Influence of radiofrequency kyphoplasty on pulmonary function

Abstract

BACKGROUND:

Vertebral compression fractures (VCF) change the natural spinal alignment and inevitably lead to a decreased quality of life.

OBJECTIVE:

The aim of the study was to evaluate changes in pulmonary function after VCF were treated by radiofrequency kyphoplasty (RF-TVA).

METHODS:

Twenty-five patients were treated with RF-TVA and analyzed in 3 subgroups taking into account the spinal location of the VCF. Pain as measured by visual analogue scale (VAS), Oswestry-Disability-Index (ODI), vertebral height, forced expiratory volume in 1 second (FEV ${}_{1}$ ), and peak expiratory flow (PEF) were assessed before, directly after and 30 days after RF-TVA.

RESULTS:

The mean vertebral height was improved in all subgroups, with a minor reduction from one to 30 days postoperatively. The mean VAS and ODI significantly decreased in the main and upper diaphragm groups from baseline to the follow-up after 30 days. Patients treated below the main diaphragm region showed a significant improvement of ODI and a clear trend to significant improvements of VAS. PEF and FEV ${}_{1}$ were significantly improved in the main diaphragm group. FEV ${}_{1}$ also increased significantly in the upper diaphragm group with a clear trend to significance in the lower diaphragm group.

CONCLUSIONS:

Results indicate that RF-TVA may improve pulmonary function especially in cases where fractures are located in the main spinal region of the diaphragm.

Keywords

Radiofrequency kyphoplasty vertebral (compression) fracture pulmonary function lung function PEF FEV

1. Introduction

Vertebral compression fractures are increasing amongst the continuously aging population, particularly in the context of osteoporosis. They mostly occur in the thoracolumbar and lumbar region [1, 2]. The symptoms are pain, kyphosis and reduced pulmonary function, which consequently reduce the quality of life [3, 4, 5, 6, 7].

Especially impaired forced expiratory volume in 1 second (FEV ${}_{1}$ ) values are associated with a wide range of diseases. There is a negative correlation between FEV ${}_{1}$ values and the risk of mortality, such that the mortality risk increases with decreasing FEV ${}_{1}$ values [8, 9].

If conservative therapies have failed, minimally invasive therapies such as vertebroplasty und kyphoplasty are applied [10, 11]. Radiofrequency kyphoplasty, also known as Radiofrequency-Targeted Vertebral Augmentation, has been devised in the past few years to refine kyphoplasty. Through this procedure the viscosity of the bone cement injected into the vertebral body is increased by means of radiofrequency. A detailed description of the procedure is given in previous publications [12, 13]. As a result, the risk of cement leakage after using radiofrequency kyphoplasty is lower than the risk of leakage after kyphoplasty, whilst maintaining the same successful results in terms of vertebral body height restoration, regenerated stability, reduction of pain and improvement of functional impairment [14, 15, 16, 17, 18].

This study investigates how the use of radiofrequency kyphoplasty for treating vertebral compression fractures, influences pulmonary function in addition to reducing back pain and functional impairment as well as achieving height restoration of the vertebral body.

2. Materials and methods

2.1 Participants

Twenty-five patients (gender: 14 female, 11 male; age: 70.4 $\pm$ 9.4 years) with one vertebral compression fracture each (17 lumbar vertebrae, 8 thoracic vertebrae) were treated with radiofrequency kyphoplasty. A detailed study of the patients’ medical history was conducted before surgery and patients underwent a complete physical examination, including MRI, to confirm the presence, location and severity of vertebral compression fractures.

Patients were excluded from the study, if they fulfilled one of the following criteria:

•
High-energy trauma
•
Known tumor involvement
•
Osteonecrotic-, burst-, or pedicle-fractures
•
Previous surgical treatment for a VCF
•
Rheumatic disorders or paget’s disease
•
Acute or chronic infections
•
BMI $>$ 35
•
Uncontrolled diabetes HbAc1c $>$ 7%
•
Severe cardiopulmonary disease
•
Myelopathy
•
Long-time steroid therapy

Included patients were divided into three groups, based on the location of the fracture as illustrated in Fig. 1.

Figure 1.
Classification of the patients.

