SPINE Volume 39, Number 8, pp E521-E528 ©2014, Lippincott Williams & Wilkins
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Factors Affecting the Postoperative Progression of Thoracic Kyphosis in Surgically Treated Adult Patients With Lumbar Degenerative Scoliosis Mitsuru Yagi, MD, PhD,* Naobumi Hosogane, MD, PhD,† Eijiro Okada, MD, PhD,‡ Kota Watanabe, MD, PhD,§ Masafumi Machida, MD, PhD,* Masaki Tezuka, MD, PhD,‡ Morio Matsumoto, MD, PhD,† Takashi Asazuma, MD, PhD,* and Keio Spine Research Group¶
Study Design. A retrospective case series of patients treated surgically for degenerative lumbar scoliosis (DLS). Objective. To determine incidence and risk factors of progressive global thoracic kyphosis (pGTK) after surgery for DLS. Summary of Background Data. Sagittal balance affects the surgical treatment of spinal deformity in adults. Little is known about the loss of sagittal balance due to pGTK, or about the risk factors for pGTK, after surgery for DLS. Methods. We reviewed records from a multicenter database of adults with DLS, treated with posterior spinal fusion. Inclusion required an age of 50 years or more at the time of surgery, an upper instrumented vertebra at T9 and below, more than 5 fused segments, and at least 2 years of follow-up. We included 73 patients with a mean age of 68.3 years (range, 51–77 yr) and a mean follow-up period of 3.6 years (range, 2–11 yr). Independent risk factors for pGTK were identified by logistic regression analysis. Results. Significant pGTK, defined as an increase in thoracic kyphosis of more than 10° from before surgery to the time of final follow-up, was observed in 41% of the patients. Loss of the sagittal vertical axis was larger in patients with pGTK than without (4.7 vs. 1.5 cm; P = 0.02). Risk analysis showed larger lumbar lordosis From the *Department of Orthopedic Surgery, National Center for Musculoskeletal Disorders, Murayama Medical Center, Tokyo, Japan; †Department of Orthopedics, Keio University School of Medicine, Tokyo, Japan; ‡Department of Orthopedics, Saiseikai Central Hospital, Tokyo, Japan; §Department of Advanced Therapy for Spine and Spinal Cord Disorders, Keio University School of Medicine, Tokyo, Japan; and ¶KSRG, Tokyo, Japan. Acknowledgment date: September 13, 2013. First revision date: January 3, 2014. Acceptance date: January 9, 2014. The legal regulatory status of the device(s)/drug(s) that is/are the subject of this manuscript is not applicable in my country. No funds were received in support of this work. Relevant financial activities outside the submitted work: grants/grants pending and payment for lectures. Address correspondence and reprint requests to Mitsuru Yagi, MD, PhD, Department of Orthopedic Surgery, National Center for Musculoskeletal Disorders, Murayama Medical Center, 2-37-1 Gakuen, Musashi-Murayama City Tokyo, Japan; E-mail: [email protected] DOI: 10.1097/BRS.0000000000000226 Spine
correction in patients with pGTK. Multivariate logistic regression analysis identified an age greater than 75 (odds ratio, 5.53; P = 0.02, 95% confidence interval [1.4–22.4]) and sacropelvic fusion (odds ratio = 2.66, P = 0.02, 95% confidence interval [1.5–11.1]) as independent risk factors for pGTK. Conclusion. The pGTK incidence after surgery for DLS was 41%. Age, sacropelvic fusion, and a larger sagittal correction were identified as pGTK risk factors. Long-term follow-up will provide more data on the clinical impact of pGTK in elderly patients. Key words: degenerative scoliosis, sagittal alignment, complication. Level of Evidence: 3 Spine 2014;39:E521–E528
S
ince Glassman et al1 reported the impact of positive sagittal balance for the surgical treatment of spinal deformities in adults, sagittal balance has become recognized as the most important factor for a favorable clinical outcome.1–7 To achieve an appropriate sagittal balance, lumbar lordosis (LL) must be corrected relative to the pelvic incidence (PI).8,9 On the contrary, we previously reported that even after the appropriate restoration of LL, the sagittal vertical axis (SVA) increased immediately after surgery and that this increase was persistent through the final follow-up in patients with adult spinal deformity (ASD) after pedicle subtraction osteotomy (PSO).10 The progressive global thoracic kyphosis (pGTK) observed in patients during the surgical follow-up period in a previous study suggested that the loss of sagittal balance could be attributed to increased thoracic kyphosis (TK).10 Information about the loss of sagittal balance due to pGTK, or about the risks for unfavorable pGTK in patients with ASD, is limited. Several factors must be considered when establishing risks for pGTK, such as posterior spinal fusion, sacral fusion, and degree of correction,11–18 and the significant risk factors have not yet been fully elucidated. This study was conducted to report the incidence of pGTK after instrumented fusion surgery to correct adult www.spinejournal.com
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DEFORMITY thoracolumbar degenerative lumbar scoliosis (DLS), and to identify risk factors for pGTK.
