In this study, coronal parameters showed some correlations with sagittal spinopelvic parameters in the DLKS group, suggesting a similar etiology between coronal and sagittal deformities. Characteristic lumbar degenerative pathology includes spinal stenosis, segmental instability (olisthesis and rotatory subluxation), and malalignment of the spine in the sagittal, coronal, and axial planes [6–9]. Patients with degenerative lumbar scoliosis (DLS) share a common presentation, with degenerative changes of the spinal motion segment affecting the intervertebral disc and facet joints. DLS has been reported to be triggered by asymmetrical disc degeneration [10, 11]. Jimbo et al  suggested that disc degeneration should be evaluated as a predictor of curvature progression in DLS. Asymmetric loading coupled with degeneration potentiates a vicious cycle of enhanced curve progression . Compared with DLS, degenerative lumbar kyphosis has a higher incidence and is associated with more serious clinical outcomes. Jang et al.  found that spinal degeneration in DLK patients included disc narrowing, spondylolisthesis, hyperosteogeny, osteophyte formation, hypertrophy of facet joints, osteoporosis, and atrophy of lumbar extensor muscles. They further speculated that serious degeneration of spinal structures, such as intervertebral discs, vertebrae or facet joints, was a major cause of DLK. One study demonstrated that the lower end vertebral disc degeneration strongly correlates with sagittal imbalance in patients with DLS, suggesting that disc degeneration may be a risk factor for sagittal imbalance. Disc degeneration strongly correlated with sagittal malalignment, as demonstrated by a more positive SVA, decreased TK and LL, suggesting explanations for low quality of life in elderly patients with DLS . In brief, degenerations originating from intervertebral disc and facet joints induce spinal coronal and sagittal imbalance.
Degenerative lumbar kyphoscoliosis, including coronal, sagittal and axial deformities, was extremely serious in adult lumbar deformities. In fact, some studies focusing on adolescent idiopathic scoliosis revealed that most coronal and sagittal parameters were not significantly correlated, and coronal deformity types did not change the global sagittal postural patterns . In our study, we were impressed by the mismatching between coronal scoliosis and sagittal morphological parameters. One reason for this result may be the differences of pathogenesis. Degenerative lumbar scoliosis mainly involves degenerative disc disease, facet incompetence, and hypertrophy of the ligamenta flava, while degenerative lumbar kyphosis results from atrophy and fatty changes of the lumbar extensor muscles and wedging changes of vertebrae in spite of degenerative disc disease. Particular life-styles, such as the prolonged crouched posture during agricultural work and certain activities of daily living play important roles in the process of DLK development. Another reason may be that patients enrolled in our study all had local or global sagittal imbalance because of degenerative lumbar kyphosis. To maintain sagittal balance, co-adjustment of each sagittal spinopelvic parameters lead to close interrelations, covering the effects of scoliosis. The third reason is that complex deformities might give rise to these apparent inconsistencies: severe coronal deformities without corresponding sagittal deformities. With the aging process, we begin to see deformities in coronal and sagittal, such as subluxation, spondylolisthesis, hyperlordosis, and hypolordosis. Gradually, vertebral rotation, thoracic and pelvic compensation alter sagittal balance, inducing relatively moderate changes of sagittal morphology.
As noted in the study of Glassman et al., quality of life in patients with adult spinal deformity was substantially related to sagittal deformity, not to coronal deformity. Between sagittal balanced and imbalanced DLKS patients, we found that PI-LL, LL-TK, PI, PT were significantly different. As we know, Schwab et al. brought out standardized evaluation of the sagittal plane and the goal for correction surgery in adult spinal deformity: SVA < 50 mm, PI-LL < 10° and PT < 25°, which had been widely used in clinical practice. Moreover, another study demonstrated that LL-TK could be a good predictor for sagittal balance in Chinese elderly people, which reflected the regional compensatory mechanism and significantly associated with SVA.
Our study was limited by small sample size: if more patients were included, our findings may be validated. In our future study, clinical outcomes, like Japanese Orthopedics Association scale (JOA), Visual Analog Score (VAS) and Oswestry Disability Index (ODI) should be included for the analysis between functional scores and radiological parameters. Nevertheless, we wish to consider this study as the first series of explorations focusing on the relationships between degenerative lumbar coronal, sagittal, and axial deformities, in order to properly make treatment plans for degenerative lumbar kyphoscoliosis.