The study was conducted in accordance with the ethical principles as laid down in the Declaration of Helsinki and was approved by the local ethical committee. It was registered at www.clinicaltrials.gov, identifier NCT01609712.
2.2 Intervention

All procedures were performed unipedicular with the DFine-StabiliT ${}^{\@setsize{\scriptsize}{9.5pt}{\viiipt}{\@viiipt}{{\textregistered}}}$ Vertebral Augmentation System (DFine, San Jose, California, USA) under fluoroscopic control and conscious sedation of the patient in prone position. As kyphoplasty formally also falls under bone surgery and thus has a comparable risk of contamination, each patient received a single-shot antibiotic prophylaxis at the beginning of the procedure [12]. Cefuroxime 1,5 g i.v. was the treatment of choice, if no history of anaphylaxy or allergy was known. A working cannula with stylet (VertecoR ${}^{\@setsize{\scriptsize}{9.5pt}{\viiipt}{\@viiipt}{{\textregistered}}}$ Introducer) was introduced into the posterior to middle third of the vertebral body. Then, a straight hollow osteotome was introduced into the anterior third of the vertebral body. Drilling and rotating the osteotome, as required, creates a small cavity. After removing the osteotome, targeted small pathways beyond the midline of the vertebral body were placed with the VertecoR ${}^{\@setsize{\scriptsize}{9.5pt}{\viiipt}{\@viiipt}{{\textregistered}}}$ MidLine osteotome. Before the cement was introduced, it was activated by a radiofrequency generator, with a hydraulic regulator (MultiPlex controller). The ultra-high viscose cement (StabiliT ER ${}^{2}$ bone cement) was directly introduced into the created cavity. As the appropriate mass of cement was injected into the vertebral body, all instruments were removed and the incisions were closed. Further details of the treatments were already described elsewhere [12, 13].

2.3 Outcome

Patient reported pain and clinical data were measured one day before, one day after and 30 days after the treatment. The functional impairment caused by the vertebral compression fractures was measured one day before the surgery and 30 days after the treatment. A directly postoperative evaluation of the functional impairment was not conducted, because the patient’s activity one day after the surgery was not comparable with the preoperative examination. Back pain was evaluated with the standard Visual Analogue Scale (VAS) and the condition-specific functional impairment was evaluated with the Oswestry Disability Index (ODI) score. The anterior, medial and posterior height of the treated vertebrae was analyzed by evaluation of radiographs. Pulmonary function was measured using a calibrated spirometer (Vitalograph Micro, Vitalograph GmbH, Germany). The measurements were conducted at each examination at the same daytime to avoid circadian influences. The forced expiratory volume in 1 second (FEV ${}_{1})$ and the peak expiratory flow (PEF) were documented for each patient as percentages of the excepted values.

All inter-operative adverse events and adverse events occurring during the follow-up period were recorded.

2.4 Statistical analysis

Data were analyzed by using the statistic software PSPP (GPL version 3.). All data were expressed as mean $\pm$ standard deviation. The statistical analysis was done within the 3 patient groups (group 1 $=$ main region of the diaphragm ( $n=$ 16), group 2 $=$ above the main region of the diaphragm ( $n=$ 4), group 3 $=$ below the main diaphragm region ( $n=$ 5)). Statistical comparison was done within the groups using the paired-sample 2-tailed t-test. The significance level was determined as a 95% confidence interval.

Table 1
Mean differences and standard deviations of the height of the treated vertebrae in mm

Region	Axis	Preoperative to postoperative		Preoperative to 30 days preoperative
Group 1	Anterior	$+$ 2.9	$\pm$ 2.7 ${}^{*}$	$+$ 1.4	$\pm$ 3.4
	Medial	$+$ 4.6	$\pm$ 3.7 ${}^{*}$	$+$ 3.0	$\pm$ 4.0 ${}^{*}$
	Posterior	$+$ 0.9	$\pm$ 1.5 ${}^{*}$	$+$ 0.6	$\pm$ 1.7
Group 2	Anterior	$+$ 3.1	$\pm$ 3.6	$+$ 2.5	$\pm$ 3.8
	Medial	$+$ 2.6	$\pm$ 3.2	$+$ 2.4	$\pm$ 2.8
	Posterior	$-$ 0.3	$\pm$ 0.9	$-$ 0.6	$\pm$ 1.4
Group 3	Anterior	$+$ 3.2	$\pm$ 6.3	$+$ 2.5	$\pm$ 6.3
	Medial	$+$ 4.9	$\pm$ 4.4	$+$ 3.9	$\pm$ 3.3
	Posterior	$+$ 0.5	$\pm$ 0.9	$+$ 0.4	$\pm$ 1.0

Significant differences are marked with ${}^{*}$ .