MATERIALS AND METHODS This multicenter study was approved by the institutional review board of each participating hospital. We conducted a retrospective review of a multicenter database of prospectively collected patients with DLS who were treated with posterior correction and instrumented spinal fusion surgery. The minimum follow-up period was 2 years. To be included in the study, patients had to be older than 50 years at the time of the surgery, and the surgery had to involve the fusion of more than 5 motion segments. To assess pGTK, patients with an upper instrumented vertebra (UIV) at T8 and above were excluded. Other causes of scoliosis were ruled out through clinical examination.19 Patients with a history of adult idiopathic scoliosis, syndromic scoliosis, neuromuscular scoliosis, or a similar condition, or who had undergone any revision surgery, were excluded from this study. This review required that adequate anteroposterior and lateral standing 36-inch–long cassette radiographs be obtained before the surgery, within 8 to 12 weeks after surgery, and at the most recent follow-up. Seven patients were either lost to follow-up or had incomplete radiographs because they had left the geographic area. Five patients had left the geographic area and 2 patients had incomplete radiographs. We analyzed the preoperative and postoperative radiographical measurements, age, sex, fusion level, bone fusion, complications, and clinical outcomes for 73 patients who met the inclusion criteria.
Radiographical Measurements The SVA was measured as the distance from the C7 plumb line to the perpendicular line drawn from the superior posterior endplate of the S1 vertebral body on lateral radiographs. TK was measured from the upper endplate of T5 to the lower endplate of T12. LL was measured from the lower endplate of T12 to the upper endplate of S1. PI was measured as the angle subtended by a perpendicular line from the upper endplate of S1 and a line connecting the center of the femoral head to the center of the cephalad endplate of S1. The proximal junction was defined as the caudal endplate of the UIV to the cephalad endplate of the 2 proximal vertebrae. Abnormal proximal junctional kyphosis (PJK) was defined by a proximal junctional angle that was more than 10° and was at least 10° greater than the corresponding preoperative measurement; the presence of both criteria was necessary to be considered abnormal.20–22 Sagittal malalignment was defined as an imbalance greater than 5 cm.20–22
Surgical Procedure All patients underwent the same intraoperative technique and postoperative protocol. All patients underwent posterior spinal instrumentation and fusion with pedicle screw constructs. Fusion levels were selected by criteria that remained consistent throughout the entire study period. The UIV was chosen on the basis of the patient’s bone quality, coronal imbalance, and local sagittal alignment, along with the magnitude of the coronal E522
Progressive Postoperative Thoracic Kyphosis in DLS • Yagi et al
curve. The lower instrumented vertebra (LIV) was chosen on the basis of the status of the lumbar spine curve and the discs. If spinal stenosis, degenerative listhesis, significant obliquity, or disc degeneration were present according to the Scoliosis Research Society classifications for adult scoliosis, arthrodesis was extended to the sacrum.5 In these cases, we augmented the posterior instrumentation construct using iliac screw fixation and an anterior column support at L5–S1, in addition to bilateral or unilateral S1 screws.
Risk Factors Potential risk factors for pGTK were evaluated using the following data for each patient: age, sex, curve magnitude, LIV level, number of fused vertebrae, TK (grouped by T2– T5, T5–T12, T2–T12, and T10–L2), LL, PI, pelvic tilt (PT), spinopelvic balance (PI + LL), and global sagittal spine alignment (GSA) (TK + LL + PI).
Statistical Analysis
Ordinal and nominal data were analyzed by χ2 test when more than 5 observations were expected in the category. SVA and its correlation with sagittal parameters were analyzed by correlation coefficient test. Relationships between patient characteristics and the progression of TK were investigated by univariate and multivariate logistic regression analyses. The outcomes of interest were: (1) age, (2) sex, (3) LIV level, (4) preoperative SVA, (5) preoperative PI + LL, and (6) GSA. Patients older than 75 years were considered elderly. A preoperative SVA greater than 10 cm indicated preoperative sagittal malalignment. A preoperative PI + LL greater than 30° indicated preoperative spinopelvic malalignment. A preoperative GSA greater than 60° was considered a significant global spinal sagittal malalignment. We calculated overall summary statistics, including the means and standard deviations for continuous variables, and frequencies and percentages for categorical variables. After the descriptive analysis, independent associations between potential risk factors and pGTK were analyzed by univariate comparison. Differences between patients who developed postoperative pGTK and those who did not were evaluated using independent sample t tests for continuous variables. Differences among discrete variables were examined by the χ2 test. We created a multivariate binary logistic regression model to evaluate the adjusted associations of each potential explanatory variable and predict the likelihood of developing postoperative pGTK. Clinically relevant variables and variables with a univariate significance level of 0.25 or less were included in the multivariate logistic regression analysis. For all regression models, a P value less than 0.05 with a confidence interval of 95% was considered significant. All analyses were performed with SPSS software (IBM, Chicago, IL).
