Effect of Vertebroplasty with Bone Filler Device and Comparison with Balloon Kyphoplasty

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Effect of Vertebroplasty with Bone Filler Device and

Comparison with Balloon Kyphoplasty

by

DONG-HOON YANG

Major in Medicine

Department of Medical Sciences

The Graduate School, Ajou University

Effect of Vertebroplasty with Bone Filler Device and

Comparison with Balloon Kyphoplasty

by

DONG-HOON YANG

A Dissertation Submitted to

the Graduate School of Ajou University

in Partial Fulfillment of the Requirements of

the Degree of Master of Medicine

Supervised by

Ki Hong Cho, M.D., Ph.D.

Major in Medicine

Department of Medical Sciences

The Graduate School, Ajou University

This certifies that the dissertation of Dong-Hoon Yang

is approved.

SUPERVISORY COMMITTEE

________________________

Ki Hong Cho

________________________

Soo Han Yoon

________________________

Young Hwan Ahn

The Graduate School, Ajou University

December 13rd, 2013

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- ABSTRACT -

Effect of Vertebroplasty with Bone Filler Device and Comparison

with Balloon Kyphoplasty

BACKGROUND CONTEXT: Vertebroplasty and kyphoplasty are popular procedures for

osteoporotic vertebral compression fractures. Although the kyphoplasty has a superior effect, it destroys normal vertebral trabecular structure and it has a higher cost.

PURPOSE: To analyze vertebroplasty with a bone filler device compared with conventional

kyphoplasty.

STUDY DESIGN: A cross-sectional study for comparison of two operation groups. PATIENT SAMPLE: Two-hundred twenty-two patients treated from January 2008 to

October 2012

OUTCOME MEASURES: Vertebral height, compression ratio, and segmental Cobb’s

angle were measured in preoperative and postoperative lateral X-rays.

METHODS: One hundred ninety-five patients were included after exclusion of 27 patients.

One level fractures numbered 169 (86.7%) cases and two level fractures numbered 26 (13.3%). A total of 221 vertebral levels were analyzed consequently. Statistical analysis was performed to identify significant differences between the two groups.

RESULTS: Vertebral height and compression ratio had stronger correlations than did

segmental Cobb’s angle. The compression ratio was the most influential parameter among the three variables. Adjusted postoperative compression ratio was not significantly different between the two operation groups, whereas adjusted postoperative vertebral height and

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segmental Cobb’s angle differed significantly (p < 0.05). Bone cement leakage rates did not differ (p < 0.05). Bone cement distribution was spongy type in the majority of the

vertebroplasty group (94.5%), but only spongy type in 42.0% of the kyphoplasty group. High bone densitometry (BMD) readings and long period from diagnosis to operation were

significant risk factors for bone cement leakage among preoperative conditions.

CONCLUSION: Compared with kyphoplasty, vertebroplasty with a bone filler device could

achieve equivalent compression reduction and bone cement leakage rate, as well as greater sponge-type bone cement distribution, which were advantages over conventional

vertebroplasty and kyphoplasty.

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TABLE OF CONTENTS

ABSTRACT ... i

TABLE OF CONTENTS ...iii

LIST OF FIGURES ... iv

LIST OF TABLES ... v

I. INTRODUCTION ... 1

II. MATERIALS AND METHODS ... 3

A. Inclusion and Exclusion Criteria... 3

B. Subjects ... 3 C. Measurement ... 3 D. Surgical technique... 4 E. Statistical Analysis ... 4 III. RESULT ... 6 IV. DISCUSSION ... 16

A. Vertebral height, compression ratio, and segmental Cobb’s angle ... 16

B. Equality of preoperative variables and adjusted postoperative variables ... 16

C. Intravertebral cleft and bone cement distribution ... 17

D. Bone cement volume ... 18

E. Bone cement leakage rate ... 19

F. Leakage risk factors due to preoperative conditions ... 20

G. Limitations ... 20

V. CONCLUSION ... 21

REFERENCES ... 22

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LIST OF FIGURES

Fig. 1. Plunger-type bone filler device.. ... 2 Fig. 2. Different bone cement distributions ... 8 Fig. 3. Bone cement leakage after procedure ... 9 Fig. 4. Correlation relationship between vertebral height restoration, compression ratio

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LIST OF TABLES

Table 1. Demographic data and comparison of preoperative condition.오류! 책갈피가 정의 되어 있지 않습니다.

