Comparison of the clinical outcomes and cement distribution patterns after percutaneous vertebroplasty in the treatment of thoracolumbar Kümmell’s disease and OVCFs CURRENT STATUS: POSTED

Background The purpose of this study is to investigate and compare the therapeutic effect and distribution characteristics of bone cement in the PVP treatment for thoracolumbar diseases and OVCFs. Methods A prospective analysis of 35 patients with Kümmell ’s disease (K group) and 35 patients with OVCFs (O group) who underwent PVP treatment from February 2016 to February 2018 was conducted. The vertebral compression rate and degree of osteoporosis were more serious in the K group than in the O group ( P <0.05, respectively). Distribution pattern, volume and leakage rate of bone cement, operation time, VAS score, ODI, correction rates of vertebral compression and kyphosis, re-fracture rate of adjacent vertebrae in 2 years between the two groups were compared to assess clinical effect. Results The follow-up time of the two groups was 24-48 months. The amount of intraoperative bone cement injection was significantly higher in the K group than in the O group ( P =0.025). The cement distribution pattern of local solid lump was dominant in the K group (65.71%), while intercalation with trabeculae was dominant in the O group (74.29%) ( P <0.001). VAS score and ODI were significantly lower both in the two groups at 1 day, 1 year and 2 years after surgery than before surgery (all P <0.05), but significantly lower in the K group than in the O group at each time point after surgery (all P <0.05). The correction rates of kyphosis and vertebral compression in both groups was significantly corrected ( P <0.05, respectively) and gradually lost with time ( P <0.05, respectively). The correction rates of kyphosis and vertebral compression were significantly higher in the K group than in the O group at each time point after surgery (all P <0.05). Conclusions PVP has the advantages of simple operation, short operation time, small trauma and quick recovery in treating both Kümmell's disease and OVCFs. However, PVP can better restore partial vertebral height and correct kyphosis in the treatment of Kümmell's disease, while can better are expressed mean standard deviation. test used to test the homogeneity of variance. Independent sample t test was used for inter-group comparison. One-way ANOVA (Bonferroni or Dunnett T3) was used for comparison between different time points between groups. Repeated measurement ANOVA was used for intra-group comparison between different time

relatively rare [1]. Persistent pain of low back persists several weeks or months after a minor injury.
Radiological examination shows transversely or irregularly shaped transmittal areas of the vertebral body with peripheral sclerosis signals [2]. Some scholars also call it ischemic vertebral collapse or vertebral pseudarthrosis [3]. Thoracolumbar vertebra is the most common site of its occurrence.
Kümmell's disease has the characteristic of "open sign", that is, the crack is obvious in the extension position of the body, while the crack can disappear in the flexion position [4]. The characteristic performance of Kümmell's disease is called intravertebral vacuum cleft (IVC) or intravertebral vacuum phenomenon (IVP) [5] [6].
Percutaneous Vertebroplasty (PVP) is a minimally invasive approach to infuse bone cement into vertebral body for stabilizing fractured vertebra, which can quickly relieve the pain of low back, restore partial vertebral height and correct kyphosis [7,8]

Selection criteria
Inclusion criteria are as follows: (1) single-thoracolumbar Kümmell's disease or OVCFs patients without adjacent OVCFs; (2) physical examination of the location of the "pain vertebra" was consistent with imaging examination. (3) dual-energy X-ray bone mineral density(BMD) T value < -2.5; (4) bilateral pedicle PVP was performed; (5) follow-up time was more than 2 years; (6) Calcium supplementation and anti-osteoporosis drugs were used after the operation. Exclusion criteria are as follows: (1)  received PVP treatment (Fig. 1). This study was approved by the ethics committees of our hospitals.
All clinical data and pictures of the patients were obtained with the written informed consent from the patients or their families.
There was no significant difference in gender, age, injury segment, preoperative VAS and Oswestry dysfunction index (ODI) between the two groups (all P > 0.05). The course of disease in the K group was significantly longer than that in the O group (P = 0.000). Most cases in the K group had no history of trauma, while most cases in the O group had a history of falls (P = 0.001). The vertebral compression rate and the degree of osteoporosis of the K group were more serious than those of the O group (P < 0.05, respectively). (Table 1)

Postoperative Management
After the operation, patients were kept in the horizontal position for 8-12 h, and the rest was mainly bed rest in the 1-2 months. For 1-2 months after the operation, the low back support was used to get out of bed. Drugs such as bisphosphonates, vitamin D and calcium tablets were given for antiosteoporosis treatment.

