Abstract
-
Objective
This study aimed to evaluate and compare the structural and functional characteristics of commercially available percutaneous epidural neuroplasty (PEN) catheters. Correlations among catheter properties were also examined to identify potential implications for clinical practice.
-
Methods
Nine PEN catheter products from different manufacturers were analyzed. Various physical properties were assessed, including catheter diameter, length, lever rotation angle, bending degree, and advancing force. Bending degree was measured at maximal and half-maximal lever rotation angles, with and without the guidewire inserted. Advancing force was determined by measuring pressure generated at the catheter tip upon contact with the electronic scale plate. Wilcoxon signed-rank and Spearman correlation tests were used for statistical analysis.
-
Results
Catheters exhibited considerable variations in structural and functional properties. The average catheter diameter and length were 2.0±0.6 mm and 287.8±30.3 mm, respectively; the mean lever rotation angle was 57°±21°. When the steering lever was rotated to its maximum allowable angle, proximal bend angle significantly increased in the wire-off state relative to the wire-on state, suggesting a trade-off between flexibility and structural support. Advancing force significantly varied across products; a positive correlation was observed between catheter diameter and advancing force.
-
Conclusion
This study identified substantial variations in catheter characteristics across different products. Increased catheter flexibility after guidewire removal may lead to positional instability, requiring careful consideration during PEN procedures. Larger catheter diameters were correlated with increased advancing force, which could influence ease of insertion and patient comfort. These findings emphasize the need for standardized PEN catheter specifications to optimize safety and efficacy in clinical practice.
-
Keywords: Percutaneous epidural neuroplasty, Catheter, Characteristics, Flexibility, Advancing force
INTRODUCTION
Chronic spinal pain is highly prevalent and not only leads to significant physical limitations and increased absenteeism from work but also severely diminishes overall quality of life [
1,
2], Percutaneous epidural neuroplasty (PEN) is a minimally invasive interventional technique used to treat chronic spinal pain, particularly in cases refractory to conservative treatments [
3-
7]. The procedure involves insertion of a flexible, steerable catheter into the epidural space through the sacral hiatus under fluoroscopic guidance [
3,
4]. Mechanical, chemical, and hydrostatic pressure methods are utilized to perform adhesiolysis, followed by the injection of therapeutic agents such as local anesthetics, corticosteroids, and hypertonic saline [
5,
6,
8]. Several studies have demonstrated the efficacy of PEN in reducing pain and improving function among patients with various spinal disorders [
3,
9].
Although generally considered safe, PEN carries potential risks and complications, including dural puncture, catheter shearing or breakage, epidural hematoma, spondylitis, epidural abscess, meningitis, intravascular injection, and neurological deficits [
10-
17]. The procedure requires catheter placement directly into the epidural space, an area in close proximity to critical structures such as nerve roots, the dura, and the venous plexus. This anatomical proximity introduces risks of neural and vascular injury. Two primary mechanisms of such injuries include direct laceration via the catheter tip and sustained compression from the catheter itself. These risks highlight the need for extreme caution and precision during catheter insertion and positioning to minimize the likelihood of damage to these sensitive structures. In addition to these factors, the physical properties of the catheter may have a substantial impact on the procedure’s efficacy and safety [
18-
20]. However, comprehensive research on PEN remains limited.
Standardization of catheter design may help reduce the incidence of such complications by minimizing variability in mechanical behavior during the procedure. For instance, catheters with inconsistent flexibility or steerability may lead to malposition, difficulty in reaching the target site, or unintended tissue damage. By establishing evidence-based design parameters— such as optimal stiffness, diameter, and bending angles—procedural predictability can be improved, potentially reducing risks such as dural puncture, catheter buckling, or migration.
The increasing adoption of PEN in clinical practice, attributed to its minimally invasive approach and favorable outcomes, has led to an expanding diversity of PEN catheters available on the market. Different manufacturers offer catheters with varying designs and properties. However, the absence of comparative studies limits the ability of clinicians to select the most suitable catheter for specific patient needs. This lack of standardization contributes to variations in procedural efficacy and safety, particularly given the high-risk placement of catheters near critical spinal structures.
