How does sagittal spinopelvic alignment of lumbar multisegmental spondylolysis differ from monosegmental spondylolysis?

Abstract

Objective: The aim of this study was to investigate sagittal alignment and compensatory mechanisms in patients with monosegmental spondylolysis (mono-lysis) and multisegmental spondylolysis (multi-lysis). Methods: A total of 453 adult patients treated for symptomatic low-grade spondylolytic spondylolisthesis were retrospectively studied at a single center. Patients were divided into 2 subgroups, the mono-lysis group and the multi-lysis group, based on the number of spondylolysis segments. A total of 158 asymptomatic healthy volunteers were enrolled in this study as the control group. Radiographic parameters measured on standing sagittal radiographs and the ratios of L4-S1 segmental lordosis (SL) to lumbar lordosis (L4-S1 SL/LL) and pelvic tilt to pelvic incidence (PT/PI) were compared between all experimental groups. Results: There were 51 patients (11.3%) with a diagnosis of multi-lysis in the spondylolysis group. When compared with the control group, the spondylolysis group exhibited larger PI (p < 0.001), PT (p < 0.001), LL (p < 0.001), and L4-S1 SL (p = 0.025) and a smaller L4-S1 SL/LL ratio (p < 0.001). When analyzing the specific spondylolysis subgroups, there were no significant differences in PI, but the multi-lysis group had a higher L5 incidence (p = 0.004), PT (p = 0.018), and PT/PI ratio (p = 0.039). The multi-lysis group also had a smaller L4-S1 SL/LL ratio (p = 0.012) and greater sagittal vertical axis (p < 0.001). Conclusions: A high-PI spinopelvic pattern was involved in the development of spondylolytic spondylolisthesis, and a larger L5 incidence might be associated with the occurrence of consecutive multi-lysis. Unlike patients with mono-lysis, individuals with multi-lysis were characterized by an anterior trunk, insufficiency of L4-S1 SL, and pelvic retroversion.