Drop Body Syndrome

STUDY DESIGN A retrospective observational study. OBJECTIVE This study examined the role of skeletal muscles in the spinal alignment of lumbar degenerative kyphosis (LDK). SUMMARY OF BACKGROUND DATA Adult spinal deformity (ASD) may present as LDK, which is unusual in that it typically lacks any coronal deformity. METHODS This retrospective study included 367 female patients with ASD. Demographic and radiographic data from LDKs were compared with those with other ASD. The LDK multifidus was also subjected to histological analysis. The muscle volume and strength were analyzed using whole-body dual x-ray absorptiometry and pulmonary function tests. Magnetic resonance images were used to determine the cross-sectional area (CSA) and fatty infiltration area (FIA) of the psoas and multifidus. RESULTS A total of 52 patients (15%) were classified as LDK. Compared with other ASDs, those with LDK had a significantly larger sagittal vertical axis (16.3 ± 5.0 cm), and pelvic incidence minus lumbar lordosis (52.8° ± 9.2°). The LDK had significantly lower CSA and higher FIA of the multifidus, but not in the psoas (multifidus CSA 223 ± 96 vs. 477 ± 129 mm, P