This study aims to evaluate and compare the structural and mechanical properties of commercially available PEN catheters to identify differences that could affect procedural precision, safety, and clinical efficacy. Key parameters assessed include catheter diameter, length, steerability, bending characteristics, and advancing force. The central hypothesis is that significant interproduct variation exists and that certain design features, such as excessive flexibility following guidewire removal, may contribute to catheter malposition or loss of target access, potentially compromising treatment outcomes.
Here, we aimed to identify and compare these characteristics among commercially available PEN catheters. We examined the physical properties of various PEN catheters currently on the market, then investigated correlations among these properties.
MATERIALS AND METHODS
1. Subjects
Nine different catheter products from various manufacturers, all produced in Korea and approved for use within the country, were analyzed. These catheters were selected based on their widespread clinical use across multiple institutions. As this study does not involve human subjects, approval from the Institutional Review Board of a university hospital was waived. Additionally, no conflicts of interest exist with the company that supplied the catheters.
2. Structural Features of the Catheter
The PEN catheter consists of a body with a lever and a tube designed for insertion into the spinal canal (
Fig. 1). The proximal end of the tube, exposed at one end of the body, serves as a connection port for medication injection. Some catheter models exhibit separate ports for medication delivery and guidewire insertion, allowing improved functionality. The body’s lever enables the operator to bend the tube and adjust its direction for precise navigation. Additionally, the lever is equipped with a locking mechanism that allows the tube to be fixed in its bent position as needed. The tube length is defined as the distance from the point where it emerges from the body to its distal end, ensuring consistency in measurements and performance evaluation. Tube length, tube diameter, lever rotation angle, and lever lock presence were measured. Moreover, the bending mechanism (bidirectional or unidirectional) was assessed.
The catheter’s body was secured to examine its bending behavior. Angles were measured using a protractor. The proximal bend angle (i.e., angle at which the proximal starting section of the catheter bends) and distal deflection angle (i.e., angle at which the distal tip bends) were recorded. To measure these angles, the steering lever was rotated to its maximum allowable angle, simulating extreme operational conditions. This approach provides insight into the catheter’s maximum performance capabilities. The steering lever was rotated to half of its maximum angle; the proximal bend and distal deflection angles were then measured, representing typical use scenarios that require precise control. All measurements were conducted with and without the guidewire inserted. The measurement method is illustrated in
Fig. 2.
Pressure generated at the catheter tip as it advances into the epidural space is critical because it may cause damage to important anatomical structures [
19,
20]. The method for measuring pressure at the catheter tip was as follows (
Fig. 3). First, an electronic scale was prepared. The catheter tip was positioned to face the direction of the scale. Next, the catheter was perpendicularly advanced onto the measurement plate of the scale, bending upon contact, until a plateau in pressure was observed. As the catheter tip contacted the measurement plate, it began to bend, such that the degree of bending varied according to catheter stiffness. As the catheter advanced and bent, pressure at the tip continued to rise until it reached a plateau. This plateau pressure was defined as the advancing force. A stiffer catheter generated higher pressure readings on the scale. Advancing force measurements were performed with and without the guidewire inserted.
The difference in bending degree between the wire-in and wire-out states was analyzed using the Wilcoxon signed-rank test. The Spearman correlation test was used to assess potential correlations between catheter diameter and proximal bend angle and between catheter diameter and advancing force. The statistical significance threshold was set at p<0.05.
RESULTS
1. Structural Components and Functional Features of the Catheter
The average catheter diameter was 2.0±0.6 mm, ranging from a minimum of 1.0 mm to a maximum of 3.2 mm (
Table 1). The average length was 287.8±30.3 mm, with a minimum of 210.0 mm and maximum of 310.0 mm. The average steering lever rotation angle was 57.3°±20.7°, ranging from 40° to 100°, indicating some variation in rotation capabilities. Five of the 9 products included a lever lock, a mechanism designed to secure the catheter at a desired bending angle after manipulation. Bidirectional products comprised the majority of catheters (7 of 9), whereas unidirectional products were fewer (two: P7 and P9). The average steering lever rotation angle was 57.3°±20.7°.
Bending degrees (proximal bend and distal deflection angles) varied among the included catheters (
Table 1).
