SPONDYLOLYSIS AND SPONDYLOLISTHESIS
Spondylolysis may represent a stress fracture of the pars interarticularis of the fifth lumbar vertebra. When the fracture allows L5 to slip forward on S1, it is called isthmic spondylolisthesis. Dysplastic, or congenital, spondylolisthesis, in contrast, is due to anomalous development of the posterior structures of the lumbosacral junction.
In children, spondylolysis rarely occurs before 5 years of age and is more common at age 7 or 8. Although a history of minor trauma is common, the injury is seldom severe. The onset of symptoms coincides closely with the adolescent growth spurt.
Lumbar lordosis is exacerbated by the normal hip flexion contractures of childhood. This posture focuses the force of weight bearing on the pars interarticularis, gradually leading to disruption. Shear stresses are greater on the pars interarticularis when the spine is extended and are further accentuated by lateral flexion of the extended spine.
Clinical Manifestations. Symptoms are relatively uncommon in children. Pain, when it occurs, is localized to the low back and, to a lesser extent, to the posterior buttocks and thighs. Symptoms are usually initiated and aggravated by repetitive and strenuous activity particularly the flexion-extension of the spine common in rowing, gymnastics, and diving and are decreased by rest or limitation of activity.
Palpation may elicit some tenderness in the low back, and there may be some splinting or guarding with restriction of side-to-side motion, particularly in acute conditions. Hamstring tightness and marked restriction of forward hip flexion are seen in 80% of symptomatic patients. Distortion of the pelvis and trunk may be clinically apparent in the late stages of spondylolisthesis.
Children, unlike adults, seldom have objective signs of nerve root compression such as motor weakness, reflex change, or sensory deficit and rarely have an associated disc protrusion. The examination must include a careful search for sacral anesthesia and bladder dysfunction.
Radiographic Findings. Large defects in the pars interarticularis (spondylolysis) are visible on nearly all radiographic views of the lumbar spine. However, if the spondylolysis is unilateral or not accompanied by spondylolisthesis, special techniques and oblique views of the lumbar spine may be needed.
In an acute injury, the gap in the pars interarticularis is narrow with irregular edges, whereas in the long-standing lesion, the edges are smooth and rounded. Bone scans may be needed to detect an early prespondylolytic stage (before fracture) in children. In dysplastic spondylolisthesis, the posterior facets appear to sublux and the pars interarticularis may become attenuated like pulled taffy ( the “greyhound” described by Hensinger).
In unilateral spondylolysis, the radiographic appearance of reactive sclerosis and hypertrophy of the contralateral pedicle and lamina may be confused with osteoid osteoma. This is an important concern because excision of a sclerotic pedicle associated with a contralateral spondylolysis may increase instability, leading to spondylolisthesis. Bone scans are not helpful in differentiating the two conditions.
Treatment. Spondylolysis usually responds well to conservative measures, restriction of some activities, and exercises for the back and abdominal muscles. Asymptomatic spondylolisthesis is more problematic, because the risk of further slippage is difficult to determine. Symptomatic spondylolisthesis may require surgical stabilization of the spine. Surgery may entail an in-situ fusion or reduction. Currently, most fusions are instrumented, which eliminates the need for a prolonged period of bracing.