Incidence, Mode, and Location of Acute Proximal Junctional Failures After Surgical Treatment of Adult Spinal Deformity

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1 SPINE Volume 38, Number 12, pp , Lippincott Williams & Wilkins DEFORMITY Incidence, Mode, and Location of Acute Proximal Junctional Failures After Surgical Treatment of Adult Spinal Deformity Richard Hostin, MD, * Ian McCarthy, PhD, Michael O Brien, MD, * Shay Bess, MD, Breton Line, BSME, Oheneba Boachie-Adjei, MD, Doug Burton, MD, Munish Gupta, MD, ** Christopher Ames, MD, Vedat Deviren, MD, Khaled Kebaish, MD, Christopher Shaffrey, MD, Kirkham Wood, MD, Robert Hart, MD, *** and International Spine Study Group Study Design. Multicenter, retrospective series. Objective. To analyze the incidence, mode, and location of acute proximal junctional failures (APJFs) after surgical treatment of adult spinal deformity. Summary of Background Data. Early proximal junctional failures above adult deformity constructs are a serious clinical problem; however, the incidence and nature of early APJFs remain unclear. Methods. A total of 1218 consecutive adult spinal deformity surgeries across 10 deformity centers were retrospectively reviewed to evaluate the incidence and nature of APJF, defined as any of the following within 28 weeks of index procedure: minimum 15 post-operative increase in proximal junctional kyphosis, vertebral fracture of upper instrumented vertebrae (UIV) or UIV + 1, failure From the * Department of Orthopaedic Surgery, Baylor Scoliosis Center, Plano, TX ; Institute for Health Care Research and Improvement, Baylor Health Care System, Dallas, TX ; Southern Methodist University, Department of Economics Dallas, TX ; Department of Orthopaedic Surgery, Rocky Mountain Scoliosis and Spine, Denver, CO ; Department of Orthopaedic Surgery, Hospital for Special Surgery, New York, NY ; Department of Orthopaedic Surgery, University of Kansas Medical Center, Kansas City, KS ; ** Department of Orthopaedic Surgery, University of California Davis, Sacramento, CA ; Department of Neurosurgery, University of California San Francisco, San Francisco, CA ; Department of Orthopaedic Surgery, University of California San Francisco, CA ; Department of Orthopaedic Surgery, Johns Hopkins University, Baltimore, MD ; Department of Neurosurgery, University of Virginia, Charlottesville, VA ; Department of Orthopaedic Surgery, Massachusetts General Hospital, Boston, MA ; *** Department of Orthopaedic Surgery, Oregon Health Sciences University, Portland, OR; and Denver, CO. of UIV fixation, or need for proximal extension of fusion within 6 months of surgery. Results. Sixty-eight APJF cases were identified out of 1218 consecutive surgeries (5.6%). Patients had a mean age of 63 years (range, yr), mean fusion levels of 9.8 (range, 4 18), and mean time to APJF of 11.4 weeks (range, wk). Fracture was the most common failure mode (47%), followed by soft-tissue failure (44%). Failures most often occurred in the thoracolumbar region (TL-APJF) compared with the upper thoracic region (UT-APJF), with 66% of patients experiencing TL-APJF compared with 34% experiencing UT-APJF. Fracture was significantly more common for TL-APJF relative to UT-APJF ( P = 0.00), whereas soft-tissue failure was more common for UT-APJF ( P < 0.02). Patients experiencing TL-APJF were also older ( P = 0.00), had fewer fusion levels ( P = 0.00), and had worse postoperative sagittal vertical axis ( P < 0.01). Conclusion. APJFs were identified in 5.6% of patients undergoing surgical treatment of adult spinal deformity, with failures occurring primarily in the TL region of the spine. There is evidence that the mode of failure differs depending on the location of UIV, with TL failures more likely due to fracture and UT failures more likely due to soft-tissue failures. Key words: acute proximal junctional failure, upper thoracic proximal junctional failures, thoracolumbar proximal junctional failures. Spine 2013 ; 38 : The Acknowledgment date: March 28, Revision date: August 22, development of proximal junctional kyphosis after Acceptance date: August 26, posterior segmental