How dimensions can guide surgical planning and training: a systematic review of Kambin’s triangle

Romaric Waguia KouamCampbell University School of Osteopathic Medicine, Lillington;

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Troy Q. TabarestaniDuke University School of Medicine, Durham;

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David A. W. SykesDuke University School of Medicine, Durham;

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Nithin GuptaCampbell University School of Osteopathic Medicine, Lillington;

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Brittany G. FutchDuke University School of Medicine, Durham;

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Elisabeth KakmouDepartment of Neurosurgery, Duke University Hospital, Durham, North Carolina;

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C. Rory GoodwinDepartment of Neurosurgery, Duke University Hospital, Durham, North Carolina;

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Norah A. FosterDepartment of Orthopedic Surgery, Miami Valley Hospital, Centerville, Ohio; and

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Khoi D. ThanDepartment of Neurosurgery, Duke University Hospital, Durham, North Carolina;

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Walter F. WigginsDepartment of Radiology, Duke University Hospital, Durham, North Carolina

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Muhammad M. Abd-El-BarrDepartment of Neurosurgery, Duke University Hospital, Durham, North Carolina;

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OBJECTIVE

The authors sought to analyze the current literature to determine dimensional trends across the lumbar levels of Kambin’s triangle, clarify the role of imaging techniques for preoperative planning, and understand the effect of inclusion of the superior articular process (SAP). This compiled knowledge of the triangle is needed to perform successful procedures, reduce nerve root injuries, and help guide surgeons in training.

METHODS

The authors performed a search of multiple databases using combinations of keywords: Kambin’s triangle, size, measurement, safe triangle, and bony triangle. Articles were included if their main findings included measurement of Kambin’s triangle. The PubMed, Scopus, Ovid, Cochrane, Embase, and Medline databases were systematically searched for English-language articles with no time frame restrictions through July 2022.

RESULTS

Eight studies comprising 132 patients or cadavers were included in the study. The mean ± SD age was 66.69 ± 9.6 years, and 53% of patients were male. Overall, the size of Kambin’s triangle increased in area moving down vertebral levels, with L5–S1 being the largest (133.59 ± 4.36 mm2). This trend followed a linear regression model when SAP was kept (p = 0.008) and removed (p = 0.003). There was also a considerable increase in the size of Kambin’s triangle if the SAP was removed.

CONCLUSIONS

Here, the authors have provided the first reported systematic review of the literature of Kambin’s triangle, its measurements at each lumbar level, and key areas of debate related to the definition of the working safe zone. These findings indicate that CT is heavily utilized for imaging of the safe zone, the area of Kambin’s triangle tends to increase caudally, and variation exists between patients. Future studies should focus on using advanced imaging techniques for preoperative planning and establishing guidelines for surgeons.

ABBREVIATIONS

ENR = exiting nerve root; MISS = minimally invasive spine surgery; PRISMA = Preferred Reporting Items for Systematic Reviews and Meta-Analyses; SAP = superior articular process.

OBJECTIVE

The authors sought to analyze the current literature to determine dimensional trends across the lumbar levels of Kambin’s triangle, clarify the role of imaging techniques for preoperative planning, and understand the effect of inclusion of the superior articular process (SAP). This compiled knowledge of the triangle is needed to perform successful procedures, reduce nerve root injuries, and help guide surgeons in training.

METHODS

The authors performed a search of multiple databases using combinations of keywords: Kambin’s triangle, size, measurement, safe triangle, and bony triangle. Articles were included if their main findings included measurement of Kambin’s triangle. The PubMed, Scopus, Ovid, Cochrane, Embase, and Medline databases were systematically searched for English-language articles with no time frame restrictions through July 2022.

RESULTS

Eight studies comprising 132 patients or cadavers were included in the study. The mean ± SD age was 66.69 ± 9.6 years, and 53% of patients were male. Overall, the size of Kambin’s triangle increased in area moving down vertebral levels, with L5–S1 being the largest (133.59 ± 4.36 mm2). This trend followed a linear regression model when SAP was kept (p = 0.008) and removed (p = 0.003). There was also a considerable increase in the size of Kambin’s triangle if the SAP was removed.

CONCLUSIONS

Here, the authors have provided the first reported systematic review of the literature of Kambin’s triangle, its measurements at each lumbar level, and key areas of debate related to the definition of the working safe zone. These findings indicate that CT is heavily utilized for imaging of the safe zone, the area of Kambin’s triangle tends to increase caudally, and variation exists between patients. Future studies should focus on using advanced imaging techniques for preoperative planning and establishing guidelines for surgeons.

Since its introduction in 1973, Kambin’s triangle has become an ever more important and studied aspect of minimally invasive spine surgery (MISS). When this concept was first coined by Parviz Kambin, Professor of Orthopedic Surgery at Drexel University College of Medicine, it served as a landmark to perform percutaneous lateral discectomy, which at the time was a new surgical method for decompressing herniated intervertebral lumbar discs.1 In his initial description, four anatomical structures were cited as borders of the safe zone: the exiting nerve root (ENR), the proximal plate of the lower lumbar segment, the proximal articular process of the inferior vertebra, and the traversing nerve root/dural sac.1,2 In much of the current literature, the triangle is defined with the hypotenuse as the ENR, the base as the superior endplate of the caudal vertebra, and the height as the traversing nerve root (Fig. 1).3 This three-sided boundary clearly leaves out the superior articular process (SAP). For this reason, there have been differences regarding the exact definition, sizes, and anatomical limits of Kambin’s triangle.412

FIG. 1.
FIG. 1.

Anatomical boundaries of Kambin’s triangle (green triangle). Reproduced from Yeung A, Gore S. Endoscopic foraminal decompression for failed back surgery syndrome under local anesthesia. Int J Spine Surg. 2014;8:22. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4325507/#__ffn_sectitle. © 2014 ISASS—International Society for the Advancement of Spine Surgery, published with permission. CC BY-NC 3.0 (https://creativecommons.org/licenses/by-nc/3.0/).

Understanding the triangle’s borders and size trends is crucial during the preoperative planning phase for surgeons.13,14 Multiple groups have compared nerve root injuries, rates of paresthesias, and other common neurovascular complications during percutaneous entrance into the disc. In contrast to Kambin’s original intent to perform discectomy through Kambin’s triangle, there has been increasing interest in performing instrumented fusion through this small corridor. The dimensions of the triangle thus limit the sizes of the cannulas and static cages that can be used; hence, there has been increased interest in placing expandable implants within this corridor.15 With the mounting incidence of MISS in the last several decades, the impact of resident involvement on spine surgical procedures has also been tested across both orthopedics and neurosurgery. Although varying results have been proposed, the overarching theme has been that resident involvement increases infection rates, length of stay, and postoperative morbidity.1619 Considering that the approach through Kambin’s triangle is a more advanced procedure owing to the key surrounding anatomical structures and decreased visibility, understanding trends in its dimensions could help guide attending surgeons about when and how to include resident participation.