Table 2. Comparison of vertebral height, compression ratio, Cobb’s angle, and bone cement. ... 오류! 책갈피가 정의되어 있지 않습니다. Table 3. Correlation of vertebral height, compression ratio, and Cobb’s angle.오류! 책갈피

가 정의되어 있지 않습니다.

Table 4. Comparison of postoperative values after correction of preoperative variables.오류! 책갈피가 정의되어 있지 않습니다.

Table 5. Risk factor assessments of bone cement leakage오류! 책갈피가 정의되어 있지 않습니다.

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I.

INTRODUCTION

Osteoporotic vertebral compression fracture is a major health problem in the elderly. More than 1.4 million persons per year suffer from pain and morbidity related with this condition worldwide (Johnell and Kanis, 2006). Vertebroplasty and kyphoplasty for vertebral compression fracture have gained popularity over the past several years, and can overcome the disadvantages of non-surgical management with bed rest (Lyles et al., 1993). Although a recently published randomized controlled trial showed no superior advantage, subsequent meta-analysis study revealed that vertebroplasty and kyphoplasty provided greater pain relief and fewer subsequent fractures when compared to non-surgical management (Rousing et al., 2009; Ma et al., 2012; Papanastassiou et al., 2012). Class I evidence has been presented to support the advantages of vertebroplasty and kyphoplasty (Voormolen et al., 2007; Wardlaw et al., 2009; Berenson et al., 2011).

The effects of vertebroplasty and kyphoplasty extend beyond pain control to include vertebral height restoration, compression ratio reduction, and segmental Cobb’s angle reduction (Hiwatashi et al., 2003; Teng et al., 2003; Dublin et al., 2005; Pradhan et al., 2006; Hiwatashi et al., 2009).

The most annoying problem of this procedure is bone cement leakage, although most leakage does not cause clinical symptoms. Balloon kyphoplasty is more recently developed, and generally has a superior effect compared to vertebroplasty (Belkoff et al., 2001; Phillips et al., 2002; Hiwatashi et al., 2005; Shindle et al., 2006; Kim et al., 2012a; Papanastassiou et al., 2012). Meta-analysis study indicated that the incidence of bone cement leakage was lower than with kyphoplasty (Ma et al., 2012; Papanastassiou et al., 2012).

The distribution of the injected bone cement can be classified as spongy (trabecular, inter-digitation) and lumped (solid, cleft) (Oka et al., 2005; Tanigawa et al., 2007; Kim et al., 2012b). The lumped distribution is related with vertebral re-collapse and new fractures of adjacent vertebra and tends to be associated with kyphoplasty (Tanigawa et al., 2007; Kim et al., 2012b). Another unavoidable disadvantage of kyphoplasty is its higher medical cost compared to vertebroplasty.

The advantages of vertebroplasty, in turn, are a greater extent of sponge-shaped bone cement distribution and a lower medical cost; however, kyphoplasty causes less bone cement

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In the present study, we have combined the advantages of these two procedures by performing vertebroplasty using a bone filler device (a plunger system with a nozzle and a stylet) that is commonly used for bone cement insertion during kyphoplasty (Fig. 1). This device has a larger diameter than the conventional 10-gauge vertebroplasty needle and allows injection of a bone cement of a higher viscosity than is possible with a syringe (Heini and Orler, 2004). The purpose of the present study was to establish whether this

vertebroplasty with a bone filler device could accomplish an equivalent compression reduction and bone cement leakage rate to that seen with balloon kyphoplasty.

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II. MATERIALS AND METHODS

Inclusion criteria for patients were one or two level osteoporotic vertebral body fractures within two months after symptom onset. The diagnosis was based on preoperative magnetic resonance imaging (MRI), except when MRI was contraindicated such as in heart pacemaker patients. Exclusion criteria were three or more levels of fracture, re-fracture, more than two months after symptom onset, severe degeneration that could not be checked for exact value, non-osteoporotic fracture, and adjacent segment fracture at the fusion level.

B. Subjects

A total of 222 patients underwent operations from January 2008 to October 2012. One hundred ninety-five patients were included and 27 patients were excluded based on the exclusion criteria.

