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The Risk of Proximal Junctional Kyphosis Decreases in Patients With Optimal Thoracic Kyphosis
Spine Deformity 7 (2019) 759e770 www.spine-deformity.org
The Risk of Proximal Junctional Kyphosis Decreases in Patients With Optimal Thoracic Kyphosis Shin Oe, MDa,*, Daisuke Togawa, MD, PhDa, Tomohiko Hasegawa, MD, PhDb, Yu Yamato, MD, PhDb, Go Yoshida, MD, PhDb, Sho Kobayashi, MD, PhDc, Tatsuya Yasuda, MDb, Tomohiro Banno, MD, PhDb, Hideyuki Arima, MD, PhDb, Yuki Mihara, MDb, Hiroki Ushirozako, MDb, Yukihiro Matsuyama, MD, PhDb a
Department of Orthopedic Surgery and Division of Geriatric Musculoskeletal Health, Hamamatsu University School of Medicine, 1-20-1 Handayama, Higashi-ku, Hamamatsu City, Shizuoka, Japan 431-3192 b Department of Orthopedic Surgery, Hamamatsu University School of Medicine, 1-20-1 Handayama, Higashi-ku, Hamamatsu City, Shizuoka, Japan 431-3192 c Department of Orthopedic Surgery, Hamamatsu Medical Center, 3-2-8, Tomitsukacho, Naka Ward, Hamamatsu, Shizuoka Prefecture 432-8580, Japan Received 6 April 2018; revised 13 December 2018; accepted 28 December 2018
Abstract Study Design: A retrospective study of surgical outcomes. Objective: This study aimed to investigate the preoperative risk factors for proximal junctional kyphosis (PJK) in adult spinal deformity (ASD) surgery. Summary of Background Data: The cause of PJK is still unclear, although some risk factors have been reported in ASD surgery. Methods: A total of 185 patients who were followed up for more than two years and underwent ASD surgery were recruited. PJK was defined as a proximal junctional angle >20 or reoperation due to PJK within two years after surgery. These patients were divided into PJK and non-PJK groups. Whole-spine standing radiography was performed before and immediately, one year, and two years after the surgery. Results: The PJK and non-PJK groups comprised 58 and 127 cases, respectively. The incidence of PJK demonstrated significant differences according to preoperative thoracic kyphosis (TK): 37% (TK <19 ), 33% (TK 20 e29 ), 9% (TK 30 e39 ), 32% (TK 40 e49 ), and 41% (TK >50 ) (p ! .05). Logistic regression analysis suggested that the amount of change in TK before and just after the surgery (DTK) was a significant risk factor for PJK (p ! .001; odds ratio 1.062, 95% confidence interval 1.029e1.097). Conclusion: DTK was less in the TK group of 30 e39 because the TK of patients who underwent ASD surgery converged to 34.5 just after surgery. Consequently, a lower or higher TK was likely to result in a large DTK just after surgery. Therefore, patients who had an optimal TK (30 e39 ) had a lower risk of PJK. Level of Evidence: Level IV. Ó 2019 Scoliosis Research Society. All rights reserved. Keywords: Proximal junctional kyphosis; Risk factor; Thoracic kyphosis; Complication; Adult spinal deformity
Author disclosures: SO (other from Medtronic Sofamor Danec Inc., Japan Medical Dynamic Marketing, and Meitoku Medical Institution Jyuzen Memorial Hospital, outside the submitted work), DT (other from Medtronic Sofamor Danec Inc., Japan Medical Dynamic Marketing, and Meitoku Medical Institution Jyuzen Memorial Hospital, outside the submitted work), TH (none), YY (none), GY (none), SK (none), TY (none), TB (none), HA (none), YM (none), HU (none), YM (none).
IRB approval: The study protocol was approved by the institutional review board of Hamamatsu University School of Medicine, Shizuoka, Japan. *Corresponding author. Department of Orthopedic Surgery and Division of Geriatric Musculoskeletal Health, Hamamatsu University School of Medicine, 1-20-1 Handayama, Higashi-ku, Hamamatsu, Shizuoka 431-3192, Japan. Tel.: 81-53-435-2299; fax: 81-53-435-2296. E-mail address: [email protected] (S. Oe).
2212-134X/$ - see front matter Ó 2019 Scoliosis Research Society. All rights reserved. https://doi.org/10.1016/j.jspd.2018.12.007
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Introduction Proximal junctional kyphosis (PJK) was first reported by Lowe and Kasten and is considered a common complication in adult spinal deformity (ASD) surgery [1-5], with an incidence of 20% to 40% [2,3,6-12]. Glattes et al. defined PJK as a proximal junctional angle (PJA) of >10 that is at least 10 greater than the preoperative value [6]. However, Scheer et al. reported that 86.2% of the Scoliosis Research Society members considered PJK as PJA >20 [12]. This is because of the possibility that patients with a PJA of !20 are frequently less symptomatic [4,7], implying that the Glattes et al. definition of PJK may need readjustment. However, the incidence of PJK is still unclear with the definition of PJA >20 . PJK has been associated with many risk factors. A metaanalysis showed that important risk factors were age O55 years, fusion to S1, preoperative thoracic kyphosis (TK; T5eT12 angle) O40 , low bone mineral density (BMD), and sagittal vertical axis (SVA) difference O5 cm [13]. Other factors include the contouring and stiffness of the rod and the location of the upper instrumented vertebra (UIV) [14-16]. However, the mechanism of PJK is unknown, and these risk factors are also controversial. This study aimed to assess the preoperative risk factors and clinical outcomes of PJK and proximal junctional failure (PJF) using PJA >20 as the definition of PJK. However, most ASD surgeries employ spinal long fusion, and fusion to the sacrum using an iliac screw is frequently needed to correct severe lumbopelvic malalignment [17,18]. Hence, it is important that the lower instrumented vertebra (LIV) in all cases be unified with the pelvis. Thus, patients who underwent fusion to the pelvis as LIV were evaluated in a subanalysis. Materials and Methods Ethical considerations The study protocol was approved by the institutional review board of our university. Patients Between March 2010 and October 2015, a total of 282 consecutive patients who underwent ASD surgery in our hospital were recruited. ASD was defined as the presence of at least one of the following: degenerative or idiopathic scoliosis with a spinal curvature of >20 in the coronal plane, SVA >50 mm, pelvic tilt (PT) >25 , and/or TK >60 . The inclusion criteria were 1) age >18 years, 2) follow-up greater than two years or reoperation because of PJF within two years, 3) fused vertebra of five or more segments, 4) instrumentation of UIV with a pedicle screw alone, 5) availability of standing whole-spine radiographs, and 6) provision of informed consent by the patient for participation in this study. In the subanalysis, the LIVs were limited only to the ilium. The exclusion criteria were 1) the
presence of neuromuscular disease, congenital and syndromic scoliosis, infection, and spinal tumor and 2) revision surgery (rod exchange or fusion extension) to change spinal alignment, except for PJF, within two years after the primary surgery. In our surgical strategy, the UIV is generally selected as the spine beyond the apex of kyphosis or end vertebra of scoliosis. The implant of UIV was the polyaxial screw in all patients without hook or sublamina taping (wiring). The rod contouring was left to the discretion of the operator. In this study, PJF was defined as a vertebral fracture of the UIV or adjacent UIV, including screw cut-out or pull-out. The subjects were divided into two groups: the PJK group included patients who underwent reoperation for PJF within two years after the primary ASD surgery or DPJA (PJA at two years after surgery minus PJA before surgery) >20 , whereas the non-PJK (NPJK) group included patients who had DPJA !20 . Measured parameters Whole-spine radiographs were taken using 36-inch-long cassettes, with the patient in the standing position. All radiographs taken preoperatively, at the first postoperative follow-up (approximately within four weeks), and at two years after the surgery were evaluated. The measured parameters on the radiographs were 1) PT, 2) lumbar lordosis (LL), 3) pelvic incidence (PI) minus LL (PIeLL), 4) TK, 5) T1 slope (TS), 6) cervical lordosis (CL: C2eC7 angle), 7) SVA, 8) PJA (the angle between the inferior end plate of the UIV and the superior end plate two levels above the UIV), 9) functional TK (FTK; TK in the standing position minus TK in the supine position), 10) DLL (postoperative minus preoperative LL), 11) DTK (postoperative minus preoperative TK), 12) DSVA (postoperative minus preoperative SVA), and 13) DPJA (postoperative minus preoperative PJA). The amount of change (D) was defined as an absolute value. Health-related quality of life (HRQOL) was evaluated with the Oswestry Disability Index (ODI) and Scoliosis Research Societye22 (SRS-22) questionnaires. HRQOL questionnaires were evaluated preoperatively and two years after the surgery. Statistical analysis All statistical analyses (unpaired t test, analysis of variance, Tukey test, Pearson chi-squared test, Spearman rank correlation coefficient, and logistic regression analysis) were performed using SPSS version 23 (IBM-SPSS, Inc., Chicago, IL). Statistical significance was set at p ! .05. Results Main analysis As shown in Figure 1, a total of 185 patients (mean age, 61.6 years; range, 18e82) were enrolled in the main
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A total of 283 Patients Re-Operation
Parkinson disease: 29
(except for Proximal junctional failure):
Unclear X-ray: 14
Dropout: 21
Spinal tuberculosis: 3
Syndromic scoliosis:7
LIV: Lower instrumented vertebra
Death: 2
Main analysis
22
185 Pt. Lower instrumented vertebra was not ilium: 64 Pt.
Sub-analysis
121 Pt.
Fig. 1. The number of patients enrolled in main analysis and sub-analysis. A total of 185 patients were enrolled in main analysis, while 121 patients in subanalysis.
analysis. Ninety-eight patients were excluded for Parkinson disease (n 5 29), revision surgery except for PJF within two years after surgery (n 5 22), dropout (n 5 21), difficulty in evaluating radiograph (n 5 14), syndromic scoliosis (n 5 7), spinal caries (n 5 3), and death within two years after surgery (n 5 2). There were 58 and 127 patients in the PJK and NPJK group, respectively (Table 1). The incidence of PJK was 31.4%. Reoperation because of PJK was performed in 12 of the 58 patients in the PJK group. Therefore, they were excluded from the evaluation of radiographic parameters and HRQOL questionnaires at two years postoperatively.