Prior studies have performed radiographic or cadaveric analysis to better categorize Kambin’s triangle, as well as both quantify and visualize the safe zone. However, no systematic reviews have reported the size of the triangle or compared methodologies of measurement. The goals of this study were to 1) quantify the dimensional trends for Kambin’s triangle at multiple lumbar levels, 2) compare the dimensions of Kambin’s triangle with and without removal of SAP, 3) review the imaging modalities most commonly used to measure the area, and 4) analyze how degenerative disease can affect the dimensions of Kambin’s triangle.

Methods

Search Strategy and Study Selection

The present study was conducted according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines (Fig. 2). The PubMed, Scopus, Ovid, Cochrane, Embase, and Medline databases were systematically searched for English-language articles with no time frame restrictions through July 2022. One of our articles that reports Kambin’s triangle size, currently in print, was included in the analysis.20 The following terms in various combinations were used: Kambin’s triangle, size, measurement, safe triangle, and bony triangle. Two authors independently performed the literature searches, and conflicts were resolved through discussion. Exclusion criteria included studies investigating the size of the cannula or relationships of the cannula to Kambin’s triangle.

FIG. 2.
FIG. 2.

Using PRISMA guidelines, we systematically searched the PubMed, Ovid, Cochrane, Embase, Scopus, and Medline databases for English-language articles with no time frame restrictions through July 2022. Studies were included if the goal of the study was to measure the area of Kambin’s triangle. Exclusion criteria included studies investigating the size of the cannula or relationships of the cannula to Kambin’s triangle.

Data Extraction

From the studies included, we extracted patient demographic data, area of Kambin’s triangle at different lumbosacral levels, living status of the specimen (cadaver vs in vivo), measurement modality (dissection vs CT/MRI), and specialty of the surgeon performing the study. We extracted demographic data, patient data, and measurement method of the triangle from all studies.

Statistical Analysis

Descriptive statistics are presented as mean ± SD. For the regression models, data were analyzed with Excel using the Analysis ToolPak to extrapolate the F score, p value, and R2 coefficient. Welch’s t-test with 1 tail was used to analyze differences between the mean areas of studies with SAP maintained versus those with SAP removed. In this study, p < 0.05 was considered statistically significant. To determine the percent difference, the change in means was divided by the average of means. The percent change formula was not used because there was no clear baseline or initial value appropriate for that equation.54

Results

Results of the Systematic Review

Twenty-six papers were found using the search criteria. After we removed duplicates and studies that did not measure the area of Kambin’s triangle, the inclusion criteria were met by 8 studies that included a total of 132 patients (Fig. 2). Five studies were cadaveric, and 3 included living subjects. The preferred measurement method of the cadaveric studies was dissection (5/5 studies) with or without facetectomy, whereas CT measurement was preferred by the studies with living patients (2/3 studies). Demographically, the mean ± SD age in the entire cohort was 66.69 ± 9.6 years, with age ranging from 43 to 85 years, and 53% of the cohort was male (Table 1).

TABLE 1.

Literature review results of all 8 studies with demographic data

Authors & YearDepartmentImaging ModalityPatientsMaleAge (yrs)
Cadaver
 König et al., 20204AnatomyMeasurement209 (45)74.85 ± 13.09
 Hoshide et al., 20165NeurosurgeryKirschner wire & fluoroscopy22 (100)
 Kumari et al., 20219OrthopedicsDigital vernier calipers54 (80)60 ± 7.97
 Hardenbrook et al., 201611NeurosurgeryDissection & measurement84 (50)
 Lertudomphonwanit et al., 201610OrthopedicsDissection & measurement53 (60)65
In Vivo
 Fan et al., 202021OrthopedicsDeep learning 3D model77
 Dalton et al., 202122NeurosurgeryCT105 (50)62.2 ± 2.1
 Tabarestani et al., in press20NeurosurgeryMRI 52 (40)71.4 ± 8.3
Total13229 (53)*66.69 ± 9.6

Values are shown as number, number (%), or mean ± SD.

Total number of patients (mean percent of all studies) is shown.

Area of Kambin’s Triangle

The areas reported by the included studies generally trended toward an increasing area of Kambin’s triangle from L1–2 to L5–S1; however, there were discrepancies in this pattern upon examination of the nonaggregated data.

Three studies performed full facetectomy prior to calculation of the area of Kambin’s triangle, increasing the overall size at each level (Table 2). Five studies measured the size of the triangle without removing SAP, and 2 studies reported operative measurement of Kambin’s triangle. These data are summarized in Table 2.

TABLE 2.

Kambin’s triangle area data extracted from each study

Authors & YearL1–2L2–3L3–4L4–5L5–S1SAP Removed
König et al., 20204123.2181.2172.2186.14Yes
Hoshide et al., 201656071.593.5108No
Kumari et al., 2021953.91 ± 7.1870.63 ± 6.8379.25 ± 9.72104.72 ± 5.95No
Hardenbrook et al., 201611175172171178219Yes
Lertudomphonwanit et al., 201610100.2398.73115.7153.04150.16Yes
Fan et al., 202021161.27 ± 40.10No
Dalton et al., 20212269 ± 12.9459 ± 7No*
Tabarestani et al., in press2095.5 ± 8.376.1 ± 14.678.5 ± 4.1No*
Mean ± SD102.47 ± 32.36118.81 ± 36.46121.19 ± 20.31125 ± 41.21133.59 ± 4.36

Values are reported in square millimeters as mean or mean ± SD.

Operative measurement.

König et al. examined L1–5 levels in 20 cadavers and found that L2–3 was larger than L3–4 (181.2 mm2 vs 172.2 mm2).4 Additionally, in Hardenbrook et al.’s analysis of 8 cadavers, L1–2 (175 mm2) was larger than both L2–3 (172 mm2) and L3–4 (171 mm2).11 On the other side, Lertudomphonwanit et al. found that L1–2 (100.23 mm2) was larger than L2–3 (98.73 mm2).10 These 3 studies performed full facetectomy prior to calculation of the area of Kambin’s triangle, increasing the overall average size at each level (Table 2). When compared with the average percent differences of the studies that did not remove SAP, overall area increased by an average of 64.53% after removal. Comparison of the mean areas at each lumbar level between studies with SAP maintained and those with SAP removed revealed statistically significant differences at all levels except L2–3 and L5–S1 (Table 3).

TABLE 3.

Area of SAP maintained versus SAP removed at each level

CharacteristicL1–2L2–3L3–4L4–5L5–S1
SAP maintained, mm59.9671.0789.4289.4699.60
SAP removed, mm132.81150.64152.97172.39184
Δ Mean, mm72.8579.5763.5582.9384.4
% Difference75.5871.7852.4463.3459.52
p value0.04*0.050.02*0.0010.09

Mean values are shown unless indicated otherwise.