Female patients were 155 (79.5%) cases whereas males were 40 (20.5%). Mean age was 73.30 ± 8.4 years old, ranging from 44 to 104 years old. One level fractures numbered 169 (86.7%) cases and two level fractures numbered 26 (13.3%). A total of 221 vertebral levels were subsequently included.

Although vertebroplasty and kyphoplasty are simple procedures, a different operator could bias the results. The present study has included only the first author’s operations in order to maintain an identical operative technique. The first author had more than two years’ experience performing vertebroplasty and kyphoplasty prior to the present study.

The polymethylmetacrylate (PMMA) bone cements were Exolent spine bone cement (Elmdown Ltd. London, U.K.) and Biomet bone cement V (Biomet Inc. Indiana, USA). A Sewon balloon syringe pump and bone filler device (Sewon Medical Co., Ltd., Rep. of Korea) were used for ballooning and bone cement injection, respectively.

C. Measurement

Preoperative and postoperative values of vertebral height, compression ratio, and segmental Cobb’s angle were measured in lateral X-ray from a workstation display (Raypax Co. Ltd. Rep. of Korea). Checking the exact length and angle from the spine of an elderly

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patient was difficult because of bony spurs and degenerative kyphoscoliosis. In order to minimize inter-rater measurement errors, the first author checked all the data.

The measurement standard followed Keynan’s method (Keynan et al., 2006). The vertebral height was checked at the anterior aspect of the vertebral body. The compression ratio was calculated by subtracting the height of compressed vertebra from an average height of two adjacent vertebrae. Segmental Cobb’s angle was measured from upper endplate of the upper vertebral body and the lower endplate of the lower vertebral body.

D. Surgical technique

Conventional 10-gauge vertebroplasty needles were inserted into both pedicles. A guide wire was inserted through the needle, and then the needle was removed. A working cannula was inserted through the guide wire. The anterior tip of the working cannula was located within 5 mm of the posterior vertebral body margin. A reamer was advanced toward the anterior margin of the vertebral body to make a hollow tract. The bone filler device (a

plunger system with a nozzle and a stylet) was then filled with liquefied bone cement (Fig. 1). A bone cement-filled bone filler device was inserted into each of the working cannulas, and both were injected at the same time. Although the tract was created close to anterior vertebral body margin, the bone filler device was placed at the center of the vertebral body, as this was considered to reduce bone cement leakage.

One bone filler device was filled with 1.8 cc of bone cement. Four bone filler devices were injected for thoracolumbar lesion unless the leakage was prominent. Two or three bone filler devices were used for small upper- to mid-thoracic level injections. Every procedure was performed under fluoroscopic guidance.

E. Statistical Analysis

Comparisons between the vertebroplasty and kyphoplasty groups were analyzed with independent t-test for continuous variables and Pearson chi-square test for categorical variables. Relationship between vertebral height, compression ratio, and segmental Cobb’s angle were examined by correlation analysis. The general linear model (ANCOVA) was used to adjust effects of preoperative conditions. Risk factors for bone cement leakage were analyzed with logistic regression analysis. For all analyses, a two-sided p < 0.05 was

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considered statistically significant. Statistical analysis was performed using SPSS (version 15, SPSS Inc., Chicago, IL).

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III. RESULT

Vertebroplasty was performed for 109 (49.3%) levels and kyphoplasty for 112 (50.7%) (Table 1). The fracture level was categorized into three groups: thoracic spine fractures (T5-10) numbered 46 (20.8 %) levels, thoracolumbar (T11-L1) numbered 129 (58.4%), and lumbar (L2-5) numbered 46 (20.8%).

The preoperative period was divided into symptom-to-diagnosis and diagnosis-to-operation. The mean interval from pain onset to hospital arrival was 7.24 ± 10.8 days. The mean interval from diagnosis to operation was 14.14 ± 10.3 days.

The age, fracture level group, and BMD were not statistically different between the vertebroplasty and kyphoplasty groups (p > 0.05, Table 1).

Diagnosis to operation interval was not statistically different, whereas symptom onset to hospital arrival interval was significantly lower in the vertebroplasty group (3.70 ± 4.90 days) than in the kyphoplasty group (10.67 ± 13.48 days, p < 0.05, Table 1). Existence of an

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Table 1. Demographic data and comparison of preoperative condition.

