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Cement augmentation for treatment of high to mid-thoracic osteoporotic compression fractures, high-viscosity cement percutaneous vertebroplasty versus balloon kyphoplasty

VP and BKP are common interventions for the treatment of osteoporotic VCFs. The difference between VP and BKP is that BKP adds a procedure of balloon inflation in the collapsed vertebrae. Both interventions use bone cement to stabilize the fracture. Clinical studies of different cement augmentation procedures have been encouraging. Several studies have suggested both VP and BKP improve quality of life, pain relief, functionality, and restores vertebral body height10. Zhao et al. performed a meta-analysis study which demonstrated patients treated with BKP was more effective than VP according to superior scores for long term VAS and Oswestry Disability Index, improved KA and mean vertebral body height, and significantly reduced risk of cement leakage17. However, some studies did not support that BKP is superior to VP for pain relief and functional improvement18,19. In this current study, VAS outcomes reflecting pain relief after vertebral body augmentation at high to mid-thoracic vertebrae was similar for  HVC VP and LVC BKP.

The most frequent area involved in VCFs is the thoracolumbar junction (T12-L2), followed by the lower lumbar area (L3–L5)20. By contrast, the incidence of VCFs at high (T4–T6) and mid- (T7–T9) thoracic vertebrae is lower and associated research is limited. The thoracic spine is part of the thoracic cage, which serves to protect vital organs and provide rigid support to bear and disperse substantial axial loading forces. Patients with a compression fracture over the high to mid-thoracic vertebrae can suffer high to mid-back pain, which can be exacerbated with respiration and may radiate to the anterior chest. Anatomically, the thoracic vertebrae is characterized by small pedicles with the diameter becoming narrower as the thoracic level gets higher. Therefore, nervous tissue would likely be intolerable when cement leakage into the thoracic canal occurs. To minimise the risk of cement leakage, Liu et al. recommended that LVC BKP is preferred over LVC VP for osteoporotic VCFs of mid-thoracic vertebrae21. Another key factor to reduce the incidence of cement leakage is viscosity of the cement in VP. Alhashash et al. demonstrated that HVC VP had a relatively low risk of cement leakage for patients with VCFs22. However, they focused mostly on lower thoracic and lumbar spine levels. Based on our study, the cement leakage rate is lower with HVC VP in relation to LVC BKP (36% vs. 64%, p = 0.004) after cement augmentation for high to mid-thoracic vertebrae. A meta-analysis study by Chen et al. also confirmed that HVC VP holds the lowest rate for cement leakage after cement augmentation when compared to LVC BKP and LVC VP23.

Cement injection volume has been reported as one of the risk factors for cement leakage in percutaneous VP and BKP. Zhu et al. recommended that < 3.5 mL of bone cement per vertebrae should be injected to minimize the risk of volume-associated cement leakage24. Similar results are also observed in BKP with Chen et al. demonstrating decreased volume of cement injection could also reduce the incidence of cement leakage25. Although most leaks were clinically asymptomatic, they carry the risk of pulmonary embolism and neurologic compression which are considered major complications in cement augmentation procedures. In this study, cement volume of injection was significantly lower in the HVC VP group (3.66 ml vs. 4.40 ml, p < 0.001). Moreover, HCV VP alleviates the need for bone cavity creation within the injured vertebra, thus significantly reducing the procedure time (31 min vs 39 min, p = 0.011), Thus, we believe HVC VP is more reliable than LVC BKP when applied to high to mid-thoracic vertebrae.

The biomechanics of the fractured segment are altered following cement augmentation. The reconstructed vertebrae is more rigid than its adjacent segments. It acts as an upright pillar that reduces the inward physiologic bulging of the endplates of the augmented vertebrae. Liao et al. made a finite element model of osteoporotic VCFs with cement augmentation with VP, BKP, and vertebral stents26. The results showed all these procedures would increase stress on the endplates of the adjacent segments, especially the superior levels during flexion. Another finite element study revealed that when cement filling volume reached 30–40.5% of the volume of a vertebral body, this also increases the stress tolerated by the adjacent segments. However, when the injected cement volume exceeded the defined range, stress distributions on fractured and adjacent vertebral bodies not only increased but led to development of adjacent vertebral fractures27. Clinically, the incidence of adjacent fractures have been reported to range from 5.5 to 52% after VP and BKP17,28,29. In our study, the incidence of adjacent fractures following HVC VP and LVC BKP was 8.3% and 9.1%, respectively. We believed the incidence of adjacent fractures at high to mid-thoracic vertebral levels would be far less than that at the thoracolumbar junction because a smaller vertebral body size has consequently less cement injection and additional protection is encouraged by the thoracic cage.

In this study, all radiographic results including AVH, MVH, PVH, local kyphotic angle, and Cobb angle showed significant postoperative improvement in both groups. The HVC VP group showed comparable radiographic outcomes to those of the LVC BKP group in terms of kyphotic reduction, but with less vertebral body height restoration (determined by postoperative AVH and MVH). It is believed that the effect of balloon inflation on the injured vertebrae and more cement injected in the LVC BKP group resulted in these radiographic advantages immediately after surgery. However, more severe re-collapsed vertebrae were also shown in the LVC BKP group, which resulted in final follow-up radiographic parameters that had no statistical difference between two groups. These changes in radiographic data did not influence clinical outcomes.

In the past two decades, the majority of the literature published discuss the differences LVC VP and LVC BKP for spinal compression fractures. However, studies that compare HVC VP and LVC BKP is very scarce. After a search in PubMed, we found only four clinical research studies published discussing the use of HVC VP versus LVC BKP in the treatment of osteoporotic VCFs13,14,30,31. Dr. Georgy was the first author to describe his experiences in using HVC VP and BKP for osteoporotic VCFs, and his data showed HVC VP had a significantly lower rate of cement leakage30. Data from Wang et al. revealed injected volume was higher with BKP but cement leakage rate was lower in HVC VP14. Sun et al. and Lin et al. all demonstrated similar clinical results for VAS and Oswestry Disability Index (ODI) scores with either HVC VP or BKP, and restoration of height for the middle vertebrae appeared superior in the BKP group13,31. The biggest difference between our study and the above four reference papers was that our study included cases that involved only the high to mid-thoracic spine, but the thoracolumbar junction stood the majority of cases in the reference articles. Nevertheless, our data drew similar results to that of the above references.

Indeed, there are limitations to our study. First, the nature of a retrospective study might include inherent bias. Moreover, clinical outcomes for daily function such as ODI or 36-Item Short Form Survery (SF-36) would provide additional beneficial clinical functional information but could not be evaluated due to unavailability of data in a retrospective study. Second, the procedures were performed by different surgeons at our center, and we were unable to account for technique variation. Third, although the results were clear and comparable between the groups, a longer follow-up period is necessary to assess whether HVC can alleviate BKP-related risks in the treatment of osteoporotic VCFs in high to mid-thoracic vertebrae. Fourthly, the medical insurance policy in Taiwan does not subsidize the use of CT or MRI for evaluating bone cement leakage or adjacent fractures respectively, therefore the diagnosis using plain film inherently has a high false negative incidence and data may therefore be restricted.

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