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Comparison of unipedicular and bipedicular percutaneous kyphoplasty for treating osteoporotic vertebral compression fractures: a meta-analysis

LI, Lian-hua; SUN, Tian-sheng; LIU, Zhi; ZHANG, Jian-zheng; ZHANG, Yan; CAI, Yan-hong; WANG, Hao

doi: 10.3760/cma.j.issn.0366-6999.20131398
Meta analysis
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Background Percutaneous vertebroplasty (PKP) has proved its effectiveness regarding minimal invasion, rapid pain reduction, safe cement augmentation, restoring vertebral height, and accelerating complete recovery of osteoporotic vertebral compression fractures (OVCFs). Whether unipedicular or bipedicular PKP provides a better outcome is controversial.

Methods We searched PubMed, Cochrane Database of Systematic Reviews, Cochrane Central Register of Controlled Trials, Web of Knowledge, Chinese Biomedical Literature Database, and Wanfang Data from January 1980 to March 2013 with “kyphoplasty”, “unipedicular”, “bipedicular”, “compression fracture”, and “randomized controlled trial”. Risk of bias in the included studies was assessed according to a 12-item scale. Meta-analysis was performed. Dichotomous and continuous variables were calculated using the odds ratio (OR) and standardized mean difference (SMD), respectively.

Results Seven studies involving 440 patients and 559 vertebral bodies met the criteria for inclusion. Among them, one randomized controlled trial had a high risk of bias and six a low risk. The pain visual analogue scale (VAS) SMDs were -0.02 (P=0.88) for short-term follow-up (≤3 months) and 0.03 (P=0.82) for long-term follow-up (≥1 year). Oswestry Disability Index (ODI) SMDs at short- and long-term follow-up were not statistically significant (-0.04, P=0.77 and -0.07, P=0.74, respectively). This meta-analysis showed greater polymethylmethacrylate volume (SMD -1.08, P=0.00) and operation time (SMD -2.40, P=0.00), favoring unipedicular PKP. Radiographic outcomes—preoperative kyphosis angle, restoration rate, reduction angle, loss of reduction angle—were not statistically different between the groups. Pooled analyses of cement leakage and subsequent adjacent OVCFs showed no significant differences between the groups, with OR=0.82 (P=0.79) and OR=1.41 (P=0.70), respectively.

Conclusions This meta-analysis comparing unipedicular and bipedicular PKP demonstrated no significant differences regarding VAS, ODI, radiographic outcomes, or complications. Considering the longer operation time and radiation exposure with bipedicular PKP, we recommend unipedicular PKP over bipedicular PKP for treating OVCFs.

People's Liberation Army Institute of Orthopedics, Beijing Army General Hospital, Beijing 100700, China (Li LH, Sun TS, Liu Z, Zhang JZ, Zhang Y, Cai YH and Wang H)

Correspondence to: Dr. SUN Tian-sheng, People's Liberation Army Institute of Orthopedics, Beijing Army General Hospital, Beijing 100700, China (Tel: 86-10-84015545. Email: suntiansheng-@163.com)

This research was supported by a grant from the Beijing Science and Technology Project (No. D101100049910004).

(Received May 28, 2013)

Edited by CUI Yi

The incidence of osteoporosis has been increasing with the aging of the world's population. Osteoporotic vertebral compression fractures (OVCFs) are the most common complication of osteoporosis, affecting more than 200 million individuals worldwide.1,2 Galibert et al first reported percutaneous vertebroplasty (PVP) in 1987 for minimally invasive treatment of hemangiomas. Since then, the technique has been adapted to treat OVCFs. Percutaneous kyphoplasty (PKP), developed from PVP, was introduced in 1998 to restore vertebral body height and help realign the spine using an inflatable balloon to reduce the fracture before injecting cement. Compared with conservative therapy and open surgery, PKP has proved to be effective. It is minimally invasive, quickly reduces pain, provides safe cement augmentation, restores vertebral height, and accelerates complete recovery of OVCFs.3–7

The standard technique for kyphoplasty involves a bipedicular approach using two balloon tamps. Recently, however, a unipedicular approach has been advocated that offers the potential advantages of reducing the operating time, providing less radiation exposure, and lowering the risk of cement leakage. It is also increases the costeffectiveness of the procedure.8–11 Surgeons, however, cannot reach a consensus on whether unipedicular or bipedicular PKP is optimal for OVCF patients.