When the steering lever was rotated to its maximum allowable angle, the mean proximal bend angle in the wire-in state was 54.9°±29.7°, whereas that in the wire-out state was 103.8°± 104.7° (
Table 1). The proximal bend angle was significantly greater when the guidewire was not inserted than when it was inserted (Wilcoxon signed-rank test, p=0.004). In 7 of 9 cathe-ters, the proximal bend angle was reduced in the presence of a guidewire, highlighting the trade-off between flexibility and structural support. When the steering lever was rotated to half of its maximum angle, the mean proximal bend angle in the wire-in state was 31.3°±16.3°, whereas that in the wire-out state was 52.9°±43.6°. The proximal bend angles in the wire-in and wire-out states were not significantly different (Wilcoxon signedrank test, p=0.203). In the cases of the steering lever was rotated to half, 6 of 9 catheters exhibited a reduced proximal bend angle in the wire-in state. When the steering lever was rotated to half of its maximum angle, catheter flexibility was less affected by the guidewire than when the steering lever was fully rotated. In the analysis of relationships between catheter diameter and proximal bend angle when the steering lever was fully rotated, no significant correlations were observed in the wire-in (Spearman correlation test, ρ=-0.393, p=0.295) or wire-out (Spearman correlation test, ρ=-0.366, p=0.333) states.
Additionally, when the steering lever was fully rotated, the mean distal deflection angle in the wire-in state was 62.6°±28.2°, whereas that in the wire-out state was 67.1°±26.5° (
Table 1). The distal deflection angle did not significantly differ between the wire-in and wire-out states when the steering lever was fully rotated (Wilcoxon signed-rank test, p=0.910). When the steering lever was rotated to half of its maximum angle, the mean distal deflection angle in the wire-in state was 40.9°±27.9°, whereas that in the wire-out state was 42.1°±18.8°. No significant difference in distal deflection angle was observed between the wirein and wire-out states when the steering lever was rotated to half of its maximum angle (Wilcoxon signed-rank test, p=0.652). The distal deflection angle was not affected by guidewire insertion.
Advancing force significantly varied between products and under different conditions (
Table 1). P6 exhibited the highest advancing force in the wire-in condition (96 g), reflecting its exceptional stiffness and potential suitability for procedures that require enhanced stability. Conversely, P7 and P9 recorded the lowest advancing forces (5 g and 8 g, respectively, in the wire-in condition), indicating greater flexibility and reduced resistance. P2 and P8 showed moderate advancing forces (72 g and 61 g, respectively, in the wire-in condition), achieving a balance between stiffness and flexibility. Significant positive correlations were observed between catheter diameter and advancing force in both the wire-in (Spearman correlation test, ρ=0.850, p=0.004) and wire-out (Spearman correlation test, ρ=0.826, p=0.006) states, indicating that as catheter diameter increases, advancing force also tends to increase.
DISCUSSION
PEN is a procedure in which a flexible catheter is inserted through the sacral hiatus and positioned at the target site in the epidural space for drug injection and adhesiolysis [
4,
21,
22]. PEN is generally considered a safe procedure; however, in rare cases, the catheter may puncture the dura, tear a vein, or cause nerve damage [
13,
15]. Such injuries occur when the catheter damages soft tissue, which may result from the operator’s level of experience as well as the catheter’s physical properties [
18,
19,
23,
24]. One previous study examined the characteristics of a PEN catheter [
25]. However, that study focused on a nonnavigable catheter, rather than navigable PEN catheters. Axial and torsional forces of the catheter were measured to assess the effectiveness of PEN in adhesion removal. Additionally, the study did not provide data regarding various other catheter characteristics or comparative analyses between different catheters.
Accordingly, the present study explored catheter properties that may influence the PEN procedure and compared these properties across different products. We developed several criteria to compare the physical characteristics of PEN catheters, including catheter diameter, length, lever rotation angle, overall catheter flexibility (measured by proximal bend angle), tip flexibility (measured by distal deflection angle), and advancing force. The findings revealed that each PEN catheter exhibited distinct characteristics. Among the features of catheter, bending degree and advancing force were selected for quantitative analysis, as they are considered primary mechanical factors that influence catheter behavior during the critical stage of adhesiolysis [
26,
27]. Excessive flexibility or stiffness may hinder effective navigation or result in unintended tissue trauma [
28,
29]. In particular, inadequate bending resistance or excessive advancing force can lead to unintended penetration or shear stress against the dura mater or surrounding neural structures, increasing the risk of complications such as dural injury or loss of catheter position.