Vertebroplasty-BF† _{Kyphoplasty p value}

Cases (%) 109 (49.3%) 112 (50.7%) Gender (M:F) 14:95 30:82 Age (years) 73.39 ± 8.58 73.48 ± 8.39 0.939¶

Bone densitometry -3.10 ± 1.05 -2.93 ± 0.98 0.186¶

Onset to diagnosis (day) 3.70 ± 4.90 10.67 ± 13.48 0.000*,¶

Diagnosis to operation (day) 13.16 ± 6.56 15.09 ± 12.85 0.186¶

Level group 0.413§

Thoracic 24 (10.9%) 22 (10.0%) Thoracolumbar 59 (26.7%) 70 (31.7%) Lumbar 26 (11.8%) 20 (9.0%)

Intravertebral cleft 10 (4.5%) 14 (6.3%) 0.427§

†Vertebroplasty with bone filler device

*p < 0.05, ¶ _{independent t-test,} § _{Pearson chi-square test}

The distribution shape of the injected bone cement was categorized into spongy, lumped, and mixed type (Table 2) (Oka et al., 2005; Tanigawa et al., 2007; Kim et al., 2012b). Most vertebroplasty groups had the spongy type (103 cases, 94.5%) (Fig. 2-a). The kyphoplasty group numbered only 47 cases (42%); even if mixed type (32 cases, 28.6%) were included, the difference between the kyphoplasty and vertebroplasty groups was obvious. The lumped type accounted for 29.5% of the kyphoplasty group, which was much greater than the 4.6% observed in the vertebroplasty group (Fig. 2-b).

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Fig. 2. Different bone cement distributions. a) Spongy shape after vertebroplasty with

bone filler device. b) Lumped shape after kyphoplasty.

Bone cement leakage was defined as cement leakage to the paravertebral area, disc space, vein, or lung. The leakage was verified at postoperative X-ray. Most leakage was minimal and none of the leakage had clinical importance. Leakage occurred in 56 cases (51.4%) of vertebroplasty and 49 cases (43.8%) of kyphoplasty (Fig. 3). However, these values were not statistically different (p > 0.05, Table 2).

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A greater amount of bone cement was used in the vertebroplasty group (6.00 ± 1.39 cc) than in the kyphoplasty group (5.54 ± 1.40 cc, p < 0.05, Table 2).

Fig. 3. Bone cement leakage after procedure. a) Venous leakage after vertebroplasty with

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Table 2. Comparison of vertebral height, compression ratio, Cobb’s angle, and bone cement.

Vertebroplasty-BF† _{Kyphoplasty p value}

Bone cement distribution 0.000*,§

Sponge 103 (94.5%) 47 (42.0%) Lump 5 ( 4.6%) 33 (29.5%) Mixed 1 ( 0.9%) 32 (28.6%) Bone cement leakage 56 (51.4%) 49 (43.8%) 0.256§

Bone cement volume (cc) 6.00 ± 1.39 5.54 ± 1.40 0.014*,¶

Pre-operative

Vertebral height (mm) 20.71 ± 3.93 16.79 ± 5.71 0.000*,¶

Compression ratio (%) 20.67 ± 11.33 37.17 ± 18.20 0.000*,¶

Segmental Cobb’s angle (°) 5.83 ± 14.56 14.52 ± 14.14 0.000*,¶

Post-operative

Vertebral height (mm) 23.48 ± 3.70 21.42 ± 5.09 0.001*,¶

Compression ratio (%) 10.61 ± 8.31 19.93 ± 14.49 0.000*,¶

Segmental Cobb’s angle (°) 3.84 ± 12.89 7.98 ± 12.87 0.018*,¶

Vertebral height restoration (mm) 2.76 ± 2.35 4.63 ± 3.48 0.000*,¶

Compression ratio reduction (%) -10.06 ± 8.60 -17.25 ± 13.16 0.000*,¶

Cobb’s angle restoration (°) 3.82 ± 4.14 7.82 ± 5.68 0.000*,¶

†Vertebroplasty with bone filler device

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The vertebral height and compression ratio had a strong correlation: r = -0.871 for preoperative, -0.762 for postoperative (p < 0.05, Table 3, Fig. 4). However, the segmental Cobb’s angle had relatively weak correlation with the vertebral height and compression ratio: r = -0.658, -0.591 for preoperative, r = -0.529, -0.411 for postoperative (p < 0.05, Table 3, Fig. 4).