Several randomized controlled trials (RCTs) have compared unipedicular and bipedicular balloon kyphoplasty for treatment of OVCFs, but they were all limited with regard to their small sample size and methodological deficiencies. We therefore performed a systematic review and meta-analysis to evaluate the entire evidence based on the RCTs, comparing the efficacy and safety of unipedicular and bipedicular balloon kyphoplasty for treatment of OVCFs.

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METHODS

Search strategy

Our search strategy followed the Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines.12 We searched PubMed, Cochrane Database of Systematic Reviews, Cochrane Central Register of Controlled Trials, Web of Knowledge, Chinese Biomedical Literature Database, and Wanfang Data. We also hand-searched several Chinese orthopedic journals. The electronic databases were searched from January 1980 to March 2013. Medical Subject Headings terms “kyphoplasty” and “compression fracture” were used in each database. In addition, the keyword approach used “kyphoplasty”, “unipedicular”, “bipedicular”, “compression fracture”, and “randomized controlled trial”. The Clinical Queries filter was used on the “therapy” category and “narrow” scope. A filter for “randomized controlled trials” was also separately searched using the above keywords. Reference lists were reviewed for any additional studies not identified by the search. The search strategy was not limited by language.

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Eligibility criteria

Two review authors (ZHANG Yan and WANG Hao) independently reviewed the abstracts and full text of articles to determine eligibility based on the criteria listed below. If a consensus could not be reached, a third review author (LI Lian-hua) resolved the disagreement.

The following eligibility criteria were used when selecting the trials: types of study included: any published RCT or quasi-RCT that compared unipedicular and bipedicular PKP for OVCFs; types of participant included: male and female patients aged >50 years who had an acute or chronic OVCF that caused pain and functional limitations in their daily activities; exclusion criteria: patients with primary or secondary neoplasm, preexisting chronic pain or functional disability unrelated to vertebral fracture, and/or vertebral fractures without signal changes seen on magnetic resonance imaging; types of intervention: unipedicular or bipedicular kyphoplasty; clinical outcome measures: visual analogue scale (VAS), Oswestry Disability Index (ODI), polymethylmethacrylate (PMMA) volume, and operation time; radiographic outcomes: kyphosis angle and anterior vertebral body height; and complication outcomes: PMMA leakage and adjacent OVCF.

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Data extraction

Two review authors (ZHANG Jian-zheng and CAI Yanhong) independently selected trials satisfying the inclusion criteria and extracted data for the outcomes using a data-extraction form. Relevant data included patients' demographics, study characteristics, types of interventions, numbers of vertebral bodies, surgical procedures, and outcome parameters. Another review author (LI Lian-hua) rechecked the extracted data.

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Assessment of methodological quality

The risk of bias in the included studies was independently assessed by two authors (ZHANG Jian-zheng and WANG Hao), in accordance with a 12-item scale13 that was suggested by the Cochrane Back Review Group (CBRG). It assessed factors such as randomization, allocation concealment, similar baseline, blinding, selective reporting, patient compliance, lost to follow-up, similar timing, and ITT analysis. A third author (LI Lian-hua) was the adjudicator when no consensus was achieved.

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Statistical analysis

Meta-analyses were performed using STATA 12.0 software (Stata Corporation, College Station, TX, USA). For dichotomous outcomes, the odds ratio (OR) and 95% confidence interval (CI) were assessed. For continuous outcomes, means and standard deviations were pooled to a standardized mean difference (SMD) and 95% CI. Egger's test was used to assess publication bias among the included trials. A probability of P <0.05 was regarded as statistically significant.