Catheter flexibility is a crucial factor in determining insertion characteristics and ability to accurately reach the target point, which affect the procedure success rate. Although a more flexible catheter may reduce the risk of dural puncture, it also has the potential limitation of increased susceptibility to changes in advancement angle due to interactions with epidural structures. Considering these factors, further research is needed to determine the optimal flexibility for PEN catheters. Future studies should aim to balance the benefits of flexibility (e.g., reduced dural puncture risk and easier navigation) with the need for sufficient rigidity to maintain the intended trajectory and accurately reach the target site. Additionally, when the steering lever was rotated to its maximum allowable angle, the proximal bend angle was significantly greater in the wire-out state than in the wire-in state. This finding suggests that the removal of the guidewire to permit injectate administration increased catheter flexibility, potentially causing the tip to deviate from its intended target position.
Furthermore, this study revealed a distinct correlation between catheter diameter and advancing force. Whereas catheters with a larger diameter offer advantages such as a wider working channel for easier drug administration and the ability to accommodate additional instruments, they may also present some disadvantages. Larger catheters tend to be more rigid and may cause increased discomfort due to their thickness. Conversely, thinner catheters are generally softer, potentially reducing the risk of dural puncture. However, they may lack the straightness necessary for easy insertion, which could create substantial challenges during placement at the target lesion. In this study, no significant correlation was observed between catheter diameter and flexibility, as measured by the proximal bend angle. Notably, statistical significance, as indicated by the p-value, depends on the number of subjects included in the analysis. Because data from only 9 catheters were used, the small sample size may have limited the ability to detect a significant correlation. The optimal catheter diameter should be determined on an individual basis considering various factors, including the patient’s anatomical characteristics, prior surgeries in the target area, degree of disc protrusion, severity of stenosis, and presence of bone spurs. Further research is needed to establish evidence-based guidelines concerning selection of the most appropriate catheter diameter for different clinical situations. Additionally, future studies should evaluate the long-term in vivo performance of catheters with varying physical properties, focusing on procedural success rate, patient-reported pain relief, and complication incidence.
This study had some limitations. First, the small number of catheters examined may not fully represent the range of products available on the market. Also, given the small sample size, non-significant findings regarding the relationship between catheter diameter and flexibility should be interpreted with caution. Second, measurements were not conducted using highly specialized analytical instruments, which limited measurement reproducibility and precision. Third, this study did not evaluate the relationship between catheter properties and clinical outcomes, including patient safety, malposition, or procedural success rate. Finally, this study did not explore all catheter characteristics that could influence clinical performance. For example, catheter surface properties may also be an important factor, but they were not assessed in this study. Future studies addressing these limitations are warranted. Nevertheless, the present findings may guide future innovations in catheter technology, potentially leading to improved patient outcomes and reduced complication rates in PEN. The development of standardized recommended specifications for PEN catheters could strongly contribute to enhanced safety and efficacy in PEN procedures.
CONCLUSION
This study advances the field of PEN by proposing criteria for the classification and evaluation of PEN catheter characteristics. Variations were identified across different catheters. Additionally, Increased flexibility following guidewire removal may compromise accurate catheter tip positioning. Furthermore, larger catheter diameters were associated with greater advancing force. These factors should be carefully considered by interventionists when selecting catheters based on individual patient conditions.
NOTES
-
Conflict of Interest
The authors have nothing to disclose.
-
Funding/Support
This work was supported by the National Research Foundation of Korea grant funded by the Korean government (MSIT) (No. RS-2023-00219725).
-
Acknowledgments
MID (Medical Illustration & Design), as a member of the Medical Research Support Services of Yonsei University College of Medicine, providing excellent support with medical illustration.
