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Charles Kuntz IV, Linda S. Levin, Stephen L. Ondra, Christopher I. Shaffrey and Chad J. Morgan

comparison of the gore and cobb methods . J Spinal Disord Tech 17 : 301 – 305 , 2004 26 Suk K , Kim K , Lee S , Kim J : Significance of chin-brow vertical angle in correction of kyphotic deformity of ankylosing spondylitis patients . Spine 28 : 2001 – 2005 , 2003 27 Van Royen BJ , Toussaint HM , Kingma I , Bot SD , Caspers M , Harlaar J , : Accuracy of the sagittal vertical axis in a standing lateral radiograph as a measure of balance in spinal deformities . Eur Spine J 7 : 408 – 412 , 1998 28 Vedantam R , Lenke LG

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Jeong Yoon Park, Yong Eun Cho, Sung Uk Kuh, Jun Hyung Cho, Dong Kyu Chin, Byung Ho Jin and Keun Su Kim

prognostic factor, 7 but the most common method of checking sagittal balance is the plumb line. A plumb line is defined as a line dropped from the center of the C-7 vertebra. The horizontal distance from the anterosuperior corner of the sacrum to plumb line was recorded as the magnitude of the sagittal vertical axis, and the degree of sagittal vertical axis indicates the sagittal balance. 5 It is often difficult to measure the plumb line, however. The authors of several studies have shown that pelvic parameters, especially PIA, are an indirect method to check sagittal

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Roy R. Pigge, Famke J. Scheerder, Theo H. Smit, Margriet G. Mullender and Barend J. Van Royen

Object

The object of this study was to assess the effectiveness of preoperative planning in the restoration of balance and view angle in patients treated with lumbar osteotomy in ankylosing spondylitis (AS).

Methods

The authors prospectively analyzed 8 patients with a thoracolumbar kyphotic deformity due to AS that was treated using a closing wedge osteotomy (CWO) of the lumbar spine to correct sagittal imbalance and horizontal view. Preoperative planning to predict postoperative balance, defined by the sagittal vertical axis (SVA) and the sacral endplate angle (SEA), and the view angle, defined by the chin-brow to vertical angle (CBVA), was performed using the ASKyphoplan computational program.

Results

All patients were treated with a CWO at level L-4 and improved in balance and view angle. The mean correction angle was 35° (range 24–47°). The postoperative SEA improved from 21 to 36° for a mean correction of 15°. In addition, the SVA and CBVA improved significantly. Note, however, that the postoperative results did not exactly reflect the predicted values of the analyzed parameters.

Conclusions

Preoperative planning for the restoration of balance and view angle in AS improves understanding of the biomechanical and clinical effects of a correction osteotomy of the lumbar spine. The adaptation of basic clinical and biomechanical principles to restore balance is advised in such a way that the individual SEA is corrected by 15° (maximum 40°) in relation to the horizon and C-7 is balanced exactly above the posterosuperior corner of the sacrum.

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Charles A. Sansur, Kai-Ming G. Fu, Rod J. Oskouian Jr., Jay Jagannathan, Charles Kuntz iv and Christopher I. Shaffrey

to the chin and brow with the neck in neutral or fixed position and the knees and hips extended. The CBVA is a clinical measurement of the total sagittal deformity of the spine and the effect on horizontal gaze. Sagittal spinal balance is defined from the cervicothoracic spine to the sacrum or hip axis. The C7–S1 sagittal vertical axis is defined as the horizontal distance from a vertical plumb line centered in the middle of the C-7 VB to the posterosuperior corner of the S-1 endplate. The T1–HA sagittal tilt angle is defined as the angle subtended by a vertical

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Ralf A. Kockro, Rainer Giacomelli, Martin Scheihing, Alfred Aschoff and Juergen A. Hampl

and local anesthesia, a 3–4-mm bur hole was placed on the right side 9.5-mm behind the bregma and 4-mm lateral to it. Then the sterile stereotactic frame was fixed onto the base with the screws penetrating the drape. The incline of the vertical bars was set to 54° and the bore canal for the Cushing needle in the rotating wheel was set to the angle of 20° deviating from the sagittal vertical axis. The Cushing brain needle was introduced through the bore canal and its tip was positioned over the bur hole. The positioning was achieved by sliding the 2 vertical bars

