Abstract
Background
Endoscopic procedures nowadays are successful, minimally invasive, and safer, with fewer intraoperative and postoperative complications and shorter hospital stays. Kambin's triangle (KT) is the three-dimensional configuration that is used as a transforaminal anatomical corridor for epidural steroid injections and endoscopic surgeries for various lumbar pathologies. This study aims to estimate the dimensions of KT and diameter of the cannula for the transforaminal surgical approaches using KT in the Chhattisgarh population.
Methods
Seven human cadavers (three males and four females) were included in the study for observing KT. Dissection was done to carefully clear landmarks, including the vertebral bodies, intervertebral disc, exiting nerve root, and superior articular process. Base (a horizontal plane passing through the superior border of the caudal vertebra) and height (along the superior articular process of the inferior vertebra in line with the articular facet) were measured. Hypotenuse, semiperimeter of the triangle, area of triangle, diameter, and area of the inscribed circle were calculated.
Results
Height, base, and inscribed circle diameter increased from L1-L2 to L4-L5 then decreased to L5-S1. There was no statistically significant difference between males and females. The safest admissible cannula diameter according to the current study that can be used at all levels in KT was 6.06 mm.
Conclusion
This study provides the safest cannula size to be considered in the patients of the Chhattisgarh population during transforaminal approaches in the lumbar area. Minimally invasive surgery and shorter hospitalization are vital criteria to evaluate any surgery these days.
Keywords: Endoscopic discectomy, Kambin's triangle, Superior articular process, Transforaminal approach
Introduction
Surgical approaches in the lumbar areas have been researched extensively due to common pathologies such as intervertebral disc prolapse, lumbar stenosis, nerve compression, and so on. Kambin's triangle (KT) is a three-dimensional right-angled triangle described in the posterolateral aspect of the intervertebral disc (IVD), which is used as a transforaminal anatomical corridor for epidural steroid injections and endoscopic surgeries for various lumbar pathologies. Neurosurgeons, pain physicians, orthopedicians, spine surgeons, and anesthesiologists find practical use of this triangle in their therapeutic practice.
Kambin and his colleague Gellman first described this safety triangle in 1983 for the transforaminal approach in percutaneous endoscopic lumbar discectomy (PELD).1 The transforaminal approach was a minimally invasive method to access the IVD. Exiting nerve root (ENR) injury is the most common complication of this procedure.2 So the right choice of cannula size, as well as a good knowledge of anatomy, is required while accessing this area to prevent injuries.
Cadaveric studies are advantageous as structures can be visualized three-dimensionally and measured accurately. The ENR from each intervertebral foramen goes obliquely in an inferoventral direction. Imaging done in different planes will provide inaccurate anatomic data to calculate the permissible cannula diameter in a three-dimensional triangle.3 In magnetic resonance neurography, the positional relationship between ENR and superior articular process (SAP) cannot be noted precisely as the images can be viewed only in a two-dimensional plane that cannot be rotated.4 3D MRI requires the use of adjusting obliquity in reformatted images which can lead to subjective errors in measurements.5
Regional variations can be seen in the dimensions of KT. This study provides the safest cannula size to be considered in the patients of the Chhattisgarh population before transforaminal approaches in the lumbar area as minimally invasive surgery and shorter hospitalization are vital criteria to evaluate any surgery these days. Cannula sizes ranging from 6.3 mm to 7.5 mm can be used to approach the IVD as per Mirkovic et al.6
This study aimed to estimate the dimensions of the bony Kambin's triangle (bKT) and calculate the diameter of the cannula for transforaminal surgical approaches using Kambin's triangle in the Chhattisgarh population.
