Transverse process-pedicle approach versus conventional transpedicular approach in percutaneous kyphoplasty for osteoporotic vertebral compression fracture

Abstract

Background

Osteoporotic vertebral compression fracture (OVCF) has been shown to achieve favorable clinical outcomes after percutaneous kyphoplasty (PKP) performed via the transverse process–pedicle approach (TPPA). The aim of this study was to investigate the clinical advantages of PKP via TPPA for the treatment of OVCF, by comparing it with the conventional transpedicular approach (CTPA).

Methods

A retrospective study was conducted to analyze data from 124 patients with single-segment OVCF who were treated in our department between January 2019 and December 2022. A 1:1 propensity score matching was performed based on characteristics including sex, age, BMI, injury location, and bone mineral density T-values. The patients were divided into two groups: the TPPA group (62 cases), in which PKP was performed via the TPPA, and the CTPA group (62 cases), in which PKP was performed via the CTPA. Clinical efficacy was evaluated by comparing the two groups in terms of operative time, frequency of intraoperative fluoroscopy, rate of satisfactory bone cement distribution, rate of bone cement leakage, incidence of refractures, and visual analogue scale (VAS) and Oswestry Disability Index (ODI) scores recorded at preoperative, 1-day, 3-month, 6-month, and 12-month postoperative time points. The Beck Index was also evaluated preoperatively, and at 1 day and 12 months postoperatively.

Results

There were no significant differences in baseline characteristics between the two groups, indicating comparability (P > 0.05). All surgeries were completed successfully without complications such as nerve injury or pedicle fracture. No significant differences were found between the groups in terms of operative time, intraoperative bleeding, or radiation frequency (P > 0.05). However, the amount of bone cement injected was significantly greater in the TPPA group compared to the CTPA group (P < 0.05). At 1 day postoperatively, the VAS score and ODI in the TPPA group were significantly lower than those in the CTPA group (P < 0.05), indicating better immediate pain relief and function. No significant differences in VAS or ODI were observed between the groups at preoperative, 3-month, 6-month, or 12-month time points (P > 0.05). Both VAS and ODI scores showed steady improvement within each group, with significant differences between all consecutive time points (P < 0.05). The Beck Index at both 1 day and 12 months postoperatively was significantly higher in the TPPA group compared to the CTPA group (P < 0.05). Within-group comparisons also showed significant improvement in the Beck Index at both postoperative time points compared with preoperative values (P < 0.05). Additionally, the TPPA group demonstrated a significantly higher rate of satisfactory bone cement distribution than the CTPA group (P < 0.05).

Conclusions

In the treatment of OVCF with PKP, the TPPA demonstrated comparable surgical safety to the CTPA. However, TPPA offered advantages in achieving better bone cement distribution, more effective immediate postoperative pain relief, and superior restoration and maintenance of the height of the injured vertebral body.

Clinical trial number

Not applicable. This study is a retrospective study, it is not a clinical trail.

Introduction

With the advent of population aging, age-related disorders of the skeletal and muscular systems have become serious public health issues in recent years [1, 2]. As a severe consequence of osteoporosis, osteoporotic vertebral compression fracture (OVCF) primarily affects the thoracolumbar spine, leading to intense back pain, immobility, and spinal deformity [3, 4]. As a minimally invasive surgical treatment, percutaneous kyphoplasty (PKP) has become a commonly adopted procedure for managing such fractures and has been reported to significantly improve clinical symptoms and restore the morphology of the fractured vertebra [5, 6].

Unilateral and bilateral punctures are two typical approaches used in PKP [7–9]. However, bilateral puncture requires a longer operative time, increased X-ray exposure, and higher hospitalization costs, while bone cement distribution in unipedicular PKP is often limited to the puncture side [7]. In addition, the conventional transpedicular approach (CTPA) has been associated with increased risks of pedicle fractures and facet joint violations, which may result in spinal cord or nerve root injury and persistent back pain after PKP [10, 11]. Several anatomical and imaging studies have suggested that the transverse process–pedicle approach (TPPA) may be a favorable alternative for PKP, offering larger abduction angles and improved safety by accessing the vertebra through the transverse process and the lateral aspect of the pedicle [12–14].