The assessment for statistical heterogeneity was calculated using the χ2 and I2 tests. A fixed-effects model was applied only in the absence of heterogeneity. If the P value for the χ2 test was ≤0.1 or the I2 value was >50%, there was substantial evidence of heterogeneity. We then tried to identify the source of heterogeneity by subgroup analysis and sensitivity analysis. A random-effects model should be applied in a corresponding meta-analysis when the source of heterogeneity cannot be found.

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RESULTS

Characteristics of eligible studies

After a complete systematic review was performed, seven RCTs14–20 met the inclusion criteria (Figure 1). They consisted of 440 patients (63 males and 377 females) and 559 vertebral bodies, with the individual study sample size ranging from 46 to 127 patients. In all, 222 patients underwent unipedicular PKP, and 218 underwent bipedicular PKP. Five15–19 of the seven RCTs were conducted in China, one20 in the United States, and one14 in South Korea. The study designs for the RCTs' inclusion criteria varied. Two RCTs14,20 reported acute painful OVCFs, with the interval from injury to surgery time <3 months. Two RCTs16,17 reported on chronic painful OVCFs, with the injury-to-surgery interval >6 months. The remaining three RCTs15,18,19 did not describe the interval duration. One study16 was an update of another investigation,17 with two weeks and 24 months follow-up, respectively. The characteristics of the original studies are presented in Table 1.

Figure 1.

Figure 1.

Table 1

Table 1

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Quality assessment

The studies were rated as having a “low risk of bias” when at least 6 of the 12 CBRG criteria were met and the study had no serious flaws. Studies with serious flaws—those in which fewer than six of the criteria were met—were rated as having a “high risk of bias”. Of the seven included studies, only one RCT16 had a high risk of bias. The other six RCTs had a low risk of bias. One trial19 reported inadequate generation of the allocation sequence, and one trial20 reported adequate allocation concealment. One study20 reported a single blinding to patients. None reported double blinding. Six others did not mention the blinding method. The methodological quality of the included studies is illustrated in Figure 2. Judgments about each risk-of-bias item are presented as percentages across all of the included studies in Figure 3.

Figure 2.

Figure 2.

Figure 3.

Figure 3.

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Visual analogue scale

The pain intensity measured by a VAS pain score was extracted and summarized as the VAS before PKP and VAS after PKP at the short-term follow-up (≤3 months) and the long-term follow-up (≥1 year). We then pooled the mean differences across the groups. Statistical evidence of heterogeneity was not found, and a fixed-effects model was applied. The SMD value on VAS before PKP was 0.11 (95% CI: -0. 10 to 0.31, P=0.72). Similar to the short- and long-term follow-up VAS, outcomes revealed no statistically significant difference between these two interventions, with SMD values of -0.02 (95% CI: -0.24 to 0.20, P=0.88) and 0.03 (95% CI: -0.21 to 0.27, P=0.82), respectively, as shown in Figure 4.

Figure 4.

Figure 4.

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ODI

Disability measured by the ODI was extracted and was summarized as the ODI before PKP and the short-term follow-up ODI (≤3 months) and the long-term follow-up ODI (≥1 year) after PKP. We then pooled the data across the groups. Statistical evidence of heterogeneity was indicated on the ODI before PKP (P=0.09, I2=57.3). The sensitivity analysis showed that the heterogeneity of outcomes could be attributed to the reason reported in the study of Luo et al.19 We did not drop this study because only three studies provided ODI information before the PKP data. A random-effects model was applied to the ODI before PKP, and the SMD was 0.06 (95% CI: -0. 37 to 0.48, P=0.90). No statistical evidence of heterogeneity was found for short- and long-term follow-up ODI values after PKP, and a fixed-effects model was applied. The overall pooled mean difference values of -0.04 (95% CI: -0.30 to 0.22, P=0.77) and -0.07 (95% CI: -0.38 to 0.34, P=0.74), respectively, showed no significant difference between the unipedicular and bipedicular PKP groups.