Outcome Measurements
The dispersion morphology, leakage rate and injected amount of bone cement, operation time, VAS score of low back [11], ODI [12] and the incidence of new adjacent vertebral re-fracture in 2 years were recorded in the two groups.
Anteroposterior and lateral X-ray images were taken before and after the operation to measure the Measurement data are expressed as mean ± standard deviation. The Levene test was used to test the homogeneity of variance. Independent sample t test was used for inter-group comparison. One-way ANOVA (Bonferroni or Dunnett T3) was used for comparison between different time points between groups. Repeated measurement ANOVA was used for intra-group comparison between different time points. The counting data were tested with χ 2 test. P < 0.05 was considered statistically difference.

Results
The two groups were followed up for 24-48 months, and there was no statistically difference in followup time, operation time, intraoperative blood loss, or fluoroscopy times between the two groups (all P > 0.05). Intraoperative amount of bone cement injected was significantly higher in the K group than in the O group (P = 0.025). In the K group, 23 cases (65.71%) were local solid lump of distribution However, none of the patients both in the two groups had any related clinical symptoms. There was no significant difference in the incidence of cement leakage between the two groups (P > 0.05).
(  VAS score and ODI were significantly lower in the two groups 1 day, 1 year and 2 years after surgery than before surgery (all P < 0.05), but significantly lower in the K group than in the O group at each time point after surgery (all P < 0.05). During the 2-year follow-up, 6 patients (17.14%) in the K group and 4 patients (11.43%) in the O group had adjacent vertebral fractures (P = 0.243). (Table 2) The correction rates of kyphosis and vertebral compression were significantly corrected in both groups (P < 0.05, respectively), but gradually decreased significantly with time (P < 0.05, respectively), suggesting that vertebral height and kyphosis angle were gradually lost after the surgery. The correction rates of kyphosis and vertebral compression were significantly higher in the K group than in the O group at each time point after surgery (all P < 0.05). (Table 3)  Biomechanical studies have confirmed that the strength of vertebral body can be restored by injecting about 2 ml bone cement and the stiffness of the vertebrae can be restored by injecting about 4 ml bone cement [22]. In this study, the average injection amount of bone cement in the K and O group were 4.2 ± 1.15 ml and 3.6 ± 1.35 ml, respectively. All of them met the requirements of restoring vertebral strength, and the K group met the requirements of restoring vertebral stiffness.
After filling the fissures with bone cement in the fractured vertebrae, the height of the vertebrae was partially restored and kyphosis deformity was partially corrected, and the abnormal activity of the fractured vertebrae was eliminated, which was an important reason for pain relief [2].  We found that the correction rates of vertebral compression rate and kyphosis in the two groups gradually decreased with time, suggesting that the vertebral height and kyphosis angle gradually lost after surgery, which was consistent with previous findings [16,35]. In the treatment of OVCFs by PVP and PKP, the bone cement injected during the operation of the former is mainly embedded in cancellous bone, while the bone cement of the latter is mainly filled with clumps, so stress occlusion is more likely to occur after PKP and leads to recollapse [36]. In this study, it was found that local solid lump distribution pattern of bone cement was dominant in the K group (65.71%), while embedded trabeculae distribution pattern was dominant in the O group (74.29%). In the two groups, two years after the surgery, re-collapse and intervertebral height loss occurred in the enhanced vertebra, and the loss in the K group was more significant than that in the O group. As a "reservoir" of IVC region, bone cement was filled in the IVC region in the form of solid mass. The limited bone cement mass cannot connect with the adjacent endplates of the upper and lower levels to strengthen cancellous bone of the vertebrae, thus failing to support the normal physiological stress from the body and prone to collapse again [37].
The most common complications of PVP are bone cement leakage and adjacent vertebral fracture [38,39]. Krauss et al. [40] reported that in OVCFs treated with IVC by PVP, the bone cement leakage rate was 18.2%. Wang et al. [41] reported that for OVCFs treated with IVC by PKP, the bone cement leakage rate was 7.4%. This study found that the leakage rate of bone cement in the K and O groups were 14.29% and 8.57%, respectively, which may be related to accurate preoperative surgical approach measurement, careful intraoperative operation and not pursue the maximum amount of bone cement. There was no significant difference in cement leakage rate between the two groups, which was consistent with previous research results [42,43]

Consent for publication
Not Applicable.

Availability of data and materials
The datasets used and/or analysed during the current study are available from the corresponding author on reasonable request.

Competing interests
No potential conflict of interest relevant to this article was reported.

Fundings
There is no funding for the current study.