Statistically significant according to the Welch’s t-test (1-tailed) (p < 0.05).

Statistically significant according to the Welch’s t-test (1-tailed) (p < 0.005).

Five studies reported information regarding the area of the L5–S1 level: 2 studies (Lertudomphonwanit et al. and Hardenbrook et al.) included cadavers and 3 studies (Fan et al., Dalton et al., and Tabarestani et al.) included in vivo subjects.10,11,2022 Interestingly, Hardenbrook et al. found that the area of Kambin’s triangle at L5–S1 was larger than at superior levels, whereas Fan et al. did not compare the area of L5–S1 to the areas at other lumbar spine levels. In contrast, Lertudomphonwanit et al., Dalton et al., and Tabarestani et al. reported that the L5–S1 level had a smaller area than at the L4–5 level. It should be noted that Dalton et al. and Tabarestani et al. reported data on the operative level of the area of Kambin’s triangle; this was performed by outlining a freehand region of interest along the borders of Kambin’s triangle just proximal to the entrance of the disc space.22

Upon examination of the operative studies, where pathology such as degenerative disc disease and/or spondylolisthesis was evident, the size of Kambin’s triangle decreased in size caudally from L3–4 to L5–S1. As such, comparison of the pathological levels directly with those of the nonoperative studies where SAP was maintained showed that the L4–5 levels decreased by an average of 37.8% and the L5–S1 levels decreased by 80.45% (Table 4). Using Welch’s 1-tailed t-test, we found that there was a significant difference between the average areas reported for L4–5.

TABLE 4.

Area of operative levels versus nonoperative levels

CharacteristicL1–2L2–3L3–4L4–5L5–S1
Operative, mm95.572.5568.75
Nonoperative, mm56.9671.0786.375106.36161.27
Δ Mean, mm–9.12533.8192.52
% Difference–10.0337.8080.45
p value 0.04*

Mean values for Kambin’s triangle are shown unless indicated otherwise.

Statistically significant using Welch’s t-test (1-tailed) (p < 0.05).

Overall, Kambin’s triangle area increased caudally in both cohorts (SAP retained vs SAP removed), with the largest area being between L4–5 and L5–S1 (Table 3). The increase in area down the lumbar spine follows a linear regression model, with R2 = 0.966 (p = 0.003) for the SAP-removed group and R2 = 0.930 (p = 0.008) for the SAP-maintained group (Fig. 3). Both models showed statistical significance after regression analysis based on their respective F scores.

FIG. 3.
FIG. 3.

Linear regression models for the mean area of Kambin’s triangle at each lumbar level when SAP was maintained (blue) and removed (orange). Linear fit equation when the SAP was maintained: y = 9.767x + 52.601, with R2 = 0.9301. Linear fit equation when the SAP was removed: y = 12.529x + 121.09, with R2 = 0.9658.

Discussion

There has been increased interest in minimizing tissue dissection and manipulation in all realms of surgery. In traditional posterior surgery, Kambin’s triangle has been an important landmark. Endoscopic spine surgeons have long appreciated the triangle as a corridor to perform these operations without having to disrupt the vascularized facet joint. However, with the increasing incidence of these procedures, rates of ENR injuries, and incoming resident surgeons, a better understanding of the triangle’s borders and dimensional trends will play a key role in improving preoperative planning and training. Likewise, establishing an imaging modality of choice that best quantifies the triangle will further benefit both the surgeon and patient. Our study and analysis of the current literature is the first review to compile studies that specifically examined the area of the triangle.

Importance of Proper Sizing for Preoperative and Operative Planning

The importance of determining this trend in the triangle’s size is multifold. Primarily, it can help guide the surgeon in determining the feasibility of the operation, risks versus benefits, and potential complications. More practically, understanding of the trends in Kambin’s triangle can help to prepare approximately sized cannulas and endoscopes, thereby minimizing the risk of nerve injury during the procedure. With the adoption of the railroad technique, which introduces a tapered dilator followed by a snugly fitting cannula, the rates of ENR injuries have decreased.23,24 Even with this new method, the endoscopic cannula is still placed between the dural canal and the ENR lateral to the SAP, which could limit the size of hardware for instrumented fusion. Thus, there has been an increased interest in using expandable technology, whether it be unique moldable devices or traditional titanium implants.15 Interestingly, if one assumes that base equals height in the equation for area of a triangle, then the largest implant that could possibly fit would be 10–14 mm for the range of Kambin’s triangle area of 60–100 mm2 when SAP was maintained.

In such a small corridor, the slightest of errors or aberrant movements can damage the surrounding neurovascular structures. Morgenstern et al. showed a 32% rate of postoperative complications that consisted of ipsilateral dysesthesia and transitory muscle weakness after trans-Kambin procedures.25 Similarly, foot drop injuries have been reported in the literature, especially for patients who underwent anterior lumbar fusion leading to irritation of the L5 ENR.26 Of significant note, these studies that report rates of neurovascular injuries also mentioned that Kambin’s triangle was not visualized before surgery. That being said, preoperative knowledge of the working safe zone at each lumbar level can put surgeons on heightened awareness when crossing the threshold of cannula diameters that may begin to infringe on the upper limits of safety.

More specifically, some groups have recommended foraminoplasty when working on levels L4–5 and L5–S1 due to the difficult angle to maneuver past the SAP.27 Our data seem to partially corroborate this because the areas of Kambin’s triangle were considerably larger if the SAP had been removed. This may also explain why 3 of the papers included in our study did not measure the area of Kambin’s triangle at the L5–S1 level.4,5 Some groups do not recommend a transforaminal approach at all for the L5–S1 level due to impeding pelvic and abdominal structures.26,28 However, this contradicts the fact that L5–S1 has, in general, the largest Kambin’s triangle area among the lumbar levels, illustrating the need for further studies evaluating specific approaches into that disc space.29

Importance of Dimensional Trends for Resident Involvement

Understanding the basic trends of Kambin’s triangle across the lumbar spine could prove helpful when planning a surgeon’s training. There are two main factors to take into account: the learning curve for MISS, and the impact of resident involvement on patient care. The learning curve for MISS has been reported extensively in the literature, and the general conclusion is that operative time, blood loss, and complication rate are increased during the earlier phase of training for MISS.3032 Some studies have reported rates as high as 20% for ENR injuries after transforaminal percutaneous endoscopic lumbar discectomy.3335 As Son et al. showed in their work, the risks of incomplete decompression and ENR injuries were higher in an earlier novice stage of training.36 Tangentially, surgeons in training who may not be as far along the learning curve would benefit from a greater appreciation of the precision needed to perform these procedures at lumbar levels with statistically smaller safe zones.3739

While conflicting data exist regarding the presence of resident surgeons, multiple studies have shown that, for more complex procedures, resident assistance is associated with higher infection rates, lengthier surgical procedures, longer lengths of stay, and increased morbidity rates for orthopedic and neurosurgical procedures.1719,40 Notably, 1 study revealed that resident involvement was associated with greater 30-day reoperation rates for spinal fusion cases.18 From an attending surgeon’s perspective, understanding the basic trends for Kambin’s triangle would allow them to set realistic expectations for residents and better plan their training trajectory. Overall, it would be beneficial to both the operating team and patient for newly trained surgeons to start operating via the large Kambin’s triangles in the lower lumbar levels. As they progress with their training and improve their minimally invasive skills, they can move up the lumbar spine to the more technically challenging levels with smaller Kambin’s triangles.