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Ian G. Dorward and Lawrence G. Lenke

patients (33 with 2 or more years of follow-up), Bridwell et al. 5 found a 7.6% rate of transient neurological complications, all of which improved; meanwhile these patients had significant improvements in pain scale, ODI, and SRS score outcomes. When follow-up was extended to 5 years in 35 patients, SRS scores and the ODI remained statistically unchanged, as did radiographic measures such as proximal junctional change, thoracic kyphosis, lumbar lordosis, and global sagittal balance—although a trend toward an increasingly anterior sagittal vertical axis was noted. 23 A

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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

Object

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.

Methods

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.

Results

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).

Conclusions

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.

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Vedat Deviren, Justin K. Scheer and Christopher P. Ames

values are presented in degrees unless otherwise noted. Abbreviation: SVA = sagittal vertical axis. Computed Tomography Findings Postoperative CT scans at a minimum of 1 year follow-up were obtained in 4 of the 9 patients. None showed any evidence of pseudarthrosis ( Fig. 6 ). F ig . 6. Left: Postoperative CT scan showing C-7 PSO (white oval) . Right: One-year follow-up CT showing fusion. Clinical Outcomes There was a statistically significant decrease in the NDI scores (24.6%, 51.1 to 38.6, p = 0.03), and VAS scores (52.6%, 8.1 to 3.9, p = 0

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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

Object

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.

Methods

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.

Results

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).

Conclusions

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.

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Chi Heon Kim, Chun Kee Chung, Hee Suk Hong, Eun Hyun Kim, Min Jung Kim and Byung Joo Park

Object

Recent studies have emphasized measuring the sagittal vertical axis (SVA) and pelvic parameters (pelvic incidence, sacral slope, and pelvic tilt) when evaluating spinal disorders. An accurate and reproducible measurement is important for a reliable result. Although computerized measurement is more consistent than manual measurement, computerized measurement requires an expensive software program, the need to transfer images to a workstation, and additional education for users. An inexpensive and convenient computerized measurement program is desirable and necessary. The object of this study was to propose a computerized tool for measuring spinal and pelvic parameters and to evaluate the efficacy of this new tool compared with manual measurement.

Methods

The authors devised a tool that provides computerized measurements of the SVA and pelvic parameters in a picture archiving and communication system (PACS) without transferring images to another program. This tool was created by merging functions in the PACS. The resulting tool is easy to implement by merging functions (indicate the center of 2 points, plot a vertical and a horizontal line from a point, and measure the angles between lines) in any image viewer. The tool was made into icons on a toolbar in the PACS. Measurements of distance and angle were computerized by identifying crucial points after selecting the icon. For SVA, 4 points were identified around each corner of the C-7 body and a fifth point at the superior/posterior corner of the S-1 body. For pelvic parameters, 4 points were identified at the centers of each femoral head and at the anterior/superior and posterior/superior corners of S-1. Thirty-three whole-spine lateral radiographs were randomly selected from the radiographic database. To evaluate inter- and intraobserver variability between observers and method, skilled (2 years of experience) and unskilled (1 week of experience) observers measured SVA and pelvic parameters 3 times with a 7-day interval between each time using both computerized and manual measurement methods. The reliability was measured using the intraclass correlation coefficient.

Results

The computerized method showed better congruity than the manual method in both skilled and unskilled observers (p < 0.05), and the intraclass correlation coefficients were > 0.9. The skilled observer showed better agreement than the unskilled observer with both computerized and manual methods, and this difference was prominent in measuring pelvic parameters (p < 0.05). The computerized method required less time than the manual method, especially for the unskilled observer (p < 0.05).

Conclusions

A computerized measurement of pelvic parameters may be a more reliable and efficacious approach than manual measurements. This benefit is more prominent in the unskilled observer, and adding this simple function to an image viewer may be recommended in future studies.