Impact of lowest instrumented vertebra tilt and rotation on uninstrumented lumbar curve and L4 tilt in thoracic adolescent idiopathic scoliosis

Abstract

<jats:sec><jats:title>OBJECTIVE</jats:title><jats:p>Controversy exists regarding the effects of lowest instrumented vertebra (LIV) tilt and rotation on uninstrumented lumbar segments in adolescent idiopathic scoliosis (AIS) surgery. Because the intraoperative LIV tilt from the inferior endplate of the LIV to the superior sacral endplate is not stable after surgery, the authors measured the LIV angle of the instrumented thoracic spine as the LIV angle of the construct. This study aimed to evaluate the effects of the LIV angle of the construct and the effects of LIV rotation on the postoperative uninstrumented lumbar curve and L4 tilt in patients with thoracic AIS.</jats:p></jats:sec><jats:sec><jats:title>METHODS</jats:title><jats:p>A retrospective correlation and multivariate analysis of a prospectively collected, consecutive, nonrandomized series of patients at a single institution was undertaken. Eighty consecutive patients with Lenke type 1 or type 2 AIS treated with posterior correction and fusion were included. Preoperative and 2-year postoperative radiographic measurements were the outcome measures for this study. Outcome variables were postoperative uninstrumented lumbar segments (LIV tilt, LIV translation, uninstrumented lumbar curve, thoracolumbar/lumbar [TL/L] apical vertebral translation [AVT], and L4 tilt). The LIV angle of the construct was measured from the orthogonal line drawn from the upper instrumented vertebra to the LIV. Multiple stepwise linear regression analysis was conducted between outcome variables and patient demographics/radiographic measurements. There were no study-specific biases related to conflicts of interest.</jats:p></jats:sec><jats:sec><jats:title>RESULTS</jats:title><jats:p>Predictor variables for postoperative uninstrumented lumbar curve were the postoperative LIV angle of the construct, number of uninstrumented lumbar segments, and flexibility of TL/L curve. Specifically, a lower postoperative uninstrumented lumbar curve was predicted by a lower absolute value of the postoperative LIV angle of the construct (p &lt; 0.0001). Predictor variables for postoperative L4 tilt were postoperative LIV rotation, preoperative L4 tilt, and preoperative uninstrumented lumbar curve. Specifically, a lower postoperative L4 tilt was predicted by a lower absolute value of postoperative LIV rotation (p &lt; 0.0001).</jats:p></jats:sec><jats:sec><jats:title>CONCLUSIONS</jats:title><jats:p>The LIV angle of the construct significantly affected the LIV tilt, uninstrumented lumbar curve, and TL/L AVT. LIV rotation significantly affected the LIV translation and L4 tilt.</jats:p></jats:sec>

Influence of Lateral Translation of Lowest Instrumented Vertebra on L4 Tilt and Coronal Balance for Thoracolumbar and Lumbar Curves in Adolescent Idiopathic Scoliosis

“…PSF was performed according to the previously reported posterior corrective surgery protocol for the main thoracic curve [ 1 , 6 , 24 , 25 ] ( Figure 1 ). Briefly, after posterior exposure, side-loading polyaxial pedicle screws were placed bilaterally at all possible vertebrae.…”

“…Briefly, after posterior exposure, side-loading polyaxial pedicle screws were placed bilaterally at all possible vertebrae. After all-level facetectomy, two rods were connected to the screw heads and simultaneously rotated [ 1 , 6 , 25 ]. Compression force was segmentally applied between the screws on the convex side to create lumbar lordosis, followed by a distraction force on the concave side.…”

“…Patients with a Lenke type 5 AIS curve, which is characterized by a major thoracolumbar/lumbar (TL/L) curve with a compensatory nonstructural thoracic curve [ 3 ], are often reported with coronal imbalance [ 4 , 5 ], and obtaining good global balance forms an important part of treatment. A favorable correction of the L4 tilt is also known to be critical in preventing the progression of the uninstrumented lumbar curve, lumbar disc degeneration, and low back pain [ 6 , 7 , 8 ]. Lenke 5 curve treatment planning should, thus, consider the TL/L curve correction, as well as the global spinal balance and L4 tilt.…”

“…Since there have been some reports of low back pain progression and loss of the lumbar range of motion when L4 is included in the fusion segment [ 10 ], L3 is often selected as the LIV to maximize the lumbar motion segments and minimize future disc degeneration [ 11 , 12 , 13 , 14 , 15 , 16 ]. It has also been reported that the LIV translation and inclination should be considered when selecting the LIV [ 6 , 14 , 17 ]. Leveling and centering the LIV is expected to restore the vertebrae to their anatomically normal position, correct the lumbar curve, and provide a better global balance of the spine [ 6 , 14 , 17 ].…”

“…It has also been reported that the LIV translation and inclination should be considered when selecting the LIV [ 6 , 14 , 17 ]. Leveling and centering the LIV is expected to restore the vertebrae to their anatomically normal position, correct the lumbar curve, and provide a better global balance of the spine [ 6 , 14 , 17 ]. However, there are limited data on the factors associated with favorable outcomes for LIV selection [ 14 ].…”