CT Is the Major Modality for Measuring Kambin’s Triangle

From our review, 2 (66%) of the in vivo studies implemented CT as their main modality for measuring the triangle. Considering the evidence that MRI excels in showing neurovascular structures, this was a notable finding given that the ENR is arguably the most important border of the triangle.7,41 Additionally, MRI is the modality of choice over CT when measuring the density or thickness of thin structures.42 However, MRI does fall behind CT scans for examining the bony landscape of a patient, which makes up two of the triangle’s borders (the SAP and superior endplate of the caudal vertebra).43,44 CT is also less expensive, more readily available, and provides better imaging resolution in patients with metallic hardware, which may be more prevalent among patients with previous instrumented fusion.

For this reason, researchers have begun to test the efficacy of MRI/CT fusion to extract the benefits of both technologies.7,45,46 Using either an artificial intelligence model or manual fusion, 3D visualizations have been created by merging MRI with CT images of the lumbar vertebrae. This methodology appears to compensate for the disadvantages of each individual scan and enables analysis of the relationship between the bony components and neural tissue of Kambin’s triangle in 3D. Unfortunately, these studies did not measure the area of Kambin’s triangle using their new technique, but our group at Duke University has started to use novel methods to merge these two imaging modalities. For example, Tabarestani et al. used preoperative T2-weighted MR images in combination with BrainLab Smartbrush technology to "draw out" the ENR at the pathological lumbar level. By doing so, a more accurate 3D visualization and measurement of Kambin’s triangle was created to outline the borders of the corridor prior to surgery. These segmented scans were then fused with intraoperative CT scans to confirm the placement of the endoscopes while accessing the disc space.20

Variability of Kambin’s Triangle

As seen with the results of our literature review, the variability in Kambin’s triangle is self-evident. Although the increasing size trend is consistent, some studies such as those by Hardenbrook et al. showed that L1–2 was larger than the next two lower levels. Additionally, laminectomy, severity of disease, and/or removal of SAP can all significantly affect the dimensions of the triangle by altering its borders. Not only is there individuality in Kambin’s triangle size, but also the anatomy of the bony and neurovascular structures surrounding the space. The presence of conjoined or scarred nerve roots, facet hypertrophy, impeding artery of Adamkiewicz, and degenerative changes to the anatomy can all affect a patient’s unique spinal landscape.47 Haijiao et al. found a 17% incidence of nerve root anomalies in 376 lumbar MRI scans, whereas prior studies relied mainly on CT scans and caught only 2% of conjoined roots.48,49 Simon et al. reported that key arteries were found in both the safe zone and Kambin’s triangle at statistically significant rates.50 It may also be beneficial to determine the laterality of the approach, as seen by Tabarestani et al., who reported noticeable size differences for some patients when comparing the left and right triangles at the same level.20 As described by Zhang et al., the distance between the ENR and SAP in Kambin’s triangle was narrow in both cadaver and CT imaging studies, with the L5–S1 intervertebral foramen having the largest distance.51 Their results further corroborated ours by showing that the distance between the ENR and SAP increased across their cohort as they went down lumbar levels. For this reason, the presence of a scarred, enlarged nerve root, hypertrophied SAP, or overall smaller triangle could preclude the patient from receiving a percutaneous procedure without also an enlarging foraminoplasty.

Area Increases Linearly With Lower Lumbar Levels

From the studies examined in this review, there is a clear trend of increasing Kambin’s triangle area as one goes down the levels of the lumbar spine. These results align nicely with prior research on actual ENR sizes. Hogan found increased root size at segments L3 through S2, but patients still showed high levels of interindividual variability in nerve sizes.52 Similarly, Liu et al. used anatomical and histological analysis to corroborate this increase in nerve root size from L1 to S1 followed by a sharp decrease to S2.53 Additionally, the linear regression models for both the removed and maintained SAP groups fit the data significantly. However, the clinical applicability of these models is still under question. Although an equation based on a high cohort of patients would appropriately predict the size of the triangle at a certain lumbar level, our data still show high variability between studies. On the other hand, a regression model could be helpful when patients require multiple level fusions because surgeons would then be able to preemptively plan for a linear increase in area down the spine. Especially for surgeons who do not have access to more advanced preoperative planning technology, this could help estimate the range of cannulas/endoscopes needed for multilevel fusion.

Presence of Pathology Can Affect the Dimensions of Kambin’s Triangle

Many of the original studies concentrated on the intact anatomy of Kambin’s triangle. Several salient points were found with measurement of the dimensions of Kambin’s triangle in patients with degenerative disease, whether degenerative disc disease and/or spondylolisthesis. The overall increase in the size of Kambin’s triangle, as one traveled caudally, was in fact not true. As seen in Table 4, the area of Kambin’s triangle at a pathological level was generally smaller than at nonpathological levels, indicating that the presence of disease or degeneration could play a key factor in the variability of the area and should be taken into account during preoperative planning. This may be the reason that many endoscopic experts have discouraged percutaneous entrance into the disc at L5–S1 without foraminoplasty.27,29

Limitations and Future Directions

The most significant limitation of this investigation of Kambin’s triangle is the relative novelty of the procedure and scarce research in the current literature. Though the earliest paper about this topic was published in 1973, studies dedicated to measuring the triangle were only published from 2016 to 2021. Even after filtering through multiple different databases, this literature review was unable to provide statistical comparison between the various studies. Additionally, of the studies that did investigate specific measurements, there was variability in the types of measurements collected. Larger cohort studies with more standardized evaluation techniques are needed to generalize our findings.