Table 3. Correlation of vertebral height, compression ratio, and Cobb’s angle. Compression ratio Cobb’s angle

Preoperative Preoperative Postoperative Postoperative Vertebral height Preoperative -0.871 (0.000*) -0.658 (0.000*) Postoperative -0.762 (0.000*) -0.591 (0.000*) Compression ratio Preoperative -0.529 (0.000*) Postoperative -0.411 (0.000*) Examined by Pearson correlation analysis, *p < 0.05

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Fig. 4. Correlation relationship between vertebral height restoration, compression ratio restoration, and segmental Cobb’s angle change.

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Preoperative vertebral height was significantly larger in the vertebroplasty group; preoperative compression ratio and segmental Cobb’s angle were significantly larger in the kyphoplasty group (p < 0.05, Table 2). This meant that the kyphoplasty group had a more prominent preoperative compression when compared to the vertebroplasty group.

The postoperative vertebral height, compression ratio, and segmental Cobb’s angle showed the same statistically significant differences (p < 0.05, Table 2). The vertebral height restoration of the vertebroplasty group was 2.76 ± 2.35 mm, whereas the kyphoplasty group was 4.63 ± 3.48 mm (p < 0.05, Table 2). The compression ratio reduction of the

vertebroplasty group was 10.06 ± 8.60%, whereas it was 17.25 ± 13.16% in the kyphoplasty group (p < 0.05, Table 2). The segmental Cobb’s angle change was also lower in the

vertebroplasty group (3.82 ± 4.14°) than in the kyphoplasty group (7.82 ± 5.68°, p < 0.05, Table 2). Simple comparisons of changes of the three variables showed the kyphoplasty technique was more effective than vertebroplasty with the bone filler device.

Postoperative values were adjusted with the general linear model using analysis of covariance (ANCOVA). Variables for adjustment included age, BMD, onset-to-diagnosis, diagnosis-to-operation, and bone cement volume. In addition, adjusted postoperative vertebral height included preoperative height, adjusted postoperative compression ratio included preoperative ratio, and adjusted postoperative segmental Cobb’s angle included preoperative angle. The adjusted postoperative vertebral height and segmental Cobb’s angle had statistically significant differences, whereas adjusted postoperative compression ratio failed to show statistical difference (15.194 ± 0.859 for vertebroplasty, 15.460 ± 0.845 for kyphoplasty, p < 0.05, Table 4).

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Table 4. Comparison of postoperative values after correction of preoperative variables. Postoperative value Adjusted mean

¶

p value

Vertebroplasty-BF† Kyphoplasty

Vertebral height (mm) 21.988 ± 0.244 22.869 ± 0.241 0.016* Compression ratio (%) 15.194 ± 0.859 15.460 ± 0.845 0.838 Segmental Cobb’s angle (°) 7.170 ± 0.484 4.741 ± 0.477 0.001* †Vertebroplasty with bone filler device, *p < 0.05

¶ _{Examined by general linear model analysis (ANCOVA)}

- Postoperative values were adjusted for age, BMD, onset to diagnosis interval, diagnosis to operation interval, and injected bone cement volume.

- Variables of each preoperative value were added to adjust each postoperative value.

Risk factors for bone cement leakage were analyzed by logistic regression analysis. Included factors were operation type, age, gender, level group, onset to admission interval, diagnosis to operation interval, injected bone cement volume, intravertebral cleft, BMD, bone cement distribution type, preoperative vertebral height, preoperative compression ratio, and preoperative segmental Cobb’s angle. The analysis indicated that BMD and diagnosis to operation interval were statistically significant risk factors for bone cement leakage (p < 0.05, Table 5). The odds ratio of leakage increased by 48.2% when BMD increased by one unit and increased by 3.4% when diagnosis to operation interval increased by one day.

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Table 5. Risk factor assessments of bone cement leakage.

B p value Odds ratio 95.0% C.I.