To our knowledge, TPPA has been used in some researches, which shown satisfied clinical outcomes, TPPA has been used in several studies with favorable clinical outcomes; however, a standardized puncture protocol has yet to be established, and literature on its clinical efficacy remains limited. Therefore, the purpose of this study was to investigate the clinical advantages of PKP via TPPA in the treatment of osteoporotic vertebral compression fractures, in comparison with PKP via CTPA.

Methods

Patient selection

This study was conducted in the authors’ department from January 2019 to December 2022. The research protocol was reviewed and approved by the ethics committee of the authors’ hospital. All participants diagnosed with single-segment osteoporotic vertebral compression fractures (OVCF) signed informed consent forms prior to their inclusion in the study. A 1:1 propensity score matching was performed based on patients’ characteristics, including sex, age, BMI, injury location, and bone mineral density T-scores.

The inclusion criteria were as follows: (1) patients diagnosed with fresh single-segment OVCF; (2) age between 60 and 80 years; (3) bone mineral density examined by dual-energy x-ray examination (T-score < -2.5); (4) post-operative follow-up was at least 1 year.

The exclusion criteria were as follows: (1) combination of spinal tuberculosis, spinal metastases, or spinal infection; (2) bleeding and clotting dysfunctions that could not be corrected; (3) patients who are unable to cooperate with surgery, such as mental disorders or impaired consciousness; (4) > 70% compression degree of vertebral bodies.

Surgical intervention

All PKP procedures in this study were performed by the same lead spinal surgeon (CH), who is well experienced in kyphoplasty and vertebroplasty in our department. All PKP operations were conducted in the operating room of our hospital, which is equipped for immediate decompression surgery. Patients were placed in the prone position with two lateral support pads under the chest and pelvis to reduce abdominal pressure.

To locate the damaged vertebral body and determine and mark the pedicle puncture needle point, the C-arm was adjusted so that there was no bilateral shadowing of the fractured vertebra and the shape of the vertebral arch was symmetrical and equidistant from the spinous process. All patients underwent local infiltration anesthesia with 1% lidocaine before puncture. The side of needle entry was chosen based on the side where vertebral compression was more pronounced or symptoms were more severe. If compression and symptoms were similar on both sides, the side that was easier to puncture was selected.

The sketch of these two types of puncture techniques is shown in Fig. 1. In the TPPA group, the puncture point was on the transverse process, which allowed for a larger extended angle, and the tip of the puncture needle could even extend beyond the midline (Fig. 1A). However, in the CTPA group, the puncture point was on the articular process, with a smaller extended angle, and the tip of the puncture needle was difficult to reach the midline (Fig. 1B). As shown in Fig. 1, the fourth red longitudinal line from left to right is a parallel line, one vertebral arch width away from the third red longitudinal line. The intersection of the fourth red longitudinal line and the transverse process was used as the puncture point. The patient’s transverse arch diameter was measured on CT preoperatively.

Fig. 1.

The sketch of these two kinds of puncture techniques

With the help of fluoroscopy, the puncture point and the angle of puncture (10–30° of lateral inclination) were confirmed. On the anteroposterior radiograph, the puncture needle reached the outer wall of the vertebral arch, while on the lateral view, the needle reached halfway up the vertebral arch. When the lateral radiograph showed that the puncture needle had reached the medial wall of the arch, it also indicated that the needle had reached the posterior edge of the vertebral body. The needle was then advanced further to enter the anterior one-third of the vertebral body. Once the tip of the puncture needle was close to the midline, the needle was removed, and a guide wire was inserted. After that, the working channel and balloon expansion system were established, and the working sleeve was placed step by step.