Conclusions

We present the findings of a literature review that included 8 articles describing various methodologies for quantifying the dimensions of Kambin’s triangle. These articles revealed multiple key points: an increase in area going down the levels of the lumbar spine, variability between patients, and a strong predilection toward CT for visualizing the safe zone. From this, we have concluded that although operating through Kambin’s triangle is an effective technique, there is still room for improvement in reducing the rates of ENR injuries and understanding the complex variations in the triangle’s structure. From a clinical standpoint, a better grasp of general dimensional trends could benefit both the patient and the operating team in determining the laterality of approach, presence of neurovascular abnormalities, and feasibility for residents to assist with the operation. Advancements in 3D MRI/CT fusion for preoperative planning and improved guidelines for surgeons in training should be the next steps in making percutaneous endoscopic discectomy as safe as possible.

Disclosures

Dr. Goodwin reported grants from NIH/NINDS, grants from FDA, grants from Robert Wood Johnson, and personal fees from Medtronic outside the submitted work. Dr. Than reported personal fees from Bioventus, personal fees from DePuy Synthes, personal fees from Accelus, personal fees from Cerapedics, and personal fees from SI Bone outside the submitted work. Dr. Wiggins reported grants from NIH/NINDS, personal fees from Qure.ai, and personal fees from the University of Wisconsin–GE CT Protocols Partnership outside the submitted work. Dr. Abd-El-Barr reported consulting fees from Spineology, consulting fees from DePuy Synthes, consulting fees from TrackX, grants from NIH, and grants from Abbvie outside the submitted work.

Author Contributions

Conception and design: Abd-El-Barr, Waguia Kouam, Tabarestani, Sykes, Futch, Foster, Than, Wiggins. Acquisition of data: Abd-El-Barr, Waguia Kouam, Tabarestani, Gupta, Kakmou. Analysis and interpretation of data: Abd-El-Barr, Waguia Kouam, Tabarestani, Sykes, Gupta, Futch, Kakmou, Goodwin, Foster, Than. Drafting the article: Abd-El-Barr, Waguia Kouam, Tabarestani, Sykes, Futch, Kakmou, Foster, Than. Critically revising the article: Abd-El-Barr, Tabarestani, Sykes, Futch, Kakmou, Goodwin, Foster, Than, Wiggins. Reviewed submitted version of manuscript: Abd-El-Barr, Waguia Kouam, Tabarestani, Sykes, Futch, Goodwin, Foster, Than, Wiggins. Statistical analysis: Waguia Kouam, Tabarestani. Administrative/technical/material support: Abd-El-Barr, Tabarestani. Study supervision: Abd-El-Barr, Tabarestani.

References

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    Kambin P, Gellman H. Percutaneous lateral discectomy of the lumbar spine a preliminary report. Clin Orthop Relat Res. 1983;174:127132.

  • 2

    Fanous AA, Tumialán LM, Wang MY. Kambin’s triangle: definition and new classification schema. J Neurosurg Spine. 2020;32(3):390398.

  • 3

    Yeung A, Gore S. Endoscopic foraminal decompression for failed back surgery syndrome under local anesthesia. Int J Spine Surg. 2014;8:22.

  • 4

    König A, Joseph F, Janse van Rensburg C, Myburgh J, Keough N. Kambin’s triangle and the position of the dorsal nerve root in the lumbar neural foramen. Clin Anat. 2020;33(8):12041213.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 5

    Hoshide R, Feldman E, Taylor W. Cadaveric analysis of the Kambin’s triangle. Cureus. 2016;8(2):e475.

  • 6

    Ozer AF, Suzer T, Can H, et al. Anatomic assessment of variations in Kambin’s triangle: a surgical and cadaver study. World Neurosurg. 2017;100:498503.

  • 7

    Pairaiturkar PP, Sudame OS, Pophale CS. Evaluation of dimensions of Kambin’s triangle to calculate maximum permissible cannula diameter for percutaneous endoscopic lumbar discectomy: a 3-dimensional magnetic resonance imaging based study. J Korean Neurosurg Soc. 2019;62(4):414421.

    • Crossref
    • PubMed
    • Search Google Scholar
    • Export Citation
  • 8

    Zhang L, Yang J, Hai Y, et al. Relationship of the exiting nerve root and superior articular process in Kambin’s triangle: assessment of lumbar anatomy using cadavers and computed tomography imaging. World Neurosurg. 2020;137:e336e342.

    • Crossref
    • PubMed
    • Search Google Scholar
    • Export Citation
  • 9

    Kumari C, Gupta T, Gupta R, et al. Cadaveric anatomy of the lumbar triangular safe zone of Kambin’s in North West Indian population. Anat Cell Biol. 2021;54(1):3541.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 10

    Lertudomphonwanit T, Keorochana G, Kraiwattanapong C, Chanplakorn P, Leelapattana P, Wajanavisit W. Anatomic considerations of intervertebral disc perspective in lumbar posterolateral approach via Kambin’s triangle: cadaveric study. Asian Spine J. 2016;10(5):821827.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 11

    Hardenbrook M, Lombardo S, Wilson MC, Telfeian AE. The anatomic rationale for transforaminal endoscopic interbody fusion: a cadaveric analysis. Neurosurg Focus. 2016;40(2):E12.

    • Crossref
    • PubMed
    • Search Google Scholar
    • Export Citation
  • 12

    Hurday Y, Xu B, Guo L, et al. Radiographic measurement for transforaminal percutaneous endoscopic approach (PELD). Eur Spine J. 2017;26(3):635645.

  • 13

    Mayer HM, Brock M. Percutaneous endoscopic discectomy: surgical technique and preliminary results compared to microsurgical discectomy. J Neurosurg. 1993;78(2):216225.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 14

    Kambin P, Sampson S. Posterolateral percutaneous suction-excision of herniated lumbar intervertebral discs. Report of interim results. Clin Orthop Relat Res. 1986;(207):37-43.

    • Search Google Scholar
    • Export Citation
  • 15

    Wang TY, Mehta VA, Gabr M, et al. Percutaneous lumbar interbody fusion with an expandable titanium cage through Kambin’s triangle: a case series with initial clinical and radiographic results. Int J Spine Surg. 2021;15(6):11331141.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 16

    Kothari P, Lee NJ, Lakomkin N, et al. Impact of resident involvement on morbidity in adult patients undergoing fusion for spinal deformity. Spine (Phila Pa 1976). 2016;41(16):12961302.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 17

    Lee NJ, Kothari P, Kim C, et al. The impact of resident involvement in elective posterior cervical fusion. Spine (Phila Pa 1976). 2018;43(5):316323.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 18

    Pugely AJ, Gao Y, Martin CT, Callagh JJ, Weinstein SL, Marsh JL. The effect of resident participation on short-term outcomes after orthopaedic surgery. Clin Orthop Relat Res. 2014;472(7):22902300.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 19

    Seicean A, Kumar P, Seicean S, Neuhauser D, Selman WR, Bambakidis NC. Impact of resident involvement in neurosurgery: an American College of Surgeons’ National Surgical Quality Improvement Program database analysis of 33,977 patients. Neurospine. 2018;15(1):5465.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 20

    Tabarestani TQ, Maquoit G, Wang T, et al. Novel merging of CT and MRI to allow for safe navigation into Kambin’s triangle for percutaneous lumbar interbody fusion—initial case series investigating safety and efficacy Case series. Oper Neurosurg (Hagerstown). In press.

