Unilateral percutaneous kyphoplasty for lumbar spine: A comparative study between transverse process-pedicle approach and conventional transpedicular approach.

Anatomical differences of unilateral percutaneous kyphoplasty (PKP) between transverse process-pedicle approach (TPPA) and conventional transpedicular approach (CTPA) are not well discussed. To investigate the anatomical distinctions of unilateral PKP between TPPA and CTPA, we have discussed the unilateral PKP through a 3-dimensional-computed tomography database.Five hundred lumbar spines from 100 patients have been retrospectively collected and unilateral CTPA and TPPA were simulated. Distance between the entry point and the midline of the vertebral body (DEM), the puncture inclination angle (PIA), and the success rate (SR) of puncture were measured and compared.The male presented with significantly larger DEM than the female. The TPPA group presented with larger DEM than the CTPA group according to different level, the difference was 1.5 ± 1.1 mm to 3.8 ± 2.3 mm. The PIAs in the TPPA group were larger than that in the CTPA group. The SR including 1 side SR and bilateral SR was 72.0% in the CTPA group and 98.0% in the TPPA group. Compared with CTPA group, the SR in TPPA group was significantly higher for L1 to L4 no matter in the left, right side and female patients.The TPPA group presented with more lateral entry point, larger PIAs and higher SRs than that in the CTPA group. PKP surgery through a TPPA was safer and could provide a more symmetrical distribution of bone cement than the CTPA group.

Introduction

Osteoporotic vertebral compression fractures (OVCFs) are frequent in elderly females, and may result in debilitating pain, spinal deformity, and severe morbidity. Percutaneous kyphoplasty (PKP) was popularly adopted to treat painful OVCFs, both unilateral and bilateral PKP provided effective and safe treatment for patients with painful OVCFs, unilateral PKP presented with less operation time, cement volume, surgery-related costs, radiation dose and lower rate of cement leakage compared with bilateral PKP.[ A study showed that bilateral PKP was better than unilateral PKP in the restoration rate.[ Although so many puncture approaches and intraoperative guidance techniques and equipments have been devised, PKP using conventional transpedicle approach (CTPA) under the C-arm is the most commonly used method.[

It has been shown that the stable biomechanics of the fractured vertebra can be achieved by unilateral PKP if the bone cement distribution exceeds the midline of the vertebral body.[ Transverse process-pedicle approach (TPPA) has been investigated in previous studies.[ Unilateral TPPA has been shown more advantages over bilateral PKP such as due to smaller cement volume and radiation dose, shorter operation time, more restoration of kyphotic angle, and less complications.[ Anatomical differences of unilateral PKP between TPPA and CTPA are not well discussed. So we discuss the anatomical distinctions of unilateral PKP through a 3-dimensional-computed tomography (3D-CT) database and compare the CTPA and TPPA especially on different levels, sexes, and sides.

Materials and methods

Study population and measurement of data

One hundred outpatients (45 males, 55 females, age from 50 to 85 years old, mean age of 58.5 years old) who have done 3D-CT scans (GE Light Speed VCT 64-Slice CT, scan slice of 0.625 mm) of L1-L5 were collected from May 1, 2015 to December 20, 2015. Inclusion criteria were as follows: patients experienced lower back pain that could be determined with CT scans available; images must be clear with a CT scan slice of 0.625 mm. Exclusion criteria: a history of lumbar surgery vertebral abnormalities and developmental abnormalities. The distance between the entry point and the midline of the vertebral body (DEM), the puncture inclination angle (PIA), the range of the safe puncture angle (RSA), and the success rate (SR) of puncture (Fig. 1) were measured and recorded according to previous studies[ on the Aquarius iNtuition workstation. Measurement software: Aquarius iNtuition workstation was used to perform measurements with a length precision of 0.1 mm and an angles precision of 0.1°. Two spinal surgeons have measured and collected the data, and the average values were considered as the final measurement values. This study was approved by the ethics committee of General Hospital of Northern Theater Command of Chinese PLA.

Figure 1

Measurement methods of the distance, angles and success rates. (A) CTPA group. (B) TPPA group. M indicates the midline, P indicates the entry point in the CTPA which was at lateral edge of pedicle projection, N indicates the entry point in the TPPA which was defined as the crossing point between the puncture course and the transverse process. MP indicates the vertical distance between M and P, MN indicates the vertical distance between M and N, DEM means MP or MN, T indicates the target point (at the anterior one-third of the midline), ∠1 indicates the maximum puncture inner inclination angle, ∠2 indicates the middle puncture inner inclination angle, ∠3 indicates the minimum puncture inner inclination, B indicates the medial cortical points of the narrowest pedicle, D indicates the lateral cortical points of the narrowest pedicle, C indicates the midpoint of BD, E indicates the crossing point between BD and PT. If BE in CTPA or BC in TPPA was more than 2 mm, the puncture would achieve success, if not, the puncture would fail certainly. CTPA = conventional transpedicle approach, DEM = distance between the entry point and the midline of the vertebral body, TPPA = transverse process-pedicle approach.

Statistical analysis

Software IBM SPSS Statistics 24.0 was adopted on data analysis. Level of statistical significance was defined as P-value <.050. T tests were used to analyze the differences in the mean value. The enumerated data were analyzed using Chi-squared test. The data were recorded as means ± standard deviations.

Results

DEM

The DEM in the TPPA group was slightly larger than that in the CTPA group. There were significant differences in the mean DEM between the CTPA group and TPPA group (P < .05). Male presented with significantly larger DEM than female in CTPA group or TPPA group (P < .05) (Table 1).

