EVALUATION OF THE SAGITTAL BALANCE OF THE SPINE AFTER UNINSTRUMENTED IN SITU FUSION OF SPONDYLOLISTHESIS IN CHILDREN

Abstract

This study is a retrospective monocentric analysis of changes in spinopelvic sagittal alignment after in situ fusion of L5-S1 spondylolisthesis. In situ fusion is a safety procedure with good functionnal outcome, but the consequences on the spinopelvic sagittal balance remains unclear. The aim is to evaluate the adaptative changes in the sagittal balance after such treatment.

This is an analysis of 22 patients (mean age 13,5 years) with an average follow-up of 5,2 years (range 1–11 years). This study includes 6 grade II spondylolisthesis, 7 grade III and 9 grade IV. 13 patients were operated with a non instrumented posterolateral arthrodesis and 9 with a circumferential in situ fusion. Among the 13 grade II and III spondylolisthesis, 12 had a posterolateral arthrodesis and only 1 had a circumferential fusion. As for the grade IV spondylolisthesis 8 out of 9 had a circumferential arthrodesis and only 1 had a posterolateral fusion.

Before and after surgery, all patients had lateral standing radiographs of the spine and pelvis. Different parameters were evaluated before surgery: pelvic incidence, sacral slope, pelvic tilt, lumbar lordosis, thoracic kyphosis, T9 sagittal tilt, L5 incidence, L5 slope and L5 tilt. After surgery, the pelvic parameters were not evaluated because of the difficulty to visualise the upper part of S1 after arthrodesis. The discs were evaluated by MRI.

The functionnal outcome was evaluated with the Oswestry score.

A global evaluation including all the patients doesn’t show any influence of the surgery on the sagittal alignment. But when evaluating the datas after classifying the patients in function of the severity of the spondylolisthesis, some differences raise. On one side, the patients with grade II and III spondylolisthesis keep a normal T9 sagittal tilt while slightly increasing lumbar lordosis and thoracic kyphosis. On the other side, the patients with grade IV spondylolisthesis operated with a circumferential in situ fusion worsen the T9 sagittal tilt, increase the L5 incidence, decrease their lombar lordosis (L4/L5 discal kyphosis) and thoracic kyphosis.

To conclude, we can say that patients with grade II and III spondylolisthesis have good functionnal outcome and keep a balanced spine. Patients with grade IV have a good clinical outcome as well but keep worsening their sagittal balance despite the circumferential in situ fusion. An unbalanced sagittal alignment might theorically compromise the long term clinical results, but the radiological outcome doesn’t seem to be linked to the functionnal outcome. A long term follow-up has to be done in order to evaluate the outcome of these unbalanced spines and compare it to the functionnal and radiological results obtained with reduced high grade spondylolisthesis.