Khoi D. Than, Paul Park, Kai-Ming Fu, Stacie Nguyen, Michael Y. Wang, Dean Chou, Pierce D. Nunley, Neel Anand, Richard G. Fessler, Christopher I. Shaffrey, Shay Bess, Behrooz A. Akbarnia, Vedat Deviren, Juan S. Uribe, Frank La Marca, Adam S. Kanter, David O. Okonkwo, Gregory M. Mundis Jr., Praveen V. Mummaneni and the International Spine Study Group
Minimally invasive surgery (MIS) techniques are increasingly used to treat adult spinal deformity. However, standard minimally invasive spinal deformity techniques have a more limited ability to restore sagittal balance and match the pelvic incidence–lumbar lordosis (PI-LL) than traditional open surgery. This study sought to compare “best” versus “worst” outcomes of MIS to identify variables that may predispose patients to postoperative success.
A retrospective review of minimally invasive spinal deformity surgery cases was performed to identify parameters in the 20% of patients who had the greatest improvement in Oswestry Disability Index (ODI) scores versus those in the 20% of patients who had the least improvement in ODI scores at 2 years' follow-up.
One hundred four patients met the inclusion criteria, and the top 20% of patients in terms of ODI improvement at 2 years (best group, 22 patients) were compared with the bottom 20% (worst group, 21 patients). There were no statistically significant differences in age, body mass index, pre- and postoperative Cobb angles, pelvic tilt, pelvic incidence, levels fused, operating room time, and blood loss between the best and worst groups. However, the mean preoperative ODI score was significantly higher (worse disability) at baseline in the group that had the greatest improvement in ODI score (58.2 vs 39.7, p < 0.001). There was no difference in preoperative PI-LL mismatch (12.8° best vs 19.5° worst, p = 0.298). The best group had significantly less postoperative sagittal vertical axis (SVA; 3.4 vs 6.9 cm, p = 0.043) and postoperative PI-LL mismatch (10.4° vs 19.4°, p = 0.027) than the worst group. The best group also had better postoperative visual analog scale back and leg pain scores (p = 0.001 and p = 0.046, respectively).
The authors recommend that spinal deformity surgeons using MIS techniques focus on correcting a patient's PI-LL mismatch to within 10° and restoring SVA to < 5 cm. Restoration of these parameters seems to impact which patients will attain the greatest degree of improvement in ODI outcomes, while the spines of patients who do the worst are not appropriately corrected and may be fused into a fixed sagittal plane deformity.
Abstracts of the 2013 Annual Meeting of the AANS/CNS Section on Disorders of the Spine and Peripheral Nerves
Phoenix, Arizona • March 6–9, 2013
Frank J. Schwab, Ashish Patel, Christopher I. Shaffrey, Justin S. Smith, Jean-Pierre Farcy, Oheneba Boachie-Adjei, Richard A. Hostin, Robert A. Hart, Behrooz A. Akbarnia, Douglas C. Burton, Shay Bess and Virginie Lafage
Pedicle subtraction osteotomy (PSO) is a surgical procedure that is frequently performed on patients with sagittal spinopelvic malalignment. Although it allows for substantial spinopelvic realignment, suboptimal realignment outcomes have been reported in up to 33% of patients. The authors' objective in the present study was to identify differences in radiographic profiles and surgical procedures between patients achieving successful versus failed spinopelvic realignment following PSO.
This study is a multicenter retrospective consecutive PSO case series. The authors evaluated 99 cases involving patients who underwent PSO for sagittal spinopelvic malalignment. Because precise cutoffs of acceptable residual postoperative sagittal vertical axis (SVA) values have not been well defined, comparisons were focused between patient groups with a postoperative SVA that could be clearly considered either a success or a failure. Only cases in which the patients had a postoperative SVA of less than 50 mm (successful PSO realignment) or more than 100 mm (failed PSO realignment) were included in the analysis. Radiographic measures and PSO parameters were compared between successful and failed PSO realignments.
Seventy-nine patients met the inclusion criteria. Successful realignment was achieved in 61 patients (77%), while realignment failed in 18 (23%). Patients with failed realignment had larger preoperative SVA (mean 217.9 vs 106.7 mm, p < 0.01), larger pelvic tilt (mean 36.9° vs 30.7°, p < 0.01), larger pelvic incidence (mean 64.2° vs 53.7°, p < 0.01), and greater lumbar lordosis–pelvic incidence mismatch (−47.1° vs −30.9°, p < 0.01) compared with those in whom realignment was successful. Failed and successful realignments were similar regarding the vertebral level of the PSO, the median size of wedge resection 22.0° (interquartile range 16.5°−28.5°), and the numerical changes in pre- and postoperative spinopelvic parameters (p > 0.05).
Patients with failed PSO realignments had significantly larger preoperative spinopelvic deformity than patients in whom realignment was successful. Despite their apparent need for greater correction, the patients in the failed realignment group only received the same amount of correction as those in the successfully realigned patients. A single-level standard PSO may not achieve optimal outcome in patients with high preoperative spinopelvic sagittal malalignment. Patients with large spinopelvic deformities should receive larger osteotomies or additional corrective procedures beyond PSOs to avoid undercorrection.