Materials and methods
After taking Institute ethical committee clearance (AIIMSRPR/IEC/2022/1079), the present study was conducted on seven human cadavers (three males and four females) belonging to the Chhattisgarh population donated to the Department of Anatomy. Cadavers with a history of spinal trauma or other relevant spinal pathology were excluded from the study. Cadavers were initially placed in prone position for dissection. After careful removal of paraspinal muscles, the posterolateral surface of the lumbar part of the vertebral column was exposed on both sides extending from L1 to L5 levels. The bKT was traced in the IVD levels of L1-L2, L2-L3, L3-L4, L4-L5, L5-S1 bilaterally (total 70 bKT). The ENRs were identified which formed one of the boundaries of the bKT. Intertransverse ligaments were cut to give a better picture of the region (Fig. 1). Bony landmarks were pinned at each space. With the cadaver in prone position, measurements of the sides of the triangle were taken by using digital vernier callipers (Mitutoyo) with an accuracy of 0.02 mm. Photographs were taken using a digital camera Nikon D5600 camera (Nikon Co., Tokyo, Japan).
Fig. 1.
Cadaveric demonstration of Kambin's triangle H = height, B= Base, Hy = Hypotenuse, IVD = intervertebral disc L1, L2, L3, L4, L5 = Lumber vertebrae.
Two important landmarks were identified to locate a bKT at an intervertebral space—the SAP and the superior border of the caudal vertebra. Two planes were taken into consideration to measure the base and the height of the bKT—a horizontal plane passing through the superior border of the caudal vertebra and a vertical plane along the SAP of the inferior vertebra in line with the articular facet. bKT is formed by the meeting point of the horizontal plane, vertical plane, and ENR (Fig. 1).
The base and height of the bKT were measured in the cadaver. The hypotenuse of the triangle was calculated by the formula Hypotenuse Hy= (H2 +B2)1/2, where H and B are the height and base of the triangle, respectively (Fig. 2). The area of the triangle was calculated by the formula AT = ½ x base x height. Semiperimeter of the triangle was calculated by the formula sP= (H + B + Hy)/2. The radius of the circle inscribed inside the triangle was calculated by formula R = [(sP-H) (sP-B) (sP-Hy)]1/2. The diameter of the circle gives the value of the cannula diameter to be used for the surgical approach. Statistical analysis was done by using SPSS 22.0 (SPSS, Inc., Chicago, IL, USA) to compare left and right sides and male and female cadavers using paired t-test and unpaired t-test respectively, and a p-value <0.05 was considered significant.
Fig. 2.
Schematic representation of Kambin's triangle. H = height, B = base, Hy = hypotenuse, r = radius of inscribe circle.
Results
Cadavers of age 64.37 ± 11.43 years (49–85 years) with a height of 162.12 ± 5.51 cm (155–171 cm) were included in the study. The values of the mean height of bKT showed an increasing trend from the L1-L2 level to L4-L5 and then decreased at the L5-S1 level [Table 1]. A similar trend was noted on comparing left and right sides and male and female. On the right side, the mean height increased from 19.02 ± 3.43 mm at the L1-L2 level to 22.76 ± 4.22 mm at the L4-L5 level, and then further decreased to 19.09 ± 2.67 mm at the L5-S1 level. On the left side, the mean height of KT increased from 18.33 ± 3.83 mm at the L1-L2 level to 22.64 ± 3.30 mm at the L4-L5 level and then further decreased to 21.68 ± 3.78 mm. The mean height in males and females also showed a similar trend (Table 1).
Table 1.
Measurements of various parameters in Kambin's triangle from the L1-L2 level to the L5-S1 level.
