Osteotomies for the Correction of Deformities

Summary of Key Points

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Rigid deformity requires an osteotomy for rebalancing of the spine.
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Mild sagittal deformity with intact mobile discs can be treated with posterior column osteotomies.
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Severe sagittal and coronal deformity lacking mobile disc spaces requires a three-column osteotomy such as a pedicle subtraction osteotomy, which can result in 25 to 35 degrees of correction.
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Vertebral column resection is reserved for the most severe fixed combined sagittal and coronal deformities that require greater correction than can be obtained with lower-grade osteotomies.
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Intraoperative neurophysiologic monitoring is critical to prevent neurologic deficits while closing the osteotomy.

Some spinal deformities with flexible curves and relatively mild sagittal and coronal imbalance can be successfully treated with posterior instrumented fusion, often combined with anterior interbody constructs. More severe imbalance and rigid deformities, including those iatrogenically resulting from previous spinal fusions and spondyloarthropathies (i.e., ankylosing spondylitis), require osteotomies to achieve appropriate spinal balance. This is particularly critical in the older adult spinal deformity patient, as these curves are less likely to be flexible. Adult spinal deformity is highly prevalent with rates approaching 68% in asymptomatic volunteers 60 years and older. Spinopelvic imbalance is highly correlated with pain and disability in this population. Furthermore, the degree of correction, especially in the sagittal plane, is associated with improvement in validated patient-reported pain and disability indices. As the population ages, all spine surgeons will be evaluating these patients in clinical settings. A complete and modern understanding of the indications and techniques for spinal osteotomies will be necessary in the diagnosis and management of the adult spinal deformity patient. This chapter highlights the major types of spinal osteotomies and describes the indications, techniques, outcomes, and complications of these procedures. When discussing osteotomies, the Schwab anatomic osteotomy classification is a useful and reliable tool for standardizing the terminology ( Fig. 156-1 ).

Type 1 Posterior Column Osteotomies

A type 1 posterior column osteotomy (PCO) involves resection of the inferior facet and joint capsule. This osteotomy is used frequently to enhance fusion surface area, to uncover pedicle entry sites, and, most important, to assist in mobilization of more flexible curves. The Smith-Petersen osteotomy is classified as a grade 2 osteotomy in the Schwab classification system ( Fig. 156-2 ). This extension osteotomy, classically described through an anterior fusion, pivots on the middle column, thus shortens the posterior column while lengthening the anterior column. Pseudarthrosis may be a problem due to less bony surface contact for fusion. In fact, some argue for anterior interbody fusion to prevent pseudarthrosis, especially in cases with substantial correction and thus a larger anterior opening. Neurologic deficits, although reported, may be less common than in higher-grade osteotomies.

Ponte Osteotomy

The Ponte osteotomy, also a grade 2 PCO, involves resection of the superior and inferior articular processes at multiple sequential spinal levels as well as the spinous processes and posterior ligaments. It is thus classified as a grade 2 osteotomy. These osteotomies require intact, mobile disc spaces. Approximately 5 to 10 degrees of correction can be attained per level allowing for gradual deformity correction ( Fig. 156-3 ). This results in good maintenance of correction and high fusion rates. Due to the relatively wider posterior release, some correction in the coronal plane can be obtained as well.

Pedicle Subtraction Osteotomy

The pedicle subtraction osteotomy (PSO) is a three-column destabilizing procedure involving removal of the spinous processes, laminae, pedicles, and a wedge of the vertebral body, leaving the superior and inferior discs intact. Pedicle screws are placed above and below the intended osteotomy level. The spinous process, lamina, and transverse processes are removed to delineate the pedicles. The pedicles are removed with a combination of angled chisels and rongeurs with careful attention to protecting the thecal sac and nerve roots. A wedge is then removed from the cancellous portion of the vertebral body with angled rasps, curettes, and rongeurs. The lateral cortex is removed with a rongeur and lastly the posterior cortex is removed with curettes and osteotomes. The osteotomy wedge then can be closed either by compression over a short temporary rod or by cantilevering a longer rod. The PSO is considered a shortening operation as the posterior column is shortened when the wedge is closed without lengthening the anterior column. This is considered a grade 3 osteotomy, whereas a grade 4 osteotomy is a PSO that extends the resection into the disc. Anywhere from 25 to 35 degrees of correction can be obtained from grade 3 and 4 osteotomies. The rationale for including the disc in the resection is less great vessel stretching. A PSO is indicated for severe sagittal and coronal deformity and patients who have no anterior mobility at the level of the planned osteotomy such as those with a prior circumferential fusion. PSO is ideal for patients with sharp, angular kyphoses. Likewise, a PSO is indicated in patients with severe spinopelvic malalignment. Although the vertebral level of a PSO does not change the affect on global sagittal balance, a PSO at more caudal levels has a more beneficial affect on relaxing the pelvic tilt. In fact, a predictive formula described by Lafage and colleagues integrating key spinopelvic parameters has been developed to preoperatively estimate the pelvic tilt and sagittal vertical axis after a PSO. In multicenter retrospective analysis, the Lafage formulas performed better than other formulas in predicting successful and unsuccessful outcomes and global balance. An asymmetric PSO, in which more bone is resected to one side, is useful in the correction of combined sagittal and coronal imbalance when the shoulder and pelvis tilt to opposite sides ( Fig. 156-4 ).