A comparison of long-term efficacy of K-rod-assisted non-fusion operation and posterior lumbar interbody fusion for single-segmental lumbar disc herniation

DOI: https://doi.org/10.21203/rs.3.rs-273166/v1

Abstract

BACKGROUND

Since the development of internal fixation, posterior lumbar interbody fusion (PLIF) surgery has become the gold standard for the treatment of lumbar disc herniation. Although it has good short-term clinical efficacy, it can result in problems such as postoperative intractable lower back pain and degeneration of adjacent segments. K-rod-assisted non-fusion surgery for the treatment of lumbar disc herniation has also been proven to have clinical efficacy; however, its long-term effects have not been examined.

AIM

To compare the long-term clinical efficacy of K-rod-assisted non-fusion operation to the clinical efficacy of PLIF in the management of single-segment lumbar disc herniation.

METHODS

This study retrospectively analyzed 22 patients with lumbar disc (L4/5) herniation who underwent K-rod-assisted non-fusion operation (n=13) or PLIF (n=9) between December 2010 and December 2013 and were followed-up for more than 5 years. Clinical outcomes were evaluated by the Oswestry Disability Index (ODI), pain Visual Analogue Score (VAS), and Japanese Orthopaedic Association Back Pain Evaluation Questionnaire (JOABPEQ). Imaging evaluations included adjacent segmental intervertebral height, range of motion (ROM) of the vertebrae, incidence of lumbar instability, spino-pelvic parameters, Pfirrmann grading, Modic changes, and University of California Los Angeles (UCLA) grading.

RESULTS

Clinical outcomes, namely operation times (110.5±11.15 min vs. 134.44±12.36 min, P <0.05) and blood loss (59.2±7.03 ml vs. 80.0±8.66 ml, P <0.05), were significantly reduced in the K-rod group compared to the PLIF group. At the last follow-up, the clinical outcomes of the K-rod group were improved compared to those of the PLIF group as observed by the VAS score (2.1±0.9 vs. 3.0±0.7, P <0.05), JOABPEQ (26.7±1.1 vs. 25.2±1.5, P <0.05), and ODI (21.0±3.7 vs. 28.4±6.9, P <0.05). Imaging outcomes at the last follow-up indicated that the loss of height in the L3/4 intervertebral space (0.4±0.9 mm vs. 1.5±0.7 mm, P <0.05) and L5/S1 intervertebral space (0.2±0.5 mm vs. 1.8±1.7 mm, P <0.05), the ROM of L3/4 (4.9±2.0 vs. 8.8±2.4, P <0.05), the ROM of L5/S1 (5.7±1.7 vs. 8.6±1.2, P <0.05), and the incidence of adjacent segment degeneration (7.7% vs. 38.9%, P <0.05) in the PLIF group were significantly higher than those in the K-rod group. According to Pfirrmann grading, Modic changes, and UCLA grading, the incidence of adjacent segment degeneration was 55.6% in the PLIF group and 15.4% in the K-rod group. Changes in spino-pelvic parameters between the two groups were as follows: pelvic index remained unchanged, pelvic tilt angle increased, and lumbar lordosis and sacral slope decreased.

CONCLUSION

Compared to PLIF, single-segment lumbar disc herniation using K-rod-assisted non-fusion surgery resulted in better long-term clinical efficacy. Our results demonstrate that this procedure can delay adjacent segment degeneration after lumbar surgery.