Continuous variables

Age -0.016 0.398 0.984 0.949 - 1.021 Onset to admission 0.018 0.247 1.018 0.988 - 1.049 Diagnosis to operation 0.034 0.036 1.034 1.002 - 1.067 Bone densitometry 0.394 0.015 1.482 1.078 - 2.038 Bone cement volume -0.168 0.188 0.845 0.658 - 1.086 Preoperative height 0.066 0.489 1.068 0.886 - 1.288 Preoperative compression 0.002 0.936 1.002 0.954 - 1.052 Preoperative Cobb’s angle -0.004 0.812 0.996 0.966 - 1.027

Categorical variables Operation Vertebroplasty-BF† _1.000 Kyphoplasty -0.357 0.350 0.700 0.331 - 1.481 Gender Male 1.000 Female 0.309 0.424 1.362 0.638 - 2.905 Level group Thoracic 0.322 1.000 Thoracolumbar 0.042 0.932 1.043 0.397 - 2.744 Lumbar -0.738 0.288 0.478 0.123 - 1.864 Cleft sign on MRI

No 1.000

Yes 0.093 0.852 1.098 0.413 - 2.917 Bone cement distribution

Sponge 0.865 1.000

Lump 0.015 0.977 1.015 0.366 - 2.818 Mixed -0.237 0.634 0.789 0.298 - 2.090 Examined by binary logistic regression analysis, C.I.: confidence interval

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IV. DISCUSSION

A. Vertebral height, compression ratio, and segmental Cobb’s angle

The present study compared vertebral height, compression ratio, and segmental Cobb’s angle change following the two procedures. Many studies have measured preoperative and postoperative values of the vertebral height and/or wedge angle to compare the

vertebroplasty and kyphoplasty, but the compression ratio has not been included previously (Hiwatashi et al., 2005; Pradhan et al., 2006; Hiwatashi et al., 2009; Sun et al., 2011). Normal vertebral height varies according to the patient’s height, gender, level, and

degenerative changes. Although the vertebral height is increased after the operation, it is not a consistent indicator for the measurement of compression. In contrast, Keynan’s method defines the vertebral compression ratio as including the vertebral height of the compressed level and two adjacent levels (Keynan et al., 2006). This measurement represents a practical change of the vertebral body and is more constant than the vertebral height.

The vertebral height and compression ratio showed very strong correlation, whereas segmental Cobb’s angle change had weak correlation with the vertebral height and

compression ratio (Fig. 4, Table 3). The cause of the weak correlation of segmental Cobb’s angle was assumed to reflect the relative position of the patient: a postoperative X-ray was taken in the supine position, whereas the preoperative X-ray was taken in the supine or erect position, according to the patient’s pain severity. Teng et al. reported that the effect of vertebroplasty on kyphosis reduction was less marked than on the vertebral height restoration, because the kyphosis angle was affected by the relative position of adjacent vertebral bodies and the intervertebral disc (Teng et al., 2003).

Based on the correlation and regularity of variables, the present study regarded that the compression ratio is a more important and influential factor than the vertebral height and segmental Cobb’s angle.

B. Equality of preoperative variables and adjusted postoperative variables

The vertebroplasty and kyphoplasty groups had similar frequencies (109, 112 cases). Preoperative covariances including age, BMD, fractured level group, diagnosis to operation interval did not differ between the two groups. Symptom onset to diagnosis interval was

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significantly different; the reason for this was unclear but represented an unequal factor between the two groups.

Preoperative values of vertebral height, compression ratio, and segmental Cobb’s angle were significantly different between the two groups (p < 0.05, Table 2). In other words, the compression of the kyphoplasty group was more prominent. Although postoperative variables showed more changes in the kyphoplasty group, these were based on different preoperative conditions (Table 2). For example, 5% of the compression cases did not show increases greater than 5%, whereas 30% of the compression cases showed increases up to 30%. The group with greater compression had more potential for restoration. Clearly, these different preoperative conditions would have affected postoperative values.

The postoperative results were adjusted using a general linear model to overcome the different preoperative conditions (Table 4). The adjusted postoperative values were quite different from the pre-adjusted results (Table2). The adjusted postoperative vertebral height was significantly higher in the kyphoplasty group. The adjusted segmental Cobb’s angle was smaller in the kyphoplasty group. These results were the opposite of those obtained from the pre-adjusted comparison. Kyphoplasty showed a more effective recovery of the vertebral height and segmental Cobb’s angle. However, the postoperative compression ratio, a principal and most influential factor, differed, as it failed to show any advantage of the kyphoplasty. The vertebroplasty with the bone filler device achieved the same compression reduction as was observed with kyphoplasty.