| Parameters | Left mean ± SD (Range) | Right mean ± SD (Range) | Male mean ± SD (Range) | Female mean ± SD (Range) | |
|---|---|---|---|---|---|
| Height (mm) | H1 (L1-L2) | 18.33 ± 3.84 (15.04–23.99) | 19.02 ± 3.43 (15.02–23.50) | 18.46 ± 6.05 (15.02–23.5) | 18.84 ± 3.41 (15.04–23.99) |
| H2 (L2-L3) | 21.46 ± 3.19 (17.47–26.38) | 20.91 ± 3.47 (15.31–25.88) | 20.85 ± 6.05 (15.3126.38) | 21.43 ± 2.67 (18.63–25.88) | |
| H3 (L3-L4) | 22.64 ± 3.30 (17.60–27.14) | 21.97 ± 2.81 (19.73–26.86) | 22.97 ± 6.00 (20.11–27.14) | 21.81 ± 3.21 (17.60–26.86) | |
| H4 (L4-L5) | 22.42 ± 3.44 (17.55–28.52) | 22.76 ± 4.23 (17.69–27.36) | 22.35 ± 6.00 (18.39–28.52) | 23.02 ± 3.24 (17.69–27.36) | |
| H5 (L5-S1) | 21.69 ± 3.78 (16.36–26.4) | 19.09 ± 2.67 (15.98–24.49) | 20.66 ± 6.05 (15.98–26.04) | 20.19 ± 3.23 (16.36–25.27) | |
| Base (mm) | B1 (L1-L2) | 10.51 ± 1.87 (8.49–12.74) | 10.42 ± 1.99 (8.36–12.71) | 10.56 ± 6.05 (8.36–12.74) | 10.39 ± 1.73 (8.49–12.7) |
| B2 (L2-L3) | 10.62 ± 2.42 (7.52–13.8) | 10.81 ± 2.26 (8.3–14.31) | 11.35 ± 6.05 (8.2–13.8) | 10.25 ± 2.12 (7.52–14.31) | |
| B3 (L3-L4) | 12.23 ± 2.28 (10.38–15.76) | 11.07 ± 1.13 (10.02–12.67) | 11.53 ± 6.05 (10.04–15.22) | 11.74 ± 1.82 (10.02–15.76) | |
| B4 (L4-L5) | 13.36 ± 2.54 (10.07–16.49) | 12.10 ± 1.49 (10.47–15.15) | 12.63 ± 6.00 (10.70–16.49) | 12.81 ± 1.88 (10.47–15.88) | |
| B5 (L5-S1) | 13.13 ± 3.03 (8.44–17.09) | 10.94 ± 1.82 (8.79–13.39) | 11.64 ± 6.05 (9.15–14.94) | 12.33 ± 3.02 (8.44–17.09) | |
| Hypotenuse (mm) | HT1 (L1-L2) | 21.25 ± 3.46 (18.24–26.29) | 21.76 ± 3.45 (17.19–26.71) | 21.32 ± 6.05 (17.19–26.71) | 21.64 ± 2.89 (18.27–26.01) |
| HT2 (L2-L3) | 23.98 ± 3.71 (19.29–29.39) | 23.57 ± 4.00 (17.41–29.57) | 23.78 ± 6.05 (17.41–23.39) | 23.78 ± 3.25 (20.16–29.57) | |
| HT3 (L3-L4) | 25.72 ± 3.89 (20.43–31.12) | 24.53 ± 2.78 (22.48–29.7) | 25.74 ± 6.00 (22.56–31.12) | 24.76 ± 3.58 (20.43–30.81) | |
| HT4 (L4-L5) | 26.51 ± 4.27 (20.23–32.94) | 24.34 ± 4.22 (19.85–30.59) | 25.39 ± 6.00 (19.85–32.94) | 25.67 ± 3.44 (21.32–31.08) | |
| HT5 (L5-S1) | 25.40 ± 4.74 (18.41–30.33) | 22.04 ± 2.87 (18.79–27.91) | 23.73 ± 6.05 (18.79–30.33) | 23.72 ± 4.20 (18.41–29.79) | |
| Semiperimeter (mm) | sP1 (L1-L2) | 25.04 ± 3.85 (21.47–30.88) | 25.61 ± 3.96 (20.29–31.46) | 25.17 ± 45.57 (20.29-31-46) | 25.44 ± 3.13 (21.47–30.02) |
| sP 2 (L2-L3) | 28.10 ± 4.47 (22.48–34.35) | 27.65 ± 4.75 (20.51–34.88) | 27.98 ± 5.40 (20.51–34.35) | 27.79 ± 3.97 (23.19–34.88) | |
| sP 3 (L3-L4) | 30.30 ± 4.63 (24.21–36.74) | 28.84 ± 2.98 (26.44–34.62) | 30.12 ± 3.57 (26.44–36.74) | 29.16 ± 4.19 (24.21–36.51) | |
| sP 4 (L4-L5) | 31.63 ± 4.63 (36.67–38.98) | 28.75 ± 4.74 (23.72–36.16) | 30.02 ± 6.11 (23.72–38.98) | 30.31 ± 3.87 (25.53–36.67) | |