Introduction

Although posterior lumbar interbody fusion (PLIF) has gradually become the "gold standard" for the surgical treatment of degenerative diseases of the spine, complications such as adjacent segment degeneration (ASD) 1 and postoperative low-back pain, 2 affect the long-term clinical efficacy of the operation. A previous study observed that the incidence of complications identified through symptomatology was 5–20%, while the incidence of complications identified through imaging studies was 8–100%.3–6 The reason for such a wide range of incidences among imaging studies may be the differing diagnostic criteria for degeneration observed by imaging. Imagama et al.7 and Iorio et al.,8 found that the main cause of degeneration after lumbar surgery was not age, but changes in spinal mechanics caused by lumbar surgery and internal fixation. Therefore, to prevent the degeneration of adjacent segments after spinal surgery, choosing an optimal surgical method and internal fixation device is highly important. Dynamic fixation has been proposed as a potential method, and it aims to prevent lumbar instability, intractable low-back pain, and ASD 9−−11 by partially restricting movement or load. Dynamic fixation seeks to preserve normal lumbar activity and to reduce abnormal activity. The K-rod system (which stands for K-rod system-assisted elastic internal fixation) is another surgical modality for the management of degenerative diseases of the spine, such as disc herniation. The short-term clinical efficacy of the K-rod system in the treatment of lumbar degenerative diseases has been confirmed, 1214 but there are few reports examining its long-term clinical efficacy. Furthermore, considering that ASD occurs approximately 2 years after lumbar surgery and the incidence of ASD increases at a rate of approximately 3% per year, 1,3 it is necessary to explore the long-term clinical efficacy of surgical treatment methods for degenerative diseases of the spine. This study aimed to compare the clinical outcomes of K-rod-assisted non-fusion surgery and those of PLIF for the treatment of lumbar disc herniation and the roles of these procedures in delaying the degeneration of adjacent spinal segments.

Materials And Methods

General data

This study retrospectively analyzed the clinical data of patients who had lumbar disc herniation and underwent surgical treatment between December 2010 and December 2013; the study participants were followed-up for more than 5 years.

Patients who met the following criteria were included in the study: (1) patients less than 55 years of age, (2) patients who had a single lumbar disc herniation (L4/5) and whose symptoms were not significantly alleviated after conservative treatment for more than 3 months, and (3) patients who underwent K-rod system-assisted non-fusion surgery or PLIF for the treatment of disc herniation.

Patients with any of the following criteria were excluded from the study: (1) patients with complications of other diseases of the spine, such as inflammatory disease, infections, rheumatism, fractures, and immune system diseases, (2) patients with a history of spine surgery and trauma, (3) patients who had undergone internal fixator removal, and (4) patients with incomplete clinical data, (5) age greater than 55 years.

Based on the above criteria, 13 and 9 cases were included in the K-rod and PLIF groups, respectively.

Surgical method

K-rod group: After administering general anesthesia, the patient was placed in a prone position and support paddings were used to lift the abdomen in order to fully increase the intervertebral spaces. A digital radiography machine was used to locate the segment to be operated, and the segment was well marked. The skin over the identified segment was then disinfected, and sterile, single-use instruments were employed. Incisions measuring approximately 7 cm in length were made along the posterior midline of the lower back to expose the lamina and articular process. Pedicle screws were implanted while carefully retaining the posterior column ligament complex, including the supraspinal ligament. An appropriate length of elastic K-rod and polyetheretherketone shells were used, and the screw cap was tightened. Decompression was performed at the L4/5 level by fenestration to expose the dural sac. After stripping and protecting the nerve root, the position of the protruding disc was defined. The posterior longitudinal ligament was then cut with a sharp knife, and nucleus pulposus forceps were used to remove the free nucleus pulposus tissue and broken disc tissue. Bipolar electrocoagulation was used to control bleeding. The nerve root passage was explored, and the tension at the nerve root was palpated. After confirming that there was no obvious nerve root entrapment, the incision was fully washed with saline, and the lamina window was covered with a gelatin sponge. An indwelling drainage tube was then fixed and free drainage through the tube was ensured after layer-by-layer suturing of the surgical incision.

PLIF group: The procedure for PLIF was similar to that of K-rod insertion, except that a rigid titanium rod was used instead of a K-rod. The spinous process and the lamina of the L4 vertebrae were also removed. After discectomy, the upper and lower endplates were scraped with a curette. Autogenous bone or allogeneic artificial bone was then implanted into the intervertebral space.

All the surgeries in this study were performed by the same surgical team.

The patients were treated with dehydration, anti-inflammatory drugs, antibiotics, nerve nutrition, etc. When the surgical site drainage volume was < 50 mL over 24 h, the drainage tube was removed. Patients who underwent K-rod surgery were allowed to walk with thoracolumbar brace one week after surgery. Patients who underwent PLIF, were recommended to walk 3 weeks after the operation. All patients performed active muscle exercises during bed rest and were advised to wear thoracolumbar brace when walking within 3 months after surgery.

