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.
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.
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.
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.
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.
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).
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.
1. Van Schoor NM, Smit JH, Twisk JW, Lips P. Impact of vertebral deformities, osteoarthritis, and other chronic diseases on quality of life: a population-based study. Osteoporos Int 2005; 16: 749-756.
2. Garfin SR, Buckley RA, Ledlie J. Balloon kyphoplasty
for symptomatic vertebral body compression fractures results in rapid, significant, and sustained improvements in back pain, function, and quality of life for elderly patients. Spine 2006; 31: 2210-2220.
3. Zheng ZM, Kuang GM, Dong ZY, Cheung KM, Lu WW, Li FB. Preliminary clinical outcomes of percutaneous kyphoplasty
with Sky-bone expander. Chin Med J 2007; 120: 761-766.
4. Ledlie JT, Renfro M. Balloon kyphoplasty
: one-year outcomes in vertebral body height restoration, chronic pain, and activity levels. J Neurosurg 2003; 98: 36-42.
5. Crandall D, Slaughter D, Hankins PJ, Moore C, Jerman J. Acute versus chronic vertebral compression fractures treated with kyphoplasty
: early results. Spine J 2004; 4: 418-424.
6. Wardlaw D, Cummings SR, Van Meirhaeghe J, Bastian L, Tillman JB, Ranstam J, et al. Efficacy and safety of balloon kyphoplasty
compared with non-surgical care for vertebral compression fracture (FREE): a randomised controlled trial. Lancet 2009; 373: 1016-1024.
7. Boonen S, Van Meirhaeghe J, Bastian L, Cummings SR, Ranstam J, Tillman JB, et al. Balloon kyphoplasty
for the treatment of acute vertebral compression fractures: 2-year results from a randomized trial. J Bone Miner Res 2011; 26: 1627-1637.
8. Sun G, Jin P, Li FD, Liu XW, Hao RS, Yi YH, et al. Preliminary study on a single balloon cross-midline expansion via unipedicular approach in kyphoplasty
. Chin Med J 2008; 121: 1811-1814.
9. Papadopoulos EC, Edobor-Osula F, Gardner MJ, Shindle MK, Lane JM. Unipedicular balloon kyphoplasty
for the treatment of osteoporotic vertebral compression fractures: early results. J Spinal Disord Tech 2008; 21: 589-596.
10. Lee SB, Cho KS, Huh PW, Yoo DS, Kang SG, Kim DS, et al. Clinical and radiographic results of unilateral transpedicular balloon kyphoplasty
for the treatment of osteoporotic vertebral compression fractures. Acta Neurochir Suppl 2008; 101: 157-160.
11. Hu MM, Eskey CJ, Tong SC, Nogueira RG, Pomerantz SR, Rabinov JD, et al. Kyphoplasty
for vertebral compression fracture via a uni-pedicular approach. Pain Physician 2005; 8: 363-367.
12. Moher D, Liberati A, Tetzlaff J, Altman DG; PRISMA Group. Preferred reporting items for systematic reviews and meta-analyses: the PRISMA statement. J Clin Epidemiol 2009; 62: 1006-1012.
13. Furlan AD, Pennick V, Bombardier C, van Tulder M; Editorial Board, Cochrane Back Review Group. 2009 Updated method guidelines for systematic reviews in the Cochrane Back Review Group. Spine 2009; 34: 1929-1941.
14. Chung HJ, Chung KJ, Yoon HS, Kwon IH. Comparative study of balloon kyphoplasty
with unilateral versus bilateral approach in osteoporotic vertebral compression fractures. Int Orthop 2008; 32: 817-820.
15. Gu XH, Zhang Z, Wu J, Lv J, Wu XY. Contrast study between unilateral and bilateral percutaneous balloon kyphoplasty
for osteoporotic thoracolumbar compression fractures. Chin J Surg Integr Tradit West Med (Chin) 2009; 15: 246-249.
16. Chen C, Chen L, Gu Y, Xu Y, Liu Y, Bai X, et al. Kyphoplasty
for chronic painful osteoporotic vertebral compression fractures via unipedicular versus bipedicular approachment: a comparative study in early stage. Injury 2010; 41: 356-359.
17. Chen C, Wei H, Zhang W, Gu Y, Tang G, Dong R, et al. Comparative study of kyphoplasty
for chronic painful osteoporotic vertebral compression fractures via unipedicular versus bipedicular approach. J Spinal Disord Tech 2011; 24: E62-E65.
18. Chen L, Yang H, Tang T. Unilateral versus bilateral balloon kyphoplasty
for multilevel osteoporotic vertebral compression fractures: a prospective study. Spine 2011; 36: 534-540.
19. Luo XL, Zheng CK, Kan WS, Li P. Unilateral versus bilateral percutaneous kyphoplasty
for the treatment of osteoporotic compression fractures. Chin J Tissue Eng Res 2012; 16: 567-570.
20. Rebolledo BJ, Gladnick BP, Unnanuntana A, Nguyen JT, Kepler CK, Lane JM. Comparison of unipedicular and bipedicular balloon kyphoplasty
for the treatment of osteoporotic vertebral compression fractures: a prospective randomised study. Bone Joint J 2013; 95-B: 401-406.
21. Kayanja MM, Ferrara LA, Lieberman IH. Distribution of anterior cortical shear strain after a thoracic wedge compression fracture. Spine J 2004; 4: 76-87.
22. Kado DM, Browner WS, Palermo L, Nevitt MC, Genant HK, Cummings SR. Vertebral fractures and mortality in older women: a prospective study. Study of Osteoporotic Fractures
Research Group. Arch Intern Med 1999; 159: 1215-1220.
23. Lieberman IH, Dudeney S, Reinhardt MK, Bell G. Initial outcome and efficacy of “kyphoplasty
” in the treatment of painful osteoporotic vertebral compression fractures. Spine 2001; 26: 1631-1638.
24. Song BK, Eun JP, Oh YM. Clinical and radiological comparison of unipedicular versus bipedicular balloon kyphoplasty
for the treatment of vertebral compression fractures. Osteoporos Int 2009; 20: 1717-1723.
25. Belkoff SM, Mathis JM, Jasper LE, Deramond H. The biomechanics of vertebroplasty. The effect of cement volume on mechanical behavior. Spine 2001; 26: 1537-1541.
26. Togawa D, Bauer TW, Lieberman IH, Takikawa S. Histologic evaluation of human vertebral bodies after vertebral augmentation with polymethyl methacrylate. Spine 2003; 28: 1521-1527.
27. Schofer MD, Efe T, Timmesfeld N, Kortmann HR, Quante M. Comparison of kyphoplasty
and vertebroplasty in the treatment of fresh vertebral compression fractures. Arch Orthop Trauma Surg 2009; 129: 1391-1399.
28. Hulme PA, Krebs J, Ferguson SJ, Berlemann U. Vertebroplasty and kyphoplasty
: a systematic review of 69 clinical studies. Spine 2006; 31: 1983-2001.
29. Steinmann J, Tingey CT, Cruz G, Dai Q. Biomechanical comparison of unipedicular versus bipedicular kyphoplasty
. Spine 2005; 30: 201-205.
Keywords:© 2013 Chinese Medical Association
kyphoplasty; osteoporosis; osteoporotic fractures; meta-analysis