There were no significant differences in gender, number of fused vertebrae, T score (23 and 46 patients in the PJK and NPJK group, respectively), FTK, DLL, and DSVA. However, the mean age and DTK were significantly higher in the PJK group than in the NPJK group (p ! .01). Radiographic parameters and HRQOL There was no significant difference between the preoperative radiographic parameters of the PJK and NPJK groups except for PJA (Table 2). Preoperative PJA was significantly lower in the PJK group (2.2 ) than in the NPJK group (6.1 ) (p 5 .001).
Table 1 Characteristics of patients.
No. Reop due to PJF Age Male-female No. of fused vertebrae T score (PJK-NPJK 5 23:46) FTK DLL DTK DSVA
PJK
NPJK
58 (31.4%) 12 (6.5%) 66.4 11.2 10:48 9.2 2.4 1.3 1.5 13.8 13.7 28.7 18.1 21.5 12.4 67.5 60.9
127 (68.6%) 59.4 14:113 9.2 1.8 14.7 25.8 13.4 68.3
p value
19.2 2.2 1.0 12.2 18.0 9.8 62.5
.002* .181 .942 .121 .649 .306 .000** .935
FTK, functional thoracic kyphosis; LL, lumbar lordosis; NPJK, nonproximal junctional kyphosis; PJF, proximal junctional failure; PJK, proximal junctional kyphosis; Reop, reoperation; SVA, sagittal vertical axis; TK, thoracic kyphosis; DLL, postoperative LL e preoperative LL; DSVA, postoperative SVA e preoperative SVA; DTK, postoperative TK e preoperative TK. *p ! .01; **p ! .001.
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Table 2 The comparison of radiographic parameters, Oswestry Disability Index, and SRS-22 each domain.
PT NPJK PJK LL NPJK PJK PI NPJK PJK PI-LL NPJK PJK TK NPJK PJK TS NPJK PJK CL NPJK PJK SVA NPJK PJK PJA NPJK PJK ODI NPJK PJK Fun. NPJK PJK Pain NPJK PJK Self. NPJK PJK Men. NPJK PJK Sat. NPJK PJK Total NPJK PJK
Preop
p value
Postop
p value
2 years later
p value
31.2 14.8 30.8 12.4
.832
21.6 10.0 21.6 10.6
.980
24.5 11.8 25.7 11.1
.531
23.2 24.4 18.8 25.6
.262
43.8 12.3 42.8 14.8
.637
43.1 16.8 41.2 17.3
.498
53.4 11.2 50.8 12.2
.161
52.8 10.8 51.2 12.4
.366
54.9 11.5 52.5 13.1
.220
30.1 26.8 32.0 21.8
.621
9.0 13.9 8.4 14.8
.799
11.9 18.9 11.3 17.6
.861
28.2 20.3 28.7 24.5
.894
32.5 11.4 38.9 11.9
.001**
37.2 14.1 50.6 21.8
.000***
31.0 16.2 34.2 14.7
.206
25.1 10.3 29.1 10.0
.013*
28.9 13.3 36.2 12.8
.001**
19.6 21.1 23.0 17.4
.243
14.9 16.9 19.6 16.1
.075
15.1 19.0 24.1 18.0
.004**
83.2 81.9 96.0 69.0
.303
33.0 43.0 39.5 45.0
.352
48.5 62.2 64.8 62.4
.111
6.1 7.6 2.2 6.8
.001**
10.8 7.5 17.4 10.7
.000***
13.0 7.7 29.2 11.6
.000***
38.8 21.5 46.7 20.8
.020*
26.9 21.9 32.0 20.2
.151
2.8 1.0 2.6 0.8
.082
3.5 0.9 3.1 0.9
.019*
3.1 1.0 2.8 0.9
.062
3.9 0.9 3.6 1.0
.166
2.1 0.8 2.0 0.7
.356
3.5 0.9 3.1 0.8
.006**
2.8 0.7 2.6 0.7
.049*
3.3 0.6 3.2 0.6
.280
3.6 0.9 3.4 1.0
.285
3.6 0.7 3.3 0.7
.028*
d d 2.7 0.7 2.5 0.6
d
.033*
CL, cervical lordosis; Fun., function/activity; LL, lumbar lordosis; Men., mental health; NPJK, nonproximal junctional kyphosis; ODI, Oswestry Disability Index; PI, pelvic incidence; PJA, proximal junctional angle; PJK, proximal junctional kyphosis; PT, pelvic tilt; Sat., satisfaction with management; Self., self-image/appearance; SVA, sagittal vertical axis; TK, thoracic kyphosis; TS, T1 slope. *p ! .05; **p ! .01; ***p ! .0001.
The lumbopelvic parameters (PT, LL, PI-LL) showed no significant differences between both groups just after and two years after the surgery. However, the
cervicothoracic parameters (TK, TS, and CL) showed a significant difference between both groups after the surgery. Cervicothoracic parameters were significantly
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Table 3 Characteristics of patients in subanalysis.
No. Age Reop due to PJF Male-female No. of fused vertebrae T score (PJK-NPJK 5 20:36) FTK DLL DTK DSVA
PJK
NPJK
p value
44 (36.4%) 67.9 9.5 10 (8.3%) 8:36 9.8 2.0 1.2 1.6 12.4 13.3 31.4 18.4 22.2 12.0 76.7 62.3
77 (63.6%) 67.8 10.3
.941
11:66 10.2 1.7 13.0 33.8 14.8 92.6
.575 .216 .174 .795 .491 .000* .200
2.0 1.0 10.8 18.0 9.9 66.5
FTK, functional thoracic kyphosis; LL, lumbar lordosis; NPJK, nonproximal junctional kyphosis; PJF, proximal junctional failure; PJK, proximal junctional kyphosis; Reop, reoperation; SVA, sagittal vertical axis; TK, thoracic kyphosis; DLL, postoperative LL e preoperative LL; DSVA, postoperative SVA e preoperative SVA; DTK, postoperative TK e preoperative TK. *p ! .001.
higher in the PJK group than in the NPJK group. A significant difference was not observed in SVA before, just after, and two years after the surgery. The ODI score in both groups improved at two years postoperatively but was not significantly different between the two groups. Pain, Mental health, and Satisfaction in each domain of SRS-22 also showed no significant differences between both groups two years after the surgery. However, a significant difference was observed between the PJK and NPJK groups in the Function/Activity (3.5:3.1, p 5 .019), Self-Image/Appearance (3.5:3.1, p 5 .006), and Total (3.6:3.3, p 5 .028) domains two years after the surgery. Subanalysis As shown in Figure 1, 121 patients (mean age, 67.9 years; range, 37e82) were enrolled in the subanalysis. Sixty-four patients were excluded because their LIV was not pelvic. The subanalysis included 44 and 77 patients in the PJK and NPJK group, respectively (Table 3). The incidence of PJK was 36.4%. Reoperation due to PJK was performed in 10 of 44 patients in the PJK group. There were no significant differences in mean age, gender, number of fused vertebrae, T score (20 and 36 patients in the PJK and NPJK group, respectively), FTK, DLL, and DSVA. DTK was significantly higher in the PJK group (22.2 ) than in the NPJK group (14.8 ) (p ! .001). Radiographic parameters and HRQOL in the subanalysis There was no significant difference between the preoperative radiographic parameters of the PJK and NPJK groups except for PJA, as in the main analysis (Table 4). Preoperative PJA was significantly lower in the PJK group (1.9 ) than in the NPJK group (5.9 ) (p 5 .001).
