1 Introduction
Osteoporotic vertebral compression fractures (OVCFs) are common in elderly patients, with 1.4 million new fractures occurring worldwide each year.[1–4] [5] [6] [5] [7–9]
Conventional treatments for OVCFs include early conservative treatment such as bed rest, administration of analgesics, and physical support; however, some fractures exhibit progressive deformation and persistent pain. The goal of surgical treatment for such fractures is to resolve the associated morbidity by providing pain relief and early stabilization of the fracture.[10] [5] [11] vertebral height in patients with OVCFs.[5]
Balloon kyphoplasty (KP) is a transpedicular treatment approach that involves inserting a balloon tamp to the vertebral body to repair a vertebral fracture and fix the fracture by administering polymethylmethacrylate (PMMA) bone cement into the vertebral body.[12,13] vertebral height and kyphotic angle (KA) of the spine, rapid pain relief, improvement in mobility, and significantly reduced morbidity.[14–17] [13,18] [19–21]
A recent meta-analysis demonstrated that there is no consensus on whether bipedicular KP has similar efficacy to unipedicular KP,[20,22,23] [21,24–26]
2 Methods
2.1 Study design
This retrospective observational study adhered to the STROBE checklist (S1, https://links.lww.com/MD/E804
From January 2010 to August 2018, we analyzed patients with single-level OVCFs in the thoracic or lumbar spine (T5–L5) who underwent KP. The patients were divided into a unipedicular group, treated with unipedicular and extrapedicular KP, and a bipedicular group, treated with bipedicular and transpedicular KP. All study participants were aged >50 years, underwent KP within 6 weeks of OVCF occurrence, and had bone mineral density (BMD) ≤ -2.5. The inclusion criteria were having a numerical rating scale (NRS) pain score of ≥4 despite the use of conservative treatments such as drug administration after OVCF occurrence, having edematous fractures on T2-weighted chemical fat suppression images or a short tau inversion recovery sequence on magnetic resonance imaging (MRI), and possessing general records of radiography, including those of the spine at the surgical site, acquired preoperatively, 1 day postoperatively, and 12 months postoperatively.
Conversely, patients with fractures that occurred >6 weeks before undergoing KP, no evidence of edematous fractures on MRI, NRS pain scores of <4 after drug treatment, evidence of bleeding disorders, asymptomatic fractures, local infections, secondary post-traumatic fractures, and a lack of general radiography records immediately and 12 months after surgery, those without osteoporosis, and those who underwent multilevel KP, underwent KP for pathologic fractures caused by cancer metastasis, those lost to clinical follow-up within 12 months, and died within 12 months were excluded from this study.
KP was performed by the same physician for all patients. All patients received continuous epidural catheterization near the fracture level to alleviate pain caused by the fracture and during the KP procedure.
2.2 Procedure
2.2.1 Bipedicular group
Patients were placed in the prone position with a bolster placed under the sternum and pelvis for kyphosis correction. An aseptic dressing was applied to the procedure site. Patients were administered 6 mL of 0.19% ropivacaine through an epidural catheter. Under fluoroscopic guidance, infiltration was performed using 1% lidocaine from the skin to the target pedicle using a 24 G spinal needle. Subsequently, under fluoroscopy, a trocar was angled obliquely to the anteroposterior (AP) axis at an angle of 10° to 20° and advanced to the center of the vertebral body via the transpedicular approach. The trocar was inserted after infiltration with 1% lidocaine on the other side of the vertebral body. After inserting a guidewire, the cannula was inserted through the guidewire so that its end was positioned lateral to the posterior third of the vertebral body. The KP balloon catheter (BALANSY balloon catheter; HAN-SONG BIOBANK, Korea) was inserted through the cannula and advanced along two-thirds of the path into the anterior vertebral body. After expanding the balloon to ensure simultaneous satisfactory cavities on both sides, the balloon was deflated, and the cavities were simultaneously filled with PMMA (Fig. 1 A–F).
Figure 1: (A) The trocar is obliquely angled to the AP axis at an angle of 15° and advanced to the center of the vertebral body via the transpedicular approach. It is also inserted in the other side of the vertebral body. (B) The end of the cannula is positioned at the lateral view in the posterior-third of the vertebral body. (C, D) The balloon is expanded to ensure a satisfactory cavity on both sides at the same time. (E, F) The balloon is deflated, and the cavity is simultaneously filled with PMMA. AP = anteroposterior, PMMA = polymethylmethacrylate.