Under fluoroscopic guidance, the balloon was slowly inflated by injecting a contrast agent. Inflation was stopped once the fractured vertebral body was satisfactorily repositioned and/or the balloon expanded to the superior and inferior endplates of the affected vertebra. The balloon system was then removed. The entire cement injection phase was carried out under strict fluoroscopic monitoring in both anteroposterior and lateral views. Cement was injected starting from the anterior one-third of the vertebral body, using 0.5–0.75 ml each time. If cement leakage was observed, the injector was repositioned—typically by retracting it 1 cm—before continuing the injection until the cement reached the posterior third of the vertebral body. Once satisfactory cement distribution was confirmed under intraoperative fluoroscopy, the puncture needle was gradually withdrawn, and the incision was sutured.

All patients remained in bed on the day of surgery and began ambulation with a lumbar brace the following day. The brace was worn for 4–6 weeks, with continued use depending on the evaluation at the one-month postoperative follow-up. All patients received a personalized anti-osteoporosis treatment plan after surgery. Their medications were adjusted during follow-up by our professional team based on clinical indicators.

Outcome measurements

Operative time, intraoperative bleeding, radiation frequency, and cement volume were evaluated and analyzed in both groups. Intraoperative bleeding in this percutaneous approach was estimated based on a combination of the degree of vertebral compression observed preoperatively and the amount of blood absorbed by the gauze during the procedure.

The Visual Analog Scale (VAS) and the Oswestry Disability Index (ODI) were used to assess patients’ pain and functional status at multiple time points. Specifically, VAS and ODI scores were recorded preoperatively, and at 1 day, 3 months, 6 months, and 12 months postoperatively.

As shown in Fig. 2, the Beck Index—defined as the ratio of the anterior to posterior vertebral body height—was used to evaluate the restoration of vertebral body height. The recovery degree of the injured vertebra was assessed by comparing the Beck Index at 1 day postoperatively with the preoperative value, and the degree of height loss was evaluated by comparing the Beck Index at 12 months postoperatively with that at 1 day postoperatively (Fig. 2).

Fig. 2.

X-ray images of the vertebral height restoration. (A, pre-surgery; B, 1d post-surgery; C, 12 months post-surgery)

Moreover, the distribution and leakage of bone cement were assessed and recorded 1 day postoperatively. As shown in Fig. 3, bone cement distribution was classified into three types: Type I: Unilateral distribution, where the bone cement was concentrated on one side and did not cross the midline; Type II: Central distribution, where the cement extended beyond the midline but did not reach the contralateral side of the vertebral body; Type III: Bilateral distribution, where the bone cement was present on both sides of the midline. Therefore, Type II and Type III were considered satisfactory distributions of bone cement (Fig. 3).

Fig. 3.

Classification of bone cement distribution (A, type I; B, type II; C, type III)

Two senior spinal surgery residents independently measured each patient’s imaging data, and the average of their measurements was used for the final analysis. Postoperative adverse effects, including wound infection, incision swelling, bone cement leakage, and vertebral re-fractures, were also assessed in all patients.

Statistical analysis

A sample size calculation (G Power 3.1.9.7) was conducted in this study, based on VAS score of previous studies (using two-tailed α:0.05, β:0.20 (power: 80%)), considering an effect size = 1.33. To ensure adequate power, 10% of the estimated number was increased. Therefore, 62 participants would be required for each group in this research. Shapiro-Wilk and Kolmogorov-Smirnov tests were used for testing the normality of data distribution and showed that all measured variables were normally distributed. Unpaired t-tests and chi-square were used to compare the subjects’ characteristics of the two groups. A statistical package for the social sciences computer program (version 25 for Windows; SPSS Inc., Chicago, Illinois, USA) was used for data analysis. P < 0.05 was considered significant.

Results

Patient demographics

81 patients were assessed for eligibility, 10 patients did not meet the inclusion criteria and 9 patients refused to join the study (Fig. 4). The TPPA group consisted of 21 men and 41 women, aged 60 to 80 years old, with single-segment OVCF who underwent PKP by TPPA approach. According to characteristics including sex, age, BMI, injury location and T values of bone mineral density, a 1:1 propensity-score matching was performed. A total of 62 patients with single-segment OVCF who underwent PKP by CTPA approach were also enrolled in this study, as compare group. The two groups were comparable with no significant difference in any of the demographic characteristics (Table 1).

