Effect of mono- or bisegmental lordosizing fusion on short-term global and index sagittal balance: a radiographic study.

Background: Sagittal balance is widely recognized as an important outcome factor in reconstructive spinal surgery for lumbar degenerative conditions. However, its role in short segmental fixation is unknown. The aim of this study was to evaluate the preoperative and short-term postoperative spino-pelvic balance after short (1 or 2 levels) lordosizing lumbar fusion for degenerative disc disease (DDD).
Methods: Twenty-six consecutive patients (13 males and 13 females) undergoing mono- or bisegmental lordosizing lumbar fusion (XLIF/TLIF) for lumbar DDD were included in the study. Clinical parameters were retrospectively collected from charts. Preoperative and early postoperative (6 weeks and 3 months) full-spine EOS X-rays were evaluated. Spinal parameters evaluating sagittal curvatures, pelvic orientation, global sagittal and coronal alignment, spino-pelvic balance, index level segmental lordosis and disc height were measured and statistically analyzed.
Results: A total of 16 TLIF and 10 XLIF procedures were performed. Eighteen were mono- and 8 were bisegmental fixations for a total of 34 fused segments. Seven patients (26.9%) showed a preoperative sagittal imbalance (defined as SVA>50 mm); 7 patients presented preoperative severe pelvic retroversion (defined as PT>20°) and 1 patient presented both. Disc height, intervertebral angle and segmental lordosis at the operated level significantly increased after surgery (P<0.01). No postoperative significant change in global sagittal alignment (SVA, TPA, T1SPi, T9SPi), pelvic orientation (SS, PT), coronal alignment, lumbar and L4-S1 lordosis and thoracic kyphosis have been observed.
Conclusions: Mono- and bisegmental lordosizing fusion techniques, as XLIF and TLIF, are able to restore disc height and improve segmental lordosis. However they do not allow restoration of sagittal balance or improvement of compensatory mechanisms. A limited spinal reconstructive surgery on symptomatic levels can be reasonably proposed to patients with hidden or evident sagittal imbalance with any short-term radiographic impact.