The lumbopelvic parameters (PT, LL, PI-LL) showed no significant differences between both groups just after and at two years after the surgery, as in the main analysis. Regarding the cervicothoracic parameters, TK and TS showed significant differences between both groups after the surgery, as in the main analysis. However, unlike in the main analysis, there was no significant difference between CL of the PJK and NPJK groups in the subanalysis. There was no significant difference in SVA in both groups, as in the main analysis. The ODI score in both groups improved at two years postoperatively but without statistical significance. The Function/Activity, Pain, Mental health, Satisfaction, and Total domains of SRS-22 each showed no significant difference between both groups two years after the surgery. However, the Self-image/Appearance domain demonstrated a significant difference between both groups (3.6:3.2, p 5 .010) two years after the surgery. The incidence of PJK according to the position of UIV The incidence of PJK according to the position of UIV is shown in Table 5. The position of UIV was defined as below: upper thoracic, T2eT6; middle thoracic, T7eT10; and thoracolumbar, T11eL2. The incidence of PJK in the upper thoracic group, middle thoracic group, and thoracolumbar group were 20.6% (7/34 patients), 32.4% (44/136 patients), and 46.7% (7/15 patients), respectively. There was no significant difference among these groups (p 5 .171) although upper thoracic group tended to have less incidence of PJK than other groups. The incidence of PJK and DPJA according to preoperative TK The incidence of PJK according to preoperative TK is shown in Figure 2. The incidence of PJK was 37% (27/73
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Table 4 The comparison of radiographic parameters, Oswestry Disability index, and SRS-22 each domain in subanalysis. Preop PT NPJK PJK LL NPJK PJK PI NPJK PJK PI-LL NPJK PJK TK NPJK PJK TS NPJK PJK CL NPJK PJK SVA NPJK PJK PJA NPJK PJK ODI NPJK PJK Fun. NPJK PJK Pain NPJK PJK Self. NPJK PJK Men. NPJK PJK Sat. NPJK PJK Total NPJK PJK
p value
Postop
p value
2 years later
p value
37.1 11.2 31.3 13.2
.832
20.7 8.7 19.6 10.8
.571
25.1 9.4 25.2 11.9
.950
12.1 19.5 15.5 21.1
.262
46.3 10.4 46.0 11.8
.874
45.1 10.7 44.2 13.4
.696
54.3 10.3 50.9 11.1
.090
52.9 9.6 50.6 12.3
.264
55.4 10.3 52.4 13.5
.182
42.2 21.6 35.4 20.2
.621
6.5 12.2 4.6 13.3
.437
10.4 13.2 8.2 17.2
.463
25.7 20.8 25.5 22.6
.894
34.3 11.2 40.9 10.3
.002**
41.1 13.5 53.4 22.5
.000***
34.9 16.4 33.2 14.6
.206
25.4 10.4 28.6 9.8
.106
29.7 13.4 35.0 12.4
.040*
22.9 19.5 20.3 16.5
.243
15.6 15.7 16.5 13.9
.775
15.5 18.6 22.4 17.9
.062
114.9 76.1 101.5 65.1
.303
33.5 45.6 32.5 41.3
.901
51.5 52.8 53.1 53.8
.879
.001**
11.1 7.3 17.2 11.0
.002***
14.1 7.7 29.9 12.7
.000***
5.9 8.1 1.9 7.2 44.8 17.0 46.5 18.8
.606
28.5 20.1 31.1 19.1
.511
2.5 0.8 2.6 0.7
.208
3.3 0.8 3.2 0.9
.437
3.0 0.9 2.9 0.9
.847
3.9 0.9 3.7 0.9
.540
2.0 0.8 2.1 0.7
.641
3.6 0.8 3.2 0.7
.010*
2.7 0.7 2.6 0.7
.538
3.2 0.7 3.2 0.5
.867
3.7 0.9 3.4 0.9
.164
3.5 0.7 3.3 0.6
.206
d d 2.6 0.5 2.6 0.5
d
.972
CL, cervical lordosis; Fun, function/activity; LL, lumbar lordosis; Men., mental health; NPJK, nonproximal junctional kyphosis; ODI, Oswestry Disability Index; PI, pelvic incidence; PJA, proximal junctional angle; PJK, proximal junctional kyphosis; PT, pelvic tilt; Self., Self-image/appearance; Sat., Satisfaction with management; SVA, sagittal vertical axis; TK, thoracic kyphosis; TS, T1 slope. *p ! .05; **p ! .01; ***p ! .0001. Table 5 The cross-tabulation table of the incidence of PJK according to UIV.
Upper thoracic (T2eT5) Middle thoracic (T6eT10) Thoracolumbar (T11eL2) Total
PJK (þ)
PJK ()
Total
7 44 7 58
27 92 8 127
34 136 15 185
PJK, proximal junctional kyphosis; UIV, upper instrumented vertebra. Chi-square test, p 5 .171.
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Fig. 2. The incidence of proximal junctional kyphosis (PJK) according to preoperative thoracic kyphosis (TK). The patients with preoperative TK of 30 e39 had significantly lower incidence of PJK than that in patients with TK !20 or TK >50 . The p value was .004 in TK of 0 e19 vs. 30 e39 and 0.044 in TK of 30 e39 vs. TK >50 . Table 6 The distribution of UIV among preoperative TK. Preoperative TK
<19
20 e29
30 e39
40 e49
>50
Upper thoracic (T2eT5) Middle thoracic (T6eT10) Thoracolumbar (T11eL2) Total
8 53 10 71
3 28 2 33
8 22 2 32
2 20 0 22
13 13 1 27
TK, thoracic kyphosis; UIV, upper instrumented vertebra.
patients) in TK <19 , 33.3% (10/30 patients) in TK 20 e29 , 9.1% (3/33 patients) in TK 30 e39 , 31.8% (7/ 22 patients) in TK 40 e49 , and 40.7% (11/27 patients) in TK >50 . The incidence of PJK in group TK 30 e39 was significantly lower than that in groups TK 0 e19 and >50 (p 5 .004 and .044, respectively). The distribution of UIV among preoperative TK groups is shown in Table 6. The UIV in all groups except for TK >50 tended to be placed at middle thoracic spine (T6eT10). However, The UIV could be set at the upper thoracic spine (T2eT5) in the group with TK >50 compared with other groups. The incidence of PJK (36.2%) in the TK groups outside the 30 e39 range was significantly higher than that in the
TK 30 e39 range (9.1%) according to the chi-squared test (p 5 .002), and the odds ratio (OR) was 5.67 (Table 7). DPJA according to preoperative TK is shown in Figure 3a and b. It was 13.3 in TK <19 , 12.5 in TK 20 e29 , 7.6 in TK 30 e39 , 14.7 in TK 40 e49 , and 16.7 in TK >50 . It was significantly lower in group TK 30 e39 than in groups TK 0 e19 and >50 (p 5 .021 and .038, respectively). As shown in Figure 3b, the correlation coefficient between preoperative TK and DPJA was 0.083 (p 5 .271). Moreover, in patients with preoperative TK !40 , it was 0016 (p 5 .854). However, that in patients with preoperative TK >30 revealed a weak correlation (0.248, p 5 .025).
Table 7 The cross-tabulation table of the incidence of PJK according to TK of 30 e39 or not. Not TK of 30 e39 TK of 30 e39 Total
PJK (þ)
PJK ()
Total
55 3 58
97 30 127
152 33 185
PJK, proximal junctional kyphosis; TK, thoracic kyphosis. Chi-square test, p 5 .002; odds ratio 5 5.67.
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A
B
50 45 40 35 30 25 20 15 10 5 0 -30
-20
-10
0
10
20
30
40
50
60
70
80
90
100
Pre-OP TK Fig. 3. (A) D proximal junctional angle (PJA) according to preoperative thoracic kyphosis (TK). The patients with preoperative TK of 30 e39 had significantly lower DPJA than that in patients with TK !20 or TK >50 . The p value was .021 in TK of 0 e19 vs. 30 e39 and .038 in TK of 30 e39 vs. TK >50 . (B) The boxplot of D PJA according to preoperative TK. X-axis and Y-axis shows preoperative TK and DPJA, respectively. Correlation coefficient was 0.083 (p 5 .271). Correlation coefficient among patients with preoperative TK !40 was 0.016 (p 5 .854). Correlation coefficient among patients with preoperative TK >30 was 0.248 (p 5 .025).
Table 8 The evaluation of preoperative risk factors for PJK using multiple logistic regression analysis. DTK 5 20 Difference of 10 years of age
p value
Odds ratio
95% confidence interval
.000 .011
3.562 1.362
1.914, 6.629 1.073, 1.728
PJA, proximal junctional angle; PJF, proximal junctional failure; PJK, proximal junctional kyphosis; TK, thoracic kyphosis. Dependent variables: PJK at 2 years after the surgery or reoperation within 2 years after the surgery due to PJF; Independent variables: difference of age 10 years, DTK 5 20 , preoperative PJA, TK 30 e39 , and not-TK 30 e39 .
S. Oe et al. / Spine Deformity 7 (2019) 759e770
The evaluation of preoperative risk factors for PJK using multiple logistic regression analysis Multiple logistic regression analysis was performed to identify risk factors for PJK using 185 patients (Table 8). The dependent variable was PJK at two years after surgery or reoperation within two years after surgery due to PJF, whereas the independent variable was a difference of 10 years of age, DTK 5 20 , preoperative PJA, TK 30 e39 , and not-TK 30 e39 . The significant risk factors for PJK were DTK 5 20 (p 5 .000, OR 3.562, 95% confidence interval [CI] 1.914e6.629), and a difference of 10 years of age (p 5 .011, OR 1.362, 95% CI 1.073e1.728). Discussion We assessed the preoperative risk factors and clinical outcomes of PJK and PJF after changing the definition of PJK to PJA >20 among patients who underwent ASD surgery. None of the preoperative radiographic parameters, except for PJA, was a risk factor for PJK. There was no significant difference in preoperative TK between both groups (29 and 28 in the PKJ and NPJK groups, respectively). However, as shown in Figures 2 and 3, PJK incidence and DPJA according to preoperative TK were significantly lower in patients with TK 30 e39 . Liu et al., in their meta-analysis, suggested that TK O40 was a significant risk factor for PJK [13]. In patients with a hyperkyphotic thoracic spine, the compensatory mechanism often fails because their back muscles are weak. Therefore, PJK may be caused by a re-increase in TK because of poor muscle strength after surgery. However, studies do not indicate that a lower preoperative TK is also a risk factor for PJK. Figure 4 shows how the preoperative TK of each
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parameter changed after surgery. TK changed from 28 21.7 before surgery to 34.5 11.9 after surgery. The standard deviation decreased after the surgery and most cases including cases with high or low TK converged to a TK of approximately 34.5 . Therefore, patients with a higher or lower TK demonstrated a significant DTK after the surgery. Patients with preoperative TK !20 or O50 had a significantly larger DTK compared with other patients (p ! .05) (Figure 5a and b). Our findings demonstrated that DTK is increased not only in patients with high preoperative TK but also in patients with low preoperative TK. As shown in Figure 5b, correlation coefficient between preoperative TK and DTK was 0.549, p 5 .000, in preoperative TK !40 and 0.455, p 5 .000, in preoperative TK >30 . Figure 6 shows the mechanism behind the development of PJK in patients with a lower TK. ASD patients have lumbar and pelvic sagittal malalignment and these alignment changes cause thoracic spineecompensated change (lower TK). However, TK and PJA, in patients with lower TK (compensated TK), increase over time because lumbopelvic malalignment (compensated change) is improved postoperatively. This causes mechanical stress on the UIV. One of our patients is shown in Figure 7. She was 75 years old and had a thoracic spine with compensated change (TK of 5 ). Her TK increased to 32 after the surgery because her lumbopelvic alignment improved. However, PJK (UIV fracture) occurred 1 month later. Her TK gradually increased to 72 . Finally, she underwent revision surgery one year after the surgery. The preoperative PJA in the PJK group was significantly lower than that in the NPJK group, suggesting that a compensated thoracic spine (with a change in lordosis) is a risk factor for PJK. The optimal preoperative TK experienced less change, even if the lumbopelvic parameter
Pre-OP Mean TK 28 21.7
Post-OP Mean TK 34.5 11.9
Fig. 4. The change of thoracic kyphosis (TK) of each case before and after the surgery. The TK changed from 28 21.7 before surgery to 34.5 11.9 after surgery. The standard deviation decreased after the surgery, and almost cases including cases with high TK or low TK converged to TK of around 34.5 .