    • Search Google Scholar
    • Export Citation
  • 21

    Fan G, Liu H, Wang D, et al. Deep learning-based lumbosacral reconstruction for difficulty prediction of percutaneous endoscopic transforaminal discectomy at L5/S1 level: a retrospective cohort study. Int J Surg. 2020;82:162169.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 22

    Dalton T, Sykes D, Wang TY, et al. Robotic-assisted trajectory into Kambin’s triangle during percutaneous transforaminal lumbar interbody fusion-initial case series investigating safety and efficacy. Oper Neurosurg (Hagerstown). 2021;21(6):400408.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 23

    Ruetten S, Komp M, Merk H, Godolias G. Full-endoscopic interlaminar and transforaminal lumbar discectomy versus conventional microsurgical technique: a prospective, randomized, controlled study. Spine (Phila Pa 1976). 2008;33(9):931939.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 24

    Yeung AT, Tsou PM. Posterolateral endoscopic excision for lumbar disc herniation: surgical technique, outcome, and complications in 307 consecutive cases. Spine (Phila Pa 1976). 2002;27(7):722731.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 25

    Morgenstern C, Yue JJ, Morgenstern R. Full percutaneous transforaminal lumbar interbody fusion using the facet-sparing, trans-Kambin approach. Clin Spine Surg. 2020;33(1):4045.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 26

    Choi I, Ahn JO, So WS, Lee SJ, Choi IJ, Kim H. Exiting root injury in transforaminal endoscopic discectomy: preoperative image considerations for safety. Eur Spine J. 2013;22(11):24812487.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 27

    Hurday Y, Xu B, Guo L, et al. Radiographic measurement for transforaminal percutaneous endoscopic approach (PELD). Eur Spine J. 2017;26(3):635645.

  • 28

    Ruetten S, Komp M, Godolias G. A New full-endoscopic technique for the interlaminar operation of lumbar disc herniations using 6-mm endoscopes: prospective 2-year results of 331 patients. Minim Invasive Neurosurg. 2006;49(2):8087.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 29

    Fujita M, Kawano H, Kitagawa T, et al. Preoperative design for the posterolateral approach in full-endoscopic spine surgery for the treatment of L5/S1 lumbar disc herniation. Neurospine. 2019;16(1):105112.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 30

    Silva PS, Pereira P, Monteiro P, Silva PA, Vaz R. Learning curve and complications of minimally invasive transforaminal lumbar interbody fusion. Neurosurg Focus. 2013;35(2):E7.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 31

    Lee JC, Jang HD, Shin BJ. Learning curve and clinical outcomes of minimally invasive transforaminal lumbar interbody fusion: our experience in 86 consecutive cases. Spine (Phila Pa 1976). 2012;37(18):15481557.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 32

    Lee KH, Yeo W, Soeharno H, Yue WM. Learning curve of a complex surgical technique: minimally invasive transforaminal lumbar interbody fusion (MIS TLIF). J Spinal Disord Tech. 2014;27(7):E234E240.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 33

    Chen W, Zheng Y, Liang G, Chen G, Hu Y. Clinical effects of transforaminal approach vs interlaminar approach in treating lumbar disc herniation: a clinical study protocol. Medicine (Baltimore). 2020;99(44):e22701.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 34

    Zhou Z, Ni HJ, Zhao W, et al. Percutaneous endoscopic lumbar discectomy via transforaminal approach combined with interlaminar approach for L4/5 and L5/S1 two-level disc herniation. Orthop Surg. 2021;13(3):979988.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 35

    Sakane M. Anatomical relationship between Kambin’s triangle and exiting nerve root. Mini-Invasive Surg. 2017;1:99102.

  • 36

    Son S, Ahn Y, Lee SG, et al. Learning curve of percutaneous endoscopic transforaminal lumbar discectomy by a single surgeon. Medicine (Baltimore). 2021;100(4):e24346.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 37

    Sharif S, Afsar A. Learning curve and minimally invasive spine surgery. World Neurosurg. 2018;119:472478.

  • 38

    Sclafani JA, Kim CW. Complications associated with the initial learning curve of minimally invasive spine surgery: a systematic review. Clin Orthop Relat Res. 2014;472(6):17111717.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 39

    Ahn SS, Kim SH, Kim DW. Learning curve of percutaneous endoscopic lumbar discectomy based on the period (early vs. late) and technique (in-and-out vs. in-and-out-and-in): a retrospective comparative study. J Korean Neurosurg Soc. 2015;58(6):539546.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 40

    Edelstein AI, Lovecchio FC, Saha S, Hsu WK, Kim JY. Impact of resident involvement on orthopaedic surgery outcomes: an analysis of 30,628 patients from the American College of Surgeons National Surgical Quality Improvement Program database. J Bone Joint Surg Am. 2014;96(15):e131.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 41

    Patel VV, Andersson GBJ, Garfin SR, Resnick DL, Block JE. Utilization of CT scanning associated with complex spine surgery. BMC Musculoskelet Disord. 2017;18(1):52.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 42

    Dougherty G, Newman D. Measurement of thickness and density of thin structures by computed tomography: a simulation study. Med Phys. 1999;26(7):13411348.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 43

    Rajasekaran S, Vaccaro AR, Kanna RM, et al. The value of CT and MRI in the classification and surgical decision-making among spine surgeons in thoracolumbar spinal injuries. Eur Spine J. 2017;26(5):14631469.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 44

    Kumar Y, Hayashi D. Role of magnetic resonance imaging in acute spinal trauma: a pictorial review. BMC Musculoskelet Disord. 2016;17:310.

  • 45

    Hirayama J, Hashimoto M, Sakamoto T. Clinical outcomes based on preoperative Kambin’s triangular working zone measurements on 3D CT/MR fusion imaging to determine optimal approaches to transforaminal endoscopic lumbar diskectomy. J Neurol Surg A Cent Eur Neurosurg. 2020;81(4):302309.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 46

    Yamada K, Nagahama K, Abe Y, Hyugaji Y, Takahata M, Iwasaki N. Morphological analysis of Kambin’s triangle using 3D CT/MRI fusion imaging of lumbar nerve root created automatically with artificial intelligence. Eur Spine J. 2021;30(8):21912199.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 47

    Waguia R, Gupta N, Gamel KL, Ukachukwu A. Current and future applications of the Kambin’s triangle in lumbar spine surgery. Cureus. 2022;14(6):e25686.