instrumented fusion for spinal deformity is a complication that has been recognized in both The manuscript submitted does not contain information about medical device(s)/drug(s). adolescent 1 3 and adult 4 10 patients who had undergone reconstruction. The definition of what constitutes clinically signifi- Funding provided in part by the Baylor Health Care System Foundation, Seeger, Endowment Fund, and the Children s Specialist Foundation, Inc., as administrator for the International Spine Study Group. cant postoperative kyphosis, its incidence, and the basis for its Relevant financial activities outside the submitted work: consultancy, development has been variable. In the adult spinal deformity royalties, grants, boards, payment for lectures, stocks, support for travel, population, development of junctional changes is frequently patents, educational presentations, research support, expert testimony. clinically symptomatic and can lead to the need for revision Address correspondence and reprint requests to Ian McCarthy, PhD, Institute surgery. 7, 10 When these changes occur early in the adult population, they have been referred to by various terms such as for Health Care Research and Improvement, Baylor Health Care System, 4708 Alliance Blvd., Ste 800, Plano, TX 75093; ianmccarthy.econ@gmail. com topping-off syndrome, proximal junctional acute collapse, 6 or DOI: /BRS.0b013e c fractures at the top of long segmental pedicle screw constructs May 2013

2 These junctional failures often result in the need for revision surgery and can have potential catastrophic neurological sequelae. Old age, osteopenia, preoperative comorbidities, and severe global sagittal imbalance have been associated with these failures in the adult deformity population. 7, 9, 10 Many of the acute proximal junctional failures (APJFs) seem to occur in the early postoperative period and may result from reciprocal changes in the unfused portions of the spine or from increased loads and motion in the mobile segments adjacent to a long level fusion. Given the frequent need for extension of instrumentation proximal to these failures, the occurrence of APJFs has clear clinical significance. To date, reports on the occurrence of APJFs have been limited primarily to small single-center reviews The goal of this multicenter review is to report the incidence of failure across a large, consecutive case series and to better understand the potential differences among patients with different failure locations ( i.e., failures in the upper thoracic [UT] vs. thoracolumbar [TL] region of the spine). We identified APJFs in 5.6% of patients undergoing surgical treatment of adult spinal deformity, with failures occurring primarily in the TL region of the spine. There is evidence that the mode of failure differs depending on the location of upper instrumented vertebra (UIV), with TL failures more likely due to fracture and UT failures more likely due to softtissue failures. MATERIALS AND METHODS After institutional review board approval, all patients with adult spinal deformity who underwent posterior segmental spinal instrumentation at 10 spinal deformity centers were retrospectively and consecutively reviewed to evaluate the incidence of APJFs. Inclusion criteria consisted of age 18 years or older and diagnosis of adult spinal deformity with at least 1 of the following radiographical criteria: scoliotic curve (idiopathic or degenerative) more than 30, sagittal imbalance more than 5 cm, coronal imbalance more than 5 cm, thoracic kyphosis (TK) more than 60 (T3 or T5 T12), lumbar lordosis (LL) less than 30, or TL kyphosis (T10 L2) more than 20. The series included both primary and revision surgical cases. For inclusion, subjects also required an available preoperative clinical chart, operative summary, postoperative hospital chart, and pre- and postoperative radiographical films (full-length coronal and sagittal). Among the 1218 consecutive adult spinal deformity patients who underwent spinal instrumentation, 68 patients were identified as experiencing an APJF. Clinical data collection included the following: age, sex, weight, height, body