Measures

The following clinical measures were used: pain Visual Analogue Scale (VAS), Oswestry Disability Index (ODI), and Japanese Orthopaedic Association Back Pain Evaluation Questionnaire (JOABPEQ). The following imaging measures were used: height of the intervertebral space (H), intervertebral range of motion (ROM), lumbar lordosis (LL) angle, pelvic tilt (PT) angle, sacral slope (SS), pelvic index (PI), incidence of lumbar instability, University of California, Los Angeles (UCLA) classification of intervertebral space degeneration on X-ray, Pfirrmann classification of lumbosacral disc degeneration, and Modic classification of changes in the vertebrae on magnetic resonance imaging (MRI). The methods used to measure H15 and spino-pelvic parameters are shown in Figs. 1 and 2.

Statistical analysis

All data were analyzed with SPSS version 22.0 software. All mean values were expressed as mean ± SD. Student’s t test was used to compare the differences between intragroup variables and intergroup variables. Chi-square test (χ2) was used for the comparison of two rates. A P-value of < 0.05 was considered statistically significant.

Results

Demographic data

The clinical data of 22 patients were used in the study (K-rod group, n = 13; PLIF group, n = 9). There were no significant differences between the two groups in demographic characteristics, such as age, sex, body mass index, and follow-up duration (Table 1). Operative times (110.5 ± 11.15 min vs. 134.44 ± 12.36 min, P < 0.05) and blood loss (59.2 ± 7.03 ml vs. 80.0 ± 8.66 ml, P < 0.05) were significantly reduced in the K-rod group compared to the PLIF group (Table 1).

Table 1

Demographic data of the patients in two groups

 

K-rod group

PLIF group

P value

Sex(M/F)

(6/7)

(4/5)

0.937

Age(Y)

39.08 ± 6.18

40.44 ± 6.39

0.620

BMI

23.26 ± 3.11

23.95 ± 2.30

0.575

Follow-up time(T/M)

65.6 ± 3.20

67.9 ± 4.88

0.201

Operation time(t/min)

110.5 ± 11.15

134.44 ± 12.36

< 0.01a

Bleeding loss(V/ml)

59.2 ± 7.03

80.0 ± 8.66

< 0.01a

PID(D/N)

7/19

4/14

0.723

a: K-rod group was different from PLIF group. PID(D/N): Preoperative imaging degeneration (degeneration/no degeneration)

Clinical efficacy

In our study, we found that the incidence rates of intractable low-back pain and recurrence of neurological symptoms in K-rod group were higher than the incidence rates in PLIF group. The results were reflected by VAS score, ODI, and JOABPEQ. There was no significant difference in preoperative VAS score, ODI, and JOABPEQ between the two groups. However, at the last follow-up, VAS score (2.1 ± 0.9 vs 3.0 ± 0.7, P < 0.05) and ODI (21.0 ± 3.7 vs. 28.4 ± 6.9, P < 0.05) of patients in the K-rod group were significantly lower than those of patients in the PLIF group (Table 2). Conversely, we found higher JOABPEQ (26.7 ± 1.1 vs. 25.2 ± 1.5, P < 0.05) in the K-rod group than in the PLIF group (Table 2). Fortunately, there was no recurrence of disc herniation in surgical segments or failure of internal fixation in both groups.

Table 2

Changes of clinical measures in both groups

 

K-rod group

PRO

K-rod group

POL

PLIF group

PRO

PLIF group

POL

P1 value

P2 value

VAS

6.9 ± 0.8

2.1 ± 0.9

7.5 ± 1.0

3.0 ± 0.7

0.450

0.015a

JOABPEQ

13.4 ± 1.5

26.7 ± 1.1

13.2 ± 1.7

25.2 ± 1.5

0.836

0.003a

ODI

66.8 ± 3.6

21.0 ± 3.7

67.7 ± 3.7

28.4 ± 6.9

0.943

0.024a

a: K-rod group was different from PLIF group. P1 value: P value of preoperative comparisons between groups; P2 value: P value of intergroup comparisons at the Last Follow-up; PRO: preoperation; POL: the last follow-up after the operation

Imaging results

There were no significant differences in adjacent segmental intervertebral height, ROM, spino-pelvic parameters, and LL between the two groups preoperatively.

At the last follow-up, the ROM of adjacent segments increased in both groups and was significantly higher in the PLIF group than in the K-rod group (P < 0.001). H decreased in both groups, but the decrease was significantly more in the PLIF group (P < 0.05). According to > 5 years of follow-up data, the incidence of lumbar instability was 7.7% and 38.9%, in the K-rod and PLIF groups, respectively. There were significant differences in the incidence of lumbar instability between the two groups (P < 0.05) (Table 3).

