Background

Low back pain (LBP) is a well-known health concern in the United States. Although the incidence of low back injuries is much lower in athletes than in a corresponding population of industrial workers, such injuries are still seen in many athletes. The most common causes of LBP in athletes are musculoligamentous sprains and strains, which occur mainly at the lumbosacral region. This is true of both high-performance, world-class athletes and of "weekend athletes." With over 30 million Americans now involved in organized sports, these back injuries present health concerns on the national level.

(See also the Medscape Reference articles Mechanical Low Back Pain [in the Physical Medicine and Rehabilitation section], Lumbar Disk Problems in the Athlete [in the Sports Medicine section], and Low Back Pain and Sciatica [in the Neurology section], as well as Pain Measurement in Patients With Low Back Pain, Guidelines Issued for Management of Low Back Pain, and Epidemiology of Adolescent Spinal Pain: A Systematic Overview of the Research Literature on Medscape.)

For excellent patient education resources, see eMedicineHealth's patient education articles Low Back Pain and Sprains and Strains.

Etiology

Most athletes who sustain a low back injury do so while lifting weights during their training sessions or while performing unexpected coupled motions (eg, lateral bending and flexion, lateral bending and axial rotation). During such activities, tremendous loads are placed on the lumbar spine, which may cause a temporary instability and lead to a subsequent injury to the soft tissue that surrounds the spine.

Risk factors for LBP include the following^{[1, 2]}:

Muscular imbalances or weaknesses of the abdominal and posterior spinal muscles may constitute a risk factor to sustain a low back injury.
Deficits in the afferent or efferent pathways or proprioceptors are known risk factors for spinal soft-tissue injuries.
Preexisting structural deformities, such as scoliosis, spondylolysis, or spinal fusions, may predispose to a spinal injury. Preexisting injuries make athletes more vulnerable to sustaining a reinjury of the same area.
- See the Medscape Reference articles Idiopathic Scoliosis Imaging and Spondylolysis Imaging [in the Radiology section], Lumbosacral Spondylolysis [in the Sports Medicine section], and Lumbar Spondylolysis and Spondylolisthesis [in the Physical Medicine and Rehabilitation section].
- See also Effectiveness and Cost-Effectiveness of Three Types of Physiotherapy Used to Reduce Chronic Low Back Pain Disability: A Pragmatic Randomized Trial With Economic Evaluation, Biomechanics of the Posterior Lumbar Articulating Elements, Prevalence of Musculoskeletal Disorders at the NFL Combine - Trends from 1987 to 2000, and Lumbar Spine Injuries in Athletes on Medscape.

United States statistics

Studies document that 7-13% of all sports injuries in intercollegiate athletes are low back injuries. The most common back injuries are muscle strains (60%), followed by disc injuries (7%). Athletes are more likely to sustain injuries in practice (80%) than during competition (6%).^[3]American football (17%) and gymnastics (11%) are reported to have the highest rates of low back injury.^[3] Among professional dancers, the lumbar spine is a commonly injured area (20% of all injuries).^[4]

International statistics

Exact numbers regarding the international frequency of low back injuries are not known; however, a French study reported over 50% of French individuals aged 30-64 years had experienced at least 1 day of LBP over the previous 12 months, and 17% had suffered LBP for more than 30 days in the same 12-month period.^[5]The authors noted that the prevalence of LBP varied between men and women, that there was an increased incidence with increasing age for LBP that lasted more than 30 days, and that these data were similar to those of other countries.

In an African study, the mean LBP point prevalence among adults was 32%, with an average 1-year prevalence of 50% and an average life-time prevalence of 62%.^[6]

Functional Anatomy

Sprains are ligamentous injuries that are caused by a sudden violent contraction, sudden torsion, severe direct blows, or a forceful straightening from a crouched position. All major ligaments (ie, anterior longitudinal, posterior longitudinal, yellow, intertransversal, capsular, interspinosus, supraspinosus) can sustain sprains; however, the posterior ligaments are more prone to injury. The posterior longitudinal ligament, for example, is the biggest of this group of ligaments and is less developed than its anterior counterpart.

Strains are defined as tears, either partial or complete, of the muscle-tendon unit. Muscle strains and tears most frequently result from a violent muscular contraction during an excessively forceful muscular stretch. Any posterior spinal muscle and its associated tendon can be involved, although the most susceptible muscles are those that span several joints.

Combined with injured tendons and ligaments, all embedded structures may be temporarily or permanently damaged. Of major interest are proprioceptors that play a crucial role in the motor control of the spine. An inhibited motor control weakens spinal stability and may lead to chronic back problems or reinjury.

Sport-Specific Biomechanics

The lumbar spine bears tremendous loads: the large, superimposed body weight interacts with additional forces that are generated by lifting as well as other activities that involve powerful forces.^{[7, 8, 9, 10, 11]}The lumbar spine and the hips are responsible for the mobility of the trunk. The L4-5 and L5-S1 areas bear the highest loads and tend to undergo the most motion. Consequently, these areas are found to sustain the most spinal strain or sprain injuries. In addition, load-bearing strain and sprain injuries most frequently occur during the strongest coupling patterns (ie, lateral bending with flexion-extension, axial rotation with lateral bending).

The bony architecture and the ligamentous elements constitute the structural components of the spine.^[12]The muscles and tendons constitute the dynamic elements. With all elements intact, the biomechanical function of the spine is normal. The intrinsic translatory and rotatory stability of the spine is provided by the ligaments. The contribution of a given ligament depends not only upon its particular strength, but also upon its location. Moreover, a ligament may contribute relatively more to either the translatory or rotatory stability, depending upon the loading circumstances. Assuming that all ligaments are made of the same material, the strength of a ligament is proportional to its cross-sectional area. A ligament with a larger cross-sectional area provides greater stability and less displacement when the functional spinal unit (FSU) is subject to physiologic loads.

Another factor that contributes to spinal stability is the distance of a ligament from the center of rotation.^[13]A ligament that is located close to the center of rotation provides much less stability against bending than a ligament that is further away from the rotation center. The interspinous ligaments in the adult lumbar spine are frequently absent, ruptured, or degenerated and do not contribute to stability of the spine. However, supraspinous ligaments do play a role in stabilizing the spine. Muscles provide stability to the spine during all dynamic movements and actions. Injured trunk muscles can decrease spinal stability if the intact muscles are not able to compensate for the dysfunction of the injured unit.

Spinal instability can occur as a result of trauma, disease, surgery, or some combination of the 3 causes. Clinical instability is defined as a loss of the ability of the spine to maintain relationships between vertebrae under physiologic loads in such a way that (1) there is neither initial nor subsequent damage to the spinal cord or nerve roots, and (2) there is no development of incapacitating deformity or severe pain. Instability leads to abnormal kinetics (stiffness) and/or kinematics (coupling patterns).

When the tissues surrounding the spine are damaged, structures embedded within those tissues may also become temporarily or permanently harmed. Proprioceptors, including muscle spindles, Golgi tendon organs, and joint receptors, are of great importance for postural control. Damaged proprioceptors weaken the stability of the spine and may lead to reinjuries or chronic problems. Although some studies document changes in the normal quality and quantity of motion, there has been no compelling correlation of either with pain behavior.

Clinical Presentation

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