    • Search Google Scholar
    • Export Citation
  • 48

    Haijiao W, Koti M, Smith FW, Wardlaw D. Diagnosis of lumbosacral nerve root anomalies by magnetic resonance imaging. J Spinal Disord. 2001;14(2):143149.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 49

    Scuderi GJ, Vaccaro AR, Brusovanik GV, Kwon BK, Berta SC. Conjoined lumbar nerve roots: a frequently underappreciated congenital abnormality. J Spinal Disord Tech. 2004;17(2):8693.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 50

    Simon JI, McAuliffe M, Smoger D. Location of radicular spinal arteries in the lumbar spine from analysis of CT angiograms of the abdomen and pelvis. Pain Med. 2016;17(1):4651.

    • Search Google Scholar
    • Export Citation
  • 51

    Zhang L, Yang J, Hai Y, et al. Relationship of the exiting nerve root and superior articular process in Kambin’s triangle: assessment of lumbar anatomy using cadavers and computed tomography imaging. World Neurosurg. 2020;137:e336e342.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 52

    Hogan Q. Size of human lower thoracic and lumbosacral nerve roots. Anesthesiology. 1996;85(1):3742.

  • 53

    Liu Y, Zhou X, Ma J, Ge Y, Cao X. The diameters and number of nerve fibers in spinal nerve roots. J Spinal Cord Med. 2015;38(4):532537.

    • Crossref
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    • Export Citation
  • 54

    Cole TJ, Altman DG. Statistics notes: what is a percentage difference? BMJ. 2017;358:j3663.

  • Collapse
  • Expand

Illustration from Chan et al. (E2). © Andrew K. Chan, published with permission.

  • View in gallery
    FIG. 1.

    Anatomical boundaries of Kambin’s triangle (green triangle). Reproduced from Yeung A, Gore S. Endoscopic foraminal decompression for failed back surgery syndrome under local anesthesia. Int J Spine Surg. 2014;8:22. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4325507/#__ffn_sectitle. © 2014 ISASS—International Society for the Advancement of Spine Surgery, published with permission. CC BY-NC 3.0 (https://creativecommons.org/licenses/by-nc/3.0/).

  • View in gallery
    FIG. 2.

    Using PRISMA guidelines, we systematically searched the PubMed, Ovid, Cochrane, Embase, Scopus, and Medline databases for English-language articles with no time frame restrictions through July 2022. Studies were included if the goal of the study was to measure the area of Kambin’s triangle. Exclusion criteria included studies investigating the size of the cannula or relationships of the cannula to Kambin’s triangle.

  • View in gallery
    FIG. 3.

    Linear regression models for the mean area of Kambin’s triangle at each lumbar level when SAP was maintained (blue) and removed (orange). Linear fit equation when the SAP was maintained: y = 9.767x + 52.601, with R2 = 0.9301. Linear fit equation when the SAP was removed: y = 12.529x + 121.09, with R2 = 0.9658.

  • 1

    Kambin P, Gellman H. Percutaneous lateral discectomy of the lumbar spine a preliminary report. Clin Orthop Relat Res. 1983;174:127132.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 2

    Fanous AA, Tumialán LM, Wang MY. Kambin’s triangle: definition and new classification schema. J Neurosurg Spine. 2020;32(3):390398.

  • 3

    Yeung A, Gore S. Endoscopic foraminal decompression for failed back surgery syndrome under local anesthesia. Int J Spine Surg. 2014;8:22.

  • 4

    König A, Joseph F, Janse van Rensburg C, Myburgh J, Keough N. Kambin’s triangle and the position of the dorsal nerve root in the lumbar neural foramen. Clin Anat. 2020;33(8):12041213.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 5

    Hoshide R, Feldman E, Taylor W. Cadaveric analysis of the Kambin’s triangle. Cureus. 2016;8(2):e475.

  • 6

    Ozer AF, Suzer T, Can H, et al. Anatomic assessment of variations in Kambin’s triangle: a surgical and cadaver study. World Neurosurg. 2017;100:498503.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 7

    Pairaiturkar PP, Sudame OS, Pophale CS. Evaluation of dimensions of Kambin’s triangle to calculate maximum permissible cannula diameter for percutaneous endoscopic lumbar discectomy: a 3-dimensional magnetic resonance imaging based study. J Korean Neurosurg Soc. 2019;62(4):414421.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 8

    Zhang L, Yang J, Hai Y, et al. Relationship of the exiting nerve root and superior articular process in Kambin’s triangle: assessment of lumbar anatomy using cadavers and computed tomography imaging. World Neurosurg. 2020;137:e336e342.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 9

    Kumari C, Gupta T, Gupta R, et al. Cadaveric anatomy of the lumbar triangular safe zone of Kambin’s in North West Indian population. Anat Cell Biol. 2021;54(1):3541.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 10

    Lertudomphonwanit T, Keorochana G, Kraiwattanapong C, Chanplakorn P, Leelapattana P, Wajanavisit W. Anatomic considerations of intervertebral disc perspective in lumbar posterolateral approach via Kambin’s triangle: cadaveric study. Asian Spine J. 2016;10(5):821827.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 11

    Hardenbrook M, Lombardo S, Wilson MC, Telfeian AE. The anatomic rationale for transforaminal endoscopic interbody fusion: a cadaveric analysis. Neurosurg Focus. 2016;40(2):E12.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 12

    Hurday Y, Xu B, Guo L, et al. Radiographic measurement for transforaminal percutaneous endoscopic approach (PELD). Eur Spine J. 2017;26(3):635645.

  • 13

    Mayer HM, Brock M. Percutaneous endoscopic discectomy: surgical technique and preliminary results compared to microsurgical discectomy. J Neurosurg. 1993;78(2):216225.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 14

    Kambin P, Sampson S. Posterolateral percutaneous suction-excision of herniated lumbar intervertebral discs. Report of interim results. Clin Orthop Relat Res. 1986;(207):37-43.

    • Search Google Scholar
    • Export Citation
  • 15

    Wang TY, Mehta VA, Gabr M, et al. Percutaneous lumbar interbody fusion with an expandable titanium cage through Kambin’s triangle: a case series with initial clinical and radiographic results. Int J Spine Surg. 2021;15(6):11331141.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 16

    Kothari P, Lee NJ, Lakomkin N, et al. Impact of resident involvement on morbidity in adult patients undergoing fusion for spinal deformity. Spine (Phila Pa 1976). 2016;41(16):12961302.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 17

    Lee NJ, Kothari P, Kim C, et al. The impact of resident involvement in elective posterior cervical fusion. Spine (Phila Pa 1976). 2018;43(5):316323.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 18

    Pugely AJ, Gao Y, Martin CT, Callagh JJ, Weinstein SL, Marsh JL. The effect of resident participation on short-term outcomes after orthopaedic surgery. Clin Orthop Relat Res. 2014;472(7):22902300.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 19

    Seicean A, Kumar P, Seicean S, Neuhauser D, Selman WR, Bambakidis NC. Impact of resident involvement in neurosurgery: an American College of Surgeons’ National Surgical Quality Improvement Program database analysis of 33,977 patients. Neurospine. 2018;15(1):5465.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 20

    Tabarestani TQ, Maquoit G, Wang T, et al. Novel merging of CT and MRI to allow for safe navigation into Kambin’s triangle for percutaneous lumbar interbody fusion—initial case series investigating safety and efficacy Case series. Oper Neurosurg (Hagerstown). In press.

