For a study, researchers aimed to cross-sectionally examine the prevalence of sarcopenia and the relation between spine-pelvic deformity and skeletal muscle volume loss and ectopic fat infiltration into lumbar paravertebral muscles (PVMs) in patients who underwent lumbar surgery. About 36.1% of adults aged older than 60 years were diagnosed with sarcopenia. The values of skeletal muscle indexes of the limb and trunk were inversely correlated with the sagittal vertical axis, pelvic tilt (PT), and pelvic incidence minus lumbar lordosis (PI-LL) values. The PT and PI-LL came out to be more significant, the PVM area was smaller, and the Goutallier grade was more fantastic in sarcopenic adults than in non-sarcopenic older adults. Additionally, the PVM area correlated with the LL value, and Goutallier’s grade was associated with the PT and PI-LL values. Moreover, the ectopic fat in PVMs is inversely correlated with skeletal muscle indexes. The expression levels of atrophy gene-1 and muscle ring-finger protein-1 did not differ between the groups and did not correlate with the PVM area. The volume loss of skeletal muscle, including lumbar PVM and ectopic fat infiltration into the PVM, was found to cause lumbopelvic deformity.