Relationship between pelvic incidence-adjusted relative spinopelvic parameters, global sagittal alignment and lower extremity compensations

Sagittal Alignment in the Degenerative Lumbar Spine: Surgical Planning

➤ Sagittal alignment of the spine has gained attention in the field of spinal deformity surgery for decades. However, emerging data support the importance of restoring segmental lumbar lordosis and lumbar spinal shape according to the pelvic morphology when surgically addressing degenerative lumbar pathologies such as degenerative disc disease and spondylolisthesis.➤ The distribution of caudal lordosis (L4-S1) and cranial lordosis (L1-L4) as a percentage of global lordosis varies by pelvic incidence (PI), with cephalad lordosis increasing its contribution to total lordosis as PI increases.➤ Spinal fusion may lead to iatrogenic deformity if performed without attention to lordosis magnitude and location in the lumbar spine.➤ A solid foundation of knowledge with regard to optimal spinal sagittal alignment is beneficial when performing lumbar spinal surgery, and thoughtful planning and execution of lumbar fusions with a focus on alignment may improve patient outcomes.

Role of the Paraspinal Muscles in the Sagittal Imbalance Cascade: The Effects of Their Endurance and of Their Morphology on Sagittal Spinopelvic Alignment

BACKGROUND

The role of paraspinal muscle degeneration in the cascade of sagittal imbalance is still unclear. This study aimed to compare paraspinal muscle degeneration in the 4 stages of sagittal imbalance: sagittal balance (SB), compensated sagittal balance (CSB), decompensated sagittal imbalance (DSI), and sagittal imbalance with failure of pelvic compensation (SI-FPC). In addition, it aimed to compare the effects paraspinal muscle endurance and morphology on sagittal spinopelvic alignment in patients with lumbar spinal stenosis.

METHODS

A cross-sectional study of 219 patients hospitalized with lumbar spinal stenosis was performed. The isometric paraspinal extensor endurance test and evaluation of atrophy and fat infiltration of the paraspinal extensor muscles and psoas major on magnetic resonance imaging were performed at baseline. Spinopelvic parameters including lumbar lordosis, pelvic tilt, sacral slope, pelvic incidence, and the sagittal vertical axis were measured.

RESULTS

The patients with lumbar spinal stenosis were divided into 67 with SB, 85 with CSB, 49 with DSI, and 17 with SI-FPC. There were significant differences in paraspinal muscle endurance and morphology among the 4 groups. Furthermore, the SI-FPC group had poorer paraspinal muscle endurance than either the SB or the CSB group. In multiple linear regression analysis, paraspinal muscle endurance and the relative functional cross-sectional area of the paraspinal extensor muscles were the independent predictors of the sagittal vertical axis, and the relative functional cross-sectional area of the psoas major was the independent predictor of relative pelvic version.

CONCLUSIONS

This study indicated that paraspinal muscle degeneration is not only an initiating factor in pelvic retroversion but also a risk factor for progression from a compensated to a decompensated stage. Specifically, the impairment of muscle endurance in the CSB stage may be the reason why patients experience failure of pelvic compensation. In addition, paraspinal muscle endurance and muscle morphology (relative functional cross-sectional area of the paraspinal extensor muscles and psoas major) had different clinical consequences.

LEVEL OF EVIDENCE

Prognostic Level II . See Instructions for Authors for a complete description of levels of evidence.