Figure 2.

VAS values of the different examinations with vertical lines representing the standard deviation and significant differences to the preoperative values marked with ${}^{*}$ .

3. Results

The x-ray evaluation showed that in group 1 and group 3 the anterior, medial and posterior heights of the vertebrae increased one day after the treatment (Table 1), whereby the improvement of the vertebrae height was significant for the anterior, medial and posterior height in group 1 (p ${}_{\text{anterior}}<$ 0.001, p ${}_{\text{medial}}<$ 0.001, p ${}_{\text{posterior}}=$ 0.03). The improvement in group 3 showed a trend to a significant restoration of the medial vertebra height one day after the surgery ( $p=$ 0.06); the anterior and posterior height improvement remained non significant (p ${}_{\text{anterior}}=$ 0.42, p ${}_{\text{posterior}}=$ 0.41). However, in group 2 one day postoperative an increase of the vertebrae height was measured at the anterior and medial and posterior axis (p ${}_{\text{anterior}}=$ 0.19, p ${}_{\text{medial}}=$ 0.21, p ${}_{\text{posterior}}=$ 0.57). All groups, except of the posterior axis of group 2, showed a decrease of the height for any measured axis from the preoperative examination to the 30 days examination (Table 1).

The mean preoperative VAS values for back pain in groups 1, 2 and 3 were 77.4 $\pm$ 13.0, 78.5 $\pm$ 9.0 and 62.4 $\pm$ 39.5, respectively. One day after the surgery the VAS value increased in all groups significantly to 30.2 $\pm$ 19 in group 1, 16.2 $\pm$ 7.4 in group 2 and 40.0 $\pm$ 23.0 in group 3 ( $p_{1}<$ 0.001, $p_{2}<$ 0.001, $p_{3}=$ 0.05). The 30 days postoperative VAS values also conveyed a reduction of pain in all groups when compared with the preoperative values (Fig. 2). There was a significant improvement in VAS values to 15.6 $\pm$ 24.8 in group 1 and 0 $\pm$ 0 in group 2 ( $p_{1}<$ 0.001, $p_{2}<$ 0.001).

Table 2
Mean pulmonary function values as percentages of the predicted values

Group	PEF			FEV ${}_{1}$
	Preop.	Postop.	30 d postop.	Preop.	Postop.	30 d postop.
1	55 $\pm$ 19	68 $\pm$ 25 ${}^{*}$	78 $\pm$ 29 ${}^{*}$	73 $\pm$ 17	77 $\pm$ 18	91 $\pm$ 22 ${}^{*}$
2	64 $\pm$ 20	50 $\pm$ 17 ${}^{*}$	70 $\pm$ 12	71 $\pm$ 11	72 $\pm$ 20	86 $\pm$ 16 ${}^{*}$
3	55 $\pm$ 25	70 $\pm$ 33	67 $\pm$ 28 ${}^{*}$	72 $\pm$ 20	77 $\pm$ 23	86 $\pm$ 11

Significant differences to the preoperative values are marked with ${}^{*}$ .

Figure 3.

ODI values of the different examinations with vertical lines representing the standard deviation and significant differences to the preoperative values marked with ${}^{*}$ .

The VAS value 15.8 $\pm$ 11.0 of group 3 did not differ significantly to the preoperative data ( $p=$ 0.07).

The preoperative mean functional impairment, measured by the ODI, was 73.4 $\pm$ 17.1 in group 1, 66.5 $\pm$ 17.8 in group 2 and 53.3 $\pm$ 28.5 in group 3. The 30-day postoperative ODI values decreased significantly in all groups, ( $p_{1}<$ 0.001, $p_{2}=$ 0.01, $p_{3}=$ 0.04). Group 1 showed a mean ODI value of 18.5 $\pm$ 15.6, group 2 a value of 2.5 $\pm$ 3.8 and the mean ODI in group 3 was 18.2 $\pm$ 13.3. All data are illustrated in Fig. 3.

