Date Published: October 4, 2011
Publisher: SAGE-Hindawi Access to Research
Author(s): Eric Klineberg, Frank Schwab, Christopher Ames, Richard Hostin, Shay Bess, Justin S. Smith, Munish C. Gupta, Oheneba Boachie, Robert A. Hart, Behrooz A. Akbarnia, Douglas C. Burton, Virginie Lafage.
Introduction. Three-column vertebral resections are frequently applied to correct sagittal malalignment; their effects on distant unfused levels need to be understood. Methods. 134 consecutive adult PSO patients were included (29 thoracic, 105 lumbar). Radiographic analysis included pre- and postoperative regional curvatures and pelvic parameters, with paired independent t-tests to evaluate changes. Results. A thoracic osteotomy with limited fusion leads to a correction of the kyphosis and to a spontaneous decrease of the unfused lumbar lordosis (−8°). When the fusion was extended, the lumbar lordosis increased (+8°). A lumbar osteotomy with limited fusion leads to a correction of the lumbar lordosis and to a spontaneous increase of the unfused thoracic kyphosis (+13°). When the fusion was extended, the thoracic kyphosis increased by 6°. Conclusion. Data from this study suggest that lumbar and thoracic resection leads to reciprocal changes in unfused segments and requires consideration beyond focal corrections.
Pedicle subtraction osteotomy (PSO) has increasingly become an accepted technique to correct spinal sagittal malalignment and relieve associated pain and disability. The indications, technique, outcomes, and perioperative complications for PSO have been well described [1–13]. An aspect concerning PSO technique that has not been well described, however, relates to global changes in spinopelvic alignment that occur following thoracic and lumbar PSO. It has been well demonstrated that osteotomy techniques produce a focal change in spinal alignment and can improve sagittal vertical alignment (SVA). However, there is little data on the postosteotomy behavior of the unfused spinal segments remote from the osteotomy site(s) and how the reciprocal changes that occur through these segments may affect global alignment. Kim et al. reported on results of 35 patients treated with lumbar PSO for sagittal malalignment at minimum 5-year followup . In addition to reporting improved postoperative sagittal alignment, the authors noted that thoracic kyphosis (TK) increased from 22° to 31°, postoperatively. However, the upper instrumented vertebra (UIV) was T6 or cephalad in 20 of 35 patients and the average number of fused vertebrae was 11.7; therefore, the increase in kyphosis was likely a reflection of surgical technique and rod contouring rather than reciprocal changes occurring in segments cephalad to the osteotomy site. Similarly, Yang et al. noted an increase in postoperative TK following lumbar PSO and also noted an increase in postoperative lumbar lordosis (LL) following thoracic PSO; however, it was not indicated if these changes occurred within fused segments or occurred spontaneously . Ikenaga et al. reported a greater incidence of late onset postoperative kyphosis progression among patients receiving shorter segment fusion following lower thoracic or lumbar PSO compared to longer segment fusion; however, the authors did not specifically evaluate the behavior of the unfused vertebral segments following PSO . Jang et al. did demonstrate reciprocal changes through unfused vertebral segments following anterior and posterior spinal fusion (APSF) in the low lumbar spine for degenerative flat back syndrome and sagittal malalignment in 28 patients. The authors found that increased postoperative LL resulted in spontaneous increase in TK and sacral slope, concluding that anatomic thoracic and pelvic parameters normalize following surgical restoration of LL . However, no patients in this series received corrective spinal osteotomy.
Adult spinal deformity is a broad category that encompasses a diverse group of spinal malalignment patterns. It may range from a simple bi-planar deformity to more complex three- dimensional deformities with significant loss of coronal and sagittal alignment. For patients presenting significant rigid deformity, pedicle subtraction osteotomies can be utilized to create substantial changes in local and global alignment. This surgical technique requires multiple fixation points above and below the level of osteotomy. Extension of fusion beyond the adjacent levels is frequently required due to compensatory rigid deformity, additional deformity in adjacent regions, and the need to prevent adjacent level failure and further deformity. However, when possible, surgeons may attempt to correct the most rigid and deformed portions of the spine while leaving long segments unfused. This has the advantage of allowing continued flexibility and more normal motion in the nonfused portions. However, these unfused segments are dynamic and have the potential for ongoing changes in alignment to occur.
In an attempt to correct spinal malalignment, several key parameters are considered in preoperative planning. Although basic principles of spinopelvic alignment have been outlined, exact anticipation of postoperative alignment following correction osteotomies remains imprecise. From the findings in this study, it is evident that regional fusions with three column osteotomies can offer dramatic corrections. However, reciprocal changes require consideration beyond focal corrections in short segment fusions. In order to enhance surgical planning, and in order to avoid post operative alignment failures, greater appreciations of reciprocal changes are necessary. Accounting for these changes may prevent postoperative malalignment in some cases and permit greater confidence in pursuing selective fusions for select patients.