Lumbar spine injury in the young athlete

Micheli, Lyle J.; Allison, Gillian

doi:10.1590/S1517-86921999000200005

ARTIGO DE REVISÃO

Division of Sports Medicine, Children's Hospital, Boston, MA

Endereço para correspondência

INTRODUCTION

Lumbar spine injuries are being seen in the young athlete with increasing frequency in sports clinics today. Back injury and recurrent back pain can drastically limit the athlete's ability to participate in his or her sport. While the relatively normal anatomy of the spine may allow for enhanced range of performance before structure damage occurs, back pain is still relatively common. Examples: dance, gymnastics, and figure skating. Sward et al. found that, of 142 top athletes in Sweden, the incidence of low back pain ranged from 5 to 85%, depending on the sport¹.

Anteriorly, the lumbar spine has five vertebral bodies linked by the intervertebral discs. The neural canal lies centrally, containing peripheral nerves with dural coating. Dorsally are the posterior elements of the spine: the facets, the transverse processes, the pars interarticularis, and the pedicles. Normal lumbar lordosis is 45 to 50 degrees. Abnormal structural alignments, such as hyperlordosis of the lumbar spine or a structural "flat back", may be factors in low back pain.

Injuries to the lumbar spine usually result from two patterns of force generation: single event, acute macrotrauma, or repetitive microtrauma, with resulting "overuse injury". Overuse injuries are most commonly seen in the bony posterior elements, particularly the pars interarticularis. Some researchers have suggested that it is repetitive flexion and extension that leads to stress concentration in the pars, as this is the site of spinal rotation during flexion and extension².

A number of recent studies have employed magnetic resonance imaging to demonstrate changes in the spine caused by repetitive microtrauma. Sward et al. in a recent study compared 24 elite male gymnasts with 16 male non-athletes of comparable age³. The authors found significantly increased evidence of disc degeneration, by MR imaging, in the athletes (75%) versus the non-athletes (31%). The gymnasts also had a higher incidence of other abnormalities in the thoracolumbar spine. In a similar study, Goldstein et al. suggested that gymnasts who train for more than 15 hours per week show a significant increase in degenerative changes of their lumbar spine⁴.

The pattern of back injury is entirely different in the older athlete whose spine has already undergone age-dependent segmental degeneration. Injury is most commonly initiated in the anterior disc elements giving discogenic pain and sciatica. Bony overgrowth at the facets may compromise the lateral recesses or neural foramina resulting in nerve encroachment and spinal stenosis. A minor twist or injury may result in nerve injury or irritation with associated swelling and pain.

DIFFERENTIAL DIAGNOSIS

There are four main categories of lower back pain seen in young athletes: mechanical, discogenic, spondylolytic, and vertebral body fracture.

Mechanical back pain is the most frequent etiology and is usually a diagnosis of exclusion in the young athlete, once careful physical examination has ruled out spondylolysis, disc disease, or fracture. The pain may result from abnormal nerve stimulation at the facet.

Mechanical and musculoskeletal factors such as postural lordosis and excessive tightness of the extensor musculature or weakness of the abdominals may be risk factors for this etiology. Hyperlordotic posture is often seen in dancers and gymnasts. In many of these athletes hyperlordosis is usually an acquired posture and is potentially reversible with proper therapeutic exercise. The only complaints may be of an aching back associated with prolonged standing or sitting activities or following sports training. Diagnostic techniques such as plain film radiographs and bone scans are normal.

In many young athletes, this condition may represent a transient "overgrowth syndrome". The bony elements overgrow the ligaments and tendons during this second adolescent growth spurt, resulting in a combination of tight lumbodorsal fascia and hamstrings posteriorly, weak abdominal muscles anteriorly, and a posterior displacement of the torso over the pelvis. Abnormal demands may then be placed on the thoracic spine during forward flexion, given the extension contracture of the lumbar spine. Compensation for this structural imbalance may be made by adopting a roundback posture.

Discogenic back pain is rare in the prepubescent child, but the incidence in the adolescent, particularly the athletically-active adolescent, appears to be increasing. This must always be included in the differential diagnosis. A study carried out by the Mayo Clinic showed an increased incidence of disc disease with resultant back pain and sciatica in the adolescent age group in correlation with the increased participation in sporting activities at this time⁵. Sports involving axial compression and flexion are typically associated with this injury. The increased availability and safety of magnetic resonance imaging has greatly aided in the early diagnosis of this condition.

The clinical presentation of this disease is often quite different in the young athlete than in the adult. Pain is not always the major complaint. The patient's chief complaint may be back stiffness, abnormal gait, or a noticeable loss of hamstring flexibility.

On examination, dramatic tightness of the lumbodorsal fascia and hamstrings is frequently found, often with an associated reactive lumbar or thoracolumbar scoliosis. A positive straight leg raising test or Lasègue's sign may reflect sciatic irritation. Asymmetric hamstring tightness may sometimes be the only warning of disc herniation. Loss of reflexes or muscle wasting is unusual.