The pulmonary function, assessed by PEF and FEV ${}_{1}$ , delivered heterogeneous outcomes in the groups (Table 2, Figs 4 and 5). The preoperative mean FEV ${}_{1}$ in group 1 was 73% $\pm$ 17% of the predicted value, in group 2 71% $\pm$ 11% of the predicted value and in group 3 72% $\pm$ 20% of the predicted value. One day after the surgery the FEV ${}_{1}$ increased in all groups. However, the difference in comparison to the preoperative values was not significant ( $p_{1}=$ 0.1, $p_{2}=$ 0.77, $p_{3}=$ 0.19). A significant improvement in FEV ${}_{1}$ was reached only 30 days after the surgery in groups 1 and 2 ( $p_{1}<$ 0.001, $p_{2}=$ 0.01). The changes in group 3 showed a trend to a significant improvement after 30 days ( $p_{3}=$ 0.08).

Figure 4.

FEV ${}_{1}$ values as percentage of the predicted values at the different examinations with vertical lines representing the standard deviation and significant differences to the preoperative values marked with ${}^{*}$ .

Figure 5.

PEF values as percentage of the predicted values at the different examinations with vertical lines representing the standard deviation and significant differences to the preoperative values marked with ${}^{*}$ .

The mean preoperative PEF was 55% $\pm$ 19% of the predicted value in group 1, in group 2 64% $\pm$ 20% of the predicted value and in group 3 55% $\pm$ 25% of the predicted value. The examination one day after the surgery, showed a significant decrease in the mean PEF values in group 2 ( $p=$ 0.04). A significant increase in PEF was recorded in group 1 and 3 ( $p_{1}=$ 0.02, $p_{3}=$ 0.04), whereby the data of one patient was missing in group 1. There was no significant difference between the preoperative and the 30 day postoperative PEF values in groups 2 and 3 ( $p_{2}=$ 0.56, $p_{3}=$ 0.13). On the contrary, there was a highly significant improvement in group 1 ( $p<$ 0.001).

None of the patients had intraoperative or postoperative adverse events, which were, or could possibly be related to the intervention itself. Particularly no signs of infections such as spondylitis, spondylodiscitis or associated absceding soft tissue reactions could be noted postoperatively. Overmore no surgical revisions were required during the observation period.

4. Discussion

Vertebral compression fractures lead to pain, kyphosis and are a handicap for daily routine activities [10]. They often occur paired with weak pulmonary function [5, 7, 19, 20, 21]. Currently vertebroplasty and kyphoplasty are successful augmentation therapies for treating vertebral compression fractures, but there are also risks like cement leakage, subsequent fractures or embolism associated [22, 23]. Through radiofrequency kyphoplasty, however, a comparable treatment success could be achieved compared with vertebroplasty and balloon kyphoplasty, whilst reducing the duration of surgery and minimizing the risks [14, 15, 24, 25, 26, 27, 28, 29]. In this study a vertebra height restoration comparable to the reported outcomes of the literature was achieved by the applied radiofrequency kyphoplasty [17, 18]. Although an indication related reduction of the vertebra height was shown at the 30 days postoperative examination, the overall outcome was successful. The augmentation of the vertebrae via radiofrequency kyphoplasty significantly reduces pain and improves the daily functional impairment [16, 17, 18]. Likewise, in all groups involved in this study, a significant reduction in VAS values was recorded immediately after the surgery. The significant improvement for the VAS values in group 1 and 2 was also recorded 30 days postoperatively, group 3 showed a trend to a significant reduction of the VAS. The ODI improved significantly in all groups 30 days after the surgery, whereby the greatest improvement occurred in group 2 with a reduction of the ODI value by 96%. The improvement in the other groups was approximately 65%. The results convey that a successful pain reduction and minimizing daily handicap was achieved through radiofrequency kyphoplasty.

