Lumbar Foraminal Morphology Can Affect Outcomes of Indirect Decompression: A Systematic Review and Novel Classification

Abstract

Study Design

Systematic review.

Objective

To identify and classify intervertebral foraminal morphologies associated with failed indirect decompression (IND), with the goal of developing a preoperative classification system to assess candidacy for this procedure.

Methods

A systematic review of PubMed, EMBASE, and Google Scholar was conducted. All reported cases of failed indirect decompression secondary to abnormal foraminal morphology were included. Imaging findings were reviewed to identify distinct morphological patterns.

Results

Thirteen studies describing 22 patients with failed indirect decompression due to abnormal foraminal morphology were identified. Four distinct imaging patterns were observed: (1) hypertrophic superior articular process variant, (2) prominent posterior inferior osteophyte variant, (3) osseous ring variant, and (4) foramen crowded by disco-ligamentous material variant.

Conclusions

We propose a simple, intuitive classification system for preoperative evaluation of the foramen in candidates for indirect decompression. Each variant is presented with supporting literature implicating it in failed indirect decompression. Future studies should aim to determine the prevalence, clinical significance, and failure rates associated with each morphology type.

Keywords

indirect decompression (IND)direct decompression foraminal morphology foraminal stenosis lumbar interbody fusion nerve root compression

Introduction

Indirect decompression (IND) of the neural elements in the lumbar spine is rapidly gaining popularity among spine surgeons.¹ IND relies on the application of distraction forces on adjacent vertebrae through the entered disc space.² This typically involves the use of spacers that are positioned between vertebral bodies to elevate the disc space and restore foraminal height. This elevation is crucial as it progressively separates the vertebral bodies, thereby enlarging the intervening foramina and achieving indirect nerve root decompression.² Indirect central canal decompression, on the other hand, relies on slip reduction via ligamentotaxis, stretching as well as eventual remodeling of the posterior longitudinal ligament and ligamentum flavum.^3,4 In addition, a major advantage of IND is that it obviates the necessity for osseous resection or direct manipulation of neural tissue. Realized advantages of this strategy include decreased blood loss, shorter operative times, fewer incidents of durotomy and cerebrospinal fluid leak, as well as better achievement of spinal alignment goals compared to direct decompression strategies.^2,5

Despite these observed high radiographic and clinical success rates of IND, there remain instances where this strategy fails.^6-8 Failure of IND may occur due to inadequate segment mobilization in the setting of an ankylosed segment, graft subsidence, or persistent bony stenosis that fails to respond to disc height restoration. Yingsakmongkol et al reported that preoperative reducible disc height and low postoperative disc height are significantly associated with an increased risk of failure in indirect decompression during lateral spine surgery.⁹ Postoperative graft subsidence can significantly contribute to IND failure through the loss of intervertebral disc height restoration, notably in patients with poor bone quality.^9,10 Additionally, patient selection also plays a critical role, particularly in cases involving patients with bony or significant soft tissue stenosis.¹¹ Efforts have been made to understand why IND fails and who may benefit from concurrent direct decompression (DD), yet prediction models remain imperfect.^6,10

There have been recent reports where authors report cases with either failed IND, or worsening sciatica secondary to what they believe were particular foraminal osteophytes or morphologies.^12-14 Considering that spine surgery aims to apply distraction and lordosing forces on adjacent vertebrae, it was hypothesized that certain foraminal pathology may in fact be associated with unfavorable surgical outcomes.

We therefore conducted a literature review to collect all published cases where foraminal morphologies were believed to result in the failure of indirect foraminal decompression. The aim of this review is to systematically search the literature for all reported cases of failed IND secondary to foraminal morphology, and propose a classification system to standardize their incorporation into the preoperative evaluation of these patients.

Materials and Methods

Research Questions

1. What preoperative imaging features of the intervertebral foramen are associated with instances of IND failure or symptom worsening?

