found in 9% of pre-elite, 43% of elite, and 63% of Olympic level gymnasts. ^{[4, 5]}

Noncontact sports, such as golf and cycling, are also associated with increased low back pain, largely related to repetitive forces or long-term postures.

The lumbar spine has an average of 5 vertebrae (normal range 4-6), with an intervertebral disc interposed between adjacent vertebral bodies. A cartilaginous endplate exists between the disc and the adjacent vertebral bodies and is considered part of the disc.

The disc itself is comprised of a central nucleus pulposus surrounded peripherally by the annulus fibrosis. In healthy young adults, the nucleus is a semifluid mass of mucoid material. The nucleus is comprised of approximately 70-90% water in a young healthy disc, but this percentage generally decreases with age. The primary nuclear constituents include glycosaminoglycans, proteoglycans, and collagen. Type II collagen predominates in the nucleus. Proteoglycans are the largest molecules in the body and possess an enormous capacity to attract water through oncotic forces. These forces increase their weight by 250% and result in a gel-like composition. Biomechanically, the nucleus can display properties of either a solid or a liquid substance, depending on the transmitted loads and its posture.

The annulus fibrosis consists of 10-20 type I concentric collagen fiber layers that surround the nucleus. The layers are arranged in an alternating orientation of parallel fibers lying approximately 65 º from the vertical.

The vertebral endplate is a thin layer of cartilage located between the vertebral body and the intervertebral disc. While normally composed of both hyaline and fibrocartilage in youth, older endplates are virtually entirely fibrocartilage. Because the intervertebral disc is the largest avascular structure in the body, it is dependent on diffusion across the endplate for nutrition and waste removal. The endplate is considered part of the disc because the endplate almost always remains with the disc when the disc is traumatically displaced from the vertebral body.

The principal functions of the disc are to allow movement between vertebral bodies and to transmit loads from one vertebral body to the next. When axial loads are transmitted to the spine, the annulus and nucleus display a complex intertwined role allowing for pressure dispersal. The nucleus has the capacity to sustain and transmit pressure; this function is principally invoked during weight-bearing. In this circumstance, it transmits loads and braces the annulus. The annular lamella is capable of sustaining an axial load on the basis of its bulk. When an axial load is applied to the nucleus, it tends to shorten. The nucleus attempts to radially expand, thereby exerting pressure on the annulus. Annular resistance efficiently opposes this outward pressure, creating a hoop tension effect. The intervertebral disc is so effective at resisting these axial loads that a 40-kg load to a disc causes only 1 mm of vertical compression and only 0.5 mm of radial expansion.

During movement, the annulus acts like a ligament to restrain movements and partially stabilize the interbody joint. The oblique orientation of the annular fibers provides resistance to vertical, horizontal, and sliding movements. The alternation in the direction of the annular fibers in consecutive lamellae causes the annulus to resist twist poorly. When the segment twists one way, the fibers oriented in that direction are placed on stretch while those fibers oriented the opposite direction are placed on slack; therefore, the annulus resists the twisting motion with less than its full complement of fibers.

Any factor that creates excessive demand can lead to injury. Excessive mechanical loading may occur by repetitive fatigue overload, supramaximal overload, or unexpected overload. ^[6] Improper technique in activities such as in blocking or tackling, poor body mechanics, or improper training can lead to overload. Unexpected overloads result from falls, collisions, or improper technique. Good coaching, proper technique, and safety measures help to minimize fatigue overload and limit dangerous sport situations.

Causes of internal disc derangement (IDD) usually involve a series of traumatic events ranging in significance from minor disc injuries to more severe types of injuries. The accumulation of the injuries is generally believed to yield the degenerative nature of the annulus, and the lack of integrity is believed to allow water and protein molecules to escape the confines of the nucleus.

The difference between an asymptomatic degenerative disc and one that hurts has been in question. The nucleus pulposus has no nerve supply; however, the outer third of the annulus is innervated. It receives supply from both the gray ramus laterally and anteriorly and from the sinuvertebral nerve posterior and posterolaterally. The current model holds that in some manner, these annular sensory nerves become sensitized, and any turbulence, such as that caused by twisting or weight-bearing, provokes pain. One possibility is that the nuclear proteins become exposed to the system circulation, allowing an autoimmune reaction to the protein and an intense inflammatory process inside the disc.