Lumbar Muscle Fatty Infiltration and Atrophy in Patients with Low Back Pain and Degenerative Spinal Pathologies: A CT Imaging Study

<b>Background/Objectives:</b> Low back pain (LBP) may be related to intramuscular fatty infiltration (FI), the topography of which has been the subject of only a few studies. Our goal is therefore to determine the importance and topography of FI at the lumbar level and evaluate its correlation with LBP. <b>Methods:</b> We conducted a retrospective study and compared 254 LBP patients who underwent a lumbosacral CT scan with a sample of 115 healthy subjects, all classified into three age groups (≤35, 36-55, and >55 years old). In CT scan images from L2 to S1, muscle density (Hounsfield unit values ranging from -29 to +150), reflecting intramuscular FI, was measured. LBP was further divided into five subgroups of pathologies. <b>Results:</b> There was a significant difference in muscle density between the small and large circles at the L4/L5 and L5/S1 levels in LBP patients, which was not observed in the healthy subjects. In both LBP patients and healthy subjects, a decreasing density gradient was observed from L2 to S1, with a significant difference in density across age groups. LBP patients exhibit lower muscle densities compared to healthy subjects. <b>Conclusions:</b> In LBP patients, fatty infiltration (FI) of the paraspinal muscles is most pronounced in the lower lumbar region and appears to be localized at the level of muscle insertion. This localized muscle deficit differs from the age-related process of FI and may contribute to the development of LBP and discopathies.