Virginie Lafage, Neil J. Bharucha, Frank Schwab, Robert A. Hart, Douglas Burton, Oheneba Boachie-Adjei, Justin S. Smith, Richard Hostin, Christopher Shaffrey, Munish Gupta, Behrooz A. Akbarnia and Shay Bess
Sagittal spinopelvic imbalance is a major contributor to pain and disability for patients with adult spinal deformity (ASD). Preoperative planning is essential for pedicle subtraction osteotomy (PSO) candidates; however, current methods are often inaccurate because no formula to date predicts both postoperative sagittal balance and pelvic alignment. The authors of this study aimed to evaluate the accuracy of 2 novel formulas in predicting postoperative spinopelvic alignment after PSO.
This study is a multicenter retrospective consecutive PSO case series. Adults with spinal deformity (> 21 years old) who were treated with a single-level lumbar PSO for sagittal imbalance were evaluated. All patients underwent preoperative and a minimum of 6-month postoperative radiography. Two novel formulas were used to predict the postoperative spinopelvic alignment. The results predicted by the formulas were then compared with the actual postoperative radiographic values, and the formulas' ability to identify successful (sagittal vertical axis [SVA] ≤ 50 mm and pelvic tilt [PT] ≤ 25°) and unsuccessful (SVA > 50 mm or PT > 25°) outcomes was evaluated.
Ninety-nine patients met inclusion criteria. The median absolute error between the predicted and actual PT was 4.1° (interquartile range 2.0°–6.4°). The median absolute error between the predicted and actual SVA was 27 mm (interquartile range 11–47 mm). Forty-one of 54 patients with a formula that predicted a successful outcome had a successful outcome as shown by radiography (positive predictive value = 0.76). Forty-four of 45 patients with a formula that predicted an unsuccessful outcome had an unsuccessful outcome as shown by radiography (negative predictive value = 0.98).
The spinopelvic alignment formulas were accurate when predicting unsuccessful outcomes but less reliable when predicting successful outcomes. The preoperative surgical plan should be altered if an unsuccessful result is predicted. However, even after obtaining a predicted successful outcome, surgeons should ensure that the predicted values are not too close to unsuccessful values and should identify other variables that may affect alignment. In the near future, it is anticipated that the use of these formulas will lead to better surgical planning and improved outcomes for patients with complex ASD.
Virginie Lafage, Frank Schwab, Shaleen Vira, Robert Hart, Douglas Burton, Justin S. Smith, Oheneba Boachie-Adjei, Alexis Shelokov, Richard Hostin, Christopher I. Shaffrey, Munish Gupta, Behrooz A. Akbarnia, Shay Bess and Jean-Pierre Farcy
Pedicle subtraction osteotomy (PSO) is a spinal realignment technique that may be used to correct sagittal spinal imbalance. Theoretically, the level and degree of resection via a PSO should impact the degree of sagittal plane correction in the setting of deformity. However, the quantitative effect of PSO level and focal angular change on postoperative spinopelvic parameters has not been well described. The purpose of this study is to analyze the relationship between the level/degree of PSO and changes in global sagittal balance and spinopelvic parameters.
In this multicenter retrospective study, 70 patients (54 women and 16 men) underwent lumbar PSO surgery for spinal imbalance. Preoperative and postoperative free-standing sagittal radiographs were obtained and analyzed by regional curves (lumbar, thoracic, and thoracolumbar), pelvic parameters (pelvic incidence and pelvic tilt [PT]) and global balance (sagittal vertical axis [SVA] and T-1 spinopelvic inclination). Correlations between PSO parameters (level and degree of change in angle between the 2 adjacent vertebrae) and spinopelvic measurements were analyzed.
Pedicle subtraction osteotomy distribution by level and degree of correction was as follows: L-1 (6 patients, 24°), L-2 (15 patients, 24°), L-3 (29 patients, 25°), and L-4 (20 patients, 22°). There was no significant difference in the focal correction achieved by PSO by level. All patients demonstrated changes in preoperative to postoperative parameters including increased lumbar lordosis (from 20° to 49°, p < 0.001), increased thoracic kyphosis (from 30° to 38°, p < 0.001), decreased SVA and T-1 spinopelvic inclination (from 122 to 34 mm, p < 0.001 and from +3° to −4°, p < 0.001, respectively), and decreased PT (from 31° to 23°, p < 0.001). More caudal PSO was correlated with greater PT reduction (r = −0.410, p < 0.05). No correlation was found between SVA correction and PSO location. The PSO degree was correlated with change in thoracic kyphosis (r = −0.474, p < 0.001), lumbar lordosis (r = 0.667, p < 0.001), sacral slope (r = 0.426, p < 0.001), and PT (r = −0.358, p < 0.005).
The degree of PSO resection correlates more with spinopelvic parameters (lumbar lordosis, thoracic kyphosis, PT, and sacral slope) than PSO level. More importantly, PSO level impacts postoperative PT correction but not SVA.