Fig. 4.

Flowchart for patients’ eligibility

Table 1.

Comparisons of clinical characteristics between two groups ^a

	TPPA Group (n = 62)	CTPA Group (n = 62)	P Value b
Age, y, mean ± SD	73.38 ± 7.42	73.76 ± 7.36	0.967
Male sex (%)	21 (33.87%)	21 (33.87%)	1.000
BMI, kg/m2, mean ± SD	20.68 ± 1.01	20.90 ± 1.02	0.923
T scores	-3.05 ± 0.25	-3.04 ± 0.26	0.895
Fracture site (n, %)			0.862
Thoracic vertebra	20 (32.26%)	21 (33.87%)
Lumbar vertebra	42 (67.74%)	41 (66.13%)

^a Data are reported as n (%) or mean ± SD. BMI, body mass index, kg/m2

^b Independent t test or chi-square test. The P values shown are for intergroup comparisons. Significance was accepted for P<0.05.

Basic surgical data

There was no significant difference in operation time, intraoperative bleeding and radiation frequency in TPPA group, compared with CTPA group. Among the evaluated indicators, there was only a statistically significant difference in the amount of bone cement injected between the two groups (P < 0.05). (Table 2).

Table 2.

Comparisons of basic surgical data between two groups ^a

	TPPA Group(n = 62)	CTPA Group(n = 62)	P Value b
Operation time (min)	42.10 ± 7.11	45.32 ± 8.01	0.082
Intraoperative bleeding (ml)	11.65 ± 2.97	12.15 ± 3.06	0.223
Radiation frequency	20.7 ± 3.25	22.5 ± 3.79	0.093
Cement volume (ml)	8.11 ± 1.07	6.82 ± 0.95	0.013

^a Data are reported as n (%) or mean ± SD

^b Independent t test. The P values shown are for intergroup comparisons. Significance was accepted for P<0.05

Clinical outcomes

Within-group comparisons showed significant improvements in both VAS scores and ODI indices in each group after treatment compared with pre-treatment values. At the 3-month, 6-month, and 12-month follow-up visits, no statistically significant differences were observed between the two groups. However, a statistically significant difference in VAS and ODI scores was found between the two groups at the 1-day postoperative evaluation (P < 0.05) (Table 3).

Table 3.

Comparisons of clinical outcomes between two groups ^a

	TPPA Group (n = 62)	CTPA Group (n = 62)	P Value b
VAS score, mean ± SD
Preoperative	7.24 ± 1.35	7.01 ± 1.22	0.652
1d-Postoperative	3.29 ± 0.37	4.74 ± 0.52	0.001
3 m-Postoperative	1.05 ± 0.07	1.25 ± 0.08	0.372
6 m-Postoperative	0.65 ± 0.05	0.75 ± 0.07	0.625
12 m-Postoperative	0.25 ± 0.04	0.28 ± 0.06	0.743
P Value (within) c	< 0.001	< 0.001
ODI score, mean ± SD
Preoperative	78.52 ± 8.82	79.76 ± 7.87	0.848
1d-Postoperative	56.24 ± 7.66	59.86 ± 7.54	0.042
3 m-Postoperative	30.05 ± 5.72	31.25 ± 5.62	0.767
6 m-Postoperative	20.65 ± 4.52	22.75 ± 4.72	0.853
12 m-Postoperative	18.25 ± 4.10	19.28 ± 4.21	0.891
P Value (within) c	< 0.001	< 0.001

^a Data are reported as n (%) or mean ± SD

^b Independent t test. The P values shown are for intergroup comparisons. Significance was accepted for P<0.05

^c Paired t test. The P values shown are for intragroup comparisons. Significance was accepted for P<0.05

Radiographic outcomes

The Beck Index in the TPPA group was significantly higher than that in the CTPA group at both 1 day and 12 months postoperatively. Within each group, the Beck Index at 1 day and 12 months postoperatively was significantly improved compared to the preoperative value. However, there was no significant difference in the Beck Index within the TPPA group between 1 day and 12 months postoperatively (P > 0.05). In contrast, the Beck Index in the CTPA group at 12 months postoperatively was significantly lower than that at 1 day postoperatively (P < 0.05) (Table 4). Compared with the CTPA group, the TPPA group had a significantly higher rate of satisfactory bone cement distribution (P < 0.05).

