Introduction:

adolescent idiopathic scoliosis (AIS) is the most common of all scoliosis. Patients with progressive AIS require surgical treatment, but there is a percentage of patients who present progression of the deformity below the surgical area, a phenomenon known as Adding-on.

Objective:

describe the Adding-on phenomenon in patients with AIS treated surgically.

Material and methods:

a series of cases of patients with AIS, aged 12-17 years, who underwent surgical treatment were performed. All patients underwent measurements of Cobb angle, IDV (instrumented distal vertebra), IPV (instrumented proximal vertebra), NV (neutral vertebra), SV (stable vertebra) and apex, as well as angulation of the instrumented distal vertebra (AIDV) and angulation of the instrumented distal vertebra disk (AIDVD) in preoperative radiographs at one, six, 12 and 18 months. For statistical analysis, means and standard deviation of the mean were established.

Results:

sample 11 patients. Age: 14.0 ± 1.5 years. Lenke 1: 63.6%. The most frequent NV, SV, apex, IDV and IPV were: L3 (27.3%), L5 (63.6%), T8 (45.5%), L2 (34.6%) and T4 (45.5%), correspondingly. At 18 months, when comparing Lenke 1 vs 2, Cobb angle: PT (proximal thoracic) 17.8 ± 8.7 vs 21.8 ± 6.8, MT (greater thoracic) 13.5 ± 6.5 vs 21.8 ± 16.3 and L (lumbar) 5.8 ± 3.1 vs 8.9 ± 7.8; AIDV: 3.4 ± 2.8 vs 6.4 ± 3.7; AIDV: 1.9 ± 1.2 vs 2.9 ± 3.3. Adding-on was observed only in one patient with Lenke 2.

Conclusions:

the Adding-on phenomenon in patients with AIS who underwent posterior spinal fusion is a rare complication observed at 18 months.

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