2. Are there recurring variants that can be incorporated into a classification system?

3. Which surgical procedures are at the highest risk for requiring secondary procedures?

4. How are these failure instances best managed? Does management differ according to the specific variant?

Search Strategy

We systematically searched PubMed and EMBASE databases for articles that discussed indirect decompression failure. We supplemented our search with the use of Google Scholar database. In our search, we used a combination of the following terms: ‘lumbar spine,’ ‘intervertebral foramen,’ ‘foraminal stenosis,’ ‘osteophyte,’ ‘indirect decompression,’ and ‘indirect decompression failure.’ The procedures we included were ‘Transforaminal Lumbar Interbody Fusion (TLIF),' ‘Oblique Lumbar Interbody Fusion (OLIF),' ‘Anterior Lumbar Interbody Fusion (ALIF),' as well as ‘transpsoas lumbar interbody fusion,’ ‘pre-psoas lumbar interbody fusion,’ ‘anterior to the psoas lumbar interbody fusion,’ and ‘ante-psoas lumbar interbody fusion’. This systematic review was not registered in PROSPERO or any other systematic review database. Studies were retrieved and screened by OA, RFB and KB for inclusion. Disagreement was ultimately reconciled by discussion with MAB.

Inclusion/Exclusion Criteria

We included all the articles detailing cases of lumbar IND failures or the need for reoperation due to foraminal factors. We evaluated the full-text manuscripts of all such articles describing failures to see if images or descriptions of the foramina involved were provided. All study types were included, limited to English-language publications without any date restrictions. Studies were excluded if they did not report true indirect decompression failure due to foraminal pathology or if they lacked adequate morphological detail. Articles outside the scope of lumbar interbody indirect decompression (eg, non-lumbar pathology, endoscopic decompressions, laminectomy-only procedures), studies reporting no failure events, or papers that did not identify the specific site/mechanism of compression were also excluded.

Data Extraction

Once studies were included, we extracted data on sample size, demographics, procedural details (including alignment changes), levels involved, clinical presentation of failure, foraminal characteristics, and complication management. Based on these factors, we attempted to develop an inclusive classification system that can help guide management.

Results

Our search retrieved a total of 2516 articles. After removing duplicates and conducting initial screening, 192 abstracts were selected for review. Subsequently, 153 manuscripts were chosen for full-text evaluation. After applying inclusion and exclusion criteria, 13 studies describing 22 patients were included in our review.^12-25 A detailed summary of the study selection process is presented in Figure 1, and the summary of all included articles is outlined in Table 1.

Figure 1.

PRISMA flow diagram depicting the search process and study selection

Table 1.

Retrieved Studies of Indirect Decompression Failure Secondary to Foraminal Morphological Variants

