Frontal and Sagittal Balance Analysis of Late Onset Idiopathic Scoliosis Treated with Third Generation Instrumentation

As scoliotic curve is a rotational deformity, derotation maneuvre was used as the corrective factor, but recent studies demonstrated spinal imbalance and decompensation problems in patients treated with this method. This study evaluates 217 late onset idiopathic scoliosis patients surgically treated with third generation instrumentation (Texas Scotish Rite Hospital System - TSRH) from September 1991 to November 1996 with a minimum 2 years follow up. Preoperative and postoperative Cobb angles in the frontal plane and thoracic kyphosis and lumbar lordosis angles in the sagittal plane are measured. The balance was analyzed clinically and radiologically by measurement of the lateral trunk shift (LT), shift of head (SH) and shift of stable vertebra (SS) in vertebral unit (VU). At final follow - up correction loss, infection and other complications were documented. Mean age of the patients was 14.8 +/- 2.3 and mean follow up period 55.8 +/- 29.5 months. When all the patients were included, preoperative mean Cobb angles of major curves in the frontal plane was 59.1 +/- 20.7 degrees. Major curves that were corrected by 34.8 +/- 20.5 % in the bending radiograms were achieved by 58.9 +/- 19.5 % correction postoperatively. At the last control, 7.3 degrees +/- 6.4 degrees of correction loss was recorded in major curves in the frontal plane. Also postoperative kyphosis angle and lumbar lordosis angles were 31.4 degrees +/- 11.6 degrees and 30.6 degrees +/- 10.9 degrees respectively. Postoperatively, a statistically significant correction was obtained in LT, SH and SS values. None of the patients had complete balance (SH: 0 VU, SS: 0 VU) preoperatively. Only 39.2 % of the patients had clinically balanced curves (0 VU < SH < 0.5 VU and 0 VU < SS < 0.5 VU). Postoperatively, 47.9 % of the patients were found to be completely balanced, while 43.8 % had a balanced curve. Overall 91.7 % of the patients had a trunk balance after surgical intervention. The remaining 8.3 % imbalanced curve rate raised up to 16.6 % at final follow up, but the loss of correction rates in S S and SH values were found to be insignificant. The postoperative "imbalance" problem was mostly seen in Type II and Type IV curves. However, at final follow up, the imbalance problem due to overcorrection which became evident especially by "shift of head" to opposite side was seen in all types of curves. It is established that high correction rates can be obtained in scoliotic curves with third - generation instrumentation. No undue effects were observed in the uninstrumented lumbar curves. Thoracic sagittal contours of the hypokyphotic patients were improved. Use of this instrumentation system causes minimal imbalance problems and with proper preoperative planning high correction rates can be achieved.