2.2.2 Unipedicular group
The patients were placed in the same position as the bipedicular group; an aseptic dressing was applied and an epidural drug was administered. Infiltration with 1% lidocaine was performed along the direction in which the pedicle was seen more clearly in the AP and oblique views. The trocar was inserted under fluoroscopy, via the extrapedicular approach at an angle of 20° to 30° with respect to the AP axis and to one side of lidocaine infiltration. After inserting the guidewire, the cannula was inserted such that it was located in the posterior third of the vertebral body in the lateral view. The same type of balloon catheter as the bipedicular group was inserted through the cannula and advanced along two-thirds of the path into the anterior vertebral body. In the unipedicular group, the end of the cannula was positioned as centrally as possible, and the AP and lateral views were checked to determine whether the inserted balloon extended to the left and right as well as above and below the spine. Finally, the balloon was contracted, and the cavity was filled with PMMA (Fig. 2 A–F).
Figure 2: (A) The trocar is inserted via the extrapedicular approach at an angle of 25° with respect to the AP axis under fluoroscopy to one side of the lidocaine infiltration. (B) The cannula is inserted through the guidewire so that it is located in the area of the posterior-third of the vertebral body at the lateral view. (C, D) The end of the cannula is positioned as centrally as possible, and the AP and lateral views are checked to ensure that the inserted balloon is extended to the left and right as well as above and below the spine. (E, F) The balloon is contracted, and the cavity is filled with PMMA. AP = anteroposterior, PMMA = polymethylmethacrylate.
All patients underwent close observation in the hospital for at least 24 hours after surgery, and vital signs and other complications were assessed.
2.3 Data collection
The following data were collected for demographic analysis: age; sex; BMD; level of compression fracture; days from onset of pain to KP; history of cancer, hypertension (HTN) or angina, diabetes mellitus (DM), asthma or chronic obstructive pulmonary disease (COPD), thyroid or parathyroid disease, hepatic disease, kidney disease, use of steroids, and compression ratio (Fig. 3 ).
Figure 3: Measurement of vertebral compression ratio is done using the following formula: [(A + C)/2 – B]/[(A + C)/2]. (A) Anterior vertebral height of upper vertebra, (B) anterior vertebral height of fracture level, (C) anterior vertebral height of lower vertebra.
2.3.1 Clinical evaluation
Pain scores were recorded from 0 to 10 using the NRS, with 0 indicating “no pain” and 10 indicating the “maximum amount of pain imaginable.” We collected NRS scores corresponding to the different time points, including immediately before the procedure (baseline NRS score) and 1, 3, 6, and 12 months after the procedure from the patients’ medical records.
2.3.2 Radiological evaluation
Radiological evaluation was performed in accordance with the following 2 criteria: level of spinal deformation and KA. Spinal deformation was assessed using quantitative morphometrics,[27,28] vertebral height before surgery and then evaluating the recovery of the vertebral height at the same location after surgery (Fig. 4 ). After evaluating the height of the lowest vertebral body before surgery, we evaluated the difference in the rate of recovery of the vertebral height at the same location on the radiograph taken 1 day after the procedure as well as the difference in the rate of recovery after 1 year of the procedure. The KA was calculated on the basis of the intersection angle of the lines running parallel to the upper and lower end plates of the fractured vertebrae (Fig. 5 ).[29]
Figure 4: The level of spinal deformity is evaluated using the lowest vertebral height before and after surgery to evaluate the recovery of the vertebral height at the same location after surgery. (A) Arrow indicates the lowest vertebral height . (B) Arrow indicates the recovery of the vertebral height at the same location after surgery.
Figure 5: The kyphotic angle is calculated on the basis of the intersection angle of the lines running parallel to the upper and lower end plates of the fractured vertebrae.
2.3.3 Surgical evaluation
Surgical evaluation included assessment of the total surgical time, amount of PMMA injected, and postoperative complication ratio. The total surgical time was defined as the time between preoperative lidocaine infiltration and dressing at the end of the procedure. The postoperative complications were as follows: intradiscal cement leakage, cement leakage into the paravertebral vein or epidural space, infection, and adjacent vertebral compression fracture (AVCF) within 1 year of KP.
