Use of Supplemental Rod Constructs in Adult Spinal Deformity Surgery: A Review

Adult spinal deformity comprises a heterogeneous group of disorders that primarily affects older patients and can have a significant negative affect on health-related quality of life. Operative treatment for adult spinal deformity typically entails posterior instrumented fusions that have demonstrated the potential to significantly improve health-related quality of life outcomes. However, until fusion is achieved, the instrumentation providing structural support is subject to repetitive cyclical loading that disproportionately fatigues high-stress areas and can result in instrumentation failure. Despite considerable advances in surgical fixation techniques and technology, pseudarthrosis with subsequent implant failure still poses a challenge for surgeons and continues to be 1 of the most common complications, leading to revision surgery. The addition of supplemental rods to primary constructs has gained widespread popularity to mitigate implant failure. Theoretically, more rods will add stiffness, stability, and decreased surface strain, which will provide longer instrumentation lifespan to allow for osseous fusion. There is significant heterogeneity in these constructs, and different types of supplemental rods (eg, satellite, accessory, delta rods, "kickstand rod," and "iliac accessory rod") can be used independently or in combination to further increase strength. However, the use of supplemental rods may increase the rate of proximal junctional kyphosis/failure and paradoxically diminish anterior column fusion rates. Hence, indications and optimal configurations are still a matter of debate. The aim of this narrative review is to provide an overview of the supplemental rod constructs described in the literature and focus on the current evidence supporting their indications and potential impact.