Study no.	Author, year	Patient no.		Level	Surgery	Symptoms	Need for revision	Morphology	Underlying mechanism
Variant 1 hSAP cases
1	Chen 2021¹²	1		L4-5	L4-5 TLIF L4-S1 PSF	L4 radiculopathy	Direct decompression	hSAP	Increased lordosis
1	Chen 2021¹²	2		L4-5	L4-5 TLIF L4-S1 PSF	L4 radiculopathy	Direct decompression	hSAP	Increased lordosis
2	Choi 2011¹³	3	62F	L5-S1	ALIF with PSF - No decomp	Right L5 radiculopathy	Direct decompression	hSAP	Increased lordosis
3	Compagnone 2022¹⁹	4		L5-S1	ALIF with PSF - No decomp	L5 radiculopathy	Self-resolving	hSAP	Increased lordosis
4	Konbaz 2023¹⁷	5	63F	L3-4	L3-L5 PSF	Left L3 radiculopathy	Left L3-4 facetectomy	hSAP	Increased lordosis
		6	59F	L3-4	L3-4 TLIF above L4-5 fusion	Left L3 radiculopathy	Left L3-4 foraminotomy	hSAP	Increased lordosis
		7	50F	L4-5	L3-5 PSF with left L4-5 TLIF	Right L4 radiculopathy	Right L4-5 foraminotomy	hSAP	Increased lordosis
5	Hu 2017²¹	8	58M	L5-S1	L4-S1 TLIF	Left L5 radiculopathy	Facetectomy	hSAP	Increased lordosis
5	Hu 2017²¹	9	54M	L4-5	L4-5 TLIF	Left L4 radiculopathy	Facetectomy	hSAP	Increased lordosis
6	Lu 2023²⁴	10	56F	L4-5	L4-S1 TLIF	L4 radiculopathy	Direct decompression	hSAP	Increased lordosis
7	Jang 2015¹⁸	11	NA	NA	Contralateral TLIF	Contralateral radiculopathy	Not reported	hSAP	Increased lordosis
8	Neal 2021²⁵	12		L5-S1	L4-S1 ALIF with PSF - No decomp	L5 radiculopathy	L5-S1 facetectomy	hSAP	Increased lordosis
9	Nakashima 2019¹⁴	13	65F	L4-5	L3-4 and L4-5 LLIF with PSF - No decomp	L4 radiculopathy	Direct decompression	hSAP	Increased lordosis
Variant 2 P.I. Osteophytes
10	Dowlati 2020¹⁵	14		L5-S1	Stand-alone ALIF, A large implant: 16 mm height, 12° lordosis	Right L5 radiculopathy	Medically managed and not revised	P.I. osteophyte	Lordosis and distraction
		15		L5-S1	Stand-alone ALIF, 13 mm height, 12° of lordosis	Left L5 radiculopathy	Direct decompression	P.I. osteophyte	Lordosis and distraction
		16		L5-S1	Stand-alone ALIF at L5–S1 16 mm height, 8° of lordosis	Right L5 radiculopathy	Facetectomy and fixation	P.I. osteophyte	Lordosis and distraction
11	Lee 2021²³	17	78M	L4-5	L4-5 OLIF	L4 radiculopathy	Direct decompression	P.I. osteophyte	Distraction
Variant 3: Osseous ring (converging sublaminar ridge and P.I. osteophyte)
12	Malham 2015¹⁶	18	59M	L4-5	L4-5 stand alone LLIF	“Leg pain”	Direct decompression and L4-5 PSF	P.I. osteophyte with sublaminar ridge	Distraction
Variant 4: Foramen occupied by disc material
13	Hunt 2007²²	19	65F	L4-5	L4-5 TLIF	L4 radiculopathy	Epidural steroid injections	Mostly disc + ligamentum flavum	Increased lordosis and packing disc space with cage and graft
13	Jang 2015¹⁸	20-22	NA	NA	Contralateral TLIF	Contralateral radiculopathy	Direct decompression in one	Mostly disc + ligamentum flavum	Increased lordosis and packing disc space with cage and graft

Patient and Index Procedure Characteristics

Analysis of the reported cases revealed that the L4-5 level was the most frequently affected, with 9 cases accounting for 40.9%, followed by L5-S1 with 7 cases (31.8%), and then L3-4 with 2 cases (9.1%). No level was mentioned in the remaining 4 cases. Nine patients developed new or worsening radiculopathies after undergoing anterior or lateral lumbar approaches (40.9%), while 13 patients experienced similar complications following the TLIF procedure (59.1%).

Foraminal Morphology

When analyzing the included articles, we made several observations. Regarding foraminal patterns, we identified 4 main variants that accounted for postoperative complications secondary to foraminal morphology. The first variant is the hypertrophied superior articular process (hSAP), which was found to extend superiorly up to the level of the nerve root in the foramen.²⁶ Second is the posterior inferior osteophyte (P.I. osteophyte), seen extending from the lower endplate of the upper vertebra posteriorly and forming a tethering shelf under the nerve root. This P.I. osteophyte variant, in one case, was accompanied by a prominent sublaminar ridge which together converge to form an osseous ring (OssR), the third variant. Figure 2 shows radiographic examples of each of these 3 variants. Four additional cases^18,22 were secondary to worsened herniation on the contralateral side with posterior element compression during a TLIF (variant 4: the disco-ligamentous variant). Figure 3 illustrates each of these variants and demonstrates the morphological changes post-indirect decompression, highlighting the proposed mechanism in these cases.