2.4 Statistical analysis
Demographic data were analyzed using the Kolmogorov–Smirnov test to assess normality of the distribution. Demographic data that followed a normal distribution were compared using an independent t test. Data that were not normally distributed were compared using the Mann–Whitney U test. We evaluated whether the NRS score, KA, and vertebral height improved significantly compared with those at baseline after each procedure using the post hoc Bonferroni test with repeated measures analysis of variance (ANOVA). After correcting for confounding variables (age, sex, BMD, level of compression fracture, days from onset of the pain to the procedure, and history of cancer, HTN or angina, DM, asthma or COPD, thyroid or parathyroid disease, hepatic disease, kidney disease, use of steroids, and compression ratio), we analyzed differences in the NRS score, surgical time, and amount of cement injected between the groups using an analysis of covariance (ANCOVA). The difference and ratio of KA and vertebral height recovery were also compared between the 2 groups using ANCOVA. The patients were divided into thoracic and lumbar spine OVCF groups based on the fracture location, and ANCOVA was used to determine the degree of NRS recovery, difference and percentage of KA recovery, and difference in height recovery between the unipedicular and bipedicular groups. The intradiscal cement leakage ratio and AVCF ratio within 1 year were compared using multivariate logistic regression. Data are presented as mean ± standard deviation or median [interquartile ranges]. The Statistical Package for the Social Sciences software (version 17.0; SPSS 157 Inc., Chicago, IL) was used for analysis. All statistical tests were 2-sided, and the threshold for statistical significance was set at P < .05.
Statistical analysis was conducted after consulting with Soon Young Hwang (Korea University Medical Center, Guro Hospital), a statistical expert.
3 Results
We analyzed the medical records of 201 patients, 3 of whom died within 1 year of follow-up, and 11 were lost to follow-up or lacked data for 1 year after the procedure. Twenty-two patients with pathologic fractures associated with cancer metastasis, 6 with no edema findings in the fractured vertebrae on MRI, 61 who underwent multiple KP or VP owing to multilevel fractures, and 2 with post-traumatic secondary fractures without osteoporosis (BMD >-2.5) were excluded from the study. Finally, 96 patients were analyzed, with 28 in the unipedicular group and 68 in the bipedicular group (Fig. 6 ).
Figure 6: Flow diagram showing the patient inclusion criteria. KP = kyphoplasty, MRI = magnetic resonance imaging, VP = vertebroplasty.
No significant differences were observed in the demographic and clinical characteristics of the patients between the 2 groups ( Table 1 ).
Table 1: Baseline characteristics of patients.
3.1 Clinical findings
The NRS scores at 1, 3, 6, and 12 months after the procedure were significantly lower in both groups when compared with those at baseline (Table 2 ). In the corrected analysis of confounding variables, there were no significant differences in the NRS scores between the 2 groups at 1, 3, 6, and 12 months (Table 3 ). In addition, when the 2 groups were compared at the thoracic and lumbar levels, the NRS score was not significantly different at 1, 3, 6, and 12 months (Supplementary file 2, https://links.lww.com/MD/E805
Table 2: Comparison of the baseline pain scores at each time point.
Table 3: Comparison of the numerical rating scale scores between the groups after correction for confounding variables.
3.2 Radiological findings
The lowest vertebral height of the vertebral body significantly increased in both groups after surgery; this increase was maintained until 1 year of follow-up (Table 4 ). There was no significant difference in the recovery ratio of vertebral height between the 2 groups after 1 day and after 1 year of KP (Table 5 ). In addition, comparison of the 2 groups at the thoracic and lumbar levels revealed no significant differences in the recovery ratio of vertebral height at both 1 day and 1 year after surgery (Supplementary file 3, https://links.lww.com/MD/E806
Table 4: Comparison of baseline vertebral heights at each time point.
Table 5: Comparison of recovery of vertebral height between the groups after correction for confounding variables.
The KA significantly improved in both groups after surgery, and this improvement was maintained for up to 1 year after surgery (Table 6 ). There were no significant differences in the difference and ratio of KA recovery between the 2 groups at 1 day and 1 year after surgery (Table 7 ); this absence of differences was also seen when the 2 groups were compared at the thoracic and lumbar levels (Supplementary file 4, https://links.lww.com/MD/E807
Table 6: Comparison of baseline kyphotic angles at each time point.
Table 7: Comparison of recovery of kyphotic angle between the groups after correction for confounding variables.