| sP 5 (L5-S1) | 30.10 ± 5.71 (21.61–35.84) | 26.04 ± 3.39 (22.32–32.90) | 28.01 ± 5.31 (22.32–35.84) | 28.11 ± 5.09 (21.61–35.64) | |
| Radius of circle (mm) | R1 (L1-L2) | 3.80 ± 0.49 (3.19–4.59) | 3.84 ± 0.63 (3.1–4.75) | 3.85 ± 0.71 (3.1–4.75) | 3.80 ± 0.43 (3.19–4.58) |
| R2 (L2-L3) | 4.05 ± 0.79 (3.03–4.96) | 4.05 ± 0.76 (3.1–5.31) | 4.18 ± 0.82 (3.1–4.96) | 3.95 ± 0.72 (3.03–5.31) | |
| R3 (L3-L4) | 4.41 ± 0.92 (3.27–5.71) | 4.20 ± 0.38 (3.87–4.92) | 4.36 ± 0.65 (3.88–5.62) | 4.26 ± 0.75 (3.27–5.71) | |
| R4 (L4-L5) | 4.86 ± 0.80 (3.81–6.03) | 4.44 ± 0.57 (3.87–5.57) | 4.66 ± 0.92 (3.81–6.03) | 4.64 ± 0.55 (4.08–5.59) | |
| R5 (L5-S1) | 4.71 ± 0.99 (3.2–5.85) | 3.99 ± 0.57 (3.43–4.99) | 4.28 ± 0.84 (3.52–5.51) | 4.40 ± 0.93 (3.2–5.85) | |
| Diameter (mm) | D1 (L1-L2) | 7.61 ± 0.98 (6.39–9.18) | 7.68 ± 1.24 (6.2–9.49) | 7.72 ± 1.41 (6.2–9.49) | 7.60 ± 0.86 (6.39–9.15) |
| D2 (L2-L3) | 8.09 ± 1.58 (6.06–9.92) | 8.10 ± 1.51 (6.2–10.62) | 8.35 ± 1.64 (6.2–9.92) | 7.90 ± 1.44 (6.06–10.62) | |
| D3 (L3-L4) | 8.82 ± 1.84 (6.55–11.4) | 8.40 ± 0.76 (7.74–9.84) | 8.72 ± 1.30 (7.76–11.24) | 8.53 ± 1.50 (6.55–11.4) | |
| D4 (L4-L5) | 9.72 ± 1.59 (7.64–12.08) | 8.87 ± 1.15 (7.73–11.14) | 9.33 ± 1.85 (7.64–12.08) | 9.27 ± 1.11 (8.15–11.17) | |
| D5 (L5-S1) | 9.34 ± 1.88 (6.4–11.17) | 7.56 ± 0.77 (6.85–8.90) | 8.07 ± 1.60 (7.05–11.01) | 8.74 ± 1.76 (6.4–11.17) | |
| Area (mm2) | A1 (L1-L2) | 46.13 ± 11.91 (32.15–66.15) | 47.42 ± 15.52 (30.18–70.79) | 46.13 ± 11.91 (32.15–66.15) | 47.42 ± 15.52 (30.18–70.79) |
| A2 (L2-L3) | 53.09 ± 19.90 (28.88–77.33) | 53.06 ± 20.06 (30.15–88.54) | 53.09 ± 19.90 (28.88–77.33) | 53.06 ± 20.06 (30.15–88.54) | |
| A3 (L3-L4) | 63.37 ± 26.87 (33.59–102.48) | 55.84 ± 10.41 (47.09–76.05) | 63.37 ± 26.87 (33.59–102.48) | 55.84 ± 10.41 (47.09–76.05) | |
| A4 (L4-L5) | 75.80 ± 24.68 (45.82–114.5) | 62.69 ± 17.10 (47.04–97.4) | 75.80 ± 24.68 (45.82–114.5) | 62.69 ± 17.10 (47.04–97.4) | |
| A5 (L5-S1) | 93.73 ± 75.79 (32.17–257.1) | 50.94 ± 15.05 (36.94–78.18) | 93.73 ± 75.79 (32.17–257.1) | 50.94 ± 15.05 (36.94–78.18) |
The values of the mean area of the bKT increased from the L1-L2 level to the L4-L5 level and then decreased at the L5-S1 level. On the left side, the mean area of KT increased from 96.28 ± 26.58 mm2 at the L1-L2 level to 156.76 ± 48.38 mm2 at the L4-L5 level and then decreased to 146.84 ± 54 mm2 at L5-S1 level. On right side, mean area increased from L1-L2 level (100.14 ± 30.73 mm2) to the L4-L5 level (128.7 ± 39.05 mm2) and then a decrease in value at L5-S1 (105.47 ± 29.62 mm2) (Table 1). The mean area of bKT in males and females also showed a similar trend.