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A
B
Fig. 5. (A) D thoracic kyphosis (TK) according to preoperative TK. DTK in patients with TK !20 or TK >50 was significantly larger than that in patients with TK of 20 e29 , 30 e39 , and 40 e49 . The p value was .000 in TK of 0 e19 vs. 20 e29 , 30 e39 , and 40 e49 , .048 in TK of 20 e29 vs. TK >50, .001 in TK of 30 e39 vs. TK>50, and .001 in TK of 40 e49 vs. TK >50 . (B) The boxplot of D thoracic kyphosis (TK) according to preoperative TK. X-axis and Y-axis shows preoperative TK and DTK, respectively. Correlation coefficient was 0.121 (p 5 .106). Correlation coefficient among patients with preoperative TK !40 was 0.549 (p 5 .000). Correlation coefficient among patients with preoperative TK >30 was 0.455 (p 5 .000).
changed postoperatively. Therefore, the UIV was under less mechanical stress. The evaluation of HRQOL in the main analysis suggested that the SRS-22 domains of Function/Activity, Selfimage/Appearance, and Total were significantly lower in the PJK group than in the NPJK group. Moreover, the domain of Self-image/Appearance in the PJK group was also significantly lower in the subanalysis that excluded the influence of age and LIV. This study showed that PJK or PJF influenced HRQOL, in particular, the SRS-22 domain of Self-image/Appearance. Kim et al. [7] also reported that the SRS-22 Self-image domain was lower when patients
had PJA O20 . Therefore, it is important to prevent PJK or PJF. However, low BMD and DSVA, which were the risk factors for PJK in the report by Liu et al. [13], showed no significant differences between the PJK and NPJK groups in our study. The risk factors for PJK are still unclear. Based on our results, the PJK incidence rate was significantly higher in patients with TK !20 or O50 than in those with TK 30 e39 , which is considered to be caused by the large DTK. Therefore, extending the fixed range to suppress the increase of DTK may lead to the prevention of PJK. Soroceanu et al. [19] reported that patients with UIV in the upper thoracic spine had less implant failure
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Fig. 6. The mechanism of proximal junctional kyphosis and the change of spinal sagittal alignment before and after surgery in patients with lower thoracic kyphosis (TK). TK and proximal junctional angle (PJA) in the patients with lower TK (compensated TK) increased to regain kyphosis in the thoracic spine after the surgery because lumbo-pelvic malalignment improved postoperatively. This caused large mechanical stress on the upper instrumented vertebra (UIV).
compared with others. However, this finding is still controversial because Kim et al. reported that the prevalence of PJK was not different when UIV was fused at the upper thoracic and lower thoracic spine [20]. The present study also could not prove the relationship between UIV level and the incidence of PJK (Tables 5 and 6).
This study had several limitations. First, 23 and 46 patients in the PJK and NPJK group, respectively, had their T score evaluated in the main analysis, although our study concluded that BMD was not associated with the incidence of PJK. Second, although our study stated that the postoperative TK of patients undergoing ASD surgery
Fig. 7. Case presentation in patients with lower thoracic kyphosis (TK). She was 75 years old female who had thoracic spine with compensated change (TK of 5 ). Her TK increased to 32 after the surgery because her lumbo-pelvic alignment got better. However, PJK (upper instrumented vertebral fracture) happen to her 1 months later. Her TK gradually increased to 72 . Finally, she had re-surgery 1 year after the surgery.
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converged to approximately 34.5 , in practice, individualdependent differences in TK may occur. The convergence to a postoperative TK of approximately 34.5 may be related to the average TK of 33.6 noted in Japanese persons older than 50 years [21]. Third, in the main analysis, a significant difference was observed in the domain of Function/Activity, Self-Image/Appearance, and Total in SRS-22 at two years after the surgery, but this result did not exclude the effect of the difference in age between the PJK and NPJK groups. Therefore, considering the subanalysis that excluded the influence of age, the SRS-22 domain that significantly deteriorated because of PJK might be SelfImage alone. Fourth, preoperative TK was not a controllable parameter. Therefore, this study did not show its prevention but the mechanism of PJK. Further study is necessary to prevent it. Finally, the small sample size, multiple comparisons of evaluated parameters, and many dropouts in this study might have resulted in statistical bias and noise. Conclusion This study suggests that the incidence of PJK or PJF significantly increases not only in patients with a high preoperative TK (>50 ) but also in patients with a low preoperative TK (!20 ), compared with patients with a TK of 30 e39 . The cause of PJK was considered to be a large change in TK before and after surgery. Moreover, PJK led to a significant deterioration in the domains of Function/ Activity, Self-Image/Appearance, and Total in SRS-22. Considering these factors during patient management may help to prevent PJK or PJF. Key points The incidence of PJK or PJF significantly increases not only in patients with high preoperative TK (O50 ) but also in patients with low preoperative TK (!20 ) compared with patients with TK of 30 e39 . The cause and mechanism of PJK was considered to be a large change in TK before and after surgery. PJK significantly deteriorated the domains of Function/Activity, Self-Image/Appearance, and Total in SRS-22. References [1] 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 1994;19: 1680e5. [2] Kim HJ, Bridwell KH, Lenke LG, et al. Proximal junctional kyphosis results in inferior SRS pain subscores in adult deformity patients. Spine 2013;38:896e901.
[3] 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;37:1479e89. [4] Bridwell KH, Lenke LG, Cho SK, et al. Proximal junctional kyphosis in primary adult deformity surgery: evaluation of 20 degrees as a critical angle. Neurosurgery 2013;72:899e906. [5] Kim HJ, Lenke LG, Shaffrey CI, et al. Proximal junctional kyphosis as a distinct form of adjacent segment pathology after spinal deformity surgery: a systematic review. Spine 2012;37:S144e64. [6] 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 2005;30:1643e9. [7] 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 2008;33: 2179e84. [8] Maruo K, Ha Y, Inoue S, et al. Predictive factors for proximal junctional kyphosis in long fusions to the sacrum in adult spinal deformity. Spine 2013;38:E1469e76. [9] Wang J, Zhao Y, Shen B, et al. Risk factor analysis of proximal junctional kyphosis after posterior fusion in patients with idiopathic scoliosis. Injury 2010;41:415e20. [10] Yagi M, Akilah KB, Boachie-Adjei O. Incidence, risk factors and classification of proximal junctional kyphosis: surgical outcomes review of adult idiopathic scoliosis. Spine 2011;36:E60e8. [11] 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;470:1633e9. [12] Scheer JK, Fakurnejad S, Lau D, et al. Results of the 2014 SRS Survey on PJK/PJF: a report on variation of select SRS member practice patterns, treatment indications, and opinions on classification development. Spine 2015;40:829e40. [13] Liu FY, Wang T, Yang SD, et al. Incidence and risk factors for proximal junctional kyphosis: a meta-analysis. Eur Spine J 2016;25:2376e83. [14] Yan P, Bao H, Qiu Y, et al. Mismatch between proximal rod contouring and proximal junctional angle: a predisposed risk factor for proximal junctional kyphosis in degenerative scoliosis. Spine 2017;42:E280e7. [15] Han S, Hyun SJ, Kim KJ, et al. Rod stiffness as a risk factor of proximal junctional kyphosis after adult spinal deformity surgery: comparative study between cobalt chrome multiple-rod constructs and titanium alloy two-rod constructs. Spine J 2017;17:962e8. [16] Hey HWD, Tan KA, Neo CS, et al. T9 versus T10 as the upper instrumented vertebra for correction of adult deformity-rationale and recommendations. Spine J 2017;17:615e21. [17] Shen FH, Mason JR, Shimer AL, et al. Pelvic fixation for adult scoliosis. Eur Spine J 2013;22(suppl 2):S265e75. [18] Kebaish KM. Sacropelvic fixation: techniques and complications. Spine 2010;35:2245e51. [19] Soroceanu A, Diebo BG, Burton D, et al. Radiographical and implant-related complications in adult spinal deformity surgery: incidence, patient risk factors, and impact on health-related quality of life. Spine 2015;40:1414e21. [20] Kim HJ, Boachie-Adjei O, Shaffrey CI, et al. Upper thoracic versus lower thoracic upper instrumented vertebrae endpoints have similar outcomes and complications in adult scoliosis. Spine 2014;39: E795e9. [21] Oe S, Togawa D, Nakai K, et al. The influence of age and sex on cervical spinal alignment among volunteers aged over 50. Spine 2015;40:1487e94.