Table 4.

Comparisons of radiographic outcomes between two groups ^a

	TPPA Group (n = 62)	CTPA Group (n = 62)	P Value b
Beck index, mean ± SD
Preoperative	0.65 ± 0.21	0.65 ± 0.24	0.921
1d-Postoperative	0.81 ± 0.32	0.75 ± 0.29	0.012
12 m-Postoperative	0.77 ± 0.28	0.71 ± 0.26	0.036
P Value (within) c	< 0.001	< 0.001
Bone cement distribution types (n, %)
I type	5 (8.06%)	20 (32.26%)
II type	30 (48.39%)	28 (45.16%)
III type	27 (43.55%)	14 (22.58%)
Satisfied rate	57 (91.94%)	42 (67.74%)	0.004

^a Data are reported as n (%) or mean ± SD

^b Independent t test or chi-square test. The P values shown are for intergroup comparisons. Significance was accepted for P<0.05

^c Paired t test. The P values shown are for intragroup comparisons. Significance was accepted for P<0.05

Safety

No significant postoperative adverse effects, such as wound infection or incision swelling, were observed in any of the 124 cases. The histocompatibility of the bone cement was deemed satisfactory. In total, 12 cases of bone cement leakage were identified across both groups, with 5 cases occurring in the TPPA group (8.06%) and 7 cases in the CTPA group (11.29%) (P > 0.05). Importantly, 12 cases instances of leakage were asymptomatic and did not require additional intervention (p > 0.05). Besides, a total of 2 patients from both the TPPA and CTPA groups experienced re-fracture at the 1-year follow-up (TPPA: 1 case; CTPA: 1 case, P > 0.05).

Discussion

The most important finding of this study was that both TPPA and CTPA were safe approaches for PKP in the treatment of OVCF, with significant improvement in VAS score and ODI in both groups post-operation compared with pre-operation. In addition, TPPA could lead to better cement distribution, better pain relief at immediate post-operation, restoring and maintaining the height of the injured vertebral body.

CTPA was the typical puncture route for PKP, which has been utilized in clinical practice for several decades [15–17]. However, several previous studied have reported that CTPA might lead to some complications and issues, such as suboptimal post-operative pain relief, uneven cement distribution, and the potential for post-operative vertebral re-collapse [18, 19]. Furthermore, TPPA has been used by some surgeons in clinical practice, which gave better dispersion of bone cement [20]. However, few systematic studies have compared the clinical outcomes of TPPA and CTPA.

In this study, the amount of bone cement injected was more in TPPA group, compared with CTPA group. Lv et al. has reported that the distribution pattern and the amount of bone cement could influence the patient’s pain relief [21]. Moreover, a broader spread of bone cement within the spinal body could lead to alleviated pain relief, improved patient function, and reduced loss of vertebral height [21, 22]. Notably, patients in TPPA group in our study exhibited a more substantial improvement in VAS score and ODI score compared to those in CTPA group at the 1-day postoperative evaluation, which appears to be supported by the distribution pattern and the amount of bone cement.

In CTPA group, the puncture point was located near the inner wall of the vertebral arch on the articular eminence, which could lead to a limited abduction angle [23]. To Contrast, in TPPA group, the puncture point was situated on the transverse process, which would allow for a greater angle of abduction. Therefore, TPPA could enable the needle tip to reach, and even surpass, the midline, which might facilitate easier access to the best target location in the anterior middle third of the body of the vertebrae. As a result, a broader spread of bone cement within the spinal body would be easier to obtained in TPPA group with a higher likelihood of bone cement diffusion to the contralateral side.

