Degeneration of the Lumbar Paravertebral Muscle in Patients With Dynamic Sagittal Imbalance, A Retrospective Cohort Study

Abstract

Study Design: A retrospective cohort study.Background: Sagittal imbalance of the spine is a comprehensive concept ..In appearance, it is often manifested as body leaning forward instability; whereas on standing full-spine lateral digital radiographs, it shows an increased sagittal vertical axis (SVA) .Clinically, we found that some patients showed normal sagittal balance at initiation, but hunched or leaned forward after a period of walk or activity. This condition is called dynamic sagittal imbalance(DSI). There is no systematic study to explore the paravertebral muscles changes of dynamic sagittal imbalance.Method: The study group comprised 31 DSI patients and 42 control patients. All subjects underwent radiologic whole spine X-ray examination and lumbar MRI( Magnetic Resonance Imaging) scanning. Spinal-pelvic parameters at initiation such as sagittal vertical axis (SVA), thoracic kyphosis (TK), thoracolumbar kyphosis (TLK), lumbar lordosis (LL), sacral slope (SS), pelvic tilt (PT) and pelvic incidence (PI) was measured. The cross-sectional areas CSA of the erector spinae (ES), multifidus (MF), and vertebral body area were measured at L2/L3 and L4/L5. The fat infiltration (FI) and relative cross-sectional area (RCSA)of muscle of these above muscles were quantitatively measured though Image J softwore.Result : Compared with the control group, the DSI group had a smaller lumbar lordosis, more severe fat infiltration and lower relative functional cross-sectional area(RFCSA) of paravertebral muscle (erector spinae and multifidus) . In DSI group, the point-in-time of occurrence of dynamic sagittal imbalance was statistically correlated with degeneration of paravertbral muscles at L4/L5 level, whereas no correlation between the two above at L2/L3 level.Conclusion: In conclusion, DSI an normal SVA (SVA＜40mm) at initiation, and prominent increase in SVA after activity with thunks marked inclined. Paravertebral muscle degeneration plays an important role in the DSI process, Patients in the DSI group had more severe paravertebral muscle degeneration compared with patients in control group. There was a significant correlation between the severity of DSI symptoms and the degeneration of lower lumbar paravertebral muscles. These findings may help spinal surgeons better understand sagittal balance of spine.