RESULTS Demographics and Radiographical Outcomes of Patients Surgically Treated for DLS This study included 67 females and 6 males. The mean age at the time of surgery was 68.3 years (range, 51–77 yr), and
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TABLE 1. The Correlation of Sagittal Parameters and SVA at Postoperative Time Period T2–T5
T5–T12
T10–L2
LL
SS
PI
PT
GSA
PI + LL
SVA
0.19
0.08
0.36
0.24
−0.26
0.18
0.53
0.34
0.25
P
n.s.
n.s.
0.006*
n.s.
n.s.
n.s.
10°
73
43
30
Immediate
5.1 (5.5)
6.1 (5.2)
4.2 (5.9)
0.23
Final
7.9 (4.3)
7.6 (4.3)
8.3 (4.4)
0.59
ΔSVA
2.9 (3.1)
1.5 (3.0)
4.7 (4.1)
0.02*
Immediate
7.1 (6.8)
7 (5.1)
7.3 (7.0)
0.54
Final
8.7 (6.1)
7.9 (5.9)
9.8 (6.8)
0.21
ΔT2–T5
1.7 (2.4)
1.0 (4.1)
2.6 (3.4)
0.10
Immediate
18.9 (16.9)
15.3 (11.4)
24 (18.8)
0.11
Final
25.2 (13.3)
18.1 (14.5)
40.3 (16.3)
10°
73
43
30
Preoperation
4.3 (6.3)
4.0 (4.1)
4.7 (7.3)
0.29
Immediate
9.6 (6.6)
8.9 (4.4)
10.7 (8.1)
0.43
Final
15.3 (5.9)
13.2 (5.2)
17.9 (7.1)
0.09
Δ1 PJK
5.7 (6.4)
4.3 (5.5)
7.2 (5.2)
0.23
Δ2 PJK
10.9 (7.9)
9.2 (7.7)
13.2 (6.2)
0.21
No. of pts.
P
PJK (°)
Values are numbers and standard deviations. Δ1 PJK indicates change of PJ angle between final follow-up and preoperation; Δ2 PJK, change of PJ angle between final follow-up and immediately after operation; PJK indicates proximal junctional kyphosis; pGTK progression of global thoracic kyphosis; pts., patients; DLS, degenerative lumbar scoliosis.
after undergoing long posterior spinal fusion for ASD.20–22 Although only 16.4% of the patients in this study met the criteria for PJK, the mean PJ angle increased significantly during the follow-up period. All the patients had a fusion level below T9, and this relatively short fusion length might affect the posterior ligamentous complex. Theoretically, progressive junctional kyphosis has a greater effect on sagittal malalignment when it affects the thoracolumbar region as opposed to the proximal thoracic region. The PJ angle increased significantly in all patients after surgery, with no significant differences between those with or without pGTK. This strong postoperative increase in the PJ angle strongly suggests the role of PJK in maintaining global sagittal alignment. These data suggest that deterioration in sagittal balance may reflect progressions of both junctional and global kyphosis in the unfused spine. Loss of sagittal balance should be monitored carefully over the long term, especially in patients with DLS treated by spinal fusion below the sagittal apex. Despite the significant loss of SVA among all patients, a patient who developed PJK and neurological deficits was the only one to complain of symptoms related to a positive SVA. This finding suggests that a positive SVA, even one as large as 8.3 cm, is sufficient to maintain a positive clinical outcome. Moreover, the SVA values at the final follow-up were similar in patients with or without pGTK. This may suggest that a positive SVA is common in elderly patients due to the reciprocal progression of TK, and that the natural sagittal balance of these patients is relatively more positive than that in a healthy young population.