3.3 Surgical findings
There was no significant difference in the mean surgical time between the unipedicular and bipedicular groups (36.7 ± 9.7 minutes in the unipedicular group and 39.6 ± 12.7 minutes in the bipedicular group; P = .53). Significantly less PMMA was injected in the unipedicular group than in the bipedicular group (4.4 ± 0.8 mL in the unipedicular group and 5.6 ± 1.0 mL in the bipedicular group; P = .00). Comparison of the 2 groups at the thoracic and lumbar levels showed a significant difference in the amount of PMMA injected (thoracic level: unipedicular group, 4.2 ± 0.8 mL; bipedicular group, 5.3 ± 1.1 mL; P = .01; lumbar level: unipedicular group, 4.9 ± 0.6 mL; bipedicular group, 6.0 ± 0.7 mL; P = .01).
3.4 Postoperative complications
Life-threatening complications such as pulmonary embolism or cement leakage into the paravertebral vein were not observed in either group. In addition, no infection or cement leakage into the epidural space was found. Cement leakage into the intradiscal space was observed in 4 of 28 patients in the unipedicular group and in 12 of 68 patients in the bipedicular group, with no significant difference between the groups (P = .67) (Table 8 ). None of the patients with cement leakage into the intradiscal space complained of obvious clinical symptoms or developed neurological symptoms.
Table 8: Comparison of complication rates after kyphoplasty between the groups.
During the 1-year follow-up period, AVCF occurred in 4 of 28 patients in the unipedicular group and in 11 of 68 patients in the bipedicular group; the symptoms improved after undergoing an additional KP. There was no significant difference in the rate of AVCF occurrence within 1 year between the 2 groups (P = .84) (Table 8 ).
Anterior rib fracture induced by orienting the patient in the prone position during the surgery occurred in 1 patient in the bipedicular group; this was successfully treated with conservative treatment such as administration of analgesic agents.
4 Discussion
This study aimed to compare the clinical, radiological, and surgical findings and postoperative complications between patients who underwent unipedicular and bipedicular KP for single-level OVCF. In both groups, the NRS score, vertebral height , and KA after KP significantly improved after 1 year. The amount of cement injected was significantly higher in the bipedicular group than in the unipedicular group; however, there was no significant difference in the improvement of the NRS score and recovery of vertebral height and the KA. In addition, there were no significant differences in the ratio of cement leakage into the intradiscal space, ratio of AVCF within 1 year, and surgical time. The patients were divided into the groups based on the presence of a thoracic or a lumbar fracture, and the results were maintained across the 2 groups.
Balloon KP has been shown to be effective in treating OVCFs.[13,17,18] [30] [10,31]
In this study, unipedicular KP was found to yield similar clinical and radiological improvements as bipedicular KP. Previous cadaver studies have reported no significant differences in the restoration of vertebral body strength, stiffness, and height between the unipedicular and bipedicular groups.[32,33] [34] [5,32,35–37]
Previous studies have recommended the administration of a sufficient amount of cement because administration of an amount less than the volume of the vertebral body may result in a lack of improvement of clinical symptoms.[38] [39] [40] [10]
Chen et al[35] vertebral height . However, Feng et al[21] vertebral height . Unlike either of these studies, we found that neither approach was superior to other in improving vertebral height or KA. Chen et al[29] [41] [26]
Unless there is a significant difference in clinical and radiological findings and postoperative complications, it may be advisable to proceed with the unipedicular approach for thoracic segments with smaller pedicles. However, if the small size of the pedicle precludes the needle trajectory for cement injection from being close to the midline, a bipedicular approach may be considered.
Unipedicular KP has been reported to significantly reduce radiation exposure, surgical time, and cost when compared with bipedicular KP.[29,42] [30]
Cement leakage and AVCF are common complications that occur during and after KP. In studies conducted by Rebolledo et al[10] P = .02), who used a similar amount of cement as in this study, the cement leakage rates were 7% in unipedicular KP and 25% in bipedicular KP, which were also significantly different. Yan et al[43] [43] P = .68). In addition, there was no cement leakage into the vascular and epidural spaces in either group.
We did not observe any significant differences in the AVCF rates, despite noting a difference in the amount of cement injected. A 2019 report revealed that the risk factors for AVCF after VP include BMD, preoperative compression ratio, preoperative sagittal index, intradiscal cement leakage, and large cement volume-to-vertebral body ratio as per univariate analysis.[44]
To minimize other variables in the comparison between unipedicular and bipedicular KP, this study only included patients who underwent KP for single-level fractures and excluded those who received multiple KP or VP concurrently for multilevel fractures. The latter patients were excluded because it was not possible to compare the effects of unipedicular and bipedicular KP accurately, and it may cause variations in the comparison of complications between the 2 groups, such as AVCF caused by KP.
