A retrospective review of clinical and radiographic data from a single-center, prospectively collected scoliosis
To assess risk factors for persistent thoracic hypokyphosis
after posterior spinal fusion and instrumentation (PSFI) for adolescent idiopathic scoliosis
(AIS) and to compare clinical outcomes
between patients with residual thoracic hypokyphosis
and those with normal thoracic kyphosis after PSFI for AIS.
Summary of Background Data.
AIS is characterized by thoracic hypokyphosis
, which should be corrected at the time of surgical treatment. Risk factors for residual thoracic hypokyphosis
and the clinical ramifications have not been studied.
Radiographic and clinical assessments by using the Scoliosis
Research Society-30 (SRS-30) and Spinal Appearance Questionnaire (SAQ) were done preoperatively and at 2 years. Patients were divided into 2 groups on the basis of a threshold of 20° of thoracic kyphosis measured between T5 and T12 at 2-year follow-up.
Risk factors for being hypokyphotic at 2 years were male sex (21.69% vs.
= 0.084), preoperative kyphosis (11.4° vs.
< 0.0001), and smaller preoperative main thoracic coronal curves (58.4° vs.
= 0.004). A total of 71.5% of patients instrumented with 6.35-mm rods had normal thoracic kyphosis at 2 years compared with 47.0% instrumented with 5.5-mm rods (P
= 0.0043). All-pedicle screw constructs remained hypokyphotic compared with hook-based constructs (P
= 0.035). Logistic regression analysis demonstrated 2 parameters associated with persistent thoracic hypokyphosis
at 2 years: preoperative hypokyphosis
and larger rod diameter. Both groups had similar clinical results on the SRS-30 at 2-year follow-up (P
> 0.05). There was a small but statistically significant correlation between sagittal Cobb angle and clinical deformity at 2 years based on the sagittal components of the SAQ.
There are 2 risk factors that lead to thoracic hypokyphosis
in AIS: preoperative hypokyphosis
and use of a 5.5-mm-diameter rod. A larger-diameter rod should be considered when planning surgery for thoracic AIS, especially when there is preoperative hypokyphosis
. Despite thoracic kyphosis measuring less than 20°, these patients did not have decreased clinical outcomes
as measured by the SRS-30 or SAQ.