We were not surprised to find a close relationship between GSA and SVA, because the maintenance of sagittal balance in healthy elderly individuals can be attributed primarily to LL loss.26–28 Schwab et al27 proposed an optimal sagittal lumbosacral alignment (LL = PI + 9°) for achieving good clinical outcomes.8 Rose et al9 demonstrated that PI, LL, and TK together can predict PSO success, and that a GSA less than 45° predicted PSO success at 2 years with high sensitivity. This study is consistent with our previous report that when LL was restored appropriately, SVA increased immediately after surgery and was maintained through the final follow-up in patients with ASD who were treated by lumbar PSO to restore sagittal malalignment.10 In this study, the postoperative sagittal lumbosacral alignment was well maintained through the follow-up period in patients both with and without pGTK. Although a significant correlation was noted between preoperative spinopelvic balance and SVA, postoperative sagittal balance had a stronger correlation with GSA and with thoracolumbar kyphosis than with spinopelvic balance. This progression of kyphosis in the unfused segments of the spine is attributed to the postoperative loss of SVA observed at the final follow-up. This study found a 16.4% incidence of PJK. Recent reviews have noted a high prevalence of PJK in posterior spinal fusion, and have described several details of the pathology of this complication.12,13,20–22 Alterations in the integrity of the posterior supraspinous and interspinous ligaments, the spinous process, and the paraspinal musculature may contribute to this phenomenon. We previously reported that PJK was present in 20% of patients who were examined 2 or more years
TABLE 5. Significant Correlation of the Magnitude of Correction of LL and pGTK pGTK P
T2–T5
T5–T12
T10–L2
LL
SS
PI
PT
GSA
PI + LL
Δ LL
−0.18
−0.09
−0.04
0.12
0.01
−0.06
−0.08
−0.01
0.08
0.34
n.s.
n.s.
n.s.
n.s.
n.s.
n.s.
n.s.
n.s.
n.s.
0.002*
*Statistically significant. n.s. indicates not significant; Δ LL, operative change of LL; GSA, global sagittal spine alignment; PI, pelvic incidence; LL, lumbar lordosis; SS, sacral slope; PT, pelvic tilt.
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TABLE 6. Unadjusted and Adjusted Risk Indicators for Postoperative GTK Progression Unadjusted OR
Adjusted OR
95% CI Valuables
OR
P
Age >75 yr
6.35
0.01
1.68
Sex (M)
6.00
0.02
LIV (pelvis)
2.64
SVA >10 cm
95% CI OR
P
23.9
5.53
0.01*
1.36
22.48
0.89
40.4
1.50
0.73
0.13
16.66
0.18
1.79
10.03
2.65
0.01*
1.51
11.04
1.98
0.21
0.68
5.79
1.12
0.91
0.12
10.44
PI + LL >30°
1.59
0.39
0.54
4.67
0.79
0.83
0.09
6.60
GSA > 60°
2.07
0.19
0.69
6.23
2.28
0.29
0.48
10.69
Lower Limit Upper Limit
Lower Limit Upper Limit
*Statistically significant. SVA indicates sagittal vertical axis; CI, confidence interval; OR, odds ratio; PI; pelvic incidence; LL, lumbar lordosis; GSA, global sagittal spine alignment; pts., patients.
CONCLUSION We present the first report of the incidence and risk factors for progression of kyphosis in unfused segments of the spine above the UIV, in patients who have undergone surgical correction for DLS. Our data indicated that a large correction in LL, a UIV below the sagittal apex, or an LIV in the region of the sacropelvis will result in progressive GTK and loss of sagittal balance after the surgical correction of DLS in elderly patients. Although our report is retrospective, and the patient cohort was neither randomized nor controlled, our results indicate that the SVA deteriorates because of progressive GTK after surgery. Long-term follow-up of this patient population will further elucidate the clinical impact of postoperative pGTK in the elderly population.
➢ Key Points Among adults treated surgically for DLS, the incidence of a postoperative progression of TK greater than 10° was 41%. Patients with pGTK experienced significantly greater loss of the SVA than patients without pGTK (4.7 vs. 1.5 cm, P = 0.02). Risk factors for postoperative progression of TK included age, sacropelvic fusion, and a greater degree of correction of LL.
5. 6. 7. 8. 9. 10.
11.
12.
13.
14.
References
1. Glassman SD, Bridwell K, Dimar JR, et al. The impact of positive sagittal balance in adult spinal deformity. Spine 2005;30:2024–9. 2. Heary RF, Kumar S, Bono CM. Decision making in adult deformity. Neurosurgery 2008;63:69–77. 3. Bridwell KH, Glassman S, Horton W, et al. Does treatment (nonoperative and operative) improve the two-year quality of life in patients with adult symptomatic lumbar scoliosis: a prospective multicenter evidence-based medicine study. Spine 2009;34: 2171–8. 4. Good CR, Lenke LG, Bridwell KH, et al. Can posterior-only surgery provide similar radiographic and clinical results as combined
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DEFORMITY 19. Bridwell KH, Lewis SJ, Rinella A, et al. Pedicle subtraction osteotomy for the treatment of fixed sagittal imbalance. Surgical technique. J Bone Joint Surg Am 2004;86-A(suppl 1):44–50. 20. 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 of follow-up. Spine 2012;37:1479–89 21. Yagi M, King A, Boachie-Adjei O. Incidence, risk factors and classification of proximal junctional kyphosis: surgical outcomes review of adult idiopathic scoliosis. Spine 2011;36:E60–8. 22. Kim HJ, Yagi M, Nyugen J, et al. Combined anterior-posterior surgery is the most important risk factor for developing proximal junctional kyphosis in idiopathic scoliosis. Clin Orthop Relat Res 2012;470:1633–9. 23. Blondel B, Schwab F, Bess S, et al. Posterior global malalignment after osteotomy for sagittal plane deformity: it happens and here is why. Spine 2013;38:E394–401.
