The effect of selecting lower instrumented vertebra on sagittal balance of the spine in adolescent idiopathic scoliosis patients

English Keywords:Adolescent idiopathic scoliosis  Lower instrumented vertebra  Pedicle screws  Sagittal balance

English Abstract:

  【Abstract】 Objectives: To analyze the effect of the lower instrumented vertebra(LIV) at T12 or L1 on sagittal balance of the spine in Lenke 1 adolescent idiopathic scoliosis patients, who received posterior instrumentation and fusion using pedicle screws. Methods: The present study retrospectively reviewed the Lenke 1 adolescent idiopathic scoliosis patients, who received posterior instrumentation and fusion using pedicle screws in our hospital from January 2014 to December 2018. 37 patients were included in our study, of which there were 8 males and 29 females, with a mean age of 14.3±1.8 years old(11-18). The patients were divided into TV(LIV at T12) group and LV(LIV at L1) group. In TV group, there were 16 patients, including 4 males and 12 females, with a mean age of 14.7±2.1 years old(11-18). In LV group, there were 21 patients, including 5 males and 16 females, with a mean age of 14.0±1.7 years old(11-17). There was no significant difference in gender and age between the two groups. All patients had at least 2 years follow-up. The Risser sign, operative time, blood loss, blood transfusion, and fused segments at operation were recorded. Before operation and 2 years after operation, SRS-22 scores were used to analyze the clinical efficacy. Through X-ray images in standing position, the Cobb Angle, thoracic kyphosis(TK), lumbar lordosis(LL), sacral slope(SS), pelvic tilt(PT), pelvic incidence(PI), and sagittal vertebral axis(SVA) were measured before and 2 years after surgery. Statistical difference between the two groups was assessed through the independent sample t test. The correlative relationships among the change of sagittal parameters were analyzed through Pearson coefficients. Results: There was no significant difference in Resign sign, operative time, blood loss, blood transfusion, fused segments, and SRS-22 scores of before and 2 years after operation between the two groups(P>0.05). Before operation, the Cobb angle was 46.1°±6.6°, the TK was 24.3°±7.0°, and the LL was 46.0°±8.4°; at two years after operation, the Cobb angle was 15.9°±4.7°, the TK was 18.3°±6.7°, the LL was 38.8°±8.6°, and the correction rate was (65.6±8.9)%. There was no significant difference in Cobb Angle, LL, SS, PT, PI, SVA, change in LL, change in SS, change in PT, change in PI and change in SVA between the two groups before and 2 years after operation(P>0.05). The preoperative TK was 24.1°±6.3° and 24.3°±7.5° in TV group and LV group; the TK at 2 years after operation was 19.4°±5.8° and 17.4°±7.4° in TV group and LV group; there was no significant difference between the two groups before and 2 years after operation (P>0.05). The mean corrective rate of Cobb was (62.6±8.4)% in TV group, and (67.8±8.9)% in LV group(P=0.080). The change in TK was 4.7°±3.0° in TV group, while it was 6.9°±1.6° in LV group(P=0.015), which was statistically different. In Pearson correlation analysis, a positive relation was found between the value of change in TK and the value of change in LL(r=0.602, P<0.001). Conclusions: For Lenke 1 adolescent idiopathic scoliosis patients who underwent posterior instrumentation and fusion using pedicle screws, the TK and LL coordinated to maintain sagittal balance. The TK is more possible to decrease more in those setting L1 as the LIV rather than those fixed distally to T12 at 2 years follow-up.