Figure 2.

Radiological images of the variants presented in this article, derived from clinical cases. (A) Variant 1: hSAP. Left: Shows a CT scan that illustrates the hSAP variant (yellow arrow). Right: A T2 MRI showing the evidence and degree of foraminal stenosis secondary to hSAP (red arrow). (B) Variant 2: P.I. Osteophyte. Example 1: Left: A CT scan and right: An MRI showing the P.I. osteophyte variant, with the bony ridge acting as a shelf under the nerve root, tethering it as the disc space is distracted (yellow arrow on the CT scan and red arrow on the MRI). Similarly, Example 2: Left: A CT scan and right: An MRI with severe compromise of the foramen secondary to P.I. osteophytes (yellow and red arrows, respectively). (C) Variant 3: OssR. This CT scan shows the sublaminar ridge that almost unites with the anterior P.I. osteophyte to form the OssR variant (yellow arrow)

Figure 3.

Comparative illustrations of foraminal morphological variants and their responses to indirect decompression. [1] Normal Morphology. (1A) The Blue arrow indicates a normal disc, the orange arrow points to the nerve root, and the green arrow points to the ligamentum flavum. (1B) Demonstrates indirect decompression in normal foraminal morphology showing an increase in foraminal height resulting in decompression of the nerve root. [2] Variant 1: hSAP. (2A) Shows a hypertrophied SAP (blue arrow) that encroaches on the nerve root and compromises the canal space. (2B) Demonstrates hSAP post-IND with evidence of increased compression of the nerve root (red arrow) by the hypertrophied SAP (blue arrow) secondary to the lordosis gained at that level. [3] Variant 2: P.I. Osteophyte. (3A) Shows evidence of disc degeneration with loss of disc height and the presence of a P.I. osteophyte forming a hook around the inferior aspect of the nerve root (black arrow). (3B) Shows increased disc height post-IND with an upward tethering of the nerve root secondary to being pulled up by the P.I. hook (black arrow). [4] Variant 3: Osseous Ring (OssR). (4A) Shows evidence of P.I. osteophytes (black arrow) in addition to a sublaminar ridge (red arrow) forming a semi-complete ring around the inferior aspect of the foramen. (4B) Demonstrates upward movement of the nerve root with the ring resulting in nerve root compromise post-IND. [5] Variant 4: Disco-ligamentous Variant. (5A) Shows evidence of a full foraminal fullness with a hypertrophied ligamentum flavum (green arrow) and disc fragments (black arrow). (5B) Shows no improvement in nerve root compression with indirect decompression with evidence of nerve root compression (red arrow)

Mechanism of Neural Element Compression Secondary to Foraminal Morphology

Reviewing the postoperative films in our included articles revealed that the foraminal morphology variants resulted in iatrogenic nerve root compression post-indirect decompression via different mechanisms. Variant 1. The hSAP variant was implicated in cases where lordosis was induced by the procedure. This causes the hSAP to displace anteriorly in the already stenotic foramen and compress the exiting nerve root against the posterior vertebral body. This is made more likely when posterior disc height is not restored (anterior fishmouth opening) as would be expected in some TLIFs, or ALIFs with hyperlordotic cages. Distraction will displace the hSAP inferiorly in the widened foramen and minimize the chances of impinging on the exiting nerve root (Figure 3. 2A-2B). Variant 2. The P.I. osteophyte variant. This variant tends to be implicated in cases where disc space distraction occurs regardless of lordosis. As this osteophyte grows and extends posteriorly forming a shelf beneath the nerve root, it prevents the increased foraminal cross-sectional area afforded by distraction from translating into added space for the nerve root. In addition, as disc distraction stretches the nerve root, the P.I. may act as an inferior hook, causing a point of tethering. (Figure 3. 3A-3B). This point is only made more obvious when it is accompanied by a large sublaminar ridge, with them together forming an osseous ring (OssR; Variant 3) (Figure 3. 4A-4B). As the height restorative effect of ALIFs is well known to be superior to TLIFs, none of the cases attributed to this configuration occurred in patients undergoing TLIFs (Table 1). This may change in the future as expandable TLIF cages gain wider adoption.