The negative impact of spinal fractures on pulmonary function was already shown in several studies [5, 7, 19, 20, 21]. Lombardi et al. showed that FVC and FEV ${}_{1}$ are lower in women with osteoporotic spinal fractures than in women without osteoporotic spinal fractures. Moreover, in the presence of a kyphosis, the inspiratory vital capacity and the total lung capacity as well as the lateral thorax expansion is reduced. The more pronounced the kyphosis the more restricted are lateral thorax expansion and range of motion of the ribs. Furthermore, the trans-diaphragmatic pressure in kyphosis patients is significantly lower implying significant impairment of the inspiratory muscles [21]. This study revealed an improvement of the FEV ${}_{1}$ already one day after the surgery. Thirty days after the treatment was a significant improvement of the FEV ${}_{1}$ in all groups observed, so that the mean average FEV ${}_{1}$ was approximately 90% of the expected value. The results point out that a slight improvement of the pulmonary function occurred immediately after the operation, continuously improving over a period of time, so that substantial improvement is achieved 30 days after the treatment. Due to the negative correlation between the magnitude of the kyphosis and the pulmonary function as well as a formation of dysbalance in the respiratory muscles with advancing kyphosis angle and duration of the kyphosis, the results conveyed by the study were expected. Fractures in the upper or medial area of the thoracic spine predominantly affect the accessory inspiratory muscles and the upper accessory exspiratory muscles, causing the muscles to shorten on the ventral side and lengthen on the dorsal side. Being the main inspiratory muscle, the diaphragm should be greatly affected by fractures of the lumbar region and especially flaccid by fractures at the main region of the diaphragm. Consequently, the diaphragm becomes gradually curtate so that a successful restoration of the kyphosis to nearly natural spinal conditions brings it into a tightly stretched state. One day after surgery the inspiratory and expiratory muscles have not yet recovered completely. This explains why the substantial improvement of the FEV ${}_{1}$ values was recorded at the 30 day follow up examination. The most impressive improvement of FEV ${}_{1}$ was observed in group 1. This could have been conditioned by the more severe confinement of the organs due to the fractures in the lower thoracic and upper lumbar region. In addition, since better inspiration positively correlates with better expiration, improvement of the FEV ${}_{1}$ could be linked to an improvement of inspiration due to advanced recovery of the diaphragm 30 days after treatment.

In summary, the results in all patient groups showed that FEV ${}_{1}$ values had improved after radiofrequency kyphoplasty was performed to treat vertebral compression fractures. This may well reduce the risk of mortality according to the inverse relationship between FEV ${}_{1}$ and mortality risk. Reduced FEV ${}_{1}$ values are related to a wide range of co-morbidities, such as cancer or cardiovascular diseases, even if patients are not initially affected by these diseases [8, 9]. Radiofrequency kyphoplasty might therefore have an overall benefit for patients treated with this procedure in terms of morbidity and mortality.

The second parameter used to evaluate the pulmonary function, the PEF, depends among other factors also on the forced velocity properties of the expiratory muscles [30]. However, the inspiratory muscles also play an important role in determining this value because PEF instantaneously compiled after deep inspiration. The more air the patient can inspire, the higher is the air pressure in the lungs and so the larger the pressure in which air could be exhaled by. The data showed that there is already a significant improvement of the PEF values in groups 1 and 3, whereby the improvement 30 days after treatment was clearly greater in group 1. In fact, over this 30 day period post-operative PEF values in group 3 showed slight deterioration. Group 1 showed overall the most pronounced improvement of PEF values.

This supports the significant impairment of the inspiratory muscles, in particularly the diaphragm, through kyphosis, as described by Lisboa et al. [21]. The 30 day postoperative PEF values in group 2 were significantly lower than recorded 1 day post operatively, yet showed no significant difference to the preoperative values. Perhaps the small sample size of patients explains this outcome.

In order to generalize the obtained results, further studies with a larger number of patients and longer evaluation periods are necessary. Moreover, further pulmonary parameters, especially concerning inspiration, should be investigated in order to achieve more accurate results about the influence of the vertebral height restoration on each pulmonary muscle and the resulting inspiration and expiration forces.

5. Conclusion

Radiofrequency kyphoplasty is an effective surgery for the treatment of vertebral compression fractures. In addition to increasing vertebral body height, reducing pain and improving the functional impairment, radiofrequency kyphoplasty delivers an obvious improvement in pulmonary function, especially when the fracture is located in the main spinal region of the diaphragm

Conflict of interest

The authors have no conflict of interest to report.

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Influence of radiofrequency kyphoplasty on pulmonary function

Abstract

BACKGROUND:

OBJECTIVE:

METHODS:

RESULTS:

CONCLUSIONS:

Keywords

1. Introduction

2. Materials and methods

2.1 Participants

2.3 Outcome

2.4 Statistical analysis

Table 1 Mean differences and standard deviations of the height of the treated vertebrae in mm

Table 2 Mean pulmonary function values as percentages of the predicted values

5. Conclusion

Conflict of interest

References

Table 1
Mean differences and standard deviations of the height of the treated vertebrae in mm

Table 2
Mean pulmonary function values as percentages of the predicted values