Correlation between correction of pelvic balance and clinical outcomes in mid- and low-grade adult isthmic spondylolisthesis

Background: Pelvic balance is a version of the pelvis defined by pelvic orientation parameters of PT and SS. Two distinct versions of pelvis are defined: (1) balanced characterized by a relatively low PT and high SS, and (2) unbalanced with relatively high PT and low SS meaning excessive retroversion of the pelvis. It was proved for patients with a high-grade spondylolisthesis that rebalancing of the pelvis can positively affect clinical outcomes. Little is known about the impact of such rebalancing in low-grade isthmic spondylolisthesis.

Purpose: To determine whether clinical outcomes correlated with rebalancing of the pelvis after surgical correction of mid- and low-grade adult isthmic spondylolisthesis.

Methods: One hundred and three adult patients with a mid- and low-grade isthmic slip were the participants. Clinical outcomes were assessed at least 2 years after the surgery with the use of the Oswestry Disability Index (ODI) and a back pain visual analogue scale. Statistical analysis was used to identify differences in clinical outcomes between patients (1) with a balanced and unbalanced pelvis postoperatively, (2) who regained and did not regain pelvic balance postoperatively, (3) who maintained and lost pelvic balance postoperatively, and (4) with reduced and increased postoperative PT.

Results: There were no significant differences in clinical outcomes between patients with a balanced and unbalanced pelvis postoperatively regardless of whether they lost, maintained, or regained pelvic balance after the surgery (Student's t test for independent variables or the non-parametric Mann-Whitney U, p value = 0.05). No correlation (Spearman's rank correlation) was found between postoperative reduction of PT and postoperative: (1) level of back pain (r = -0.10, p = 0.3063), (2) degree of reduction in back pain (r = 0.03, p = 0.7927), (3) ODI scores (r = -0.18, p = 0.0696), and (4) degree of reduction in ODI scores (r = 0.13, p = 0.1893).

Conclusions: Radiological improvement of pelvic balance after surgical correction of mid- and low-grade isthmic spondylolisthesis did not correlate with clinical outcomes.