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24. Lafage V, Ames C, Schwab F, et al. Changes in thoracic kyphosis negatively impact sagittal alignment after lumbar pedicle subtraction osteotomy: a comprehensive radiographic analysis. Spine 2012;37:E180–7. 25. 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 2006;31:2359–66. 26. Gelb DE, Lenke LG, Bridwell KH, et al. An analysis of sagittal spinal alignment in 100 asymptomatic middle and older aged volunteers. Spine 1995;20:1351–8. 27. Schwab F, Lafage V, Farcy JP, et al. Age-related correlation with spinal parameters, pelvic parameters, and foot position. Spine 2006;31:1–9 28. Vedantam R, Lenke LG, Keeney JA, et al. Comparison of standing sagittal spinal alignment in asymptomatic adolescents and adults. Spine 1998;23:211–5.
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Factors Affecting the Postoperative Progression of Thoracic Kyphosis in Surgically Treated Adult Patients With Lumbar Degenerative Scoliosis Mitsuru Yagi, MD, PhD,* Naobumi Hosogane, MD, PhD,† Eijiro Okada, MD, PhD,‡ Kota Watanabe, MD, PhD,§ Masafumi Machida, MD, PhD,* Masaki Tezuka, MD, PhD,‡ Morio Matsumoto, MD, PhD,† Takashi Asazuma, MD, PhD,* and Keio Spine Research Group¶
Study Design. A retrospective case series of patients treated surgically for degenerative lumbar scoliosis (DLS). Objective. To determine incidence and risk factors of progressive global thoracic kyphosis (pGTK) after surgery for DLS. Summary of Background Data. Sagittal balance affects the surgical treatment of spinal deformity in adults. Little is known about the loss of sagittal balance due to pGTK, or about the risk factors for pGTK, after surgery for DLS. Methods. We reviewed records from a multicenter database of adults with DLS, treated with posterior spinal fusion. Inclusion required an age of 50 years or more at the time of surgery, an upper instrumented vertebra at T9 and below, more than 5 fused segments, and at least 2 years of follow-up. We included 73 patients with a mean age of 68.3 years (range, 51–77 yr) and a mean follow-up period of 3.6 years (range, 2–11 yr). Independent risk factors for pGTK were identified by logistic regression analysis. Results. Significant pGTK, defined as an increase in thoracic kyphosis of more than 10° from before surgery to the time of final follow-up, was observed in 41% of the patients. Loss of the sagittal vertical axis was larger in patients with pGTK than without (4.7 vs. 1.5 cm; P = 0.02). Risk analysis showed larger lumbar lordosis From the *Department of Orthopedic Surgery, National Center for Musculoskeletal Disorders, Murayama Medical Center, Tokyo, Japan; †Department of Orthopedics, Keio University School of Medicine, Tokyo, Japan; ‡Department of Orthopedics, Saiseikai Central Hospital, Tokyo, Japan; §Department of Advanced Therapy for Spine and Spinal Cord Disorders, Keio University School of Medicine, Tokyo, Japan; and ¶KSRG, Tokyo, Japan. Acknowledgment date: September 13, 2013. First revision date: January 3, 2014. Acceptance date: January 9, 2014. The legal regulatory status of the device(s)/drug(s) that is/are the subject of this manuscript is not applicable in my country. No funds were received in support of this work. Relevant financial activities outside the submitted work: grants/grants pending and payment for lectures. Address correspondence and reprint requests to Mitsuru Yagi, MD, PhD, Department of Orthopedic Surgery, National Center for Musculoskeletal Disorders, Murayama Medical Center, 2-37-1 Gakuen, Musashi-Murayama City Tokyo, Japan; E-mail: [email protected] DOI: 10.1097/BRS.0000000000000226 Spine
correction in patients with pGTK. Multivariate logistic regression analysis identified an age greater than 75 (odds ratio, 5.53; P = 0.02, 95% confidence interval [1.4–22.4]) and sacropelvic fusion (odds ratio = 2.66, P = 0.02, 95% confidence interval [1.5–11.1]) as independent risk factors for pGTK. Conclusion. The pGTK incidence after surgery for DLS was 41%. Age, sacropelvic fusion, and a larger sagittal correction were identified as pGTK risk factors. Long-term follow-up will provide more data on the clinical impact of pGTK in elderly patients. Key words: degenerative scoliosis, sagittal alignment, complication. Level of Evidence: 3 Spine 2014;39:E521–E528
S
ince Glassman et al1 reported the impact of positive sagittal balance for the surgical treatment of spinal deformities in adults, sagittal balance has become recognized as the most important factor for a favorable clinical outcome.1–7 To achieve an appropriate sagittal balance, lumbar lordosis (LL) must be corrected relative to the pelvic incidence (PI).8,9 On the contrary, we previously reported that even after the appropriate restoration of LL, the sagittal vertical axis (SVA) increased immediately after surgery and that this increase was persistent through the final follow-up in patients with adult spinal deformity (ASD) after pedicle subtraction osteotomy (PSO).10 The progressive global thoracic kyphosis (pGTK) observed in patients during the surgical follow-up period in a previous study suggested that the loss of sagittal balance could be attributed to increased thoracic kyphosis (TK).10 Information about the loss of sagittal balance due to pGTK, or about the risks for unfavorable pGTK in patients with ASD, is limited. Several factors must be considered when establishing risks for pGTK, such as posterior spinal fusion, sacral fusion, and degree of correction,11–18 and the significant risk factors have not yet been fully elucidated. This study was conducted to report the incidence of pGTK after instrumented fusion surgery to correct adult www.spinejournal.com
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DEFORMITY thoracolumbar degenerative lumbar scoliosis (DLS), and to identify risk factors for pGTK.