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PMMA volume

The three studies17,19,20 that provided PMMA volume data included a total of 229 patients and 323 vertebral bodies. A random-effects model was applied because significant heterogeneity was found (P=0.13, I2=50.4). Also, the sensitivity analysis showed that the heterogeneity of outcomes could be derived from the results of the study reported by Luo et al.19 The SMD value of -1.08 (95% CI: -1.43 to 0.73, P=0.00) indicated that there is significant difference between the two groups, with the unipedicular PKP having a lower PMMA volume than the bipedicular PKP group.

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Operation time

Five studies,15–18,20 consisting of 261 patients, provided operation duration data. There was no statistically significant evidence of heterogeneity (P=0.00, I2=94.7%), and a fixed-effects model was applied. The pooled results showed a significant difference between the unipedicular and bipedicular PKP groups (SMD = -2.40, 95% CI: -2.75 to 2.05; P=0.00). It appeared that unipedicular PKP had a shorter operation time than bipedicular PKP.

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Radiographic outcomes

Four studies14,15,18,20 reported the kyphosis angle before operation. It was defined as the angle between the superior and inferior endplates of the fractured vertebra. Two studies18,20 calculated the mean reduction angle, and two other studies14,16 provided the restoration rate. Two studies14,17 gave details regarding loss of the reduction angle. Statistical analysis of radiographic outcomes— preoperative kyphosis angle, restoration rate, reduction angle, loss of reduction angle—was conducted, and the main results are shown in Table 2. The pooled SMD and P results for the radiographic outcomes showed no significant differences between unipedicular and bipedicular PKP.

Table 2

Table 2

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Complications

Cement leakage and subsequent adjacent OVCFs were the only complications included in these studies. Safety assessments for these two interventions were performed by extracting and pooling the relevant data. Four studies14,16,18,20 reported complications related to cement leakage. There were eight cement leakage events in 145 vertebral bodies (6%) after unipedicular PKP and 11 such events in 143 vertebral bodies (8%) after bipedicular PKP. The pooled analysis showed no significant differences between the unipedicular and bipedicular PKP groups (OR=0.82, 95% CI: 0.16 to 3.47; P=0.79) (Figure 5). Egger's test showed minimal evidence publication bias among the included trials (P=0.09). Only one study17 provided adequate information about adjacent OVCFs.17 There was no significant difference between the two groups (OR=1.41, 95% CI: 1.24 to 8.34; P=0.70).

Figure 5.

Figure 5.

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DISCUSSION

Osteoporosis is defined as diminished bone density measuring 2.5 standard deviations below the average bone density of healthy 25-year-old same-sex members of the population. In osteoporotic patients, the overall integrity of the vertebral body progressively diminishes as the density of the central cancellous bone mass decreases. This change disperses the biomechanical load onto cortical bone, thereby increasing the risk for a vertebral compression fracture.21 OVCFs commonly occur in the middle thoracic, low thoracic, and high lumbar areas (with most at the thoracolumbar junction, especially L14). They cause substantial back pain and deformity, decreasing the patient's quality of life and increasing mortality. OVCFs have been shown to be associated with an age-adjusted increase in mortality of up to 30%.22

Lieberman et al23 reported the first clinical results of PKP in 2001. PKP has several advantages over vertebroplasty. For example, PKP can effectively restore local kyphosis by reducing the fractured vertebra with an inflatable bone tamp. It also has a low rate of complications associated with thromboembolism or neurological deficits due to PMMA leakage.4–7 The traditional bipedicular technique of PKP is associated with some risks.23 Therefore, the unipedicular technique was applied. It is considered preferable to the bipedicular technique for several reasons. There is less radiation exposure and thus less radiation damage, and it shortens the operation time. It also reduces by 50% the risk of complications caused by vertebral pedicle puncture.