mass index (BMI), preoperative diagnosis, spinal surgery history, surgical approach details, osteotomy level and type, fusion levels, type of instrumentation used, details of junctional failure, and indications for whether patient received or was scheduled to receive surgical revision. Radiographical Analysis All subjects had radiographical imaging of the spinopelvic axis using 36-in. radiographs. Digital films were obtained or films Figure 1. Illustration of thoracic kyphosis, lumbar lordosis, and SVA. SVA indicates supraventricular arrhythmias. Figure 2. Illustration of pelvic tilt, pelvic incidence, and sacral slope. Spine

3 DEFORMITY were digitized using a Vidar scanner (VIDAR Systems Corp., Herndon, VA) with 75 dpi resolution and 12 gray levels and assessed using Spineview (Surgiview, Paris, France).13,14 Spinal measurements included TK (Cobb angle superior endplate of T5 to inferior endplate of T12), TL kyphosis (Cobb angle superior endplate of T10 to inferior endplate of L2), LL (Cobb angle superior endplate of T12 to superior endplate of S1), maximal TK, maximal LL, and sagittal vertical axis (SVA) (distance from C7 plumb line to posterior superior corner sacrum; Figure 1). Pelvic measurements included pelvic tilt (angle between the vertical and the line through the midpoint of the sacral plate to the axis of femoral heads), sacral slope (angle between the horizontal and the superior S1 endplate), and pelvic incidence (angle between the perpendicular to the superior S1 endplate at its midpoint and the line connecting this point to the center of the femoral heads) (Figure 2). Proximal junctional angle was defined as the caudal endplate of the UIV to the cephalad endplate of 2 supraadjacent vertebrae above the UIV as previously described.5,7 Definitions of early proximal failure included any of the following within 28 weeks of the index procedure: an increase in proximal junctional kyphosis of 15 or more, fracture of UIV or UIV + 1, need for proximal extension of fusion, and/ or pullout or failure of UIV fixation. For study inclusion, patients needed to have complete radiographical data including good quality 36-in. standing anteroposterior and lateral radiographs from preoperation, early postoperation, and after the junctional failure. Radiographs were required to demonstrate all the vertebrae from C7 to S1 as well as the acetabuli and femoral heads. The APJFs were separated into 2 groups for analysis: TL failures were defined as occurring between T7 and the TL junction L1 L2 (TL-APJF; Figure 3A C: pre-, post-, and worst PJF radiographs, respectively), with UT failures defined as those above T7 (UT-APJF; Figure 4A C: pre-, post-, and worst PJF radiographs, respectively). Statistical Analysis Statistical analyses were performed using Stata version 12.1 (StataCorp, College Station, TX). Differences in categorical data were assessed using the Fisher exact test, whereas differences in continuous data were assessed using the t test and the Wilcoxon rank-sum test. For all tests, statistical significance was set at α = RESULTS There were 68 cases of APJF identified from a retrospective consecutive case review of 1218 adult deformity surgeries performed at 10 spine centers (overall incidence of 5.6%). Fortyfive of the 68 patients (66%) experienced a failure in the thoracolumbar region of the spine (TL-APJF, and 23 patients (34%) experienced a failure in the upper thoracic region of the spine (UT-APJF). Table 1 summarizes the age, BMI, sex, surgical details, and failure outcomes of the 68 patients identified as having APJF. Figure 3. Example of (A) pre-, (B) post-, and (C) worst radiographs for patient with thoracolumbar proximal junctional failures May 2013 BRS indd /04/13 9:10 AM

