How to Create Sagittal Balance in MIS Correction of Adult Spinal Deformity
Sagittal balance has been achieved intraoperatively through positioning, facetectomy, interbody lordotic implant, and osteotomy. Specific deformity factors such as flexibility, degree and type, extent of imbalance, instrumentation level, and prior spinal surgery must be considered when techniques are chosen to achieve sagittal balance. Morbidity and complications of open correction of ASD are especially significant in the elderly. Hence, surgical goals in the elderly should advocate the least risky path, should be age-specific, and probably should avoid the use of three-column osteotomy.
Selection among minimally invasive surgery (MIS) techniques should be predicated on judicious patient selection and basic principles of sagittal balance. Figure 1 shows our staged protocol for creating sagittal balance in ASD. Evaluation with 36” standing radiographs, magnetic resonance imaging, computed tomography, and bone density scans is followed by an MIS ante-psoas lateral approach, discectomy, and sequential placement of segmental 12° lordotic cages anteriorly from L4–5 and rostrally to L1–2 or T12–L1. On the same day, an L5–S1 anterior lumbar interbody fusion is carried out through an MIS oblique lateral approach. Patients are recovered postop, transferred to the floor, and encouraged to ambulate on the same day. This allows for documentation of relief of neurogenic claudication and radiculopathy due to indirect reduction of spinal stenosis. On the second day, a standing 36” radiograph is obtained and coronal and sagittal balance reassessed, allowing planning and fine-tuning at the posterior second stage 3 days later.
During the posterior stage, paraspinal 1” incisions allow placement of pedicle screws with extenders under fluoroscopy or navigation. The rod is contoured according to the lordosis required and is passed through the extenders. Sequential reduction allows for translation and derotation of the spine. Posterior fusion is carried out, usually at T12–L1, T11–12, and T10–11, without interbody fusion.
Our 10-year experience with a staged surgical protocol consisting of MIS lateral intradiscal release, segmental 12° lordotic cages, MIS anterior lumbar interbody fusion, staged reassessment of coronal and sagittal balance followed by second-stage percutaneous instrumentation, and rod contouring and reduction allows circumferential MIS correction of sagittal balance in ASD.