Background: Accurate prognosis and treatment decisions in adolescent idiopathic scoliosis (AIS) demand a reliable radiographic marker of growth cessation. Specifically, Sanders Stage 7 (SS7) is a useful marker of spine growth cessation in females and is proposed as a bracing endpoint. The purpose of this study was to determine the amount of curve progression noted in female individuals with AIS after achieving SS7. We hypothesize that a subset of patients continues to progress at a greater rate than the natural history at SS7.
Methods: This retrospective review included female patients with AIS treated at a single institution from May 2008 to 2018. Patients required a hand radiograph demonstrating SS7 and concurrent spine radiograph measuring <50 degrees, plus 2-year follow-up spine radiograph. Curve types were categorized by the modified Lenke Classification. Risser grade, menarche, height, weight, and bracing data were collected. Progression was defined as an increase of the main curve ≥5 degrees. Comparison between groups was analyzed using independent t tests and χ or Fisher exact tests as appropriate. Binary logistic regressions were used to construct a model predictive of progressing beyond 50 degrees or undergoing surgery.
Results: A total of 89 patients met inclusion criteria, average main curve magnitude 33 degrees (SD 9) at SS7 and 38 degrees (SD 11) at 2-year follow-up. Forty-five (51%) patients progressed ≥5 degrees and 17 (19%) progressed at least 10 degrees. Seventy patients had curves <40 degrees at SS7 and 22 (31%) progressed to >40 degrees at 2 years. Eleven (12%) patients progressed to >50 degrees or had surgery at 2-year follow-up. Receiver operating characteristic curve analysis identified a threshold of 39.5 degrees curvature at SS7 associated with progression to >50 degrees or surgery (area under the curve=0.94, P<0.001, sensitivity=100%, specificity=87%). Patients with initial curves >40 degrees did have additional height gained (2.1 cm; SD 1.5), but this was not different than those <40 degrees, P>0.05. In addition, no other variables had statistically significant association with those that progressed (P>0.05).
Conclusions: A curve >40 degrees at SS7 is at high risk for progressing to a curve measuring >50 degrees or requiring surgery. Those with curves below this threshold still have potential to make clinically significant progression after skeletal maturity. Follow-up of patients beyond SS7 is essential for curves measuring >40 degrees. Reaching SS7 with a curve <50 degrees may not be the endpoint for curve progression, even if predictive of the end of spinal growth.
Level of evidence: Level III-retrospective research study.