The values of the mean diameter of the circle inscribed (mean diameter of cannula admissible) increased from the L1-L2 level (7.64 ± 1.08 mm) to the L4-L5 level (9.30 ± 1.41 mm) and then decreased to 8.45 ± 1.66 mm at L5-S1 (Fig. 3). On the left side, the mean cannula diameter increased from 7.61 ± 0.98 mm at the L1-L2 level to 9.72 ± 1.59 mm at the L4-L5 level and decreased to 9.34 ± 1.88 mm at the L5-S1 level (Table 1, Fig. 3). No statistically significant difference was obtained on comparing male versus female and right versus left sides for mean height, mean area, and the diameter of the circle inscribed.
Fig. 3.
Bar diagram showing correlation of various parameters at different levels L1-2, L2-L3, L3-L4, L4-L5, L5-S1.
The maximum permissible diameter (MPD) of the cannula that can be safely used at all the observed bKTs at a particular intervertebral level without performing foraminoplasty is the largest admissible cannula size that can fit all the observed bKTs at a particular intervertebral level. The mean diameter states the average of the diameters obtained at a particular level, and certain spaces may be narrower not permitting entry of cannula of mean diameter.
On the right side, the MPD that can be used safely at spaces at all levels (all right side bKTs) as per the current study is 6.2 mm. At the L1-L2 level, the MPD obtained was 6.2 mm, and the mean diameter of the cannula was 7.68 mm. As observed, only three (42.86%) out of the seven spaces at the L1-L2 level permit the passage of a cannula of a mean diameter of 7.68 mm. In the L2-L3 level, the mean diameter and MPD that can be safely used were 8.10 mm and 6.2 mm, respectively. From L2-L23 level to L5-S1 levels, three (42.86%), two (28.58%), three (42.86%), and three (42.86%) spaces permitted the passage of cannula of mean diameters 8.10, 8.40, 7.73, and 7.56 mm, respectively. The MPD that can be safely placed at all spaces at levels L3-L4, L4-L5, and L5-S1 is 7.74 mm, 7.73 mm, and 6.85 mm, respectively.
On the left side, the MPD that can be safely used at all levels is 6.06 mm. The MPD that can be safely used from L1-L2 levels to L5-S1 levels are 6.39, 6.06, 6.55, 7.64, and 6.4 mm, respectively. From L1-L2 level to L5-S1 levels, four (57.14%), three (42.86%), two (28.58%), three (42.86%), and four (57.14%) spaces permitted the passage of cannula of mean diameters 7.61, 8.09, 8.82, 9.72, and 9.34 mm, respectively.
