Letter: Global Spinal Alignment Considerations in the Oncological Spine Population.

To the Editor: Distortion of spinal column alignment is a well-established factor contributing to disability and morbidity. In describing the severity of malalignment as well as extent of surgical correction, global spinal alignment has been used as a standardized set of measurements describing the relationships between the components of the spine on both a regional and comprehensive scale. In spinal deformity surgery, surgeons aim to remedy deviations from optimal spinopelvic alignment to restore stability and function, which in turn improves quality of life.1,2 However, surgical treatment in the oncological spine population is complicated by the need to balance achieving tumor control against maintaining or restoring spinal alignment and stability. A patient's oncological outcomes are typically the predominate concern, while spinopelvic considerations have historically played a negligible role in preoperative and postoperative planning. This is evidenced by the paucity of literature detailing the influence of these key metrics on outcomes in the oncological spine population.3 However, given that the goal of surgery in these patients is often palliative in nature, with a particular focus on quality of life enhancement, perhaps a shift in paradigm emphasizing the value of optimizing and maintaining global spinal alignment is in order. In the case of malignant primary spine tumors, a greater extent of resection may reduce the rates of local recurrence, but as a direct consequence may result in spinal column instability.4 Metastatic lesions comprise the most prevalent type of spine tumors. In these patients, pharmacological efforts to reduce systemic tumor burden may have a detrimental effect on bone health and structural integrity leading to instrumentation failure. Compounding this issue, the utilization of radiotherapy and chemotherapy further disrupts bone quality which may result in fractures, spinal malalignment, and poorer quality of life despite variable improvements in longevity.5,6 Critically, suboptimal spinal alignment parameters exacerbate the risk of vertebral collapse.7 These factors do not suggest that oncological spine patients are poor candidates for surgery but rather highlight the complexity of caring for this patient population and provide insights into the barriers that must be overcome to achieve optimal outcomes. Investments made toward spinal alignment optimization in conjunction with efforts to fortify constructs confer patients the greatest probability of sustained improvement in quality of life regardless of survival outcomes. Crucially, the right balance must be struck in maximizing both oncological and quality of life outcomes in the context of diminished capacity for arthrodesis as well as a greater susceptibility to the consequences of postsurgery adverse events in spine tumor patients. Such surgical complications may delay the onset of the systemic therapy, negatively affecting survival. Carbon fiber-reinforced polyethyl-ether-ether-ketone instrumentation has the potential to play a role in achieving better outcomes in this respect, by providing neurosurgeons and oncologists alike a more comprehensive understanding of the trajectory of a patient's alignment and disease status because of its radiolucent property, reducing image artifact.8 The visualization made possible allows for enhanced normal tissue delineation and radiotherapy delivery compared with conventional implant materials.9 Moreover, improvements in arthrodesis techniques and materials, focused radiotherapy, and minimally invasive approaches would be welcome avenues of further study and have existing evidence of improved outcomes in the spine tumor population.10,11 Furthermore, as cancer patients' longevity and survival rates climb, cancer-related bone deterioration is becoming an increasingly prevalent force to contend with.12 Bone health optimization describes the concerted effort to augment bone mineral density and osteoblastic activity in addition to correcting modifiable factors of bone health, thus enhancing spine healing after surgery.13 Of considerable importance is that cancer patients with lesions involving the spine frequently avoid physical exertion because of safety concerns. Consequently, the resulting losses in mobility, stabilizing muscle mass, and bone mineral density elevate the risk of fracture and quality of life deficits.14 Encouraged by extensive literature describing the benefits of physical training on measures of mobility and pain, Sprave et al15 conducted a randomized controlled trial in which they evaluated the feasibility of isometric paravertebral muscle training on various outcomes in patients with unstable spinal metastases. Although their study was not powered to evaluate the effect of this intervention on bone density, pain, or pathological fracture rate, they were able to demonstrate the feasibility of this regimen in this population of patients. The development and application of interventions such as these are a step in the right direction. Advancements in instrumentation and therapeutics continue to expand the neurosurgeon's armamentarium and improve the clinical course of oncological spine patients. In the present era, preoperative and postoperative global spinal alignment considerations are overshadowed by more pressing oncological concerns. Better imaging and tracking of spinal alignment in the spine tumor population would be a critical step in providing clinicians with data that informs clinical decision-making and to substantiate future studies. Investigations into the influence of these parameters on the clinical outcomes of the oncological spine population are important to improve the level of care for these patients.