C. Intravertebral cleft and bone cement distribution

The intravertebral cleft previously represented ischemic necrosis (Kümmell’s disease) (Laloux et al., 1991; Dupuy et al., 1996; Chou and Knight, 1997). The recent studies show that the cleft is a region of nonunion, with pseudoarthrosis of the fracture (Mochida et al., 2001; Ito et al., 2002; Lane et al., 2002; Hashidate et al., 2006). The cleft appears on non-contrast MRI as a vertebral cavity filled with fluid or gas occurring at the fractured endplate (Oka et al., 2005). It is an indication of nonunion of the bone and can show motion according to the patient’s position or respiration (Malghem et al., 1993). It is also an important factor for vertebral re-collapse and lumped type bone cement distribution (Kim et al., 2012b).

The bone cement distribution was categorized as spongy (trabecular, interdigitation), lumped (solid, cleft), and mixed type (Oka et al., 2005; Tanigawa et al., 2007; Kim et al.,

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2012b). The spongy type was considered a more physiological distribution. The lumped type was a round mass congregation of bone cement with destroyed trabecular structure. It was related to the peri-halo phenomenon that led to vertebral re-collapse and new fractures of the adjacent vertebra (Tanigawa et al., 2007; Kim et al., 2012b). Tanigawa et al. reported that the lump shaped distribution increased the incidence of new compression fractures (Tanigawa et al., 2007). In contrast, another study reported that bone cement distribution had no influence on adjacent new fractures (Rho et al., 2012).

The present study showed that the frequency of intravertebral clefts did not differ between the two groups (Table 1). However, the bone cement distribution was significantly different (Table 2). The lump shaped distribution was found significantly more frequently in the kyphoplasty group; it was considered that the balloon inflation of the kyphoplasty had destroyed the normal trabecular structure. Vertebroplasty with the bone filler device was superior to kyphoplasty for bone cement distribution, as a more physiological spongy type bone cement distribution was made possible without destroying the normal trabecular structure.

D. Bone cement volume

The amount of bone cement that is adequate for vertebroplasty and kyphoplasty remains uncertain. Molloy et al. suggested that unipedicular injection of 3.5 cc of bone cement did not lead to preferential collapse (Molloy et al., 2005). A small bone cement amount is a cause of procedure failure, whereas a large bone cement amount may not be advisable clinically as it increases the risk of cement leakage (Ryu et al., 2002). A recent study indicated the optimal bone cement fraction was 24% of the vertebral body and suggested an optimal volume based on levels and gender: e.g., T12 for female was 3.35 to 5.22 cc (Nieuwenhuijse et al., 2012).

The mean bone cement amount differed according to several studies. Kummar et al. injected 3.2 cc for vertebroplasty and 1.8 cc for kyphoplasty (Kumar et al., 2010), while Movrin et al. injected 5.8 ± 1.7 and 5.5 ± 1.1 cc, respectively (Movrin et al., 2010), Lie et al. injected 4.91 ± 0.65 and 5.56 ± 0.62 cc, respectively (Liu et al., 2010), and Schofer et al. injected 3.9 ± 1.5 and 4.9 ± 1.2 cc (Schofer et al., 2009).

In the present study, the mean bone cement volume was 6.00 ± 1.39 cc for vertebroplasty and 5.54 ± 1.40 cc for kyphoplasty, which greater amounts than were used in previous

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studies (Table 2). The bone cement volume used for the vertebroplasty group was

statistically greater than that used for the kyphoplasty group. This suggested that the cavity formation of the balloon of the kyphoplasty did not result in a greater need for bone cement injection when compared with the hollow tract formation of the bone filler device.

E. Bone cement leakage rate

The bone cement leakage is the most bothersome problem occurring during these procedures. Although most bone cement leakage did not cause clinical symptoms, some articles have reported serious complications such as symptomatic pulmonary embolism and intra-cardiac foreign body (Abdul-Jalil et al., 2007; Kim et al., 2013; Sifuentes Giraldo et al., 2013).

The combination of low-viscosity cement and high injection pressure leads to more frequent cement leakage through fractures and blood vessels (Nieuwenhuijse et al., 2011; Ma et al., 2012). More compression of the vertebral body and greater cortical disruption are also risk factors of bone cement leakage (Nieuwenhuijse et al., 2011). The presence of an

intravertebral cleft is also related to greater bone cement leakage (Ha et al., 2006; Nieuwenhuijse et al., 2011).