There are some limitations to the present study. First, our measurements did not allow for blinded assessment of vertebral height or KA before and after surgery, allowing for possible biases in the radiological assessment. Second, the loss to follow-up of 14 of 201 patients may have affected the validity of our results. The inclusion of the elderly population in this study may have contributed to a higher loss rate during follow-up. Three patients died during the 1-year follow-up period, and 11 were excluded from the study owing to loss of contact during follow-up or incomplete radiological data. Third, given that this study was retrospective, it was difficult to extend the follow-up period to more than 1 year, and a longer follow-up period may have helped in the detection of additional AVCFs, if any. Fourth, because this study was not a randomized controlled one, there may have been a selection bias when assigning patients to the 2 groups. However, there was no significant difference in the baseline demographic data, preoperative NRS score, preoperative KA, and preoperative vertebral height between the 2 groups. In addition, we evaluated each result using an analytical method (covariance and multivariable logistic regression analyses) that could correct for these variables. Fifth, it is not possible to accurately determine epidural cement leakage because cost considerations prohibit computed tomography (CT) scans if there are no abnormal symptoms (motor weakness, radiating pain, fever, unstable vital sign) after KP. Patients with neurological deficits, which may appear due to leakage of cement into the epidural space, were also not specifically reported in this study. We did not observe any images of cement passing over the posterior border of the vertebral body on the lateral view of the X-ray and therefore, noted this as “No cement leaks into the epidural space were found” in the text. Bypassing the accurate identification of cement leakage into the epidural space through CT scans may limit evaluation of the benefits of the unipedicular approach, in which significantly less cement is used. Future well-organized prospective studies will need to accurately identify epidural cement spills through CT scans.
5 Conclusion
Unipedicular and bipedicular KP significantly reduced the pain experienced by patients with single-level OVCFs, restored vertebral height , and corrected the KA, which remained stable for at least 1 year after treatment. In particular, unipedicular KP required lower amounts of cement than bipedicular KP and was as effective as bipedicular KP with respect to the radiological and clinical outcomes. The above findings have level III evidence and a grade B recommendation as per the Guidelines of the North American Spine Society.[45]
Acknowledgments
We would like to thank Editage (www.editage.co.kr
Author contributions
Conceptualization: Chung Hun Lee, Sang Sik Choi, Mi Kyoung Lee.
Data curation: Chung Hun Lee, Hyun Joong Kim, Hyo Sung Kim.
Formal analysis: Chung Hun Lee, Hyo Sung Kim.
Investigation: Chung Hun Lee, Hyun Joong Kim.
Methodology: Chung Hun Lee, Sang Sik Choi, Hyun Joong Kim.
Project administration: Chung Hun Lee, Mi Kyoung Lee.
Resources: Chung Hun Lee.
Software: Sang Sik Choi, Mi Kyoung Lee, Hyo Sung Kim.
Supervision: Sang Sik Choi, Mi Kyoung Lee, Chung Hun Lee.
Validation: Sang Sik Choi, Mi Kyoung Lee.
Visualization: Mi Kyoung Lee.
Writing – original draft: Chung Hun Lee, Sang Sik Choi.
Writing – review and editing: Chung Hun Lee, Sang Sik Choi, Mi Kyoung Lee.
References
[1]. Grigoryan M, Guermazi A, Roemer FW, et al. Recognizing and reporting osteoporotic vertebral fractures. Eur Spine J 2003;12:S10412.
[2]. Delmas PD, Van de Langerijt L, Watts NB, et al. Underdiagnosis of vertebral fractures is a worldwide problem: the IMPACT study. J Bone Miner Res 2005;20:55763.
[3]. Gronholz MJ. Prevention, diagnosis, and management of osteoporosis-related fracture: a multifactoral osteopathic approach. J Am Osteopath Assoc 2008;108:57585.
[4]. Griffith JF. Identifying osteoporotic vertebral fracture. Quant Imaging Med Surg 2015;5:592602.
[5]. 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;20:171723.
[6]. Lindsay R, Silverman SL, Cooper C, et al. Risk of new vertebral fracture in the year following a fracture. JAMA 2001;285:3203.