MATERIALS AND METHODS This multicenter study was approved by the institutional review board of each participating hospital. We conducted a retrospective review of a multicenter database of prospectively collected patients with DLS who were treated with posterior correction and instrumented spinal fusion surgery. The minimum follow-up period was 2 years. To be included in the study, patients had to be older than 50 years at the time of the surgery, and the surgery had to involve the fusion of more than 5 motion segments. To assess pGTK, patients with an upper instrumented vertebra (UIV) at T8 and above were excluded. Other causes of scoliosis were ruled out through clinical examination.19 Patients with a history of adult idiopathic scoliosis, syndromic scoliosis, neuromuscular scoliosis, or a similar condition, or who had undergone any revision surgery, were excluded from this study. This review required that adequate anteroposterior and lateral standing 36-inch–long cassette radiographs be obtained before the surgery, within 8 to 12 weeks after surgery, and at the most recent follow-up. Seven patients were either lost to follow-up or had incomplete radiographs because they had left the geographic area. Five patients had left the geographic area and 2 patients had incomplete radiographs. We analyzed the preoperative and postoperative radiographical measurements, age, sex, fusion level, bone fusion, complications, and clinical outcomes for 73 patients who met the inclusion criteria.
Radiographical Measurements The SVA was measured as the distance from the C7 plumb line to the perpendicular line drawn from the superior posterior endplate of the S1 vertebral body on lateral radiographs. TK was measured from the upper endplate of T5 to the lower endplate of T12. LL was measured from the lower endplate of T12 to the upper endplate of S1. PI was measured as the angle subtended by a perpendicular line from the upper endplate of S1 and a line connecting the center of the femoral head to the center of the cephalad endplate of S1. The proximal junction was defined as the caudal endplate of the UIV to the cephalad endplate of the 2 proximal vertebrae. Abnormal proximal junctional kyphosis (PJK) was defined by a proximal junctional angle that was more than 10° and was at least 10° greater than the corresponding preoperative measurement; the presence of both criteria was necessary to be considered abnormal.20–22 Sagittal malalignment was defined as an imbalance greater than 5 cm.20–22
Surgical Procedure All patients underwent the same intraoperative technique and postoperative protocol. All patients underwent posterior spinal instrumentation and fusion with pedicle screw constructs. Fusion levels were selected by criteria that remained consistent throughout the entire study period. The UIV was chosen on the basis of the patient’s bone quality, coronal imbalance, and local sagittal alignment, along with the magnitude of the coronal E522
Progressive Postoperative Thoracic Kyphosis in DLS • Yagi et al
curve. The lower instrumented vertebra (LIV) was chosen on the basis of the status of the lumbar spine curve and the discs. If spinal stenosis, degenerative listhesis, significant obliquity, or disc degeneration were present according to the Scoliosis Research Society classifications for adult scoliosis, arthrodesis was extended to the sacrum.5 In these cases, we augmented the posterior instrumentation construct using iliac screw fixation and an anterior column support at L5–S1, in addition to bilateral or unilateral S1 screws.
Risk Factors Potential risk factors for pGTK were evaluated using the following data for each patient: age, sex, curve magnitude, LIV level, number of fused vertebrae, TK (grouped by T2– T5, T5–T12, T2–T12, and T10–L2), LL, PI, pelvic tilt (PT), spinopelvic balance (PI + LL), and global sagittal spine alignment (GSA) (TK + LL + PI).