The Risk of Proximal Junctional Kyphosis Decreases in Patients With Optimal Thoracic Kyphosis Shin Oe, MDa,*, Daisuke Togawa, MD, PhDa, Tomohiko Hasegawa, MD, PhDb, Yu Yamato, MD, PhDb, Go Yoshida, MD, PhDb, Sho Kobayashi, MD, PhDc, Tatsuya Yasuda, MDb, Tomohiro Banno, MD, PhDb, Hideyuki Arima, MD, PhDb, Yuki Mihara, MDb, Hiroki Ushirozako, MDb, Yukihiro Matsuyama, MD, PhDb a
Department of Orthopedic Surgery and Division of Geriatric Musculoskeletal Health, Hamamatsu University School of Medicine, 1-20-1 Handayama, Higashi-ku, Hamamatsu City, Shizuoka, Japan 431-3192 b Department of Orthopedic Surgery, Hamamatsu University School of Medicine, 1-20-1 Handayama, Higashi-ku, Hamamatsu City, Shizuoka, Japan 431-3192 c Department of Orthopedic Surgery, Hamamatsu Medical Center, 3-2-8, Tomitsukacho, Naka Ward, Hamamatsu, Shizuoka Prefecture 432-8580, Japan Received 6 April 2018; revised 13 December 2018; accepted 28 December 2018
Abstract Study Design: A retrospective study of surgical outcomes. Objective: This study aimed to investigate the preoperative risk factors for proximal junctional kyphosis (PJK) in adult spinal deformity (ASD) surgery. Summary of Background Data: The cause of PJK is still unclear, although some risk factors have been reported in ASD surgery. Methods: A total of 185 patients who were followed up for more than two years and underwent ASD surgery were recruited. PJK was defined as a proximal junctional angle >20 or reoperation due to PJK within two years after surgery. These patients were divided into PJK and non-PJK groups. Whole-spine standing radiography was performed before and immediately, one year, and two years after the surgery. Results: The PJK and non-PJK groups comprised 58 and 127 cases, respectively. The incidence of PJK demonstrated significant differences according to preoperative thoracic kyphosis (TK): 37% (TK <19 ), 33% (TK 20 e29 ), 9% (TK 30 e39 ), 32% (TK 40 e49 ), and 41% (TK >50 ) (p ! .05). Logistic regression analysis suggested that the amount of change in TK before and just after the surgery (DTK) was a significant risk factor for PJK (p ! .001; odds ratio 1.062, 95% confidence interval 1.029e1.097). Conclusion: DTK was less in the TK group of 30 e39 because the TK of patients who underwent ASD surgery converged to 34.5 just after surgery. Consequently, a lower or higher TK was likely to result in a large DTK just after surgery. Therefore, patients who had an optimal TK (30 e39 ) had a lower risk of PJK. Level of Evidence: Level IV. Ó 2019 Scoliosis Research Society. All rights reserved. Keywords: Proximal junctional kyphosis; Risk factor; Thoracic kyphosis; Complication; Adult spinal deformity
Author disclosures: SO (other from Medtronic Sofamor Danec Inc., Japan Medical Dynamic Marketing, and Meitoku Medical Institution Jyuzen Memorial Hospital, outside the submitted work), DT (other from Medtronic Sofamor Danec Inc., Japan Medical Dynamic Marketing, and Meitoku Medical Institution Jyuzen Memorial Hospital, outside the submitted work), TH (none), YY (none), GY (none), SK (none), TY (none), TB (none), HA (none), YM (none), HU (none), YM (none).
IRB approval: The study protocol was approved by the institutional review board of Hamamatsu University School of Medicine, Shizuoka, Japan. *Corresponding author. Department of Orthopedic Surgery and Division of Geriatric Musculoskeletal Health, Hamamatsu University School of Medicine, 1-20-1 Handayama, Higashi-ku, Hamamatsu, Shizuoka 431-3192, Japan. Tel.: 81-53-435-2299; fax: 81-53-435-2296. E-mail address: [email protected] (S. Oe).
2212-134X/$ - see front matter Ó 2019 Scoliosis Research Society. All rights reserved. https://doi.org/10.1016/j.jspd.2018.12.007
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Introduction Proximal junctional kyphosis (PJK) was first reported by Lowe and Kasten and is considered a common complication in adult spinal deformity (ASD) surgery [1-5], with an incidence of 20% to 40% [2,3,6-12]. Glattes et al. defined PJK as a proximal junctional angle (PJA) of >10 that is at least 10 greater than the preoperative value [6]. However, Scheer et al. reported that 86.2% of the Scoliosis Research Society members considered PJK as PJA >20 [12]. This is because of the possibility that patients with a PJA of !20 are frequently less symptomatic [4,7], implying that the Glattes et al. definition of PJK may need readjustment. However, the incidence of PJK is still unclear with the definition of PJA >20 . PJK has been associated with many risk factors. A metaanalysis showed that important risk factors were age O55 years, fusion to S1, preoperative thoracic kyphosis (TK; T5eT12 angle) O40 , low bone mineral density (BMD), and sagittal vertical axis (SVA) difference O5 cm [13]. Other factors include the contouring and stiffness of the rod and the location of the upper instrumented vertebra (UIV) [14-16]. However, the mechanism of PJK is unknown, and these risk factors are also controversial. This study aimed to assess the preoperative risk factors and clinical outcomes of PJK and proximal junctional failure (PJF) using PJA >20 as the definition of PJK. However, most ASD surgeries employ spinal long fusion, and fusion to the sacrum using an iliac screw is frequently needed to correct severe lumbopelvic malalignment [17,18]. Hence, it is important that the lower instrumented vertebra (LIV) in all cases be unified with the pelvis. Thus, patients who underwent fusion to the pelvis as LIV were evaluated in a subanalysis. Materials and Methods Ethical considerations The study protocol was approved by the institutional review board of our university. Patients Between March 2010 and October 2015, a total of 282 consecutive patients who underwent ASD surgery in our hospital were recruited. ASD was defined as the presence of at least one of the following: degenerative or idiopathic scoliosis with a spinal curvature of >20 in the coronal plane, SVA >50 mm, pelvic tilt (PT) >25 , and/or TK >60 . The inclusion criteria were 1) age >18 years, 2) follow-up greater than two years or reoperation because of PJF within two years, 3) fused vertebra of five or more segments, 4) instrumentation of UIV with a pedicle screw alone, 5) availability of standing whole-spine radiographs, and 6) provision of informed consent by the patient for participation in this study. In the subanalysis, the LIVs were limited only to the ilium. The exclusion criteria were 1) the
presence of neuromuscular disease, congenital and syndromic scoliosis, infection, and spinal tumor and 2) revision surgery (rod exchange or fusion extension) to change spinal alignment, except for PJF, within two years after the primary surgery. In our surgical strategy, the UIV is generally selected as the spine beyond the apex of kyphosis or end vertebra of scoliosis. The implant of UIV was the polyaxial screw in all patients without hook or sublamina taping (wiring). The rod contouring was left to the discretion of the operator. In this study, PJF was defined as a vertebral fracture of the UIV or adjacent UIV, including screw cut-out or pull-out. The subjects were divided into two groups: the PJK group included patients who underwent reoperation for PJF within two years after the primary ASD surgery or DPJA (PJA at two years after surgery minus PJA before surgery) >20 , whereas the non-PJK (NPJK) group included patients who had DPJA !20 . Measured parameters Whole-spine radiographs were taken using 36-inch-long cassettes, with the patient in the standing position. All radiographs taken preoperatively, at the first postoperative follow-up (approximately within four weeks), and at two years after the surgery were evaluated. The measured parameters on the radiographs were 1) PT, 2) lumbar lordosis (LL), 3) pelvic incidence (PI) minus LL (PIeLL), 4) TK, 5) T1 slope (TS), 6) cervical lordosis (CL: C2eC7 angle), 7) SVA, 8) PJA (the angle between the inferior end plate of the UIV and the superior end plate two levels above the UIV), 9) functional TK (FTK; TK in the standing position minus TK in the supine position), 10) DLL (postoperative minus preoperative LL), 11) DTK (postoperative minus preoperative TK), 12) DSVA (postoperative minus preoperative SVA), and 13) DPJA (postoperative minus preoperative PJA). The amount of change (D) was defined as an absolute value. Health-related quality of life (HRQOL) was evaluated with the Oswestry Disability Index (ODI) and Scoliosis Research Societye22 (SRS-22) questionnaires. HRQOL questionnaires were evaluated preoperatively and two years after the surgery. Statistical analysis All statistical analyses (unpaired t test, analysis of variance, Tukey test, Pearson chi-squared test, Spearman rank correlation coefficient, and logistic regression analysis) were performed using SPSS version 23 (IBM-SPSS, Inc., Chicago, IL). Statistical significance was set at p ! .05. Results Main analysis As shown in Figure 1, a total of 185 patients (mean age, 61.6 years; range, 18e82) were enrolled in the main
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A total of 283 Patients Re-Operation
Parkinson disease: 29
(except for Proximal junctional failure):
Unclear X-ray: 14
Dropout: 21
Spinal tuberculosis: 3
Syndromic scoliosis:7
LIV: Lower instrumented vertebra
Death: 2
Main analysis
22
185 Pt. Lower instrumented vertebra was not ilium: 64 Pt.
Sub-analysis
121 Pt.
Fig. 1. The number of patients enrolled in main analysis and sub-analysis. A total of 185 patients were enrolled in main analysis, while 121 patients in subanalysis.
analysis. Ninety-eight patients were excluded for Parkinson disease (n 5 29), revision surgery except for PJF within two years after surgery (n 5 22), dropout (n 5 21), difficulty in evaluating radiograph (n 5 14), syndromic scoliosis (n 5 7), spinal caries (n 5 3), and death within two years after surgery (n 5 2). There were 58 and 127 patients in the PJK and NPJK group, respectively (Table 1). The incidence of PJK was 31.4%. Reoperation because of PJK was performed in 12 of the 58 patients in the PJK group. Therefore, they were excluded from the evaluation of radiographic parameters and HRQOL questionnaires at two years postoperatively.
