A few studies of HBL post cement augmentation surgery focused on the PKP/PVP in the treatment of OVCFs8–10. However, no research has been explored the hidden blood loss and its influencing factors post cement augmentation of vertebral metastasis with PVCFs. In this research, the main finding revealed that the amount of HBL was 448.2 ± 267.2 ml, which accounted for 10.8% ± 6.2% of PBV, and the mean Hb loss of 12.8 g/L in the perioperative period. Our research presented a worse result compared with the results from previous studies in OVCFs, such as, Cao et al8 and Wu et al10 found out that 279 ± 120 ml mean HBL accompanied by 8.2 ± 3.9g/L Hb loss, and a mean of 282 mL HBL with 8.7 g/L Hb loss during the perioperative period, respectively. As well, 53 patients with normal preoperative Hb levels developed into anemia, which implied that 46.7% preoperative anemia rate increased to 78.1% post operation (Fig. 1A). Advanced malignant tumor with PVCFs represents a high risk and poor ability to resist bleeding in the perioperative period. Massive blood loss will prolong the post-operative recovery time due to the potential adverse effects of anemia, which delayed the time of comprehensive treatment. However, no study focused on the risk factors of HBL during cement augmentation with or without RFA for the treatment of PVCFs. Hence confirming the amount of HBL and its related influencing variables are crucial for patients of PVCFs.
Up to now, the mainstream mechanisms of HBL that has been proposed was blood penetrating tissues or retained in a dead space and blood hemolysis.18; 19 However, no the related influencing factors associated with the HBL amount were clearly stated in the therapy of cement augmentation plus or not RFA for PVCFs. In our study, multiple linear regression analysis was employed to investigate the related influencing factors. The study considered that patients with lytic bone destruction, more numbers of PVCF(s), greater percentage of VHL, more bone cement amount, bone cement leakage would have more possibility of HBL.
Our study demonstrated that lytic bone destruction related to more HBL compared with the blastic and mixed lytic/blastic patients during perioperative period (Fig. 1B). Compared with blastic and mixed lytic/blastic spinal metastases, lytic spinal metastases mean more vertebral bone reduction and loss of vertebral structural stability. Vertebral reduction will lead to the ‘‘empty shell phenomenon’’ in the vertebral body20, which may be a source and reason for more HBL in patients with severe VHL.10 As the bearing bone, loss of vertebral structural stability is apt to occur the VHL, which was also positively related to the HBL amount in our study (p = 0.011, Table 5). In the previous study, HBL was also found a positive correlation related to the number and vertebral fracture severity.8–10
In the analysis of the relationship between bone cement leakage and HBL, multivariate linear regression analysis showed that the bone cement leakage was positively correlated with HBL in our study, which also can be confirmed in the other article.8–10 The occurrence of bone cement leakage was mostly due to the fracture gap of cortical defect,21 which also can be aggravated by the lytic bone destruction. The cortical defect will lead to persistent bleeding of the vertebra8; 10 and make it accessible to bone cement leakage during the perioperative period of cement augmentation. What’s more, large bone cement volume was strong predictor of bone cement leakage.22 In addition, there is a significant evidence that the amount of bone cement is positively associated with HBL in our study. Polymethylmethacrylate (PMMA), the most commonly used bone cement, not only can reconstruct the stability of vertebra, but also induce the tumor cell due to exothermic effect in solidification process and cells toxicity.10 In the previous study, thermal necrosis was a significant factor of hemolysis during PKP,10 which was not confirmed by us. In our study, the temperature in the process of RFA can reach a maximum of 103°C, which is higher than the 55°C of bone–cement interface temperature. However, no association was found between RFA and HBL (p = 0.413, Table 5). In summary, thermal necrosis may be not the dangerous factor for HBL, so further study should be to explore the correlation between cement and HBL.
As a retrospective study, there are still many limitations, despite being fully designed and implemented. First, the research results should be verified by multiple centers due to the occluded data in a single-center retrospective study. Second, the HBL was falsely estimated. One reason is that the postoperative Hct was evaluated in the 2 or 3 days of postoperation when the fluid shifts were not completed in this time.14 Another reason is that intravenous fluid infusion in the perioperative period will lead to the hemodilution. Third, a more specific and detailed measurement method for the degree of vertebral destruction especially for osteolysis should be involved.