Unipedicular PKP is being increasingly used to treat OVCF. Papadopoulos et al9 reported that unilateral PKP can effectively alleviate pain and restore vertebral height. Song et al, in a retrospective study, found no obvious differences between unipedicular and bipedicular PKP in regard to the degree of alleviation of vertebral compression and angular kyphosis. They did, however, state that pain relief was more effective in the unipedicular group than in the bipedicular group, which may be related to the difference in pain intensity before surgery.24 Chen et al, in an RCT that compared unipedicular and bipedicular PKP for treating chronic painful OVCFs, found that there was better restoration of vertebral height in the bipedicular PKP group than in the unipedicular PKP group.16 Thus, there is still controversy about which of these interventions provides a better outcome.

This meta-analysis found no significant difference between the two procedures regarding short- and long-term follow-up outcomes using VAS scores. The exact mechanism of pain remission remains unclear. Belkoff et al25 reported that pain reduction was attributable to the immobility and inhibition of micromovements of the fractured fragment and the cytotoxic effect of PMMA, which relieves pain by damaging the terminal nerve. In contrast, Togawa et al reported that PMMA did not create a definitive thermic effect on pain reduction.26 Our study found that there was more PMMA volume in the bipedicular PKP group, but it did not provide more pain relief than was seen in the unipedicular PKP group. There was no significant difference in the ODI scores between the two groups at the short- and long-term follow-up evaluations, suggesting that the PMMA volume was not relevant regarding the quality of life after PKP for OVCFs.

In our meta-analysis, all of the RCTs14–20 showed significant restoration and repositioning of the fractured vertebral body after either unipedicular or bipedicular PKP. By contrast, there was no difference between the groups regarding the radiographic outcomes, including the mean restoration rate, reduction angle, and loss of the reduction angle. Fracture reduction by unipedicular or bipedicular PKP can be evaluated according to restoration of the shape of the vertebral body via balloon and the patient's prone position. Schofer et al demonstrated that there was no relation between improvements in vertebral body height and clinical outcomes after PKP.27

There was no significant difference between the two groups regarding the incidence of the main complications after PKP, including PMMA leakage and adjacent OVCFs. The incidences of PMMA leakage were 6% after unipedicular PKP and 8% after bipedicular PKP, figures consistent with those in previous studies.28 Although PMMA leakage usually does not result in clinical symptoms, more serious complications such as spinal stenosis and pulmonary embolism can cause disability and even death. These situations arise most often because low-viscosity cement has been used or the injection pressure was high. Whether an adjacent OVCF is caused by bone cement augmentation is debatable.28 Only one study included an adjacent OVCF analysis, so the results should be cautiously accepted.

Cadaveric studies concluded that both unipedicular and bipedicular PKP significantly increase total vertebral body stiffness. Bipedicular PKP creates stiffness uniformly across both sides of the vertebrae, whereas unipedicular PKP creates a biomechanical balance depending on the distribution of the cement.29 Chen et al believed that unilateral PKP pushed the osteoporotic bone to the opposite side and then reduced the fracture, increasing vertebral strength and stiffness.18 We think that the two factors both play a role after unipedicular PKP.

In conclusion, this meta-analysis, which compared unipedicular and bipedicular PKP, demonstrated no significant differences regarding VAS, ODI, radiographic outcomes, or complications. Considering the longer operation time and radiation exposure associated with bipedicular PKP, we recommend unipedicular PKP over bipedicular PKP for the treatment of OVCFs.

Our meta-analysis had several limitations. First, the methodological quality of included studies was not satisfactory mainly because a blinding method was not used in the trials, except in the study of Rebolledo et al.20 This strongly calls for new evidence with appropriate blinding of both patients and outcome assessors to the intervention. The second limitation is that the included studies provided radiographic outcomes without using unified criteria, which may be a source of bias. Well-designed RCTs are recommended for future work.

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Keywords:

kyphoplasty; osteoporosis; osteoporotic fractures; meta-analysis

© 2013 Chinese Medical Association