Statistical Analysis
Ordinal and nominal data were analyzed by χ2 test when more than 5 observations were expected in the category. SVA and its correlation with sagittal parameters were analyzed by correlation coefficient test. Relationships between patient characteristics and the progression of TK were investigated by univariate and multivariate logistic regression analyses. The outcomes of interest were: (1) age, (2) sex, (3) LIV level, (4) preoperative SVA, (5) preoperative PI + LL, and (6) GSA. Patients older than 75 years were considered elderly. A preoperative SVA greater than 10 cm indicated preoperative sagittal malalignment. A preoperative PI + LL greater than 30° indicated preoperative spinopelvic malalignment. A preoperative GSA greater than 60° was considered a significant global spinal sagittal malalignment. We calculated overall summary statistics, including the means and standard deviations for continuous variables, and frequencies and percentages for categorical variables. After the descriptive analysis, independent associations between potential risk factors and pGTK were analyzed by univariate comparison. Differences between patients who developed postoperative pGTK and those who did not were evaluated using independent sample t tests for continuous variables. Differences among discrete variables were examined by the χ2 test. We created a multivariate binary logistic regression model to evaluate the adjusted associations of each potential explanatory variable and predict the likelihood of developing postoperative pGTK. Clinically relevant variables and variables with a univariate significance level of 0.25 or less were included in the multivariate logistic regression analysis. For all regression models, a P value less than 0.05 with a confidence interval of 95% was considered significant. All analyses were performed with SPSS software (IBM, Chicago, IL).
RESULTS Demographics and Radiographical Outcomes of Patients Surgically Treated for DLS This study included 67 females and 6 males. The mean age at the time of surgery was 68.3 years (range, 51–77 yr), and
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Progressive Postoperative Thoracic Kyphosis in DLS • Yagi et al
TABLE 1. The Correlation of Sagittal Parameters and SVA at Postoperative Time Period T2–T5
T5–T12
T10–L2
LL
SS
PI
PT
GSA
PI + LL
SVA
0.19
0.08
0.36
0.24
−0.26
0.18
0.53
0.34
0.25
P
n.s.
n.s.
0.006*
n.s.
n.s.
n.s.
10°
73
43
30
Immediate
5.1 (5.5)
6.1 (5.2)
4.2 (5.9)
0.23
Final
7.9 (4.3)
7.6 (4.3)
8.3 (4.4)
0.59
ΔSVA
2.9 (3.1)
1.5 (3.0)
4.7 (4.1)
0.02*
Immediate
7.1 (6.8)
7 (5.1)
7.3 (7.0)
0.54
Final
8.7 (6.1)
7.9 (5.9)
9.8 (6.8)
0.21
ΔT2–T5
1.7 (2.4)
1.0 (4.1)
2.6 (3.4)
0.10
Immediate
18.9 (16.9)
15.3 (11.4)
24 (18.8)
0.11
Final
25.2 (13.3)
18.1 (14.5)
40.3 (16.3)
10°
73
43
30
Preoperation
4.3 (6.3)
4.0 (4.1)
4.7 (7.3)
0.29
Immediate
9.6 (6.6)
8.9 (4.4)
10.7 (8.1)
0.43
Final
15.3 (5.9)
13.2 (5.2)
17.9 (7.1)
0.09
Δ1 PJK
5.7 (6.4)
4.3 (5.5)
7.2 (5.2)
0.23
Δ2 PJK
10.9 (7.9)
9.2 (7.7)
13.2 (6.2)
0.21
No. of pts.
P
PJK (°)
Values are numbers and standard deviations. Δ1 PJK indicates change of PJ angle between final follow-up and preoperation; Δ2 PJK, change of PJ angle between final follow-up and immediately after operation; PJK indicates proximal junctional kyphosis; pGTK progression of global thoracic kyphosis; pts., patients; DLS, degenerative lumbar scoliosis.
after undergoing long posterior spinal fusion for ASD.20–22 Although only 16.4% of the patients in this study met the criteria for PJK, the mean PJ angle increased significantly during the follow-up period. All the patients had a fusion level below T9, and this relatively short fusion length might affect the posterior ligamentous complex. Theoretically, progressive junctional kyphosis has a greater effect on sagittal malalignment when it affects the thoracolumbar region as opposed to the proximal thoracic region. The PJ angle increased significantly in all patients after surgery, with no significant differences between those with or without pGTK. This strong postoperative increase in the PJ angle strongly suggests the role of PJK in maintaining global sagittal alignment. These data suggest that deterioration in sagittal balance may reflect progressions of both junctional and global kyphosis in the unfused spine. Loss of sagittal balance should be monitored carefully over the long term, especially in patients with DLS treated by spinal fusion below the sagittal apex. Despite the significant loss of SVA among all patients, a patient who developed PJK and neurological deficits was the only one to complain of symptoms related to a positive SVA. This finding suggests that a positive SVA, even one as large as 8.3 cm, is sufficient to maintain a positive clinical outcome. Moreover, the SVA values at the final follow-up were similar in patients with or without pGTK. This may suggest that a positive SVA is common in elderly patients due to the reciprocal progression of TK, and that the natural sagittal balance of these patients is relatively more positive than that in a healthy young population.