[7]. Lips P, Van Schoor NM. Quality of life in patients with osteoporosis. Osteoporos Int 2005;16:44755.
[8]. Rousing R, Hansen KL, Andersen MO, et al. Twelve-months follow-up in forty-nine patients with acute/semiacute osteoporotic vertebral fractures treated conservatively or with percutaneous vertebroplasty: a clinical randomized study. Spine (Phila Pa 1976) 2010;35:47882.
[9]. Kallmes DF, Comstock BA, Heagerty PJ, et al. A randomized trial of vertebroplasty for osteoporotic spinal fractures. N Engl J Med 2009;361:56979.
[10]. Rebolledo BJ, Gladnick BP, Unnanuntana A, et al. Comparison of unipedicular and bipedicular balloon kyphoplasty for the treatment of osteoporotic vertebral compression fractures: a prospective randomised study. Bone Joint J 2013;95:4016.
[11]. Galibert P, Deramond H, Rosat P, et al. Preliminary note on the treatment of vertebral angioma by percutaneous acrylic vertebroplasty. Neurochirurgie 1987;33:1668.
[12]. Theodorou DJ, Theodorou SJ, Duncan TD, et al. Percutaneous balloon kyphoplasty for the correction of spinal deformity in painful vertebral body compression fractures. Clin Imaging 2002;26:15.
[13]. Lieberman IH, Dudeney S, Reinhardt MK, et al. Initial outcome and efficacy of “kyphoplasty” in the treatment of painful osteoporotic vertebral compression fractures. Spine (Phila Pa 1976) 2001;26:16318.
[14]. Berenson J, Pflugmacher R, Jarzem P, et al. Balloon kyphoplasty versus non-surgical fracture management for treatment of painful vertebral body compression fractures in patients with cancer: a multicenter, randomised controlled trial. Lancet Oncol 2011;12:22535.
[15]. Yang EZ, Xu JG, Huang GZ, et al. Percutaneous vertebroplasty versus conservative treatment in aged patients with acute osteoporotic vertebral compression fractures: a prospective randomized controlled clinical study. Spine (Phila Pa 1976) 2016;41:65360.
[16]. Klazen CA, Lohle PN, de Vries J, et al. Vertebroplasty versus conservative treatment in acute osteoporotic vertebral compression fractures (Vertos II): an open-label randomised trial. Lancet 2010;376:108592.
[17]. Wardlaw D, Cummings SR, Van Meirhaeghe 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;373:101624.
[18]. Garfin SR, Yuan HA, Reiley MA. New technologies in spine: kyphoplasty and vertebroplasty for the treatment of painful osteoporotic compression fractures. Spine (Phila Pa 1976) 2001;26:15115.
[19]. Cheng X, Long HQ, Xu JH, et al. Comparison of unilateral versus bilateral percutaneous kyphoplasty for the treatment of patients with osteoporosis vertebral compression fracture (OVCF): a systematic review and meta-analysis. Eur Spine J 2016;25:343949.
[20]. Huang Z, Wan S, Ning L, et al. Is unilateral kyphoplasty as effective and safe as bilateral kyphoplasties for osteoporotic vertebral compression fractures? A meta-analysis. Clin Orthop Relat Res 2014;472:283342.
[21]. Feng H, Huang P, Zhang X, et al. Unilateral versus bilateral percutaneous kyphoplasty for osteoporotic vertebral compression fractures: a systematic review and meta-analysis of RCTs. J Orthop Res 2015;33:171323.
[22]. Lin J, Zhang L, Yang H. Unilateral versus bilateral balloon kyphoplasty for osteoporotic vertebral compression fractures. Pain Physician 2013;16:44753.
[23]. Yang LY, Wang XL, Zhou L, et al. A systematic review and meta-analysis of randomized controlled trials of unilateral versus bilateral kyphoplasty for osteoporotic vertebral compression fractures. Pain Physician 2013;16:27790.
[24]. Chen H, Tang P, Zhao Y, et al. Unilateral versus bilateral balloon kyphoplasty in the treatment of osteoporotic vertebral compression fractures. Orthopedics 2014;37:e82835.
[25]. Li L, Sun T, Liu Z, et al. Comparison of unipedicular and bipedicular percutaneous kyphoplasty for treating osteoporotic vertebral compression fractures: a meta-analysis. Chin Med J (Engl) 2013;126:395661.
