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

intravertebral cleft on MRI was not statistically different (p > 0.05, Table 1).

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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 bone filler device. b) Disc space and paravertebral leakage after kyphoplasty.

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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

*p < 0.05, ^¶ independent t-test, ^§ Pearson chi-square test

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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.

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

†Vertebroplasty with bone filler device

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