When compared with kyphoplasty, the vertebroplasty itself is a risk factor because of the use of lower viscosity cement and a smaller diameter needle. Leakage rates ranging from 11% to 73% have been reported in previous studies (Garfin et al., 2001; Watts et al., 2001;

Shapiro et al., 2003). The different diagnostic criteria used for leakage detection by X-ray were assumed to be a cause of this wide range of leakage rates. As shown in the CT study, if stricter criteria were applied, the leakage rate determined by X-ray would significantly increase (Schmidt et al., 2005).

Meta-analysis of the bone cement leakage rate revealed a value of 21.6% for

vertebroplasty and 13.1% for kyphoplasty, and the difference was statistically significant (Ma et al., 2012). The lower leakage rate is a practical reason for the preference for

kyphoplasty. The leakage rate in the present study was 51.4% for vertebroplasty and 43.8% for kyphoplasty, and these values were not statistically different (Table 2). The high rate of bone cement leakage of the conventional vertebroplasty could be adequately reduced by the use of the bone filler device.

- 20 - F. Leakage risk factors due to preoperative conditions

Logistic regression analysis of the preoperative conditions showed BMD and diagnosis to operation interval to be the significant risk factors. The bone cement leakage decreased 48.2% when BMD decreased by one unit. The leakage decreased 3.4% when diagnosis to operation interval decreased by one day (Table 5). In turn, an osteoporotic vertebra with low BMD had a low risk of bone cement leakage. Early operation after diagnosis also decreased the leakage rate. The operation type was not a statistically significant risk factor; the choice of the vertebroplasty with the bone filler device was not a risk factor of bone cement leakage. Although the intravertebral cleft was generally considered to be a risk factor for bone cement leakage, a recent study reported that it was not (Tanigawa et al., 2009). The present study also supported this conclusion as the logistic regression analysis also indicated that the intravertebral cleft was not a risk factor.

G. Limitations

The present study had several limitations. It was non-randomized and observational study. A control group that underwent conservative management was not included. The bone

cement injection pressure and velocity were controlled manually. Operative results were one surgeon’s results. Multicenter research and would increase reliability. Randomized case control trials should be evaluated.

- 21 -

V. CONCLUSION

Kyphoplasty is regarded as the next step in conventional vertebroplasty. However, this procedure has a few drawbacks such as destruction of the vertebral trabecular structure, a lumped shape bone cement distribution, and higher medical costs. Vertebroplasty with a bone filler device is a simple and familiar procedure. It showed an equivalent compression ratio reduction to that achieved with kyphoplasty. The bone cement distribution was more physiological and lumped distribution was avoided. Sufficient bone cement injection was possible without increasing the rate of bone cement leakage. Therefore, vertebroplasty with a bone filler device can be considered as a compatible option for the osteoporotic compression fracture, and has the advantages of both conventional vertebroplasty and kyphoplasty.

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- 국문 요약 -

피스톤

방식 주입기를 이용한 척추체 성형술의 효과

- 28 - 정한 수술 후 척추체 높이와 Cobb 각도는 두 수술 그룹 간 유의한 차이를 보인 반면, 보정한 수술 후 압박율은 유의한 차이를 보이지 않았다 (p < 0.05). 뼈시멘 트 분포는 척추체 성형술 군에서는 대부분이 spongy형태를 보였으나 (94.5%), 풍 선 척추체 성형술 군에서는 42%로 낮았다. 높은 골밀도 (BMD) 수치와 진단 후 수술까지의 긴 기간은 뼈시멘트 누출을 증가시키는 위험 인자였다. 결론: 피스톤 방식 뼈시멘트 주입기를 이용한 척추체 성형술은 풍선 척추체 성형 술과 대등한 압박율 복원 및 뼈시멘트 누출율을 보일 뿐 아니라, 대부분이 spongy 형태의 뼈시멘트 분포를 보여. 척추체 성형술과 풍선 척추체 성형술의 이 점을 함께 보여주는 효과적인 치료 방법으로 생각된다. 핵심어: 척추체 성형술, 풍선 척추체 성형술, bone filler, 척추체 압박 골절, 뼈시멘 트