Variant 4 is the foramen already stenosed from the foraminal disco-ligamentous complex. This variant appears specific to TLIFs that attempt to achieve lordosis via aggressive compression. These factors may push more disc material into the contralateral foramen, as well as induce ligamentum flavum buckling into the foramen. These events all converge to worsen pre-morbid nerve root compression (Figure 3. 5A-5B). We encountered four such cases in our retrieved articles,^18,22 but believe this may be under-recognized and under-reported. Table 2 summarizes the variants, implicated mechanisms, and suggested procedures for each variant.

Table 2.

Summary of the Reported Variants in This Study, the Implicated Procedures and Mechanisms, and Suggested Procedures

Variant		Implicated mechanism for indirect decompression failure	Implicated procedure	Suggested procedure
1	hSAP	Lordosis	TLIF, Hyper-lordotic ALIF	If lordosis is needed, direct decompression advised
2	P.I. Osteophyte	Distraction	ALIF, LLIF, OLIF	Needs high vigilance for osseous encirclement of the nerve root, may require direct decompression if prominent P.I. Osteophyte.
3	OssR	Distraction	ALIF, LLIF, OLIF	Needs further study, may necessitate direct decompression.
4	Disco-ligamentous stenosis	Lordosis/compression	TLIF	ALIF, OLIF, LLIF, or TLIF with bilateral decompression

Clinical Evolution and Management

Symptoms ranged from new or worsening radicular pain to sensory and motor deficits. Most patients who developed symptoms underwent DD (16 patients, 72.7%) with improvement in symptoms and deficits. Three patients were managed conservatively (13.6%) with medical management and epidural injections to good effect as well.

Discussion

Indirect decompression failure remains an area of uncertainty when counseling patients. It frequently results in repeat surgeries for DD, thereby obviating one of the main advantages of IND, and incurring additional costs with associated risk of complications.^7,9,10 In this work, we review the literature to better understand the role of foraminal morphology in the failure of indirect decompression.

The success of IND relies on distancing the vertebral bodies by disc space distraction, which in turn increases foraminal cross-sectional area.²⁷ We therefore scrutinized, whenever possible, cases and series describing instances when indirect foraminal decompression has failed in the immediate postoperative period. We focused on identifying whether these cases demonstrated foraminal morphologies that would result in foraminal narrowing with surgery or prevent its expansion. Our review collected all such cases in the published literature and demonstrated recurring patterns in both morphologies and mechanisms.

Numerous attempts have been made to describe predictors of indirect decompression failure, and multiple reviews have summarized these findings.^5,7 Kirnaz et al, in their systematic review, explored predictors of failure in indirect decompression during LLIF and identified several factors.⁷ They did not comment on foraminal morphology; instead, they suggested that direct decompression should be considered in addition to IND in cases of severe lateral recess stenosis.⁷ Surprisingly, very few have attempted to look at the foraminal morphology despite it being a known culprit for radicular pain pathogenesis and, in fact, the target for indirect decompression.^4,27 Wang et al reported cases of failed indirect decompression in extreme lateral interbody fusion (XLIF) and attempted to identify preoperative radiographic risk factors for XLIF failure.¹¹ The authors analyzed various parameters including disc height, foraminal height, and degree of stenosis, and identified bony lateral recess stenosis as being associated with the failure of indirect decompression.¹¹ Similarly, in the few papers that assessed the role of foramina in predicting indirect decompression outcomes, the main imaging parameter receiving attention is the extent of postoperative restoration of foraminal height or cross-sectional area.⁹ In fact, the only preoperative foraminal imaging features identified were “severe foraminal stenosis” in one study.¹¹ However, intuitively, this term does not discriminate between morphologies that will result in foraminal expansion with disc space distraction, vs worsening of foraminal stenosis.

