Surgical Outcomes Research

Study Design. Retrospective analysis of radiographs on a prospective cohort of patients undergoing anterior instrumentation for thoracic idiopathic scoliosis.

Objectives. To analyze the change in sagittal profile after growth.

Summary of Background Data. The authors previously reported some advantages of anterior instrumentation for treatment of thoracic idiopathic scoliosis. However, postsurgery hyperkyphosis has resulted in some patients, especially those who were skeletally immature at the time of surgery.

Methods. Inclusion criteria required that participants have thoracic idiopathic scoliosis treated with anterior instrumentation and a confirmed solid fusion, no rod breakage, and a minimum follow-up period of 2 years. The 47 patients meeting the criteria were divided into a study group of 10 patients who were Risser 0 at the time of surgery and a control group of 37 patients who were Risser 1 to 5. Progressive sagittal kyphosis was defined as an increase of 10° or more (T5–T12) after surgery.

Results. Sagittal progression greater than 10° (average, 15°) occurred in 6 of 10 patients (60%) in the study group (Risser 0). Five patients progressed from 10° to 19°, and one patient from 20° to 30°. In contrast, sagittal progression occurred in only 10 of 37 patients (27%) in the control group (Risser 1 to 5).

Conclusions. Some patients with thoracic adolescent idiopathic scoliosis treated with anterior instrumentation may be at risk for progressive sagittal kyphosis secondary to growth. Skeletal immaturity (Risser 0) appears to be a risk factor. In these immature patients, preserving the sagittal profile with intervertebral spacers, rigid rods, and bone graft (allowing for an average 15° increase of kyphosis with growth) may be appropriate.

Preoperative thoracic hypokyphosis is part of the typical presentation in patients with adolescent thoracic idiopathic scoliosis, and it is well described in the literature. 4,17 In a previous study comparing the results of anterior and posterior spinal fusions, the Harms Study Group 1 reported the advantage of anterior instrumentation’s ability to save an average of 2.5 distal fusion levels while obtaining coronal correction and balance equal to that obtained by posterior instrumentation. However, these authors noted excessive postoperative hyperkyphosis in 40% of the patients undergoing anterior spinal fusion (ASF) when the preoperative kyphosis was greater than 20°. They also observed that this was more prevalent in immature patients than in mature patients. In addition, the kyphosis appeared to increase over time from first erect radiograph to 2-year follow-up radiograph.

This type of postsurgical deformity is not well described. Discussions of crankshaft in young children after posterior spinal fusion for scoliosis usually focus on coronal and axial plane deformity. 6,9,12,14,16 Sagittal profile change after posterior spinal fusion has been described as a loss of disc height, which usually is balanced by increased vertebral body height resulting in no significant change in the kyphotic angle. Hallock et al 8 noted increased kyphosis after a Hibbs type of posterior spinal fusion for tuberculosis infection in 15 young children with an average long-term follow-up period of 21 years. They found that the normal vertebrae included in the fusion grew 23% less anteriorly and 36% less posteriorly than the adjacent unfused vertebrae. In such cases, increased kyphosis after surgery is significant. Connolly et al 3 demonstrated a relation between a lower spine score and increased thoracic kyphosis after long-term instrumentation extending to the lumbar spine. Because skeletal immaturity may be an indication for thoracic anterior instrumentation in patients requiring surgery, analysis of this kyphosis appears warranted.

This study proposed the following questions: 1) With progression of the kyphotic deformity after surgery, is there a difference in skeletally immature and mature patients? 2) Could these changes in the sagittal profile be the result of continued growth of the posterior elements after ASF?