Table 1

Distance from the puncture to the midline of the vertebra (mm).

PIA

The PIAs in the TPPA group were all larger than those in the CTPA group (Table 2). The maximum PIA was significantly larger in right than left. The maximum PIA was significantly larger in male than female for L1, L2, and L4 (Table 3). The RSA in TPPA group was significantly larger than that in CTPA group for L1 and L4, but opposite for L5.

Table 2

Maximum, minimum, and safe range of inner inclination angles (°).

Table 3

SR according to different levels.

SR

The SR was lower in the CTPA group than the TPPA group. The SR including 1 side SR and bilateral SR was 72.0% in the CTPA group and 98.0% in the TPPA group (Table 3). The bilateral SR for L1 to L5 were 25.0%, 35.0%, 65.0%, 81.0%, 94.0% in CTPA group and 84.0%, 90.0%, 99.0%, 100.0%, 100.0% in TPPA group. The 1 side SR for L1 to L5 were 14.0%, 18.0%, 12.0%, 11.0%, 5.0% in CTPA group and 8.0%, 8.0%, 1.0%,0%, 0% in TPPA group. There were significant differences in the bilateral and 1 side SR among the different lumbar segments except for L5 (P < .01). There were no significant differences in the SR between the left and right sides at each vertebral level. The SR in male was significantly higher than that in female for L1 to L3 in the CTPA group and L1 in the TPPA group (Table 4).

Table 4

SR according to different levels, sides, and genders.

Discussion

PKP for OVCFs could be divided into unilateral and bilateral pedicular approaches, extrapedicular approaches and TPPAs.[ Until now, there is still no consensus about the optimal approach, but unilateral approaches have been gradually accepted because of less operation time, cement volume, radiation dose of patients, cement leakage, and surgery-related costs.[ TPPAs have been investigated in previous studies.[ Compared with the bilateral transpedicular technique, unilateral TPPA seems to have more advantages such as smaller radiation dose, shorter operation time, more restoration of kyphotic angle, and less complications.[ Evaluation of intraoperative and postoperative radiographs revealed extravertebral cement leakages in 7.6% patients (12/158) treated by unilateral transverse process-pedicle technique and in 14.6% patients (22/151) treated using bilateral transpedicular technique.[ The high rate of extravertebral cement leakages may be related to fracture patterns, surgical technique, and anatomy of the vertebral bodies. To investigate the anatomical distinctions of unilateral PKP between TPPA and CTPA, we have discussed the unilateral PKP through a 3D-CT database.

The optimal target location of unilateral PKP surgery was 1/3 anterior and middle region of the vertebral body as well as bone cement can diffuse to the contralateral side, which could obtain the same satisfactory clinical outcome as bilateral approach PKP.[ In practice, accurate location of the osseous insertion site of the needle is important, and if the position deviates, puncture needle cannot reach the target site and easily break the inner wall of the pedicle resulting in spinal cord or nerve damage. Unilateral pedicular PKP guided by preoperative CT image data is effective, convenient and safe with high puncture accuracy, shorter time and less radiation exposure in treatment of thoracic and lumbar OVCFs.[

In the present study, the entry point of the TPPA is localized at about 1.5 to 3.8 mm outside the lateral margin of the pedicle projection. The mean DEM and PIA were significantly larger from L1 to L5 in TPPA than CTPA. The mean DEM were significantly larger from L1 to L5 in male than female patients no matter in CTPA and TPPA. The mean safe range of male patients was wider than female patients no matter in the TPPA and CTPA group. The SR of lumbar unilateral PKP is closely associated with the vertebral segment, patient sex, and left or right location. The SR of puncture via a TPPA was significantly higher than that via the CTPA except for L5. The CTPA group presented with significantly higher only 1 side SR than the TPPA group. Given these findings, we present the following suggestions: for L1 to L4, it is reasonable and safe to select unilateral TPPA. The safe range of the TPPA was wider than CTPA in L1, L4, and L5. The mean safe range of male patients was wider than female patients no matter in the TPPA and CTPA group. It is very important and necessary to carefully measure and compare the imaging data before choosing the optimal puncture approach for each individual and level.

There are some limitations. The number of the cases was relatively small and there is discrepancy in terms of sex and age between the population investigated in this study and patients (elderly women) with OVCF. There is some controversy about the definition of the target point.

Conclusions

The TPPA group presented with more lateral entry point than that in the CTPA group according to different levels. Compared with CTPA, the PIA in the TPPA was much larger with a high SR. The mean RSA of male patients was wider than female patients no matter in the TPPA and CTPA group. It is very important and necessary to carefully measure and compare the imaging data before choosing the optimal puncture approach for each individual and level.

Author contributions

Data curation: Pan Hu, Weijian Ren.

Formal analysis: Pan Hu, Weijie Xu, Ying Feng, Yan Zhang, Yunpeng Zhu, Weijian Ren, Liangbi Xiang.

Methodology: Weijie Xu, Ying Feng, Yan Zhang, Yunpeng Zhu.

Software: Pan Hu.

Supervision: Liangbi Xiang.

Validation: Pan Hu.

Visualization: Liangbi Xiang.

Writing – original draft: Pan Hu, Weijie Xu, Ying Feng, Yan Zhang, Yunpeng Zhu, Weijian Ren.

Writing – review and editing: Liangbi Xiang.

Hongwei Wang orcid: 0000-0002-2367-3465.