**4. Discussion**

In the current study, the prevalence of spinal sagittal malalignment in osteoporosis patients was determined to be 79.2%. Furthermore, as the number of VFs increased, the prevalence of spinal sagittal malalignment also increased and LBP and HRQoL scores worsened. Interestingly, more than 70% of osteoporosis patients without VFs had spinal sagittal malalignment. Additionally, in patients without VFs, patients with spinal sagittal malalignment had worse LBP and HRQoL scores than patients with normal alignment.

Regarding the relationship between VFs and spinal sagittal alignment, as the number of VFs increased, the prevalence of spinal sagittal malalignment also increased, and LBP and HRQoL scores worsened in this study. Mochizuki et al. previously reported that spinal sagittal alignment is associated with age and VF in patients with rheumatoid arthritis [10]. In addition, osteoporosis patients with VFs have worse global sagittal alignment and a

worsened quality of life [6]. Scaturro et al. reported that the severity of LBP is correlated with the number of vertebral fractures [11]. These findings indicate that VFs are closely correlated with sagittal spinal malalignment and affect LBP as well as HRQoL.

With regard to cause-and-effect relationships between VFs and spinal sagittal malalignment, Zhang et al. reported that multiple VFs lead to spinal sagittal malalignment in patients with osteoporosis [12]. In contrast, several authors reported that spinal sagittal malalignment was a potential risk factor for increased VF incidence in patients with osteoporosis [4,13,14]. These findings indicate that VFs induce spinal sagittal malalignment; spinal sagittal malalignment also leads to VFs in patients with osteoporosis.

In the current study, more than 70% of patients with osteoporosis without VFs had spinal sagittal malalignment. In a longitudinal study with a minimum of 10 years of followup, Takeda et al. reported that spinal sagittal malalignment, decreased lumbar lordosis, and increased SVA were correlated with age in patients without VFs [15]. Regarding the underlying mechanism of spinal sagittal malalignment in patients without VFs, several authors reported a relationship between spinal sagittal malalignment and decreased muscle mass in patients with spinal diseases [16,17]. Additionally, Scaturro et al. reported that combination treatments with medication and postural training/resistance exercises showed improvements in the pain and QoL for patients with osteoporosis undergoing rehabilitation [18]. These findings indicate that decreasing muscle mass may induce spinal sagittal malalignment.

In the current study, the majority of osteoporosis patients had spinal sagittal malalignment. In recent years, several authors reported that long spinal fusion and corrective surgery for spinal sagittal malalignment could be used to achieve good spinal alignment. Improvements were due to recent, remarkable developments in surgical techniques and spinal instruments and contributed to improvements in ADL and LBP outcomes [19,20]. However, high perioperative complication rates for long spinal fusion and corrective surgery have been reported [21]. Therefore, performing the highly invasive and costly surgery in all osteoporosis patients is not advisable. Alternatively, we should consider early intervention for spinal sagittal malalignment in osteoporosis patients, which may prevent the need for surgery to correct adult spinal deformity.

When investigating relationships between spinal sagittal alignment and LBP or HRQoL, Schwab et al. reported that high SVA, PI-LL, and PT values induced the deterioration of HRQoL in elderly adult patients with spinal deformity and a defined SRS-Schwab classification [9]. Similarly, the current study reported that osteoporosis patients with spinal sagittal malalignment and a defined SRS-Schwab Classification had some reduced HRQoL subscale values, including PF, RP, VT, RE, and MH. On the other hand, results of a meta-analysis by Chun et al. indicated that LBP was strongly correlated with decreased LL, especially when affected patients were compared with age-matched healthy controls [22]. Additionally, Miyakoshi et al. reported that decreased LL and the limitation of total spinal extension are important risk factors for gait disturbance in patients with chronic LBP [23]. These findings indicate that osteoporosis patients with spinal sagittal malalignment, even those without VFs, had worse HRQoL and LBP compared with patients with normal spinal sagittal alignment. Further, spinal sagittal malalignment is a potential risk factor for LBP and HRQoL in patients with osteoporosis.

The current study had some limitations. First, we did not evaluate medication status, such as use of painkillers and osteoporosis medications. In addition, we included patients with osteoporosis who first visited our department, although many patients had already undergone an intervention during their consultation. Painkillers and osteoporosis medication use might affect HRQoL as well as LBP. Second, this was a cross-sectional study; therefore, we could not evaluate cause-and-effect relationships among spinal sagittal malalignment, VFs, LBP, and HRQoL. Additionally, the patho-mechanism of spinal sagittal malalignment in patients without VFs remains unclear. To further understand these mechanisms, additional studies with larger sample sizes and a longitudinal design are needed.