4 DEFORMITY Figure 4. Example of (A) pre-, (B) post-, and (C) worst radiographs for patient with upper thoracic proximal junctional failures. As illustrated in the Table, patients with TL-APJF were significantly older and had significantly fewer levels fused than the UT failure group. There were also significant differences in the mechanism of junctional failures between the TL and UT failure groups. The TL-APJF group had fractures as the most common source of failure at 62% (28 of 45 patients), whereas the UT-APJF group had fractures in only 17% (4 of 23 cases). The most common mode of failure associated with the UTAPJF group was soft-tissue failure without fracture or instrumentation failure (15 of 23 patients, or 65% cases). Trauma was reported in only 9% (6 of 68 patients) of all junctional failures, the relative frequency of which did not differ significantly between the UT and TL failure groups. Twenty-eight of the 68 junctional failures had been surgically revised at the time of data collection, and the revision rate did not differ significantly between the 2 failure groups. Table 2 summarizes pre- and postoperative spinopelvic measurements as well as the pre- to postoperative change in each respective measure. The TL-APJF and UT-APJF groups showed no significant preoperative difference in sacral slope, pelvic tilt, pelvic incidence, or SVA; however, differences in postoperative SVA were significant, with the TL-APJF group, remaining 5.9 cm positive on average, and the UT-APJF group having an average SVA of 1.9 cm. There were no significant differences between the groups in pre- to postoperative change in spinopelvic parameters including the amount of SVA alteration. Table 3 summarizes pre- and postoperative regional alignment measurements and the respective pre- to postoperative Spine change. The Table illustrates that patients in the UT-APJF group had significantly more preoperative TK than those in the TL-APJF group as measured from both T2 T12 and T5 T12. The UT-APJF group also had significantly more preoperative LL than the TL-APJF group. Postoperatively, the TLAPJF group had significantly more TK from T5 to T12 than the UT-APJF group, whereas the UT-APJF group had significantly more proximal kyphosis from T2 to T5. No significant differences emerged in postoperative LL. Finally, there were significant differences in all measures of the change in TK (with the exception of T10 L2 kyphosis) and also significant differences in the alteration in LL, with TL failures showing a greater average increase in lordosis than UT failures. DISCUSSION The 5.6% rate of APJF in this study, as well as the overall revision rate from APJF, is similar to that reported in other articles.9,12 With a multicenter review of 1218 surgeries and detailed analysis of 68 junctional failures, this study represents the largest reported series of junctional failures to date. Attempts to minimize the occurrence of these failures are important given the high rates of early revision surgery required (exceeding 40% in this series) and its associated risk and expense. Although very few of the reported APJF cases had the available preoperative bone mineral density data to be able to make any definitive statements, its role in the high rate of fractures can be seen in the TL-APJF group. The higher fracture rate seen in the TL-APJF group likely represents both BRS indd /04/13 9:10 AM

5 TABLE 1. Patient Demographics, Surgical Details, and Mode of Failure All Failure Group TL UT P * Count Demographics Age (11.26) (8.15) (13.00) BMI (5.52) (5.76) (4.97) Female % 77.78% 82.61% Surgical details Primary surgery % 62.22% 69.57% Anterior and posterior % 48.89% 39.13% Levels fused (3.25) (1.29) (2.92) Outcomes Weeks to failure (7.97) (7.57) (8.71) Revised or plan to revise % 44.44% 34.78% Mode of failure Soft tissue % 33.33% 65.22% Fracture % 62.22% 17.39% Screw pullout % 4.44% 17.39% Trauma % 11.11% 4.35% * P values for continuous data are based on t tests; however, conclusions are unchanged when using the Wilcoxon rank-sum test as an alternative to the t test. P-values for discrete variables based on Fisher s exact test. Values in bold indicate significance at the 95% confidence level. TL indicates thoracolumbar; UT, upper thoracic; BMI, body mass index. Values in parenthesis denote standard deviations. more advanced age of patients in that group and a likely higher incidence of osteopenia and/or osteoporosis, given the strong inverse correlation with bone density and age in women and the strong predominance