PURPOSE
In adolescent idiopathic scoliosis (AIS), Lenke type 5C consists of a thoracolumbar/lumbar (TL/L) structural curve accompanied by upper thoracic and main thoracic (MT) nonstructural ones (Lenke LG, JBJS 2001). Although the surgical results are excellent for both anterior and posterior spinal fusion (ASF&PSF), postoperative decompensation (PD) sometimes becomes a problem. PD is a condition that may be the cause of re-operation and may have an unfavorable impact on quality of life (QOL). Adequate fixation range should be planned to prevent PD, while reduction of fused motion-segments has been reported to have a favorable impact on back pain, QOL, and return to sports. Therefore, the determination of the appropriate fixation range is important. The Shinshu line (S-line) has been recently developed as a method to predict PD in the patients underwent selective PSF (Oba H. J Neurosurg Spine 2019). However, it remains to be clarified whether the S-line is also useful in ASF. The purpose of the current study was to investigate whether the S-line can predict the occurrence of postoperative PD in Lenke 5C AIS patients who underwent ASF.
METHOD
Fourteen Lenke 5C AIS patients (all girls; mean age 15.6) who had undergone ASF with a minimum of 2 year follow-up were included. The S-line was defined as the line connecting the centers of the concave side pedicles of the upper instrumented vertebra (UIV) and lowest instrumented vertebra (LIV). S-line+ was defined as right tilt and S-line− as left tilt relative to the central sacral vertical line (CSVL). Radiographic parameters were measured preoperatively, immediately after surgery, and at 1 year postoperatively. Outcome was the incidence of postoperative PD. PD was defined as at least one of the following 3 items; 1) an increase in thoracic Cobb angle of ≥10 degrees at 1 year postoperatively compared to the immediate postoperative period, 2) UIV tilt of ≥5 degrees, 3) coronal balance of ≥30 mm at 1 year postoperatively. Statistical analysis was performed between the S-line+ and S-line- groups (p<0.05).
RESULTS
The S-line+ and S-line− groups included 7 patients each. TL/L Cobb angle was not significantly different between the two groups both preoperatively and postoperatively. None of the patients in both groups had an MT curve increase of more than 10° at follow-up compared to the postoperative period. At the last follow-up, UIV tilt was greater than 5° in 7 patients in the S-line+ group and in 2 patients in the S-line- group. In both groups, there were no patients with coronal imbalance greater than 30 mm at the final follow-up. 7 cases in the S-line+ group and 2 cases in the S-line- group met the criteria for PD, which occurred significantly higher in the S-line+ group than S-line- one.
DISCUSSION
This is the first study to investigate the usefulness of the S-line in Lenke 5C AIS patients undergone ASF. S-line was associated with the occurrence of PD even in the ASF for Lenke 5C AIS. Adjusting the fixation range according to the S-line in the preoperative planning may prevent postoperative PD.