Table 3

Changes of H and ROM data in both groups

 

K-rod group

PRO

K-rod group

POL

PLIF group

PRO

PLIF group

POL

P1 value

P2 value

H( L3/4)(mm)

10.3 ± 1.5

10.0 ± 1.4

10.4 ± 1.5

8.9 ± 1.9

0.907

0.144

H( L5/S1)(mm)

9.1 ± 2.6

8.8 ± 2.9

8.3 ± 2.6

6.7 ± 2.7

0.503

0.100

ROM( L3/4)(°)

3.7 ± 2.3

4.9 ± 2.0

4.8 ± 2.2

8.8 ± 2.4

0.286

< 0.001a

ROM L5/S1)(°)

5.0 ± 2.9

5.7 ± 1.7

5.0 ± 2.0

8.6 ± 1.2

1.00

< 0.001a

HL( L3/4)(mm)

-

0.4 ± 0.9

-

1.5 ± 0.7

-

0.009a

HL( L5/S1)(mm)

-

0.2 ± 0.5

-

1.8 ± 1.7

-

0.004a

ILI

-

7.7%

-

38.9%

-

0.012a

a: K-rod group was different from PLIF group. P1 value: P value of preoperative comparisons between groups; P2 value: P value of intergroup comparisons at the Last Follow-up; PRO: preoperation; POL: the last follow-up after the operation; HL: height of intervertebral space loss; ILI: incidence of lumbar instability.

We found no significant difference in the PI value between the two groups before and after the surgery. There were no significant changes in PT, SS, and LL within the K-rod group before and after the operation. However, there were significant differences in the preoperative and postoperative values of these measures in patients in the PLIF group (P < 0.05). The overall trend was that SS and LL became smaller while PT became larger in the PLIF group (Table 4).

Table 4

Changes of spinal-pelvis parameters in two groups

 

K-rod group PRO

K-rod group POL

PLIF group PRO

PLIF group POL

P1 value

P2 value

P3 value

P4 value

LL(°)

32.2 ± 18.0

36.9 ± 8.2

49.3 ± 8.7

41.0 ± 6.3

0.748

0.002b

0.061

0.023a

PT(°)

17.3 ± 9.0

17.9 ± 9.2

23.0 ± 8.2

28.6 ± 10.0

0.826

0.005b

0.402

0.027a

SS(°)

28.0 ± 9.6

27.6 ± 6.7

33.4 ± 8.9

24.5 ± 5.3

0.889

0.002b

0.068

0.013a

PI(°)

45.4 ± 11.2

44.6 ± 9.4

56.0 ± 11.0

52.9 ± 7.4

0.338

0.301

0.057

0.004a

a: K-rod group was different from PLIF group; b: PLIF group POL was different from PLIF group PRO; P1 value: P value of intra-group comparisons in K-rod group; P2 value: P value of intra-group comparisons in PLIF group. P3 value: P Value of intergroup comparisons before the operation; P4 value: P value of intergroup comparisons at the last follow-up; PRO: preoperation; POL: the last follow-up after the operation.

The results of the different grading methods used to evaluate postoperative ASD in the two groups are shown in Tables 57. The incidence of ASD was higher in the PLIF group than in the K-rod group (Table 8). Further analysis of the data showed that although different methods were used to evaluate ASD, the overall incidence of aggravation of ASD was the same as that established with Pfirrmann grading.

Table 5

Changes of UCLA grade before and after operation in two groups

 

UGCV(L3/4)

UGCV(L5/S1)

-1

0

1

2

3

-1

0

1

2

3

K-rod group

0

12

1

0

0

0

13

0

0

0

PLIF group

0

6

2

1

0

0

7

1

1

0

UGCV: UCLA grading change value = UCLA grading at the last follow-up - preoperative UCLA grading

Table 6

Changes of pfirrmann grade before and after operation in two groups

 

PGCV(L3/4)

PGCV(L5/S1)

-1

0

1

2

3

4

-1

0

1

2

3

4

K-rod group

0

11

2

0

0

0

1

11

1

0

0

0

PLIF group

0

4

2

2

1

0

0

4

3

2

0

0

PGCV: Pfirrmann grading change value = grading at the last follow-up - preoperative grading.