Lumbar spine films are usually unremarkable initially, although they may occasionally show decreased disc space or an irregularity of the vertebral endplates at the level of involvement. Computed tomography or magnetic resonance are usually diagnostic. The excessive radiation exposure of the lumbar region with CT makes MRI our exam of choice in this age group.

Younger athletes with discogenic pain may have a genetic tendency for lumbar spine deterioration. A number of athletes who came to our clinics with discogenic pain and sciatica showed evidence of multilevel disease, thus indicating a possible early familial tendency. This information is often first elicited during a sports pre-participation history and screening process. A possible anatomic predisposition to adolescent disc disease has also been suggested, with a clover-shaped spinal canal and short pedicles increasing the chances of symptomatic disc protrusion⁶.

Conservative treatment of bed rest and non-steroidals with progressive mobilization is recommended initially. Bracing therapy and exercise has been effective in relieving symptoms and returning these young athletes to sports activity⁷. Surgical intervention is rarely required, in our experience. There may be a high incidence of continued back complaints in these patients as adults, but the effect of continuing athletic participation on the natural history is not known⁵. Six to 12 months of relative rest and rehabilitation may be required before returning to competition.

Spondylolysis as a cause of back pain in the young athlete today appears to be increasing in frequency. The mechanism of injury is repetitive microtrauma from flexion, extension, or rotation may result in damage to all the posterior elements of the lumbar spine, including the pars interarticularis, facets, pedicles, lamina, and the spinous processes. However, the pars is the most common site of injury. Studies have suggested that hyperextension, in particular, results in shear stress at the pars, with eventual stress fracture⁸.

The athlete is at first symptomatic only during certain sporting maneuvers. The pain often becomes progressively more severe with daily routine activities or even at rest. It is typically relieved by supine positioning or by simply reducing the exercise program. Occasionally, a single acute macrotrauma event may result in acute onset of pain.

The incidence of spondylolysis in dancers appears to be greater than in the general population, perhaps equivalent to the high incidence found in gymnasts⁹.

Spondylolysis occurs only in the bipedal human. A study carried out in a group of institutional patients who never walked showed that risk of spondylolysis in the pars was almost zero¹⁰. There do appear to be genetic risk factors, however. An association of spondylolysis with spina bifida occulta in 20 percent of young athletes has been found in previous studies¹¹.

Physical examination again often reveals a hyperlordotic posture, with a painless limitation of motion in the lumbar spine on forward flexion but pain with provocative hyperextension. A positive finding with the hyperextension test is usually indicative of posterior element damage. The athlete, on standing on one leg and then the other, will elicit pain while hyperextending the back. The pain is often exaggerated on the ipsilateral side of the pathological defect during this maneuver. Tight hamstrings and a loss of flexibility may accompany these findings.

Initial oblique radiographs as well as anteroposterior and lateral views of the lumbosacral spine may demonstrate an established pars fracture. However, if these are normal, a technetium-99 radionuclide bone scan with SPECT imaging of the lumbar spine should be obtained. We have found that simple bone scans alone may give false negatives. SPECT scans can detect these stress fractures before bony integrity has been lost and a complete fracture developed. Needless to say, early detection can result in a much higher incidence of healing of this lesion. We usually employ bracing and anti-lordotic exercises to treat these early lesions for a period of six months¹¹.

Occasionally, sciatica may be associated with spondylolysis. This may be due to compression of the L5 nerve root from hyperplasia of the synovial and fibrous tissue at the site of the pseudoarthrosis, or associated disc disease. MRI can be useful for differentiation in these cases. Eighty-five percent of lesions are at L5 and almost all the rest are at L4.

Vertebral body microfracture at the anterior margin is a fourth cause of low back pain in the young athlete. These fractures appear to be the result of repetitive microtrauma, usually repetitive flexion which injures the anterior portions of the vertebral endplates and can lead to frank wedging and Schmorl's node formation. The most frequent site of involvement in the young athlete is at the thoracolumbar junction, typically in one or two vertebral levels, but may involve three or more. These lesions have been labeled as "atypical Scheuermann's disease"¹². Often, this occurs in gymnasts who begin their training before the age of five¹³. Sorensen characterized "classic Scheuermann's" as wedging of at least three vertebral levels of the thoracic spine with Schmorl's nodes and a structural roundback¹⁴. Some cases that meet the criteria of true thoracic Scheuermann's disease may actually be the result of severe lumbar extension contracture with excessive flexion demands transferred to the thoracic spine and resultant anterior vertebral plate fracture with secondary bony deformation of the vertebra¹³. Sports in which this type of injury is seen include rowing, gymnastics, dancing, tennis, and diving.

