Defects of the pars interarticularis cause spondylolysis. This defect may allow displacement of the vertebrae, which is called spondylolisthesis.
In children, these conditions are usually due to a stress fracture through a congenitally dysplastic pars interarticularis. This inherent weakness occurs more commonly in certain races (such as Inuit peoples), families, or individuals. The defects often are associated with spina bifida occulta. Spondylolisthesis occurs in about 4% of 4-year-old children and increases to about 6% by maturity. Spondylolisthesis occurs in about a third of those with pars defects, especially in those with mechanical instability. These lesions occur more commonly in children with abnormal bone or connective tissue, as occurs in conditions such as Marfan syndrome and osteopetrosis. Lesions are common in children who participate in certain sports that cause hyperextension of the lumbar spine with rotation. Progression after adolescence is unusual.
The child usually complains of back pain. Tenderness may be present at the L5-S1 level. If the displacement is severe, a prominence is palpable over the defect. Straight leg raising and forward bending may be limited. The neurological examination is usually normal.
Imaging First, order a standing lateral radiograph. A forward displacement of the body of L5 or L4 establishes the diagnosis. If no displacement is present, order oblique radiographs of the lower lumbar spine to assess the status of the pars. A bone scan may show reaction before radiographs show a defect and may be used to determine the activity and healing potential of the lesion. Even more sensitive is SPECT imaging in demonstrating the stress reaction of spondylolysis.
Classification Wiltse classifies spondylolisthesis into two types:
Dysplastic is a congenital facet deficiency allowing slippage.
Grade the degree of slip in severity and activity (duration).
Severity Grade on the basis of slip angle and displacement. Slip angle changes usually occur with slips greater than 50%.
Activity Grade on the duration or activity. Recent fractures are active and show increased uptake on bone scan. Cold lesions are chronic, inactive, and less likely to heal.
Progression Pain is most pronounced at the time of onset or fracture. Most isthmic lesions become stable and painless with time. Pain is aggravated by activity, especially competitive sports. Lesions often are symptomatic in adolescence but become painless in adult life when activity levels are reduced. The incidence of back pain is comparable to normal population levels.
Treatment of Spondylolysis and Spondylolisthesis in Children
Management is based on the age, degree of deformity, type of lesion, activity, and physical activity level.
Spondylolysis management depends upon the activity of the lesion.
Acute lesions from an acute injury or recent overuse experience are managed by reduction of activity and usually an under-arm brace. Often these lesions will heal.
Established lesions Manage symptoms with NSAIDS and activity modification. Operative stabilization is seldom necessary.
Spondylolisthesis is managed based on the severity of the slip, considering the displacement and slip angle. If fusion is required, it is often performed without reduction.
Grade 1–2 slips Manage with NSAIDS, activity modification, and TLSO as necessary to control symptoms. Follow with standing lateral radiographs.
Grade 3 slips Most require operative stabilization. Fuse L4–S1 level with posterolateral autogenous grafting. See next page.
Grade 4 slips These slips may require fusion of L4-S1, as the displacement may be significant, making identification of the transverse process of L5 difficult. If slip angle is severe, reduction is sometimes elected.
Grade 5 (spondyloptosis) management is controversial. In situ fusion provides pain relief and safety, but the deformity remains. Reduction incurs greater risk but improves appearance and posture.
Special situations require tailoring of management.
L4 spondylolisthesis is less common, more mechanical in etiology, often causes more symptoms, and is more likely to require operative stabilization.
Spondylolysis with persisting symptoms may be managed by repair of the pars defect with grafting and fixation.
Fusion is indicated for slips of >50% and those that remain painful following nonoperative management. The need for reduction or instrumention is controversial, but may be indicated for high-grade slips. Fusion of L5–S1 is often sufficient. Fuse from L4–sacrum when the transverse process of L5 is hypoplastic or displaced anteriorly, making a solid single-level fusion less certain.
Several approaches are effective. Consider tailoring the approach to the slip severity. With increasing slip severity and angle, increase the length of fusion and immobilization following surgery.
Place on rolls in the prone position. Prepare the skin and drape to allow visualization from L2–lower sacrum.
Make a midline vertical skin incision. Alternatives include a curved transverse skin incision centered on the L1 spinous process or parallel paraspinal incisions. Keep in mind the normal transverse anatomy.
Make through the midline or through two paraspinal transfascial incisions. Make a midline incision through the lumbosacral fascia to expose the spinous process of each vertebral level to be fused. Expose the lamina, facet joints, and transverse processes. Because spina bifida is common, exercise caution in making this deep exposure to avoid accidental entry into the spinal canal.
An alternative is to make two paraspinal fascial incisions, leaving the transverse processes undisturbed and facilitating the lateral exposure.
In both approaches, extend the exposure to the tips of the transverse process. Avoid extending the exposure anterior or laterally beyond tips of the processes to avoid injury to the nerve roots and vessels.
Retract the skin and subcutaneous tissues to expose the posterior ilium. Take a substantial bone graft of corticocancellous and cancellous bone.
Decorticate the transverse processes of each level to be fused. Create a notch in each sacral ala. Place cancellous bone from the sacral alar notch to L5 or L4 as planned. Place abundant graft in each lateral gutter that extends laterally to the tips of the transverse process. Perform a facetectomy and graft the defect. A posterior fusion is optional. Some consider the posterior fusion to increase the risk of spinal stenosis without improving the rate of fusion.
After surgery care may include a pantaloon cast, TLSO, or no immobilization. The extremes include a cast and immobilization for 3–4 months or immediate mobilization with no external support. Most manage with a short period of immobilization and a TLSO for 3–4 months.