Fatty infiltration of paraspinal muscles and its association with sagittal spinal malalignment in the general...

Age-related spinal sagittal malalignment is commonly attributed to factors such as disc degeneration, osteoporotic vertebral fractures, and paraspinal muscle degeneration. These factors often coexist, making it challenging to discern their relative contributions to spinal malalignment in the elderly population. Understanding these contributions is crucial for both prevention and treatment strategies for spinal deformities in aging individuals.

A cross-sectional analysis was conducted within the second survey of the Wakayama Spine Study (2012-2013). A total of 952 participants were recruited, and 794 (239 men, 555 women; mean age, 63.5 ± 13.1 years) were eligible for magnetic resonance imaging (MRI) and standing radiographic evaluation of spinal alignment. Primary outcome measures included the C7 sagittal vertical axis (SVA), pelvic incidence (PI), and pelvic tilt (PT) from standing lateral radiographs. Secondary outcomes included MRI-based assessments of disc degeneration using the Pfirrmann classification, vertebral fractures via the semi-quantitative (SQ) method, and paraspinal muscle fatty infiltration ratio at the L1/L2 level. Spinal sagittal malalignment was defined as C7 SVA ≥ 50 mm. Statistical analyses, including logistic regression, were performed to identify significant factors associated with spinal malalignment.

Spinal sagittal malalignment was observed in 98 participants (12%), with 53 (55%) reporting low back pain in the past month. Significant factors associated with sagittal malalignment included age ≥ 70 years (odds ratio [OR], 2.48; 95% confidence interval [CI], 1.33-4.69), PT ≥ 18.7° (OR, 3.12; 95% CI, 1.77-5.63), vertebral fracture (morphometric fracture index ≥ 4; OR, 2.01; 95% CI, 1.15-3.51), and paraspinal muscle fatty infiltration ratio ≥ 10.6% (OR, 4.98; 95% CI, 2.74-9.27).

Paraspinal muscle fatty infiltration was the most significant factor associated with spinal malalignment in the general population. Among the identified risk factors, paraspinal muscle degeneration is potentially reversible, underscoring its importance in postural correction strategies and surgical planning. These findings suggest that interventions targeting muscle quality may be crucial in managing spinal malalignment in elderly individuals.