Abstract
Dear Editor,
The authors would like to thank the reviewer for the comments. We agree that the literature on structural and functional sagittal balance in the spine has been long-standing and well-established since 1987.1-4 These publications have never been more relevant than today, where the rapidly evolving concept of adult spinal deformity surgury are revolving around the sagittal profile of the spine.5,6
In our study, patients with spondylolisthesis had larger Pelvic Incidence (p < .001), Pelvic Tilt (p < .001) and Knee alignment angle (p = .011), but smaller Thoracolumbar junctional angle (p = .008), and Spinocoxa angle (p = .007). Retrolisthesis was associated with a larger Thoracolumbar junctional angle (p = .039). These findings may provide a better understanding between mutual relationship of the pathological spine and the whole-body radiographic parameters, which is paramount in the guiding corrective surgical goals. The concept of structural and functional sagittal balance was also furthered by Hey et al. In a study comparing the sagittal alignment between two frequent sitting positions: a spontaneous, patient-favoured posture, and a controlled, investigator-mandated posture, we demonstrated that during an inherent or natural seated posture, the lumbar spine assumes an arched or rounded configuration, producing a solitary C-shaped sagittal profile consisting of the lumbar and thoracic spine. This position was related to an augmentation in pelvic tilt and cervical lordosis, offering important comprehension attaining sagittal equilibrium while sitting, and providing significant insights related to the major causes of proximal junctional failure. 7
In a separate study, a progressive shift in the sagittal vertical plane axis and important transformations in thoracolumbar kyphosis, lumbar lordosis and cervical lordosis in the natural sitting position. 8 Collectively, this study and the previous studies highlight the escalating recognition of the significance of static and dynamic sagittal balance, and how it can impact the surgical strategies for the deformity correction.
Lastly, we fully agree with the importance of age-related degree of segmental degeneration on the spinal sagittal balance. As the patient’s age increases ligamentous and neuromuscular compensatory mechanisms become weaker, with subsequent progressive kyphosis. This was again shown in our study by concomitant findings of increased PT, KAA and SCA in patients with spondylolisthesis. Lee et al also reported similar results, which showed the elderly patients had less pliability with the upper lumbar spine being more flexible in individuals in their twenties compared to those in their sixties. 9
Moving forward, finite element analysis to test differential loading conditions would a great step forward to further our understanding of sagittal balance.
Once again, the authors would like to thank the reviewer for his invaluable opinion in substantiating our paper.
