**1. Introduction**

Patients with osteoporosis often report low back pain (LBP), particularly intermittent LBP such as vague LBP due to standing or walking for a long stretch of time. In clinical settings, the types of LBP reported tend be difficult to treat. Whether osteoporosis causes LBP is controversial because its pathological mechanism has not been fully elucidated. Several factors, including high bone turnover [1], low muscle mass [2], and vertebral fractures (VFs) [3], have been reported to be associated with increased risk of LBP and osteoporosis. In addition, it is well known that VFs induce spinal sagittal malalignment in osteoporosis patients [4].

**Citation:** Matsunaga, T.; Miyagi, M.; Nakazawa, T.; Murata, K.; Kawakubo, A.; Fujimaki, H.; Koyama, T.; Kuroda, A.; Yokozeki, Y.; Mimura, Y.; et al. Prevalence and Characteristics of Spinal Sagittal Malalignment in Patients with Osteoporosis. *J. Clin. Med.* **2021**, *10*, 2827. https://doi.org/10.3390/jcm10132827 Academic Editor: Alexandra Lucas

Received: 27 April 2021 Accepted: 24 June 2021 Published: 26 June 2021

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Patients with spinal sagittal malalignment presenting as adult spinal deformity often complained of severe LBP that induced the deterioration of health-related quality of life (HRQoL), requiring treatment [5]. Patients with spinal deformity tend to be elderly individuals who also have osteoporosis. Therefore, osteoporosis might be associated with adult spinal deformity. Furthermore, it has been reported that osteoporotic patients with VFs showed worse spinal sagittal alignment and LBP and HRQoL scores [6]. However, the prevalence of spinal sagittal malalignment in osteoporosis patients remains unclear. Improving our understanding of the characteristics of patients with spinal sagittal malalignment may lead to the improvement of spinal sagittal malalignment treatment. The aim of this study was to elucidate the prevalence of spinal sagittal malalignment based on VF number and the characteristics of patients with osteoporosis and spinal sagittal malalignment.

#### **2. Materials and Methods**

#### *2.1. Patient Population*

The records of patients with osteoporosis who first visited these facilities from June 2015 to March 2017 were reviewed in this cross-sectional study. We excluded patients who developed new vertebral fractures within three months. The remaining 259 patients (48 men, 211 women; mean age: 71.5 years) were included.
