Adult Degenerative Spinal Deformity: Overview and Open Approaches for Treatment
Adult degenerative spinal deformity is a complex disorder that affects the thoracolumbar spine. The spine must be balanced in both sagittal and coronal planes to allow pain-free movement and function. As the spine ages, disc degeneration and facet arthrosis can cause disc height collapse, spondylolisthesis, and loss of lumbar lordosis. Scoliosis, a coronal plane deformity, can lead to back pain and leg pain in a radicular distribution due to lateral recess and/or foraminal stenosis. Kyphosis, a sagittal plane deformity, can also cause back pain, as well as leg muscle fatigue due to compensatory mechanisms required to bring the spine back into alignment. The clinical diagnosis and treatment of degenerative thoracolumbar kyphoscoliosis require a detailed understanding of both spinal alignment and pelvic parameters. The sagittal vertical axis is determined by dropping a vertical plumb line from the C7 vertebral body. Horizontal displacement of this plumb line to the posterior superior corner of S1 defines the patient's sagittal balance, which ideally should be corrected to less than 5 cm. Other key measurements in the assessment of sagittal imbalance include pelvic incidence and lumbar lordosis, which should be matched to within 9°. Correction of sagittal plane deformity correlates with improvement in quality-of-life measures, including Short Form-36 and the Oswestry Disability Index. Surgical treatment of thoracolumbar kyphoscoliosis is selected according to whether the deformity is mobile or fixed. A mobile anterior column can be treated with a combination of posterior facet-based osteotomies (Ponte, Smith-Peterson) and/or interbody fusion. A fixed anterior column, however, typically requires a three-column osteotomy (pedicle subtraction, vertebral column resection) for adequate treatment. The main goals of surgery in patients with degenerative spinal deformity are (A) to correct the sagittal plane deformity, (B) to decompress the neural elements, and (C) to stabilize the scoliotic curve, with curve correction as a secondary goal. Effective treatment should yield a balanced spine in both sagittal and coronal planes.