There were no significant differences in gender, number of fused vertebrae, T score (23 and 46 patients in the PJK and NPJK group, respectively), FTK, DLL, and DSVA. However, the mean age and DTK were significantly higher in the PJK group than in the NPJK group (p ! .01). Radiographic parameters and HRQOL There was no significant difference between the preoperative radiographic parameters of the PJK and NPJK groups except for PJA (Table 2). Preoperative PJA was significantly lower in the PJK group (2.2 ) than in the NPJK group (6.1 ) (p 5 .001).
Table 1 Characteristics of patients.
No. Reop due to PJF Age Male-female No. of fused vertebrae T score (PJK-NPJK 5 23:46) FTK DLL DTK DSVA
PJK
NPJK
58 (31.4%) 12 (6.5%) 66.4 11.2 10:48 9.2 2.4 1.3 1.5 13.8 13.7 28.7 18.1 21.5 12.4 67.5 60.9
127 (68.6%) 59.4 14:113 9.2 1.8 14.7 25.8 13.4 68.3
p value
19.2 2.2 1.0 12.2 18.0 9.8 62.5
.002* .181 .942 .121 .649 .306 .000** .935
FTK, functional thoracic kyphosis; LL, lumbar lordosis; NPJK, nonproximal junctional kyphosis; PJF, proximal junctional failure; PJK, proximal junctional kyphosis; Reop, reoperation; SVA, sagittal vertical axis; TK, thoracic kyphosis; DLL, postoperative LL e preoperative LL; DSVA, postoperative SVA e preoperative SVA; DTK, postoperative TK e preoperative TK. *p ! .01; **p ! .001.
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Table 2 The comparison of radiographic parameters, Oswestry Disability Index, and SRS-22 each domain.
PT NPJK PJK LL NPJK PJK PI NPJK PJK PI-LL NPJK PJK TK NPJK PJK TS NPJK PJK CL NPJK PJK SVA NPJK PJK PJA NPJK PJK ODI NPJK PJK Fun. NPJK PJK Pain NPJK PJK Self. NPJK PJK Men. NPJK PJK Sat. NPJK PJK Total NPJK PJK
Preop
p value
Postop
p value
2 years later
p value
31.2 14.8 30.8 12.4
.832
21.6 10.0 21.6 10.6
.980
24.5 11.8 25.7 11.1
.531
23.2 24.4 18.8 25.6
.262
43.8 12.3 42.8 14.8
.637
43.1 16.8 41.2 17.3
.498
53.4 11.2 50.8 12.2
.161
52.8 10.8 51.2 12.4
.366
54.9 11.5 52.5 13.1
.220
30.1 26.8 32.0 21.8
.621
9.0 13.9 8.4 14.8
.799
11.9 18.9 11.3 17.6
.861
28.2 20.3 28.7 24.5
.894
32.5 11.4 38.9 11.9
.001**
37.2 14.1 50.6 21.8
.000***
31.0 16.2 34.2 14.7
.206
25.1 10.3 29.1 10.0
.013*
28.9 13.3 36.2 12.8
.001**
19.6 21.1 23.0 17.4
.243
14.9 16.9 19.6 16.1
.075
15.1 19.0 24.1 18.0
.004**
83.2 81.9 96.0 69.0
.303
33.0 43.0 39.5 45.0
.352
48.5 62.2 64.8 62.4
.111
6.1 7.6 2.2 6.8
.001**
10.8 7.5 17.4 10.7
.000***
13.0 7.7 29.2 11.6
.000***
38.8 21.5 46.7 20.8
.020*
26.9 21.9 32.0 20.2
.151
2.8 1.0 2.6 0.8
.082
3.5 0.9 3.1 0.9
.019*
3.1 1.0 2.8 0.9
.062
3.9 0.9 3.6 1.0
.166
2.1 0.8 2.0 0.7
.356
3.5 0.9 3.1 0.8
.006**
2.8 0.7 2.6 0.7
.049*
3.3 0.6 3.2 0.6
.280
3.6 0.9 3.4 1.0
.285
3.6 0.7 3.3 0.7
.028*
d d 2.7 0.7 2.5 0.6
d
.033*
CL, cervical lordosis; Fun., function/activity; LL, lumbar lordosis; Men., mental health; NPJK, nonproximal junctional kyphosis; ODI, Oswestry Disability Index; PI, pelvic incidence; PJA, proximal junctional angle; PJK, proximal junctional kyphosis; PT, pelvic tilt; Sat., satisfaction with management; Self., self-image/appearance; SVA, sagittal vertical axis; TK, thoracic kyphosis; TS, T1 slope. *p ! .05; **p ! .01; ***p ! .0001.
The lumbopelvic parameters (PT, LL, PI-LL) showed no significant differences between both groups just after and two years after the surgery. However, the
cervicothoracic parameters (TK, TS, and CL) showed a significant difference between both groups after the surgery. Cervicothoracic parameters were significantly
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763
Table 3 Characteristics of patients in subanalysis.
No. Age Reop due to PJF Male-female No. of fused vertebrae T score (PJK-NPJK 5 20:36) FTK DLL DTK DSVA
PJK
NPJK
p value
44 (36.4%) 67.9 9.5 10 (8.3%) 8:36 9.8 2.0 1.2 1.6 12.4 13.3 31.4 18.4 22.2 12.0 76.7 62.3
77 (63.6%) 67.8 10.3
.941
11:66 10.2 1.7 13.0 33.8 14.8 92.6
.575 .216 .174 .795 .491 .000* .200
2.0 1.0 10.8 18.0 9.9 66.5
FTK, functional thoracic kyphosis; LL, lumbar lordosis; NPJK, nonproximal junctional kyphosis; PJF, proximal junctional failure; PJK, proximal junctional kyphosis; Reop, reoperation; SVA, sagittal vertical axis; TK, thoracic kyphosis; DLL, postoperative LL e preoperative LL; DSVA, postoperative SVA e preoperative SVA; DTK, postoperative TK e preoperative TK. *p ! .001.
higher in the PJK group than in the NPJK group. A significant difference was not observed in SVA before, just after, and two years after the surgery. The ODI score in both groups improved at two years postoperatively but was not significantly different between the two groups. Pain, Mental health, and Satisfaction in each domain of SRS-22 also showed no significant differences between both groups two years after the surgery. However, a significant difference was observed between the PJK and NPJK groups in the Function/Activity (3.5:3.1, p 5 .019), Self-Image/Appearance (3.5:3.1, p 5 .006), and Total (3.6:3.3, p 5 .028) domains two years after the surgery. Subanalysis As shown in Figure 1, 121 patients (mean age, 67.9 years; range, 37e82) were enrolled in the subanalysis. Sixty-four patients were excluded because their LIV was not pelvic. The subanalysis included 44 and 77 patients in the PJK and NPJK group, respectively (Table 3). The incidence of PJK was 36.4%. Reoperation due to PJK was performed in 10 of 44 patients in the PJK group. There were no significant differences in mean age, gender, number of fused vertebrae, T score (20 and 36 patients in the PJK and NPJK group, respectively), FTK, DLL, and DSVA. DTK was significantly higher in the PJK group (22.2 ) than in the NPJK group (14.8 ) (p ! .001). Radiographic parameters and HRQOL in the subanalysis There was no significant difference between the preoperative radiographic parameters of the PJK and NPJK groups except for PJA, as in the main analysis (Table 4). Preoperative PJA was significantly lower in the PJK group (1.9 ) than in the NPJK group (5.9 ) (p 5 .001).
