Summary: The extent to which the lowest instrumented vertebra (LIV) is leveled during selective thoracic fusion is an object of much debate among surgeons, especially in Lenke type 1B, 1C and 3 curves. In this longitudinal study, 205 consecutive patients with correction of AIS formed two cohorts: those who were “leveled” and those who were not. We found that leveling of the LIV gives a smaller lumbar Cobb angle without increasing the risk of coronal imbalance.
Introduction: When performing a thoracic fusion for Lenke 1B, C and Lenke 3 curves, surgeons debate whether the lowest instrumented vertebra (LIV) should be leveled as much as possible, or left with some tilt to create a harmonious transition from fused to unfused spine. Our goal was to study the early effects (min.2 yr f/u) of leveling vs. leaving the tilt in the LIV.
Methods: Prospectively collected data from a multi‐center database revealed 205 patients with Lenke type 1B or 1C or 3 curves. We divided these patients into 2 cohorts: 73 with “leveled” (LIV tilt ‐5° to 5°) and 132 with “non‐leveled” LIV. Radiographic data was analyzed before surgery, at first radiographic follow‐up and at 2 years after surgery for changes in lumbar curve size, coronal balance and lumbar apical translation.
Results: The average 2 year post‐op LIV tilt for the “leveled” group was 5 ±4° compared to 9.7±4.6° for the “unleveled” group. At 2 years post‐op, the lumbar Cobb angle was smaller (17.3° vs. 21.6°, p<0.001) in the leveled group vs. the non‐leveled group. Coronal balance was similar between the leveled and non‐leveled groups at 2 years after surgery (‐1.25 vs. ‐1.21, p=0.85) with a slight tendency for trunk shift to the left in both groups The change in lumbar apical translation was not significantly different between the two groups at 2 year follow‐up. There was a weak to moderate association between pre‐operative lumbar curve and post‐operative LIV tilt. However, 90% of the variation in post‐operative LIV tilt was attributable to factors other than preoperative lumbar curve.
Conclusion: At 2 year follow‐up, leveling of the LIV in selective thoracic fusions in AIS results in a smaller absolute lumbar Cobb angle without increasing the risk of coronal imbalance.
Significance: These 2 year follow‐up results suggest leveling the thoracic LIV maximizes spontaneous correction of the lumbar curve when a selective thoracic fusion is performed for Lenke 1B, 1C and the rare 3C curves.
