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

VP and BKP are common interventions to treat osteoporotic VCFs. The difference between VP and BKP is that BKP adds a procedure to inflate the balloon in the collapsed vertebrae. Both procedures use bone cement to stabilize the fracture. Clinical studies of different cement augmentation procedures have been encouraging. Multiple studies have shown that both VP and BKP improve quality of life, pain relief, functionality, and restore vertebral body height¹⁰. Zhao et al. performed a meta-analysis study showing that patients treated with BKP were more effective than VP, according to superior long-term VAS and Oswestry Disability Index scores, improved CA and mean vertebral body height, and significantly reduced risk of cement leakage¹⁷. However, some studies did not support that BKP is superior to VP in pain relief and functional improvement^18.19. In this current study, VAS results, reflecting pain relief after vertebral augmentation at the high to mid thoracic vertebrae, were similar for HVC VP and LVC BKP.

The area most commonly affected by VCFs is the thoracolumbar junction (T12-L2), followed by the lower lumbar region (L3-L5)²⁰. In contrast, the incidence of VCFs is lower in high (T4–T6) and intermediate (T7–T9) thoracic vertebrae and related research is limited. The thoracic spine is part of the rib cage that serves to protect vital organs and to carry and distribute significant axial loading forces. Patients with a compression fracture over the high to mid-level thoracic vertebrae may experience high-to-moderate low back pain, which may worsen with breathing and radiate to the anterior chest. Anatomically, the thoracic vertebrae are characterized by small pedicles that narrow in diameter as the thoracic height increases. Therefore, neural tissue would probably not be tolerable if cement leaked into the thoracic canal. To minimize the risk of cement leakage, Liu et al. recommended that LVC BKP be preferred over LVC VP in osteoporotic VCFs of the mid-thoracic vertebrae²¹. Another key factor in reducing the occurrence of cement leakage is the viscosity of the cement in VP. Alhashash et al. showed that HVC VP had a relatively low risk of cement leakage in patients with VCFs²². However, they mainly focused on the lower levels of the thoracic and lumbar spine. Based on our study, the cement leak rate is lower in HVC VP relative to LVC BKP (36% vs. 64%, p=0.004) after cement augmentation for high to medium thoracic vertebrae. A meta-analysis study by Chen et al. also confirmed that HVC VP has the lowest rate of cement leakage after cement augmentation 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 to inject 24. Similar results are also found in BKP with Chen et al. Evidence of reduced cement injection volume 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 of cement augmentation procedures. In this study, the cement injection volume was significantly less in the HVC-VP group (3.66 mL vs. 4.40 mL, p

The biomechanics of the fractured segment is altered after cement augmentation. The reconstructed vertebra is stiffer than its adjacent segments. It acts as an upright pillar that reduces the inward physiological curvature of the endplates of the augmented vertebrae. Liao et al. created a finite element model of osteoporotic VCFs with cement augmentation using VP, BKP and spinal stents²⁶. The results indicated that all of these procedures would increase the loading on the endplates of the adjacent segments, particularly the upper planes during flexion. Another finite element study found that a cement fill volume of 30-40.5% of the volume of a vertebral body also increases the load tolerated by the adjacent segments. However, when the volume of cement injected exceeded the defined range, the stress distributions on fractured and adjacent vertebral bodies not only increased, but also led to the development of adjacent vertebral fractures²⁷. Clinically, the incidence of adjacent fractures after VP and BKP has been reported to range from 5.5 to 52%^17,28,29. In our study, the incidence of adjacent fractures after HVC VP and LVC BKP was 8.3% and 9.1%, respectively. We hypothesized that the incidence of adjacent fractures would be far lower at high to mid thoracic vertebral levels than at the thoracolumbar junction, since smaller vertebral body size consequently requires less cement injection and additional protection through the thorax is promoted.

In this study, all X-ray 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 results as the LVC BKP group in terms of kyphotic reduction, but with less restoration of vertebral body height (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 immediately after surgery resulted in these radiographic benefits. However, heavier recollapsed vertebrae were also demonstrated in the LVC-BKP group, resulting in final follow-up radiological parameters that showed no statistical difference between two groups. These changes in the X-ray data did not affect the clinical results.

Over the past two decades, the majority of the published literature has discussed the differences between LVC VP and LVC BKP for spinal compression fractures. However, studies comparing HVC VP and LVC BKP are very rare. After a search of PubMed we found only four published clinical research studies discussing the use of HVC VP versus LVC BKP in the treatment of osteoporotic VCFs^13,14,30,31. dr Georgy was the first author to describe his experience using HVC VP and BKP for osteoporotic VCFs and his data showed that HVC VP had a significantly lower rate of cement leakage³⁰. Data from Wang et al. found that the injected volume was higher in BKP but the cement leakage rate was lower in HVC VP¹⁴. Sun et al. and Line et al. all showed similar clinical outcomes for VAS and Oswestry Disability Index (ODI) scores with either HVC VP or BKP, and height restoration for the middle vertebrae appeared to be superior in the BKP group^13:31. The major difference between our study and the four reference articles above was that our study included cases involving only the high to mid thoracic spine, but the thoracolumbar junction comprised the majority of cases in the reference articles. Nonetheless, our data gave results similar to those of the references above.

Indeed, there are limitations to our study. First, the nature of a retrospective study could have an inherent bias. In addition, clinical outcomes for daily functioning such as ODI or 36-Item Short Form Survey (SF-36) would provide additional useful clinical functioning information but could not be evaluated in a retrospective study due to the unavailability of data. Second, the procedures were performed by different surgeons at our center and we could not account for the variation in technique. Third, although the results were clear and comparable between groups, a longer follow-up period is needed to assess whether HVC can mitigate BKP-related risks in the treatment of osteoporotic VCFs in high to mid-thoracic vertebrae. Fourth, health insurance policy in Taiwan does not subsidize the use of CT or MRI to assess bone cement leakage or adjacent fractures, therefore diagnosis with a simple film has an inherently high false-negative incidence and the data may be limited.