of women in the series. Given the high rate of fracture as a mechanism of failure of the TL cases, it seems clear that bone mineral density studies should be a routine part of any workup for older patients considered for fusion constructs stopping at the TL spine. Medical optimization of bone density preoperatively as well as possible intraoperative vertebral augmentation strategies should be used to try and mitigate fracture risks. Differences in the use of hybrid constructs between the 2 groups are likely not significant given the age differences between the 2 groups and the fact that prior studies have demonstrated that, when adjusted for age, all screw constructs likely do not represent an independent risk factor for junctional failure May 2013

6 TABLE 2. Spinopelvic Measurements All Failure Group TL UT P * Preoperative Sacral slope (11.34) (11.05) (11.98) Pelvic tilt (11.03) (8.80) (14.84) Pelvic incidence (13.30) (12.41) (15.17) SVA (7.50) (6.49) (9.35) Postoperative Sacral slope (10.83) (10.36) (11.62) Pelvic tilt (10.37) (9.65) (11.84) Pelvic incidence (13.09) (12.44) (14.49) SVA (6.08) (5.63) (6.19) Change (postoperative to preoperative) Sacral slope (8.12) (7.79) (8.91) Pelvic tilt (8.26) (8.01) (8.91) Pelvic incidence (4.22) (4.79) (2.90) SVA (7.04) (7.01) (6.76) Based on complete preoperative data for 67 patients and postoperative data for 64 patients. * P values are based on t tests; however, conclusions are unchanged when using the Wilcoxon rank-sum test as an alternative to the t test. Values in bold indicate significance at the 95% confidence level. TL indicates thoracolumbar; UT, upper thoracic; SVA, sagittal vertical axis. Values in parenthesis denote standard deviations. Older age, greater BMI, and osteopenia, as well as front and back surgery have all been identified as risk factors for the development of catastrophic failures at the top of long pedicle screw constructs. 7, 9 One of the interesting findings from analysis of this large study group is that the prediction of these junctional failures preoperatively may be problematic. A third of the failures was in the UT region, and within this group the average age was only 56 years, average BMI was only 25.7, and fractures occurred in less than 20% of cases (4 of the 23). Analysis of spinopelvic parameters showed that the average preoperative and postoperative SVA was greater in the TL failure group. The change in SVA from pre- to postoperation was not statistically different between the groups, eliminating greater SVA alteration and possibly greater compensatory reciprocal changes in the unfused segments of the spine as putative mechanism to explain the UT failures. The average change in SVA in the UT group measured only 4.5 cm and the average postoperative SVA in that group measured within the normal range at cm. Spine

7 TABLE 3. Regional Alignment Measurements Preoperative All Failure Group TL UT P * T2 T12 kyphosis (21.00) (16.98) (25.01) T5 T12 kyphosis (20.81) (16.63) (25.75) T2 T5 kyphosis (7.14) (6.39) (8.63) T10 L2 kyphosis (16.01) (15.91) (16.50) T12 S1 lordosis Postoperative (34.92) (30.63) (39.16) T2 T12 kyphosis (17.71) (17.49) (18.56) T5 T12 kyphosis (16.82) (16.53) (13.81) T2 T5 kyphosis (11.71) (6.78) (12.46) T10 L2 kyphosis (16.45) (18.92) (8.74) T12 S1 lordosis Change (postoperative to preoperative) (16.31) (15.07) (18.72) T2 T12 kyphosis (18.43) (13.41) (23.17) T5 T12 kyphosis (20.95) (13.59) (22.45) T2 T5 kyphosis (13.18) (8.30) (14.68) T10 L2 kyphosis (21.07) (22.59) (16.77) T12 S1 lordosis Based on complete pre- and postoperative data for 67 patients. (31.91) (29.36) (34.11) * P values are based on t tests; however, conclusions are unchanged when using the Wilcoxon rank-sum test as an alternative to the t test. Values in bold indicate significance at the 95% confidence level. TL indicates thoracolumbar; UT, upper thoracic. Values in parenthesis denote standard deviations May 2013