A sagittal "flatback" alignment of the spine with lumbar hypolordosis and thoracic hypokyphosis appears to increase the susceptibility to atypical Scheuermann's at the thoracolumbar junction. Tight lumbodorsal fascia, causing forward flexion to occur in the dorsal spine rather than in the lower lumbar spine, may also be a factor. Plain radiographs are usually sufficient for the diagnosis of this injury.

Infection or neoplasm of the musculoskeletal system must also be included as differential diagnosis in the young athlete complaining of low back pain. Plain radiographs, a bone scan, and blood work can aid in the diagnoses of these conditions.

PREVENTION

Athletes and coaches in sports which have increased risk of lumbar spine injury should be educated in preventive techniques. The athlete with back pain should seek medical assessment early, in order to prevent progression to more severe tissue injury.

Repetitive microtrauma injury in the lumbar spine has been implicated in both contact and non-contact sports, including gymnastics, ballet, figure skating, hockey, football, weight-lifting, wrestling, and rowing^9,15-23. Ferguson et al. reported an incidence of 48 percent of back pain in 25 football linemen²⁴, while Jackson revealed that 30 percent of the 100 female competitive gymnasts in his survey had problems connected with the lumbar spine⁹. Independent variables that contribute individually or in combination to lumbar spine injury include poor technique, poor conditioning, and abnormal anatomy.

Poor technique is reflected in insufficient warm-up and inadequate technical supervision. In gymnastics, rapid advancement to difficult techniques without proper attention to strength and flexibility may lead to injury^18,23. Goldberg reported low levels of abdominal strength in young gymnasts and recommended supplementary abdominal strengthening exercises¹⁶.

Hyperlordosis of the lumbar spine is frequently found in the young athlete with low back pain on physical examination. This may be due to the musculoskeletal imbalance that occurs across the joints, including the spine, during the second adolescent growth spurt. Also, the susceptibility of the growing tissue (including the vertebral endplates and apophyses) to injury is well known. Gymnasts and weightlifters should be advised of the dangers in hyperlordotic positioning, as this may contribute to the increased incidence of posterior element stress injuries to the lumbar spine²³.

REHABILITATION PROGRAM

A progressive return to activity is the general aim of any rehabilitation program. For the athlete with low back pain, a program of abdominal and pelvic strengthening exercises is of great importance. There are two important groups: Williams flexion exercises are designed to decrease the lumbar lordosis and increase flexibility²⁵, while McKenzie extension exercises can help centralize and decrease pain by restoring both range of motion and strength of the lower back with resultant stabilization of the supporting structures of the lumbar spine²⁶. Peripheral nerves will no longer be irritated or impinged, factors which frequently result in secondary nerve stimulation and pain. Medication such as analgesics, anti-inflammatories, and muscle relaxants can be used initially, but play a secondary role in this age group.

The early use of a swimming program in lumbar spine injury is usually well tolerated and can be performed in a functional and painless fashion. This is useful in synchronizing the low back and pelvic musculature. Resistance training with machines or free weights should be included in the later stages.

In the rehabilitation of any athlete, slow progression of training activities carried out in painless fashion is important if the body is to return to full function. In the case of a dancer, floor and water barré should precede any centre with advancement to jumping in later stages.

The Boston back brace evolved in the 1970s as a treatment for spinal deformities in children and adolescents. Once an anti-lordotic component was added to the brace, it was used to treat children with pathological hyperlordosis⁷. The new modified thermoplastic body braces open anteriorly and are made in various sizes and contours of 0º, 15º, and 30º of lumbar lordosis. The brace is designed to flatten and support the back, decreasing strain on the lumbosacral spine and increasing abdominal pressure²⁷. It was found that the anti-lordotic positioning of the back in the brace remained after use, thus it was hypothesized that the brace places the spine in a physiologically improved position for subsequent function.

Clinical trails have confirmed the effectiveness of the Boston back brace in the management of the various low back pain etiologies. Use of the brace in young athletes with spondylolysis and grades I to II spondylolisthesis have been particularly successful. If detected early, the brace may promote healing of the pars defect. However, women appear to have a relatively poorer prognosis in healing when compared to men¹¹. Even if complete bony healing does not occur, the patient may become asymptomatic with improved range of motion after physical therapy and bracing. The brace may reposture the spine, rendering the symptomatic pars more vertebral and decreasing posterior element stress.

The brace is initially worn for 23 out of 24 hours for the first six months in conjunction with a physical therapy regime of anti-lordotic exercises and lower extremity flexibility. The patient is gradually weaned from the brace over the next three to six months. Sporting activities, such as football, gymnastics, and hockey, may be recommenced after three to four weeks of brace wearing once the patient is symptom free. In patients with painful disc disease, we may employ a thermoplastic brace at 15º of lordosis to assist in healing and restoration of function¹³.

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