Fusing to the Sacrum/Pelvis: Does the Risk of Reoperation in Thoracolumbar Fusions Depend on Upper Instrumented Vertebrae (UIV) Selection?

Background There is controversy as to whether fusions should have the upper instrumented vertebrae (UIV) end in the upper lumbar spine or cross the thoracolumbar junction. This study compares outcomes and reoperation rates for thoracolumbar fusions to the sacrum or pelvis with UIV in the lower thoracic versus lumbar spine to determine if there is an increased reoperation rate depending on UIV selection.

Methods A retrospective review of prospectively collected data was conducted from a single-center database on adult patients with degeneration and deformity who underwent primary and revision fusions with a caudal level of S1 or ilium between 2012 and 2018. Fusions were classified as anterior, posterior, or combination approach. Revision fusions included patients who had spinal surgery at another institution prior to their revision surgery at the center. Patients were categorized into 1 of 3 groups based on UIV: T9–T11, upper lumbar region (L1–L2), and lower lumbar region (L3–L5). Inclusion criteria was age 18 years or older and at least 1 year of clinical follow-up. Patients were excluded from analysis if they had tumors, infections, or less than 1 year of follow-up after the index procedure.

Results The reoperation rates for the UIV groups in the thoracic (28%) and upper lumbar (27%) spine were nearly equal in magnitude and were both significantly higher than the reoperation rate in the lower lumbar group (18%, P = .046). Reoperation for the diagnosis of adjacent segment disease was 8.3% in the upper lumbar spine and statistically significantly higher than the reoperation rates for adjacent segment disease in the thoracic (1%) or lower lumbar (4.5%, P = .042) spine. Reoperations for pseudoarthrosis and proximal junctional kyphosis were 13% and 4%, respectively, in the thoracic spine, both of which were statistically significantly different (pseudoarthrosis, P = .035; proximal junctional kyphosis, P = .002) from the reoperation rates for the same diagnoses in the upper lumbar spine (4.6% and 1%) or lower lumbar spine (6.2% and 0%). A multivariate logistical regression model at 2-year follow up did not show a statistically significant difference between reoperation rates between the thoracic and upper lumbar spine UIV groups.

Conclusion Constructs with UIV in the thoracic spine suffer from higher rates of proximal junctional kyphosis and pseudoarthrosis, whereas those with UIV in the upper lumbar spine have higher rates of adjacent segment disease. Given this tradeoff, there is no certain recommendation on what UIV will result in a lower reoperation rate in thoracolumbar fusion constructs to the sacrum or pelvis. Surgeons must evaluate patient characteristics and risks to make the optimal decision.