Discussion
After the description of the triangle by Kambin, several authors attempted to clarify the definition of the triangle as well as the safe working zone in the triangle. Fanous et al7 and Tumialan et al,8 gave clarity to the definition of KT. They clarified that the use of the term KT should be reserved for endoscopic surgeons and pain physicians working on an anatomical corridor in an intact spine and not by surgeons accessing the area for interbody fusion by performing a complete facetectomy. The controversy in the matter is because the working triangle was always described in two dimensions. The definition of “Kambin's prism,” by adding the SAP as a separate landmark thus transformed it into a three-dimensional prism which includes the SAP contributing to the fourth border making it easily accessible for the surgeon. Lertudomphonwanit et al,9 proposed a trapezoidal IVD area as the true working zone in KT extending from L1 to S1.
Despite all confusion and controversies, KT approach has been used by many for therapeutic interventions. Pairaiturkar et al5 in 2019 performed a 3D MRI study classifying KT and estimated the maximum cannula diameter, which could traverse the two types of KT. The original KT was described as “neural KT” (nKT), and its boundaries were formed by the ENR (hypotenuse), superior endplate of the inferior vertebra (base), and dura mater (height). The boundaries of the bKT were formed by the ENR (hypotenuse), superior endplate of the caudal vertebra (base), and SAP of the caudal vertebra (height). They calculated the area of the inscribed circle in the triangle which gave the maximum outer diameter of the cannula that can be passed through this triangle. The bKT was defined by Pairaiturkar et al,5 as they realized that the SAP is an important landmark to be negotiated first before entering the intervertebral space. Kumari et al,10 in 2021 performed the first cadaveric study measuring the dimensions of the bKT from L1-L2 spaces to L4-L5 spaces. In addition to the abovementioned dimensions, the present study also measured the dimensions of bKT in L5-S1 spaces.
KT has been used as a safe route for accessing intervertebral space in IVD and spinal surgeries.11,12 With the evolution of transforaminal endoscopic surgery using KT, several surgeries such as annuloplasty, pediculotomy, foraminoplasty, and so on,13,14 can be performed with ease. KT has also been used as an IVD access point in radiology, especially for diagnostic discograms.4,15
Pain physicians and other clinicians utilize this area for providing minimally invasive steroid injections at the targeted nerve root.15, 16, 17, 18, 19, 20, 21 Park et al,16 and Glasner et al.21 found that the KT approach for epidural injection in patients is practical and safer than the subpedicular approach. According to their observations, there is less chance of nerve prick injury, venous congestion, epidural bleeding in KT approach in comparison to the subpedicular approach performed through the “safe triangle” located below the inferior surface of the pedicle.21 For the treatment of lumbar radicular pain where it is difficult to place the needle for transforaminal epidural steroid injections in anterior epidural space via the supraneural approach, the KT approach can be used instead.22 For percutaneous transforaminal adhesiolysis using an inflatable balloon catheter, the KT approach could be an alternative in cases where the safe triangle approach is difficult.23
Hoshide et al in 2016 performed the first cadaveric study by using Kirschner wire under fluoroscopic guidance to measure the dimensions of KT and calculated the area of the triangle in two human cadavers.15 In the present study, the values of the mean area of bKT obtained were 98.2 mm2, 116.89 mm2, 131.59 mm2, and 142.73 mm2, which are higher than the values obtained by Hoshide et al (Table 2). Although male–female comparison was made in the present study for the mean area of KT, no statistically significant difference was obtained.
Table 2.
Comparisons of parameters in different studies done in different geographical areas. KT= Kambin's triangle, D = Diameter of cannula.
