Purpose:

Lumbar fusion surgery has become a standard procedure in spine surgery and commonly includes the posterior placement of pedicle screws. Bone quality is a crucial factor that affects pedicle screw purchase. However, the relationship between paraspinal muscles and the bone quality of the pedicle is unknown. The aim of the study was to determine the relationship between paraspinal muscles and the ex vivo bony microstructure of the lumbar pedicle.

Methods:

Prospectively, collected data of patients undergoing posterior lumbar fusion for degenerative spinal conditions was analyzed. Pre-operative lumbar magnetic resonance imaging (MRI) scans were evaluated for a quantitative assessment of the cross-sectional area (CSA), functional cross-sectional area (fCSA), and the proportion of intramuscular fat (FI) for the psoas muscle and the posterior paraspinal muscles (PPM) at L4. Intra-operative bone biopsies of the lumbar pedicle were obtained and analyzed with microcomputed tomography (µCT) scans. The following cortical (Cort) and trabecular (Trab) bone parameters were assessed: bone volume fraction (BV/TV), trabecular number (Tb.N), trabecular thickness (Tb.Th), connectivity density (CD), bone-specific surface (BS/BV), apparent density (AD), and tissue mineral density (TMD).

Results:

A total of 26 patients with a mean age of 59.1 years and a mean BMI of 29.8 kg/m² were analyzed. fCSA_PPM showed significant positive correlations with BV/TV_Trab (ρ = 0.610; p < 0.001), CD_Trab (ρ = 0.679; p < 0.001), Tb.N_Trab (ρ = 0.522; p = 0.006), Tb.Th_Trab (ρ = 0.415; p = 0.035), and AD_Trab (ρ = 0.514; p = 0.007). Cortical bone parameters also demonstrated a significant positive correlation with fCSA_PPM (BV/TV_Cort: ρ = 0.584; p = 0.002; AD_Cort: ρ = 0.519; p = 0.007). FI_Psoas was negatively correlated with TMD_Cort (ρ = – 0.622; p < 0.001).

Conclusion:

This study highlights the close interactions between the bone microstructure of the lumbar pedicle and the paraspinal muscle morphology. These findings give us further insights into the interaction between the lumbar pedicle microstructure and paraspinal muscles.