We were not surprised to find a close relationship between GSA and SVA, because the maintenance of sagittal balance in healthy elderly individuals can be attributed primarily to LL loss.26–28 Schwab et al27 proposed an optimal sagittal lumbosacral alignment (LL = PI + 9°) for achieving good clinical outcomes.8 Rose et al9 demonstrated that PI, LL, and TK together can predict PSO success, and that a GSA less than 45° predicted PSO success at 2 years with high sensitivity. This study is consistent with our previous report that when LL was restored appropriately, SVA increased immediately after surgery and was maintained through the final follow-up in patients with ASD who were treated by lumbar PSO to restore sagittal malalignment.10 In this study, the postoperative sagittal lumbosacral alignment was well maintained through the follow-up period in patients both with and without pGTK. Although a significant correlation was noted between preoperative spinopelvic balance and SVA, postoperative sagittal balance had a stronger correlation with GSA and with thoracolumbar kyphosis than with spinopelvic balance. This progression of kyphosis in the unfused segments of the spine is attributed to the postoperative loss of SVA observed at the final follow-up. This study found a 16.4% incidence of PJK. Recent reviews have noted a high prevalence of PJK in posterior spinal fusion, and have described several details of the pathology of this complication.12,13,20–22 Alterations in the integrity of the posterior supraspinous and interspinous ligaments, the spinous process, and the paraspinal musculature may contribute to this phenomenon. We previously reported that PJK was present in 20% of patients who were examined 2 or more years
TABLE 5. Significant Correlation of the Magnitude of Correction of LL and pGTK pGTK P
T2–T5
T5–T12
T10–L2
LL
SS
PI
PT
GSA
PI + LL
Δ LL
−0.18
−0.09
−0.04
0.12
0.01
−0.06
−0.08
−0.01
0.08
0.34
n.s.
n.s.
n.s.
n.s.
n.s.
n.s.
n.s.
n.s.
n.s.
0.002*
*Statistically significant. n.s. indicates not significant; Δ LL, operative change of LL; GSA, global sagittal spine alignment; PI, pelvic incidence; LL, lumbar lordosis; SS, sacral slope; PT, pelvic tilt.
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Progressive Postoperative Thoracic Kyphosis in DLS • Yagi et al
TABLE 6. Unadjusted and Adjusted Risk Indicators for Postoperative GTK Progression Unadjusted OR
Adjusted OR
95% CI Valuables
OR
P
Age >75 yr
6.35
0.01
1.68
Sex (M)
6.00
0.02
LIV (pelvis)
2.64
SVA >10 cm
95% CI OR
P
23.9
5.53
0.01*
1.36
22.48
0.89
40.4
1.50
0.73
0.13
16.66
0.18
1.79
10.03
2.65
0.01*
1.51
11.04
1.98
0.21
0.68
5.79
1.12
0.91
0.12
10.44
PI + LL >30°
1.59
0.39
0.54
4.67
0.79
0.83
0.09
6.60
GSA > 60°
2.07
0.19
0.69
6.23
2.28
0.29
0.48
10.69
Lower Limit Upper Limit
Lower Limit Upper Limit
*Statistically significant. SVA indicates sagittal vertical axis; CI, confidence interval; OR, odds ratio; PI; pelvic incidence; LL, lumbar lordosis; GSA, global sagittal spine alignment; pts., patients.
CONCLUSION We present the first report of the incidence and risk factors for progression of kyphosis in unfused segments of the spine above the UIV, in patients who have undergone surgical correction for DLS. Our data indicated that a large correction in LL, a UIV below the sagittal apex, or an LIV in the region of the sacropelvis will result in progressive GTK and loss of sagittal balance after the surgical correction of DLS in elderly patients. Although our report is retrospective, and the patient cohort was neither randomized nor controlled, our results indicate that the SVA deteriorates because of progressive GTK after surgery. Long-term follow-up of this patient population will further elucidate the clinical impact of postoperative pGTK in the elderly population.
➢ Key Points Among adults treated surgically for DLS, the incidence of a postoperative progression of TK greater than 10° was 41%. Patients with pGTK experienced significantly greater loss of the SVA than patients without pGTK (4.7 vs. 1.5 cm, P = 0.02). Risk factors for postoperative progression of TK included age, sacropelvic fusion, and a greater degree of correction of LL.
5. 6. 7. 8. 9. 10.
11.
12.
13.
14.
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