    • Search Google Scholar
    • Export Citation
  • 21

    Fan G, Liu H, Wang D, et al. Deep learning-based lumbosacral reconstruction for difficulty prediction of percutaneous endoscopic transforaminal discectomy at L5/S1 level: a retrospective cohort study. Int J Surg. 2020;82:162169.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 22

    Dalton T, Sykes D, Wang TY, et al. Robotic-assisted trajectory into Kambin’s triangle during percutaneous transforaminal lumbar interbody fusion-initial case series investigating safety and efficacy. Oper Neurosurg (Hagerstown). 2021;21(6):400408.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 23

    Ruetten S, Komp M, Merk H, Godolias G. Full-endoscopic interlaminar and transforaminal lumbar discectomy versus conventional microsurgical technique: a prospective, randomized, controlled study. Spine (Phila Pa 1976). 2008;33(9):931939.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 24

    Yeung AT, Tsou PM. Posterolateral endoscopic excision for lumbar disc herniation: surgical technique, outcome, and complications in 307 consecutive cases. Spine (Phila Pa 1976). 2002;27(7):722731.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 25

    Morgenstern C, Yue JJ, Morgenstern R. Full percutaneous transforaminal lumbar interbody fusion using the facet-sparing, trans-Kambin approach. Clin Spine Surg. 2020;33(1):4045.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 26

    Choi I, Ahn JO, So WS, Lee SJ, Choi IJ, Kim H. Exiting root injury in transforaminal endoscopic discectomy: preoperative image considerations for safety. Eur Spine J. 2013;22(11):24812487.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 27

    Hurday Y, Xu B, Guo L, et al. Radiographic measurement for transforaminal percutaneous endoscopic approach (PELD). Eur Spine J. 2017;26(3):635645.

  • 28

    Ruetten S, Komp M, Godolias G. A New full-endoscopic technique for the interlaminar operation of lumbar disc herniations using 6-mm endoscopes: prospective 2-year results of 331 patients. Minim Invasive Neurosurg. 2006;49(2):8087.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 29

    Fujita M, Kawano H, Kitagawa T, et al. Preoperative design for the posterolateral approach in full-endoscopic spine surgery for the treatment of L5/S1 lumbar disc herniation. Neurospine. 2019;16(1):105112.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 30

    Silva PS, Pereira P, Monteiro P, Silva PA, Vaz R. Learning curve and complications of minimally invasive transforaminal lumbar interbody fusion. Neurosurg Focus. 2013;35(2):E7.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 31

    Lee JC, Jang HD, Shin BJ. Learning curve and clinical outcomes of minimally invasive transforaminal lumbar interbody fusion: our experience in 86 consecutive cases. Spine (Phila Pa 1976). 2012;37(18):15481557.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 32

    Lee KH, Yeo W, Soeharno H, Yue WM. Learning curve of a complex surgical technique: minimally invasive transforaminal lumbar interbody fusion (MIS TLIF). J Spinal Disord Tech. 2014;27(7):E234E240.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 33

    Chen W, Zheng Y, Liang G, Chen G, Hu Y. Clinical effects of transforaminal approach vs interlaminar approach in treating lumbar disc herniation: a clinical study protocol. Medicine (Baltimore). 2020;99(44):e22701.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 34

    Zhou Z, Ni HJ, Zhao W, et al. Percutaneous endoscopic lumbar discectomy via transforaminal approach combined with interlaminar approach for L4/5 and L5/S1 two-level disc herniation. Orthop Surg. 2021;13(3):979988.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 35

    Sakane M. Anatomical relationship between Kambin’s triangle and exiting nerve root. Mini-Invasive Surg. 2017;1:99102.

  • 36

    Son S, Ahn Y, Lee SG, et al. Learning curve of percutaneous endoscopic transforaminal lumbar discectomy by a single surgeon. Medicine (Baltimore). 2021;100(4):e24346.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 37

    Sharif S, Afsar A. Learning curve and minimally invasive spine surgery. World Neurosurg. 2018;119:472478.

  • 38

    Sclafani JA, Kim CW. Complications associated with the initial learning curve of minimally invasive spine surgery: a systematic review. Clin Orthop Relat Res. 2014;472(6):17111717.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 39

    Ahn SS, Kim SH, Kim DW. Learning curve of percutaneous endoscopic lumbar discectomy based on the period (early vs. late) and technique (in-and-out vs. in-and-out-and-in): a retrospective comparative study. J Korean Neurosurg Soc. 2015;58(6):539546.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 40

    Edelstein AI, Lovecchio FC, Saha S, Hsu WK, Kim JY. Impact of resident involvement on orthopaedic surgery outcomes: an analysis of 30,628 patients from the American College of Surgeons National Surgical Quality Improvement Program database. J Bone Joint Surg Am. 2014;96(15):e131.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 41

    Patel VV, Andersson GBJ, Garfin SR, Resnick DL, Block JE. Utilization of CT scanning associated with complex spine surgery. BMC Musculoskelet Disord. 2017;18(1):52.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 42

    Dougherty G, Newman D. Measurement of thickness and density of thin structures by computed tomography: a simulation study. Med Phys. 1999;26(7):13411348.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 43

    Rajasekaran S, Vaccaro AR, Kanna RM, et al. The value of CT and MRI in the classification and surgical decision-making among spine surgeons in thoracolumbar spinal injuries. Eur Spine J. 2017;26(5):14631469.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 44

    Kumar Y, Hayashi D. Role of magnetic resonance imaging in acute spinal trauma: a pictorial review. BMC Musculoskelet Disord. 2016;17:310.

  • 45

    Hirayama J, Hashimoto M, Sakamoto T. Clinical outcomes based on preoperative Kambin’s triangular working zone measurements on 3D CT/MR fusion imaging to determine optimal approaches to transforaminal endoscopic lumbar diskectomy. J Neurol Surg A Cent Eur Neurosurg. 2020;81(4):302309.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 46

    Yamada K, Nagahama K, Abe Y, Hyugaji Y, Takahata M, Iwasaki N. Morphological analysis of Kambin’s triangle using 3D CT/MRI fusion imaging of lumbar nerve root created automatically with artificial intelligence. Eur Spine J. 2021;30(8):21912199.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 47

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