Table 7

Changes of MODIC grade before and after operation in two groups

 

MGCV(L3/4)

MGCV(L5/S1)

-1

0

1

2

3

-1

0

1

2

3

K-rod group

0

13

0

0

0

0

12

1

0

0

PLIF group

0

7

2

0

0

0

7

1

1

0

MGCV: MODIC grading change value = MODIC grading at the last follow-up - preoperative MODIC grading

Table 8

Postoperative degeneration rate in K-rod group and PLIF group

 

K-rod group

PLIF group

P value

Pfirrmann grade

15.4%

55.6%

0.005

MODIC grade

3.8%

22.2%

0.059

UCLA grade

3.8%

27.8%

0.023a

ROHL

3.8%

16.7%

0.146

a: K-rod group was different from PLIF group. ROHL: The rate of intervertebral height loss(more than 20%)

Discussion

This study compared the clinical outcomes of K-rod-assisted non-fusion surgery and PLIF for the treatment of single-segment lumbar disc herniation. According to the literature report16,17 and the accumulated clinical experience of our team, it is believed that the use of a dynamic stabilization internal fixation system to treat lumbar disc herniation needs to exclude spinal instability and severe osteoporosis. In addition, we know little about the long-term clinical effects of the dynamic stabilization system in the treatment of lumbar disc herniation, and it requires a lifetime of continuous movement. In order to avoid some unpredictable potential risks, we excluded patients over 55 years of age when providing the treatment option of K-rod-assisted surgery to patients. Similarly, in order to ensure the homogeneity of the study, the patients included in the PLIF group were also less than 55 years old.

This study demonstrated that operative time and blood loss in the K-rod group were significantly lower than those in the PLIF group. This is because K-rod surgical procedure was simpler than the PLIF procedure, and this is an advantage of K-rod surgery over PLIF. After comparing follow-up results, we also found better clinical efficacy in the K-rod group. This improvement in clinical efficacy is closely related to spinal sagittal balance and ASD after spinal surgery.18 Intractable low-back pain is a common complication after lumbar spinal surgery, and in severe cases, reoperation is required.19 Previous studies have shown that the incidence of low-back pain after lumbar discectomy is 5–36%.20 Multiple factors are responsible for postoperative low-back pain, and lumbar instability plays an important role.21 Each vertebral body and its adjacent intervertebral disc tissue constitute a motion unit. After lumbar fusion surgery, the motion unit of the operated segment changes and its activity increases completely, requiring compensation from the adjacent motion unit, thus changing the stress of the adjacent intervertebral disc tissue and facet joints. Over time, instability and degeneration of the spine occur. In this study, 38.9% of PLIF patients were found to have lumbar instability after 5 years of follow-up. However, it is worth noting that although the ROM of adjacent segments did not exceed 10° in the K-rod group, the activity of the upper segments increased significantly, and was significantly different between the two groups. This suggests that the K-rod system retains the activity of the operative segments, but there may still be compensatory movement during flexion and extension after surgery. This may also be due to the age of the patient, 22 because age-related disc degeneration was found to coexist in these patients.

H indirectly reflects the height of the intervertebral disc.23 Lu et al.24 found that a decrease in the height of the intervertebral disc caused the following changes: the stress in the center of the disc decreased, the stress in the peripheral fibrous ring increased, the risk of rupture of the fibrous ring increased, and the stress in the facet process increased. All these changes accelerated the degeneration of adjacent segments. Our long-term clinical observations in this study confirmed that H decreased in adjacent segments after posterior lumbar fusion (Table 3). Similar results were not found in the K-rod group because the elastic rod not only partially retained the flexion and extension motion of the lumbar spine, but also had a much lower modulus of elasticity and a weaker stress-shielding effect than the rigid rod.