8 Analysis of the regional alignment data showed various statistically significant findings of perhaps little clinical significance. Perhaps the 2 most critical values, the postoperative global TK (from T2 to T12) as well as LL (from T12 to S1), showed no difference between TL and UT failure groups. Global postoperative TK in the UT failure group measured 56.6, indicating that flattening of the normal TK was also not a generator of junctional failures in the UT group compared with the TL group. Neither failure group demonstrated a large average alteration in SVA, which has also been studied as a causative mechanism for APJFs. 10 Given the complex nature of the problem, an appropriate identification of risk factors associated with UT-APJF and effective prophylaxis against it will require a larger study population and more sophisticated case matching. Key Points There were 68 cases of APJF identified out of 1218 consecutive surgeries (5.6%). Failures most often occurred in the thoracolumbar region (TL-APJF) compared with the upper thoracic region (UT-APJF), with 66% of patients experiencing TL-APJF compared with 34% experiencing UT-APJF. Mode of failure differs depending on the location of UIV, with TL failures more likely due to fracture and UT failures more likely due to soft-tissue failures. References 1. Kim YJ, Lenke LG, Bridwell KH, et al. Proximal junctional kyphosis in adolescent idiopathic scoliosis after 3 different types of posterior segmental spinal instrumentation and fusions: incidence and risk factor analysis of 410 cases. Spine (Phila Pa 1976) 2007 ; 32 : Lee GA, Betz RR, Clements DH III, et al. Proximal kyphosis after posterior spinal fusion in patients with idiopathic scoliosis. Spine (Phila Pa 1976) 1999 ; 24 : Lowe TG, Kasten MD. An analysis of sagittal curves and balance after Cotrel-Dubousset instrumentation for kyphosis secondary to Scheuermann s disease. A review of 32 patients. Spine (Phila Pa 1976) 1994 ; 19 : DeWald CJ, Stanley T. Instrumentation-related complications of multilevel fusions for adult spinal deformity patients over age 65: surgical considerations and treatment options in patients with poor bone quality. Spine (Phila Pa 1976) 2006 ; 31 : S Glattes RC, Bridwell KH, Lenke LG, et al. Proximal junctional kyphosis in adult spinal deformity following long instrumented posterior spinal fusion: incidence, outcomes, and risk factor analysis. Spine (Phila Pa 1976) 2005 ; 30 : Hart RA, Prendergast MA, Roberts WG, et al. Proximal junctional acute collapse cranial to multi-level lumbar fusion: a cost analysis of prophylactic vertebral augmentation. Spine J 2008 ; 8 : Kim YJ, Bridwell KH, Lenke LG, et al. Proximal junctional kyphosis in adult spinal deformity after segmental posterior spinal instrumentation and fusion: minimum five-year follow-up. Spine (Phila Pa 1976) 2008 ; 33 : Kim YJ, Bridwell KH, Lenke LG, et al. Sagittal thoracic decompensation following long adult lumbar spinal instrumentation and fusion to L5 or S1: causes, prevalence, and risk factor analysis. Spine (Phila Pa 1976) 2006 ; 31 : O Leary PT, Bridwell KH, Lenke LG, et al. Risk factors and outcomes for catastrophic failures at the top of long pedicle screw constructs: a matched cohort analysis performed at a single center. Spine (Phila Pa 1976) 2009 ; 34 : Watanabe K, Lenke LG, Bridwell KH, et al. Proximal junctional vertebral fracture in adults after spinal deformity surgery using pedicle screw constructs: analysis of morphological features. Spine (Phila Pa 1976) 2010 ; 35 : Yagi M, King AB, Boachie-Adjei O. Incidence, risk factors and natural course of proximal junctional kyphosis: surgical outcomes review of adult idiopathic scoliosis. Minimum 5 years follow-up. Spine (Phila Pa 1976 ) 2012 ; 37 : Yagi M, Akilah KB, Boachie-Adjei O. Incidence, risk factors and classification of proximal junctional kyphosis: surgical outcomes review of adult idiopathic scoliosis. Spine (Phila Pa 1976) 2011 ; 36 : E El Fegoun AB, Schwab F, Gamez L, et al. Center of gravity and radiographic posture analysis: a preliminary review of adult volunteers and adult patients affected by scoliosis. Spine (Phila Pa 1976) 2005 ; 30 : Rillardon L, Levassor N, Guigui P, et al. Validation of a tool to measure pelvic and spinal parameters of sagittal balance. Rev Chir Orthop Reparatrice Appar Mot 2003 ; 89 : Spine