Muscle Quality Over Quantity: Paraspinal and Psoas Muscle Fat Infiltration Distinguishes Patients With Osteoporotic...

Study designThis was a monocentric-retrospective study in a high-volume spine center.ObjectiveOsteoporosis and sarcopenia frequently coexist and contribute to increased fracture risk and functional decline. Their relationship is however confounded by age and sex. This study compared lumbar muscle morphology in patients with osteoporotic vertebral fractures (OVFs) and matched fracture-free controls.MethodsThis study screened 221 patients with manifest osteoporosis and radiologically confirmed OVFs and 500 fracture-free controls who underwent spinal MRI and CT. After 1:1 propensity score matching for age and sex, 166 OVF patients (OF group) and 166 controls (Non-OF group) were included. BMD was assessed using Hounsfield units (HU). Lumbar muscle metrics were quantified from axial MRI at L4, including psoas (pCSA), paraspinal (psCSA) cross-sectional areas, indices normalized to height (pMI, psMI), vertebral body-adjusted indices (pLVI, psLVI), and fat infiltration (pFI, psFI) together with functional cross-sectional area (pfCSA, psfCSA).ResultsGroups were balanced for age and sex. OF patients had significantly lower HU (73.1 ± 23.3 vs 119 ± 36.3 P < 0.001), lower hemoglobin and albumin levels. Absolute psoas and paraspinal muscle areas and muscle indices were comparable between groups. However, OF patients showed higher FI and reduced fCSA. In addition, in OF patients vertebral body-normalized muscle indices were lower, and HU correlated positively with functional muscle area and inversely with muscular fat infiltration, whereas no such associations were observed in controls.ConclusionsIn elderly OVFs patients, reduced vertebral bone mineral density is associated with impaired muscle quality rather than muscle quantity, supporting a disease-specific bone-muscle interaction relevant for integrated osteosarcopenia assessment.