It is also important to note that before intervertebral space changes become obvious, disc degeneration will have become visible on MRI. According to Pfirrmann grading, 25 disc height loss is detectable only when disc degeneration reaches grade IV or above. Modic changes refer to the expression of bone changes in the endplate and sub-endplate on MRI. Two main mechanisms are responsible for Modic changes. First, the mechanical properties of the endplate are changed by disc degeneration and micro-fractures occur under repeated loads. Second, inflammatory substances released by the degenerated disc stimulate the endplate. Disruption of the endplate results in impairment of nutrient transport that further accelerates disc degeneration.26,27 Therefore, these two mechanisms complement each other in the process of lumbar degeneration. All cases with Modic changes in this study were associated with disc degeneration corresponding to a Pfirrmann grade of at least III. In general, Modic type I and type II changes are reversible, 28 and the spinal segment involved could return to normal. In our study, the incidence of Modic changes was 3.8% in the K-rod group and 22.2% in the PLIF group, suggesting that when adjacent segments have mild Modic changes without symptoms of lumbar disc herniation and nerve compression, non-fusion and internal fixation with K-rod system may be more beneficial, and complications associated with premature fusion can be avoided.

Pelvic morphology also plays an important role in the sagittal balance of the spine.29,30 Currently, evaluation of the morphology of the pelvis mainly involves three parameters: PI, PT, and SS. There is a clear geometric relationship between these three parameters, which is expressed as PI = PT + SS. Furthermore, Schwab also found an equation for spine and pelvis parameters in asymptomatic patients: LL = PI ± 9°.31 When degenerative changes occur in the lumbar spine, these parameters change; for instance, the PI value will increase in patients with degenerative lumbar spondylolisthesis.30,32−34 Meanwhile, surgery affects spino-pelvic parameters as well as LL.3538 We found no significant differences in the PI value between the PLIF group and K-rod group before or after operation. However, in the last follow-up, we noticed an increase in PT and a decrease in both SS and LL in patients in the PLIF group. This suggests that spine instability still existed at the last follow-up after lumbar surgery.

Our study shows the K-rod system-assisted elastic internal fixation for lumbar disc herniation has superior medium- to long-term clinical efficacy when compared to PLIF. However, there are several limitations to this study. First, the number of cases involved was small, as the sample size was only 22 cases. Second, the treatment of lumbar disc herniation with the K-rod elastic internal fixation system usually uses the routine posterior spinal approach. This can cause serious muscle damage and may also cause postoperative low-back pain. These problems may have improved if the interstitial approach was used. In addition, the K-rod system, which belongs to the posterior spinal screw-rod system, is no longer removed after implantation unless necessitated by special conditions. As patients grow older, screw loosening and screw-rod electrolysis may occur. Moreover, the elastic rod can cause partial motion of the operative segment and, thus, increase the risk of failure of the spinal screw-rod system. Although in the 5-year follow-up period of this study, there was no reported case of internal fixation failure, the risk of this complication is not clear, and further studies are needed.

In conclusion, the K-rod system-assisted elastic internal fixation when used for the treatment of lumbar intervertebral disc herniation in young and middle-aged individuals can achieve greater clinical efficacy than PLIF. It can also reduce the associated pain, resolve functional disorders, and ensure spinal stability and spinal balance for the patient. It has the advantages of minimal trauma, a shorter operative time, minimal blood loss, and a faster recovery period postoperatively compared to PLIF. The K-rod system also retains the normal activities of the operative segment and limits abnormal activities. The present study shows that the K-rod system has the effect of delaying ASD after lumbar surgery from various angles. Currently, the indications for using the K-rod system in the management of lumbar degenerative diseases are not clear. We intend to further evaluate the clinical efficacy and related complications of the K-rod system in the management of lumbar degenerative diseases in order to provide a basis for establishing an optimal treatment method.

Declarations

Ethics approval and consent to participate: This study complied with the Declaration of Helsinki and was reviewed and approved by the Ethics Committee of the Second Hospital of Jilin University. All patients in our study provided informed consent.

Consent for publication: Written informed consent for publication was obtained from all participants.

Availability of data and materials: Not applicable.

Competing interests: We declare that we have no competing interests.

Funding: This work was supported by Jilin Provincial Science and Technology Agency (NO. 20170204031YY) and Graduate Innovation Fund of Jilin University (NO. 101832020CX295).

Authors’ contributions: Xue-liang Cheng designed and performed the research and wrote the paper; Yang Qu designed the research and provided clinical advice; Rong-peng Dong designed the research and contributed to the analysis; Ming-yang Kang collected the information and provided clinical advice; Jian-wu Zhao guided the research and supervised the report.

Acknowledgment: Not applicable.

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