Study design:

Retrospective cohort study OBJECTIVE.: This study aimed to identify risk factors that predict lumbar curve adding-on in patients who had selective thoracic fusion.

Summary of background data:

Selective thoracic fusion offers deformity correction of Lenke I&II thoracic curves and maintain lumbar range of movement. However, some patients may develop post-operative lumbar adding-on.

Methods:

This study included patients ≤18 years of age that underwent spinal instrumentation for Lenke I &II curves.

Results:

161 patients were included(147females,14males). The mean age was 14.0 ± 2.1years. 103patients were Lenke I, and 58 patients were Lenke II curves. 97 patients underwent posterior approach surgery, while 64 via anterior approach. In the posterior approach group, 79(81.4%) patients underwent selective fusion. 10 patients (6.2%) had lumbar curve adding-on, with 9 females and 1 male. There were 7 Lenke I and 3 Lenke II patients. All 10 patients were lumbar modifier (a), with 5 hypokyphotic patients. Selective fusion was done in 9 patients. Lumbar adding-on was seen most commonly between 6months to 1year post-operative period (5patients). 2 patients had adding-on because of incorrect distal fusion level, 6 were due to 1A-R curve, 1 due to the inadvertent fusion from the excessive long rod at the subjacent level. In multivariate analysis, hypokyphotic patients were at higher risk of lumbar adding-on (OR=9.2). Patients with Risser classification 0, 1, 2, 3 were also at higher risk of lumbar adding-on (OR =6.1).

Conclusion:

The incidence of lumbar curve adding-on was 6.2%. Patients who were hypokyphotic and skeletally immature are 9 times and 6 times more likely to have lumbar adding-on, respectively. This paper examines adding-on in patients who had either anterior or posterior approach scoliosis surgeries, with follow-up stretching up to 10 years. This offers the rare opportunity to examine the natural history of the adding-on phenomenon.

Level of evidence:

3.