September 2000

Spinal imaging spots fractures in youths

By Karen Sandrick

While active, athletic adults may suffer back pain because of muscle pull, disk disease, or arthritis, kids in pain don’t have degenerative spines to blame. Back pain in children between the ages of 12 and 18 cannot be dismissed as a strain or vaguely described as the result of arthropathy.

Children’s back pain occurs for highly specific reasons, and radiologists must look to an arsenal of tools to make the diagnosis. That means getting plain film x-rays, SPECT bone scans, and cross-gantry CT images, according to Dr. Lyle J. Micheli, director of the dvision of sports medicine at Children’s Hospital of Boston.

Increasingly, back pain in children is the result of spondylolysis, a condition caused by stress fracture of the pars interarticularis in a lumbar vertebra, usually L5 or L6. Spondylolysis occurs from repetitive movements of extension and rotation that increase the shear forces in the lumbar spine, exert pressure on the facet joints, and attack the pars interarticularis, which is too small to absorb the repeated shocks.

Specialization Aggravates Incidence

“It used to be that spinal injuries with swimming were almost nonexistent. Now that kids at the age of 10 are engaged in a pattern of repetitive maneuvers, swimming 7000 to 10,000 yards a day, you start to see these kinds of overuse injuries,” Micheli said.

Spondylolysis is so frequent it was the final diagnosis in 47 of 100 children who came to Micheli’s sports medicine clinic with back pain. Among 40 children with low back pain seen by Dr. Joseph Congeni, medical director of the Sports Medicine Center at Children’s Hospital in Akron, OH, 45% had chronic nonhealing lumbar fractures and 40% had acute lumbar fractures in various stages of healing.

The disease particularly affects certain young athletes—dancers, divers, gymnasts, high jumpers, offensive linemen, pole vaulters, weight lifters, and wrestlers—because their activity repeatedly hyperextends the lower back. It has been estimated that 15% to 20% of gymnasts develop this type of stress fracture. Football players other than linemen are also susceptible during the preseason when they are weight training to build up bulk. Weight lifters are especially at risk when they perform the squat press, which pulls the spine into a hyperextended position. Volleyball and tennis players also hyperextend the back while serving.

With today’s rigorous athletic training programs, sports medicine physicians such as Micheli and Congeni are seeing spondylolysis in young athletes active in almost any sport, with as many as 75 to 100 cases every year.

Why are young athletes so vulnerable? The vertebral structure where stress fractures occur, the part of the facet joint known as the pars interarticularis, does not fully mature until age 25. Repetitive activity that pulls the powerful muscles of the back against the fragile facet joint eventually causes fatigue, ultimately inducing a micro- or stress fracture.

As recently as the late 1980s and early 1990s, sports medicine physicians who saw children with back pain were unlikely to diagnose spondylolysis.

“We’d send these young patients away, thinking they had back strain. The kids would grit their teeth and either just live with their pain or take high doses of anti-inflammatories. But then they’d end up coming back two years later, and by then, there were clear radiographic changes in the spine or even long-term complications, such as slippage of the vertebrae or spondylolisthesis,” Congeni said.

Sports medicine physicians are becoming much more sensitive to the problem today, however, and many, such as Micheli and Congeni, encourage their colleagues to “think spondylolysis” until the source of back pain proves to be something else.

Imaging Studies Pinpoint Damage

In his workup, Micheli looks for back pain that is elicited by extension: a ballet dancer performing an arabesque or a gymnast doing a back walkover or flip. He also conducts a provocative extension of the back, one leg at a time, during the physical exam. If that exercise elicits back pain, he suspects disease or injury involving the posterior elements of the back and spine. These findings do not necessarily indicate spondylolysis, however; that’s where imaging comes in.

Although plain film x-rays are excellent for spotting traumatic fractures, they are not sensitive for repetitive injuries to bone and stress fractures. Plain film does, nevertheless, pick up between 30% and 40% of cases of spondylolysis, Congeni said. The coned lateral view of the lumbosacral junction and the anteroposterior view with a 30° cranial angulation show most spinal defects associated with spondylolysis, according to a paper from the department of radiology at the Royal National Orthopaedic Hospital Trust in Stanmore, U.K., in the October 1998 issue of Clinical Radiology (53:723-728).

Oblique views of the facet joint, the so-called Scottie dog views, do not markedly improve the detection rate of early stress fractures in the pars interarticularis. There is a great deal of overlap in the neck of the Scottie dog, which interferes with direct visualization of the facet joint, and usually only late changes appear on the oblique view.

SPECT, CT Modalities of Choice

Three-dimensional SPECT bone scans, which emerged as a mainstay in workups of active children with back pain in the 1990s, showed that spondylolysis lesions could occur in posterior elements other than the pars interarticularis. Occasionally, SPECT reveals laminar fractures, pedicle fractures, or fractures of the spinous process.

Although bone scanning is the most accurate modality for identifying early spondylolysis lesions, it still is an activity study. Bone scans do not clearly reveal anatomy, and they remain positive long after a stress fracture has been diagnosed. Consequently, SPECT scans are not entirely satisfactory for the physician who wishes to assess anatomic healing and long-term prognosis, according to Congeni.

CT, which provides superior views of bony structures, would seem to be the obvious solution. But CT scans are shot in the plane of the disk, and the pars interarticularis and other posterior spinal elements are almost perpendicular to the disk. Standard CT scans therefore yield only tangential views of the lumbar spine. By turning the gantry 180° and obtaining a reverse angle shot, however, CT reveals occult lyses in the posterior elements of the spine and demonstrates bone healing, Congeni said.

Reverse gantry angle CT has become the imaging modality of choice to scan for defects in the pars interarticularis and posterior spine. Although some orthopedists skip the bone scan completely and go directly to reverse gantry angle CT, Congeni still gets a bone scan first to pinpoint the locus of investigation.

“That way, the CT technicians don’t have to scan the entire lumbar spine; they can just do a spot image because they know from the bone scan where the fracture occurrd. They can go straight to the right side of L5 and home in on the area because they know from the bone scan that the crack was on that side of the pars at L5,” he said.

When assessing the degree of healing, Congeni usually gets a reverse gantry angle CT about 12 weeks after the patient has undergone bracing to flatten out the back. Even if bracing does not completely heal spondylolysis, kids often are able to function well. But youngsters who achieve only a fibrous union of the fractures have a greater chance of suffering recurring pain three to four years later. Micheli consequently shoots for complete bone healing through early diagnosis and treatment.

“We are trying to be a lot more aggressive and pick this up earlier. We’re also trying to remind doctors that the problems in the spines of young people under the age of 20 are very different from those in adults age 30 and over,” he said.