[26]. Tan G, Li F, Zhou D, et al. Unilateral versus bilateral percutaneous balloon kyphoplasty for osteoporotic vertebral compression fractures: a systematic review of overlapping meta-analyses. Medicine (Baltimore) 2018;97:e11968.
[27]. Genant HK, Jergas M, Palermo L, et al. Comparison of semiquantitative visual and quantitative morphometric assessment of prevalent and incident vertebral fractures in osteoporosis. J Bone Miner Res 1996;11:98496.
[28]. Guglielmi G, Diacinti D, Van Kuijk C, et al. Vertebral morphometry: current methods and recent advances. Eur Radiol 2008;18:148496.
[29]. Chen L, Yang H, Tang T. Unilateral versus bilateral balloon kyphoplasty for multilevel osteoporotic vertebral compression fractures: a prospective study. Spine (Phila Pa 1976) 2011;36:53440.
[30]. Nevitt MC, Ettinger B, Black DM, et al. The association of radiographically detected vertebral fractures with back pain and function: a prospective study. Ann Intern Med 1998;128:793800.
[31]. Papanastassiou ID, Eleraky M, Murtagh R, et al. Comparison of unilateral versus bilateral kyphoplasty in multiple myeloma patients and the importance of preoperative planning. Asian Spine J 2014;8:24452.
[32]. Tohmeh AG, Mathis JM, Fenton DC, et al. Biomechanical efficacy of unipedicular versus bipedicular vertebroplasty for the management of osteoporotic compression fractures. Spine (Phila Pa 1976) 1999;24:17726.
[33]. Steinmann J, Tingey CT, Cruz G, et al. Biomechanical comparison of unipedicular versus bipedicular kyphoplasty. Spine (Phila Pa 1976) 2005;30:2015.
[34]. Chen B, Li Y, Xie D, et al. Comparison of unipedicular and bipedicular kyphoplasty on the stiffness and biomechanical balance of compression fractured vertebrae. Eur Spine J 2011;20:127280.
[35]. Chen C, Chen L, Gu Y, et al. Kyphoplasty for chronic painful osteoporotic vertebral compression fractures via unipedicular versus bipedicular approachment: a comparative study in early stage. Injury 2010;41:3569.
[36]. Chen C, Wei H, Zhang W, et al. Comparative study of kyphoplasty for chronic painful osteoporotic vertebral compression fractures via unipedicular versus bipedicular approach. J Spinal Disord Tech 2011;24:E625.
[37]. Sun G, Jin P, Li FD, et al. Preliminary study on a single balloon cross-midline expansion via unipedicular approach in kyphoplasty. Chin Med J 2008;121:18114.
[38]. Boszczyk B. Volume matters: a review of procedural details of two randomised controlled vertebroplasty trials of 2009. Eur Spine J 2010;19:183740.
[39]. Liebschner MA, Rosenberg WS, Keaveny TM. Effects of bone cement volume and distribution on vertebral stiffness after vertebroplasty. Spine (Phila Pa 1976) 2001;26:154754.
[40]. Martinčič D, Brojan M, Kosel F, et al. Minimum cement volume for vertebroplasty. Int Orthop 2015;39:72733.
[41]. Chung HJ, Chung KJ, Yoon HS, et al. Comparative study of balloon kyphoplasty with unilateral versus bilateral approach in osteoporotic vertebral compression fractures. Int Orthop 2008;32:81720.
[42]. Yan L, Jiang R, He B, et al. A comparison between unilateral transverse process-pedicle and bilateral puncture techniques in percutaneous kyphoplasty. Spine (Phila Pa 1976) 2014;39:B1926.
[43]. Wang Z, Wang G, Yang H. Comparison of unilateral versus bilateral balloon kyphoplasty for the treatment of osteoporotic vertebral compression fractures. J Clin Neurosci 2012;19:7236.
[44]. Lee HJ, Park J, Lee IW, et al. Clinical, radiographic, and morphometric risk factors for adjacent and remote vertebral compression fractures over a minimum follow-up of 4 years after percutaneous vertebroplasty for osteoporotic vertebral compression fractures: novel three-dimensional voxel-based morphometric analysis. World Neurosurg 2019;125:e14657.
[45]. Kaiser MG, Eck JC, Groff MW, et al. Guideline update for the performance of fusion procedures for degenerative disease of the lumbar spine. Part 1: introduction and methodology. J Neurosurg Spine 2014;21:26.