The lumbopelvic parameters (PT, LL, PI-LL) showed no significant differences between both groups just after and at two years after the surgery, as in the main analysis. Regarding the cervicothoracic parameters, TK and TS showed significant differences between both groups after the surgery, as in the main analysis. However, unlike in the main analysis, there was no significant difference between CL of the PJK and NPJK groups in the subanalysis. There was no significant difference in SVA in both groups, as in the main analysis. The ODI score in both groups improved at two years postoperatively but without statistical significance. The Function/Activity, Pain, Mental health, Satisfaction, and Total domains of SRS-22 each showed no significant difference between both groups two years after the surgery. However, the Self-image/Appearance domain demonstrated a significant difference between both groups (3.6:3.2, p 5 .010) two years after the surgery. The incidence of PJK according to the position of UIV The incidence of PJK according to the position of UIV is shown in Table 5. The position of UIV was defined as below: upper thoracic, T2eT6; middle thoracic, T7eT10; and thoracolumbar, T11eL2. The incidence of PJK in the upper thoracic group, middle thoracic group, and thoracolumbar group were 20.6% (7/34 patients), 32.4% (44/136 patients), and 46.7% (7/15 patients), respectively. There was no significant difference among these groups (p 5 .171) although upper thoracic group tended to have less incidence of PJK than other groups. The incidence of PJK and DPJA according to preoperative TK The incidence of PJK according to preoperative TK is shown in Figure 2. The incidence of PJK was 37% (27/73
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Table 4 The comparison of radiographic parameters, Oswestry Disability index, and SRS-22 each domain in subanalysis. Preop PT NPJK PJK LL NPJK PJK PI NPJK PJK PI-LL NPJK PJK TK NPJK PJK TS NPJK PJK CL NPJK PJK SVA NPJK PJK PJA NPJK PJK ODI NPJK PJK Fun. NPJK PJK Pain NPJK PJK Self. NPJK PJK Men. NPJK PJK Sat. NPJK PJK Total NPJK PJK
p value
Postop
p value
2 years later
p value
37.1 11.2 31.3 13.2
.832
20.7 8.7 19.6 10.8
.571
25.1 9.4 25.2 11.9
.950
12.1 19.5 15.5 21.1
.262
46.3 10.4 46.0 11.8
.874
45.1 10.7 44.2 13.4
.696
54.3 10.3 50.9 11.1
.090
52.9 9.6 50.6 12.3
.264
55.4 10.3 52.4 13.5
.182
42.2 21.6 35.4 20.2
.621
6.5 12.2 4.6 13.3
.437
10.4 13.2 8.2 17.2
.463
25.7 20.8 25.5 22.6
.894
34.3 11.2 40.9 10.3
.002**
41.1 13.5 53.4 22.5
.000***
34.9 16.4 33.2 14.6
.206
25.4 10.4 28.6 9.8
.106
29.7 13.4 35.0 12.4
.040*
22.9 19.5 20.3 16.5
.243
15.6 15.7 16.5 13.9
.775
15.5 18.6 22.4 17.9
.062
114.9 76.1 101.5 65.1
.303
33.5 45.6 32.5 41.3
.901
51.5 52.8 53.1 53.8
.879
.001**
11.1 7.3 17.2 11.0
.002***
14.1 7.7 29.9 12.7
.000***
5.9 8.1 1.9 7.2 44.8 17.0 46.5 18.8
.606
28.5 20.1 31.1 19.1
.511
2.5 0.8 2.6 0.7
.208
3.3 0.8 3.2 0.9
.437
3.0 0.9 2.9 0.9
.847
3.9 0.9 3.7 0.9
.540
2.0 0.8 2.1 0.7
.641
3.6 0.8 3.2 0.7
.010*
2.7 0.7 2.6 0.7
.538
3.2 0.7 3.2 0.5
.867
3.7 0.9 3.4 0.9
.164
3.5 0.7 3.3 0.6
.206
d d 2.6 0.5 2.6 0.5
d
.972
CL, cervical lordosis; Fun, function/activity; LL, lumbar lordosis; Men., mental health; NPJK, nonproximal junctional kyphosis; ODI, Oswestry Disability Index; PI, pelvic incidence; PJA, proximal junctional angle; PJK, proximal junctional kyphosis; PT, pelvic tilt; Self., Self-image/appearance; Sat., Satisfaction with management; SVA, sagittal vertical axis; TK, thoracic kyphosis; TS, T1 slope. *p ! .05; **p ! .01; ***p ! .0001. Table 5 The cross-tabulation table of the incidence of PJK according to UIV.
Upper thoracic (T2eT5) Middle thoracic (T6eT10) Thoracolumbar (T11eL2) Total
PJK (þ)
PJK ()
Total
7 44 7 58
27 92 8 127
34 136 15 185
PJK, proximal junctional kyphosis; UIV, upper instrumented vertebra. Chi-square test, p 5 .171.
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Fig. 2. The incidence of proximal junctional kyphosis (PJK) according to preoperative thoracic kyphosis (TK). The patients with preoperative TK of 30 e39 had significantly lower incidence of PJK than that in patients with TK !20 or TK >50 . The p value was .004 in TK of 0 e19 vs. 30 e39 and 0.044 in TK of 30 e39 vs. TK >50 . Table 6 The distribution of UIV among preoperative TK. Preoperative TK
<19
20 e29
30 e39
40 e49
>50
Upper thoracic (T2eT5) Middle thoracic (T6eT10) Thoracolumbar (T11eL2) Total
8 53 10 71
3 28 2 33
8 22 2 32
2 20 0 22
13 13 1 27
TK, thoracic kyphosis; UIV, upper instrumented vertebra.
patients) in TK <19 , 33.3% (10/30 patients) in TK 20 e29 , 9.1% (3/33 patients) in TK 30 e39 , 31.8% (7/ 22 patients) in TK 40 e49 , and 40.7% (11/27 patients) in TK >50 . The incidence of PJK in group TK 30 e39 was significantly lower than that in groups TK 0 e19 and >50 (p 5 .004 and .044, respectively). The distribution of UIV among preoperative TK groups is shown in Table 6. The UIV in all groups except for TK >50 tended to be placed at middle thoracic spine (T6eT10). However, The UIV could be set at the upper thoracic spine (T2eT5) in the group with TK >50 compared with other groups. The incidence of PJK (36.2%) in the TK groups outside the 30 e39 range was significantly higher than that in the
TK 30 e39 range (9.1%) according to the chi-squared test (p 5 .002), and the odds ratio (OR) was 5.67 (Table 7). DPJA according to preoperative TK is shown in Figure 3a and b. It was 13.3 in TK <19 , 12.5 in TK 20 e29 , 7.6 in TK 30 e39 , 14.7 in TK 40 e49 , and 16.7 in TK >50 . It was significantly lower in group TK 30 e39 than in groups TK 0 e19 and >50 (p 5 .021 and .038, respectively). As shown in Figure 3b, the correlation coefficient between preoperative TK and DPJA was 0.083 (p 5 .271). Moreover, in patients with preoperative TK !40 , it was 0016 (p 5 .854). However, that in patients with preoperative TK >30 revealed a weak correlation (0.248, p 5 .025).
Table 7 The cross-tabulation table of the incidence of PJK according to TK of 30 e39 or not. Not TK of 30 e39 TK of 30 e39 Total
PJK (þ)
PJK ()
Total
55 3 58
97 30 127
152 33 185
PJK, proximal junctional kyphosis; TK, thoracic kyphosis. Chi-square test, p 5 .002; odds ratio 5 5.67.
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A
B
50 45 40 35 30 25 20 15 10 5 0 -30
-20
-10
0
10
20
30
40
50
60
70
80
90
100
Pre-OP TK Fig. 3. (A) D proximal junctional angle (PJA) according to preoperative thoracic kyphosis (TK). The patients with preoperative TK of 30 e39 had significantly lower DPJA than that in patients with TK !20 or TK >50 . The p value was .021 in TK of 0 e19 vs. 30 e39 and .038 in TK of 30 e39 vs. TK >50 . (B) The boxplot of D PJA according to preoperative TK. X-axis and Y-axis shows preoperative TK and DPJA, respectively. Correlation coefficient was 0.083 (p 5 .271). Correlation coefficient among patients with preoperative TK !40 was 0.016 (p 5 .854). Correlation coefficient among patients with preoperative TK >30 was 0.248 (p 5 .025).
Table 8 The evaluation of preoperative risk factors for PJK using multiple logistic regression analysis. DTK 5 20 Difference of 10 years of age
p value
Odds ratio
95% confidence interval
.000 .011
3.562 1.362
1.914, 6.629 1.073, 1.728
PJA, proximal junctional angle; PJF, proximal junctional failure; PJK, proximal junctional kyphosis; TK, thoracic kyphosis. Dependent variables: PJK at 2 years after the surgery or reoperation within 2 years after the surgery due to PJF; Independent variables: difference of age 10 years, DTK 5 20 , preoperative PJA, TK 30 e39 , and not-TK 30 e39 .
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The evaluation of preoperative risk factors for PJK using multiple logistic regression analysis Multiple logistic regression analysis was performed to identify risk factors for PJK using 185 patients (Table 8). The dependent variable was PJK at two years after surgery or reoperation within two years after surgery due to PJF, whereas the independent variable was a difference of 10 years of age, DTK 5 20 , preoperative PJA, TK 30 e39 , and not-TK 30 e39 . The significant risk factors for PJK were DTK 5 20 (p 5 .000, OR 3.562, 95% confidence interval [CI] 1.914e6.629), and a difference of 10 years of age (p 5 .011, OR 1.362, 95% CI 1.073e1.728). Discussion We assessed the preoperative risk factors and clinical outcomes of PJK and PJF after changing the definition of PJK to PJA >20 among patients who underwent ASD surgery. None of the preoperative radiographic parameters, except for PJA, was a risk factor for PJK. There was no significant difference in preoperative TK between both groups (29 and 28 in the PKJ and NPJK groups, respectively). However, as shown in Figures 2 and 3, PJK incidence and DPJA according to preoperative TK were significantly lower in patients with TK 30 e39 . Liu et al., in their meta-analysis, suggested that TK O40 was a significant risk factor for PJK [13]. In patients with a hyperkyphotic thoracic spine, the compensatory mechanism often fails because their back muscles are weak. Therefore, PJK may be caused by a re-increase in TK because of poor muscle strength after surgery. However, studies do not indicate that a lower preoperative TK is also a risk factor for PJK. Figure 4 shows how the preoperative TK of each
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parameter changed after surgery. TK changed from 28 21.7 before surgery to 34.5 11.9 after surgery. The standard deviation decreased after the surgery and most cases including cases with high or low TK converged to a TK of approximately 34.5 . Therefore, patients with a higher or lower TK demonstrated a significant DTK after the surgery. Patients with preoperative TK !20 or O50 had a significantly larger DTK compared with other patients (p ! .05) (Figure 5a and b). Our findings demonstrated that DTK is increased not only in patients with high preoperative TK but also in patients with low preoperative TK. As shown in Figure 5b, correlation coefficient between preoperative TK and DTK was 0.549, p 5 .000, in preoperative TK !40 and 0.455, p 5 .000, in preoperative TK >30 . Figure 6 shows the mechanism behind the development of PJK in patients with a lower TK. ASD patients have lumbar and pelvic sagittal malalignment and these alignment changes cause thoracic spineecompensated change (lower TK). However, TK and PJA, in patients with lower TK (compensated TK), increase over time because lumbopelvic malalignment (compensated change) is improved postoperatively. This causes mechanical stress on the UIV. One of our patients is shown in Figure 7. She was 75 years old and had a thoracic spine with compensated change (TK of 5 ). Her TK increased to 32 after the surgery because her lumbopelvic alignment improved. However, PJK (UIV fracture) occurred 1 month later. Her TK gradually increased to 72 . Finally, she underwent revision surgery one year after the surgery. The preoperative PJA in the PJK group was significantly lower than that in the NPJK group, suggesting that a compensated thoracic spine (with a change in lordosis) is a risk factor for PJK. The optimal preoperative TK experienced less change, even if the lumbopelvic parameter
Pre-OP Mean TK 28 21.7
Post-OP Mean TK 34.5 11.9
Fig. 4. The change of thoracic kyphosis (TK) of each case before and after the surgery. The TK changed from 28 21.7 before surgery to 34.5 11.9 after surgery. The standard deviation decreased after the surgery, and almost cases including cases with high TK or low TK converged to TK of around 34.5 .