-
Author Contribution
Conceptualization: JYJ, SV, DSJ, MCC; Data curation: JYJ; Formal analysis: JYJ, MCC; Methodology: JYJ, SV, MCC; Visualization: JYJ, MCC; Writing – original draft: JYJ, SV, DSJ, MCC; Writing – review & editing: JYJ, SV, DSJ, MCC.
Fig. 1.Schematic representation of the percutaneous epidural neuroplasty catheter and its key components. The catheter consists of a tube extending from the body. The steering lever allows controlled movement, with an associated rotation angle, whereas the locker secures the catheter in a desired position. The wire port facilitates insertion of a guidewire for enhanced maneuverability. These structural characteristics play crucial roles in catheter performance and procedural precision.
Fig. 2.Measurement of catheter bending angles. “a” represents the proximal bend angle, and “b” represents the distal deflection angle. A larger bending angle indicates greater catheter flexibility.
Fig. 3.Setup for advancing force measurement. Force was measured by recording changes on the scale while pressing vertically on the catheter tip at the exact center of the scale. Measurements were taken under 2 conditions: with the wire inserted and without the wire.
Table 1.Comparative analysis of product specifications and performance metrics
Table 1.
|
Variable |
P1 |
P2 |
P3 |
P4 |
P5 |
P6 |
P7 |
P8 |
P9 |
Mean ± SD |
|
Diameter (mm) |
1.7 |
2.1 |
1.7 |
2.25 |
2.3 |
3.2 |
1 |
2 |
1.7 |
2.0 ± 0.6 |
|
Length (mm) |
290 |
290 |
292 |
288 |
310 |
300 |
210 |
310 |
300 |
287.8 ± 30.3 |
|
Balloon |
× |
× |
× |
× |
o |
× |
× |
× |
× |
|
|
Direction |
bi |
bi |
bi |
bi |
bi |
bi |
uni |
bi |
uni |
|
|
Steering lever locker |
o |
o |
× |
o |
o |
× |
v |
o |
× |
|
|
Steering lever rotation angle (°) |
40 |
72 |
40 |
54 |
40 |
70 |
40 |
60 |
100 |
57.3 ± 20.7 |
|
Proximal bend angle (°) |
|
|
|
|
|
|
|
|
|
|
|
Wire-in |
|
|
|
|
|
|
|
|
|
|
|
Full rotation of steering lever |
54 |
36 |
36 |
30 |
63 |
45 |
90 |
26 |
114 |
54.9 ± 29.7 |
|
Half rotation of steering lever |
45 |
18 |
17 |
22 |
33 |
28 |
39 |
15 |
65 |
31.3 ± 16.3 |
|
Wire-out |
|
|
|
|
|
|
|
|
|
|
|
Full rotation of steering lever |
56 |
90 |
70 |
79 |
77 |
40 |
132 |
20 |
370 |
103.8 ± 104.7 |
|
Half rotation of steering lever |
36 |
52 |
35 |
49 |
38 |
25 |
65 |
14 |
162 |
52.9 ± 43.6 |
|
Distal deflection angle (°) |
|
|
|
|
|
|
|
|
|
|
|
Wire-in |
|
|
|
|
|
|
|
|
|
|
|
Full rotation of steering lever |
10 |
60 |
90 |
106 |
58 |
82 |
65 |
45 |
47 |
62.6 ± 28.2 |
|
Half rotation of steering lever |
5 |
31 |
43 |
97 |
17 |
72 |
35 |
37 |
31 |
40.9 ± 27.9 |
|
Wire-out |
|
|
|
|
|
|
|
|
|
|
|
Full rotation of steering lever |
107 |
59 |
91 |
92 |
60 |
72 |
30 |
62 |
31 |
67.1 ± 26.5 |
|
Half rotation of steering lever |
75 |
30 |
44 |
49 |
23 |
63 |
20 |
48 |
27 |
42.1 ± 18.8 |
|
Advancing force (g) |
|
|
|
|
|
|
|
|
|
|
|
Wire-in |
41 |
72 |
15 |
69 |
41 |
96 |
5 |
61 |
8 |
45.3 ± 31.7 |
|
Wire-out |
29 |
24 |
11 |
37 |
36 |
78 |
1 |
48 |
2 |
29.6 ± 24.3 |
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