| Studies | Type(N) | Location | Distance |
||||||
|---|---|---|---|---|---|---|---|---|---|
| L1-L2 | L2-L3 | L3-L4 | L4-L5 | L5-S1 | |||||
| Hoshide et al (2016) | Cadaveric (2 cadavers = 4 sides = 16 KTs) | California,USA | Height (mm) | 10 | 11 | 11 | 12 | ||
| Base (mm) | 12 | 13 | 17 | 18 | |||||
| Area (mm2) | 60 | 71.5 | 93.5 | 108.0 | |||||
| Pairaiturkar et al (2019) | MRI based (50 patients = 100 sides = 500 KTs) | Pune (Maharashtra) India |
D Bony KT | R L |
4.03 4.06 |
4.41 4.46 |
4.26 4.44 |
5.32 4.95 |
5.72 6.11 |
| D neural KT | R L |
5.67 5.77 |
6.15 6.46 |
7.07 7.52 |
8.31 8.3 |
7.88 9.7 |
|||
| Hardenbrook et al (2016) | Cadaveric (8 cadavers = 16 sides = 80 KTs) | Boston, USA | Working triangle area (mm2) | 1.75 | 1.72 | 1.71 | 1.78 | 2.19 | |
| Safe zone area (mm2) | 1.15 | 1.2 | 1.19 | 1.16 | 1.26 | ||||
| Zhang et al (2020) | Cadaveric (6 cadaver = 12 sides = 60 KTs and CT imaging of living (60 patients = 120 sides = 600 KTs | Beijing, China | Distance between exiting nerve root and SAP (cadaver) (mm) | 4.25 | 5.13 | 5.96 | 6.47 | ||
| Distance between exiting nerve root and SAP (CT) max Distance (mm) | 4.29 | 4.36 | 4.61 | 4.92 | 5.77 | ||||
| Kumari et al (2021) | Cadaveric (5 cadavers = 10 sides = 40 KTs) | Chandigarh, India | Height (mm) | R L |
13.15 13.43 |
16.37 16.23 |
16.85 17.88 |
20.31 21.54 |
|
| Base (mm) | R L |
8.19 7.99 |
8.34 9.06 |
8.84 9.39 |
9.30 10.73 |
||||
| Area (mm2) | R L |
54.01 53.81 |
66.84 73.42 |
74.59 83.91 |
94.44 115.84 |
||||
| Diameter of canula | R L |
5.83 5.67 |
6.29 6.69 |
6.66 7.05 |
7.27 8.16 |
||||
| König et al (2020) | Cadaveric (20 cadavers = 40 sides = 160 KTs) and 20 MRI scans = 160 KTs | South Africa | Height | 16.0 | 16.7 | 16.4 | 16.4 | ||
| Base | 15.4 | 15.5 | 15.7 | 17.1 | |||||
| Hypotenuse | 21.6 | 21.7 | 21.0 | 22.7 | |||||
| Present study | Cadaveric (7 cadavers = 14 sides = 70 KTs) | Raipur (CG), India | Height | R L |
18.33 19.02 |
21.46 20.91 |
22.64 21.97 |
22.42 22.76 |
21.69 19.09 |
| Base | R L |
10.51 10.42 |
10.62 10.81 |
12.23 11.07 |
13.36 12.10 |
13.13 10.94 |
|||
| Diameter | R L |
7.68 7.61 |
8.10 8.09 |
8.40 8.81 |
8.86 9.72 |
7.56 9.34 |
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Pairaiturkar et al5 measured the maximum cannula diameter permissible through the “neural KT” and the “bony KT.” The mean maximum cannula diameter of bKT measured by MRI in 50 patients increased from 5.67 ± 1.38 mm at the L1-L2 level to 8.31 ± 1.98 mm at the L4-L5 level and further decreased to 7.88 ± 1.58 mm at L5-S1 level. The present study showed a similar trend but higher values as compared to Pairaiturkar et al (Table 2). The values of the mean diameter of cannula admissible in the present study increased from the L1-L2 level (7.64 ± 1.08 mm) to the L4-L5 level (9.29 ± 1.4 mm) and then decreased to 8.45 ± 1.66 mm at L5-S1.