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A
B
Fig. 5. (A) D thoracic kyphosis (TK) according to preoperative TK. DTK in patients with TK !20 or TK >50 was significantly larger than that in patients with TK of 20 e29 , 30 e39 , and 40 e49 . The p value was .000 in TK of 0 e19 vs. 20 e29 , 30 e39 , and 40 e49 , .048 in TK of 20 e29 vs. TK >50, .001 in TK of 30 e39 vs. TK>50, and .001 in TK of 40 e49 vs. TK >50 . (B) The boxplot of D thoracic kyphosis (TK) according to preoperative TK. X-axis and Y-axis shows preoperative TK and DTK, respectively. Correlation coefficient was 0.121 (p 5 .106). Correlation coefficient among patients with preoperative TK !40 was 0.549 (p 5 .000). Correlation coefficient among patients with preoperative TK >30 was 0.455 (p 5 .000).
changed postoperatively. Therefore, the UIV was under less mechanical stress. The evaluation of HRQOL in the main analysis suggested that the SRS-22 domains of Function/Activity, Selfimage/Appearance, and Total were significantly lower in the PJK group than in the NPJK group. Moreover, the domain of Self-image/Appearance in the PJK group was also significantly lower in the subanalysis that excluded the influence of age and LIV. This study showed that PJK or PJF influenced HRQOL, in particular, the SRS-22 domain of Self-image/Appearance. Kim et al. [7] also reported that the SRS-22 Self-image domain was lower when patients
had PJA O20 . Therefore, it is important to prevent PJK or PJF. However, low BMD and DSVA, which were the risk factors for PJK in the report by Liu et al. [13], showed no significant differences between the PJK and NPJK groups in our study. The risk factors for PJK are still unclear. Based on our results, the PJK incidence rate was significantly higher in patients with TK !20 or O50 than in those with TK 30 e39 , which is considered to be caused by the large DTK. Therefore, extending the fixed range to suppress the increase of DTK may lead to the prevention of PJK. Soroceanu et al. [19] reported that patients with UIV in the upper thoracic spine had less implant failure
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Fig. 6. The mechanism of proximal junctional kyphosis and the change of spinal sagittal alignment before and after surgery in patients with lower thoracic kyphosis (TK). TK and proximal junctional angle (PJA) in the patients with lower TK (compensated TK) increased to regain kyphosis in the thoracic spine after the surgery because lumbo-pelvic malalignment improved postoperatively. This caused large mechanical stress on the upper instrumented vertebra (UIV).
compared with others. However, this finding is still controversial because Kim et al. reported that the prevalence of PJK was not different when UIV was fused at the upper thoracic and lower thoracic spine [20]. The present study also could not prove the relationship between UIV level and the incidence of PJK (Tables 5 and 6).
This study had several limitations. First, 23 and 46 patients in the PJK and NPJK group, respectively, had their T score evaluated in the main analysis, although our study concluded that BMD was not associated with the incidence of PJK. Second, although our study stated that the postoperative TK of patients undergoing ASD surgery
Fig. 7. Case presentation in patients with lower thoracic kyphosis (TK). She was 75 years old female who had thoracic spine with compensated change (TK of 5 ). Her TK increased to 32 after the surgery because her lumbo-pelvic alignment got better. However, PJK (upper instrumented vertebral fracture) happen to her 1 months later. Her TK gradually increased to 72 . Finally, she had re-surgery 1 year after the surgery.
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converged to approximately 34.5 , in practice, individualdependent differences in TK may occur. The convergence to a postoperative TK of approximately 34.5 may be related to the average TK of 33.6 noted in Japanese persons older than 50 years [21]. Third, in the main analysis, a significant difference was observed in the domain of Function/Activity, Self-Image/Appearance, and Total in SRS-22 at two years after the surgery, but this result did not exclude the effect of the difference in age between the PJK and NPJK groups. Therefore, considering the subanalysis that excluded the influence of age, the SRS-22 domain that significantly deteriorated because of PJK might be SelfImage alone. Fourth, preoperative TK was not a controllable parameter. Therefore, this study did not show its prevention but the mechanism of PJK. Further study is necessary to prevent it. Finally, the small sample size, multiple comparisons of evaluated parameters, and many dropouts in this study might have resulted in statistical bias and noise. Conclusion This study suggests that the incidence of PJK or PJF significantly increases not only in patients with a high preoperative TK (>50 ) but also in patients with a low preoperative TK (!20 ), compared with patients with a TK of 30 e39 . The cause of PJK was considered to be a large change in TK before and after surgery. Moreover, PJK led to a significant deterioration in the domains of Function/ Activity, Self-Image/Appearance, and Total in SRS-22. Considering these factors during patient management may help to prevent PJK or PJF. Key points The incidence of PJK or PJF significantly increases not only in patients with high preoperative TK (O50 ) but also in patients with low preoperative TK (!20 ) compared with patients with TK of 30 e39 . The cause and mechanism of PJK was considered to be a large change in TK before and after surgery. PJK significantly deteriorated the domains of Function/Activity, Self-Image/Appearance, and Total in SRS-22. References [1] 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 1994;19: 1680e5. [2] Kim HJ, Bridwell KH, Lenke LG, et al. Proximal junctional kyphosis results in inferior SRS pain subscores in adult deformity patients. Spine 2013;38:896e901.
[3] 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;37:1479e89. [4] Bridwell KH, Lenke LG, Cho SK, et al. Proximal junctional kyphosis in primary adult deformity surgery: evaluation of 20 degrees as a critical angle. Neurosurgery 2013;72:899e906. [5] Kim HJ, Lenke LG, Shaffrey CI, et al. Proximal junctional kyphosis as a distinct form of adjacent segment pathology after spinal deformity surgery: a systematic review. Spine 2012;37:S144e64. [6] 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 2005;30:1643e9. [7] 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 2008;33: 2179e84. [8] Maruo K, Ha Y, Inoue S, et al. Predictive factors for proximal junctional kyphosis in long fusions to the sacrum in adult spinal deformity. Spine 2013;38:E1469e76. [9] Wang J, Zhao Y, Shen B, et al. Risk factor analysis of proximal junctional kyphosis after posterior fusion in patients with idiopathic scoliosis. Injury 2010;41:415e20. [10] Yagi M, Akilah KB, Boachie-Adjei O. Incidence, risk factors and classification of proximal junctional kyphosis: surgical outcomes review of adult idiopathic scoliosis. Spine 2011;36:E60e8. [11] 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;470:1633e9. [12] Scheer JK, Fakurnejad S, Lau D, et al. Results of the 2014 SRS Survey on PJK/PJF: a report on variation of select SRS member practice patterns, treatment indications, and opinions on classification development. Spine 2015;40:829e40. [13] Liu FY, Wang T, Yang SD, et al. Incidence and risk factors for proximal junctional kyphosis: a meta-analysis. Eur Spine J 2016;25:2376e83. [14] Yan P, Bao H, Qiu Y, et al. Mismatch between proximal rod contouring and proximal junctional angle: a predisposed risk factor for proximal junctional kyphosis in degenerative scoliosis. Spine 2017;42:E280e7. [15] Han S, Hyun SJ, Kim KJ, et al. Rod stiffness as a risk factor of proximal junctional kyphosis after adult spinal deformity surgery: comparative study between cobalt chrome multiple-rod constructs and titanium alloy two-rod constructs. Spine J 2017;17:962e8. [16] Hey HWD, Tan KA, Neo CS, et al. T9 versus T10 as the upper instrumented vertebra for correction of adult deformity-rationale and recommendations. Spine J 2017;17:615e21. [17] Shen FH, Mason JR, Shimer AL, et al. Pelvic fixation for adult scoliosis. Eur Spine J 2013;22(suppl 2):S265e75. [18] Kebaish KM. Sacropelvic fixation: techniques and complications. Spine 2010;35:2245e51. [19] Soroceanu A, Diebo BG, Burton D, et al. Radiographical and implant-related complications in adult spinal deformity surgery: incidence, patient risk factors, and impact on health-related quality of life. Spine 2015;40:1414e21. [20] Kim HJ, Boachie-Adjei O, Shaffrey CI, et al. Upper thoracic versus lower thoracic upper instrumented vertebrae endpoints have similar outcomes and complications in adult scoliosis. Spine 2014;39: E795e9. [21] Oe S, Togawa D, Nakai K, et al. The influence of age and sex on cervical spinal alignment among volunteers aged over 50. Spine 2015;40:1487e94.