In current research, Beck index in TPPA group was significantly higher than that in CTPA group at1-day and 12-month after operation. Besides, there was no significant difference in Beck index between the TPPA group at 12-month and1-day after surgery. The Beck index of CTPA group at 12-month after operation was significantly lower than that at1-day after operation. Compared with CTPA Group, Satisfied rate of bone cement distribution was higher in TPPA Group, with significant difference. The result implied that TPPA has an advantage in preserving vertebral height compared with CTPA. We believe that the type of bone cement distribution could play an important role in vertebral height loss of the injured vertebrae. Increasing the volume of injected cement in PKP, without raising the risk of cement leakage, might enhance injection pressure and facilitate optimal cement distribution. An ideal cement distribution pattern could be obtained in TPPA Group, which would prove beneficial for maintaining vertebral height. Qiao et al. also found that the modified transverse process-pedicle approach could facilitate an adequately homogeneous distribution of bone cement and provided significant pain relief at immediate post-operation, which was similar to the result in our study [24].

In our study, 5 cases of cement leakage were observed in TPPA group, compared with 7 cases in the CTPA group. All cases were asymptomatic and did not require specific management, and the difference was not statistically significant. This result was similar to previous studies [25, 26], which providing that increasing the volume of bone cement pumped does not relate to a higher leakage rate. Therefore, the safety profile of TPPA was confirmed to be similar to that of CTPA. Besides, Wang et al. [27] suggested that the cement injection site which was placed as close as possible to the posterior third of the vertebral body might avoid blood vessels in the spinal canal, and intraoperative monitoring of bone cement injection using a c-arm could be implemented to avoid cement leakage.

In addition, a patient in TPPA group and a patient in CTPA experienced re-fracture at the 1-year follow-up. The rate of vertebral re-fractures previous studies, ranged from 2.9 to 27.6% [28]– [29], was higher than that in our study. We suggest that low bone mineral density was a significant risk factor for recurrent fractures, and the increased emphasis on anti-osteoporosis treatment in this study might explain the result.

It is important to consider the limitations of this study. The duration of follow-up period in this study was limited to a specific timeframe, and the long-term effects of TPPA versus CTPA therapy were not evaluated. Future studies with longer follow-up periods are needed to provide more comprehensive insights into the comparative effects of these two treatment approaches. While our study demonstrated significant positive outcomes of TPPA, several questions remain unanswered, presenting avenues for future research. Firstly, the long-term effects of TPPA versus TPPA on clinical outcomes need to be explored. Secondly, exploring the biomechanical and histological outcomes of TPPA versus TPPA in treatment of OVCF with PKP. Future researches endeavors addressing these unanswered questions will contribute to a deeper understanding of the therapeutic potential of TPPA and further optimize its application in clinical practice.

Conclusion

In the treatment of OVCF with PKP, the TPPA demonstrated comparable surgical safety to the CTPA approach. However, TPPA offered advantages in achieving better bone cement distribution, providing more effective immediate postoperative pain relief, and preserving the height of the injured vertebral body.

Author contributions

CH and FP designed and supervised this study. CH and BL wrote this manuscript. XT and BZ participated in the exercise instruction, follow-up and outcomes measurements. All authors were involved in the data collection, statistics analysis. XT and BZ were involved in the revision of this manuscript. All authors read and approved the final manuscript.

Funding

Anhui Provincial Health Commission Natural Science Key Project (AHWJ2021a015). Wuhu Science and Technology Plan Project (2020ms3-10).

Data availability

No datasets were generated or analysed during the current study.

Declarations

Ethics approval and consent to participate

All methods of this study were carried out in accordance with relevant guidelines and regulations, which were approved by medical ethics committee of the Second Affiliated Hospital of Wannan Medical College. Written informed consent was obtained from all subjects.

Consent for publication

Not applicable.

ADM statement request

All data generated or analyzed during this study are included in this published article.

Competing interests

The authors declare no competing interests.