Majority of the cases of IVD prolapse requiring percutaneous endoscopic lumbar discectomy are seen at two spaces- L4-L5 and L5-S1 level.7 Unlike previous cadaveric studies, the present study measures the dimensions of the bKT and calculated the MPD at L5-S1 level. Pairaiturkar et al, found that mean maximum diameter of cannula at L5-S1 was 5.72 mm and 6.11 mm on right and left side, respectively. In present study, MPD at L5-S1 were 6.85 mm and 6.11 mm on right and left side, respectively. The values obtained are higher as compared to Pairaiturkar et al. As per their study, in 3D MRI, sections should pass through oval nerve root. However, root visualization is not always perfect oval shape, which leads to error. Also, the visualization of L5-S1 level in some patients was not possible due to the overhang of higher iliac crest.7
The mean areas of bKT obtained in all spaces in current study were higher than those of Kumari et al10 (Table 2). The MPD at L1-L2 space to L4-L5 spaces were 5, 5.5, 5,6, and 6.5 mm, respectively, as per Kumari et al. The MPD at L1-L2 space to L5-S1 spaces as calculated in the present study were 6.2, 6.06, 6.55, 7.64, and 6.4 mm, respectively, which were higher as compared to Kumari et al10 (Table 2). As per current study, a cannula of 6.06 mm or smaller would be admissible at all levels. Only a considerable percentage (40–60%) of the spaces at an IVD level permit passage of the cannula with the specific mean diameter in contrast to Kumari et al.
Generally, cannulas of size ranging from 7 to 11 mm are available for any transforaminal approach.10 Pairaturkar et al5 classified the KT's as admitting cannulas in the range of <4 mm, 4–8 mm, and >8 mm. As per their findings, 36%, 62%, and 2% of the KT's admitted <4 mm, 4–8 mm, and >8 mm cannulas, respectively.5 In the present study and in study by Kumari et al, none of the spaces were found to admit only <4 mm cannula. As per Kumari et al, 97.5% of the KT's admitted cannula in the range 4–8 mm, while 2.5% of the KTs admitted cannula of diameter >8 mm.10 In the present study, 43% of the KTs could admit cannulas ranging from 4 to 8 mm and 57% of the KTs could admit cannula >8 mm. This shows that regional variations do exist in the dimensions of KT.
Ozer et al,24 classified the anatomic variations of the KT into three types. Type 1 triangle has no space in the triangle, while type 2 triangle has narrow space in the triangle. Type 3 triangle was the wide classical KT. They found only 10.8% and 17.6% of the KTs to be of the classical type in patients and cadavers, respectively, thus concluding that there were variations in KT. No such classification has been done in the present study due to the different methodology used. As per the observations in the present study, none of the triangles belonged to type 1, while majority of the KTs belong to type 3 “classic” type.
Konig et al25 determined the dorsal root ganglion's position and measured the dimensions of the KT (Table 2). Based on their observations, they speculated the possibility of population-specific trends in measurements. Analysis of previous literature revealed that regional variations do exist in dimensions of KT. Clinicians should be aware of this for selection of adequately sized instruments.
Zhang et al,4 by using CT imaging, established the relationship between ENR and SAP. Also, they studied six cadavers (48 spaces) and concluded that there was decreased space between the bone and the ENR and suggested performing foraminoplasty to reduce the complication of ENR injury. In the present study, similar trend on increasing diameter from L1-L2 to L4-L5 spaces have been observed but wider spaces.
The present study has some limitations. It has been performed only on seven cadavers. Limited availability of cadaver, time-consuming extensive dissection, and careful approach of triangle for each dissection compelled the authors to choose 70 KTs for the study. Studies using a larger sample size will give a more accurate prediction of the cannula size to be used in a particular population. However, it was stated that formalin induces shrinkage by about 10–15% in cadaveric tissues which may alter the original dimensions.26,27 A previous study noted that in almost 96% of the cases, there is no significant difference in fresh and embalmed tissue.28 Also, formalin does not induce significant shrinkage in bone.29 Radiological correlation has not been done in the present study, and we propose that future studies include it to compare with the values of live patients.
Conclusion
Despite the many studies that have been carried out in an attempt to support the dimensions of KT, regional variations do exist. We propose that cannula of diameter 6.06 mm or smaller can be used at all levels in the KT. This study will benefit neurosurgeons, spine surgeons, orthopedics, and pain physicians in planning their procedures and deciding the appropriate cannula diameter for minimally invasive procedures.
Patients/ Guardians/ Participants consent
Not applicable.
Ethical clearance
Institute/hospital ethical clearance certificate was obtained.
Source of support
Nil.
Disclosure of competing interest
The authors have none to declare.
Acknowledgment
None.
References
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