In our review, we identified the main forming morphological variants that appear to recur across studies. The first morphology is that of the hypertrophied SAP (hSAP) (Figures 2A and 3. 2A-2B). This refers to the SAP encroaching superiorly reaching close proximity to the exiting nerve root in the upper foramen. This puts the nerve root at risk of being compressed with the anterior deflection of the SAP should segmental lordosis be increased. This was the mechanism most often seen with TLIFs complicated by contralateral sciatica. We believe that this morphology’s association with the TLIF procedure results from its inability to result in a significant increase in posterior disc height especially in cases relying on posterior compression to achieve lordosis. This combination of forward displacement of an enlarged hSAP without sufficient disc space distraction results in further worsening the nerve root compression in the foramen. It remains unclear whether preoperative foraminal stenosis, due to disc fragments or ligamentum flavum, contributes to the clinical findings in this group of patients, and this could be a topic for further research.

The second variant, the “P.I. osteophyte variant”, corresponds to the posterior outgrowth of the inferior bony endplate of the vertebra. As this osteophyte grows, not only does it prevent distraction from translating into gains in the foraminal cross-sectional area, but it may tether the nerve root with disc space distraction. Closely related is the third variant, the “osseous ring” morphology, which results in progressive osseous encircling of the exiting nerve root by both the P.I. osteophyte anteriorly and another foraminal osteophyte, the sublaminar ridge (SLR) posteriorly. The “osseous ring” results from these 2 osteophytes approximating and possibly eventually converging. The posteriorly based SLR is very poorly described in the literature, with few reports on its nature. A recent cadaveric study found it to be rather common, and to correspond anatomically to the hypertrophied superior bony attachment of the ligamentum flavum.²⁸ These 2 osteophytes converging to complete the osseous ring pose a unique problem, as they are both related to the upper instrumented vertebral body and hence will move in unison and will not be distanced by disc space distraction. These “P.I. osteophyte’ and “OssR” morphologies therefore constitute risk factors for indirect foraminal decompression failure with distraction.

The fourth class, “the disco-ligamentous stenosis” variant, serves as merely a reminder to the surgeon to evaluate the contralateral foramen for disco-ligamentous stenosis. Should it be significant, lordosis achieved by posterior element compression may require prophylactic direct decompression to avoid IND failure.^18,22 Another strategy is to steer towards anterior or lateral procedures in these instances as they provide powerful disc space distraction and foraminal height restoration to avoid procedure-induced disc herniation or ligament buckling into the foramen.^4,14

These summarized findings are presented to the reader in the hope that surgeons may add inspection of the foraminal configurations to their routine preoperative checklist. This may help in approach selection, as well as understanding what segmental manipulation can be achieved safely with each approach. We suggest that in warranted cases, such as borderline instances of potential foraminal pathology, the use of a CT scan could be beneficial. Alternatively, BoneMRI technology may serve as a radiation-free option that provides high-resolution 3D visualization of osseous structures while allowing simultaneous evaluation of both bone and soft tissue.^29-31 Furthermore, recent advancements in segmentation technology enable detailed 3D analysis of foraminal anatomy, including the nerve root, disc, thecal sac, and vertebral bodies, allowing for precise assessment of nerve root pathways and the foraminal space.^32,33 These additional imaging may enhance the surgeon’s ability to accurately delineate the anatomical relationships within the foramen, particularly between the nerve root, bony margins, and surrounding structures, thus supporting more informed and individualized preoperative planning.

Our classification also provides a unified terminology that allows these high-risk morphologies to be pooled across multi-center cohorts with the aim of better understanding their clinical relevance. If the clinical relevance of these morphologies is borne in future studies, then one can tailor the need for direct decompression according to the planned correction of that segment. Pinpointing the exact cause may also allow minimally invasive highly targeted prophylactic decompression, avoiding unnecessarily generous decompressions. Interestingly, recent work³⁴ has surfaced that calls into question the clinical relevance of the osseous ring morphology. In that study, only the lower posterior osteophyte was taken into consideration. A “high grade” P.I. osteophyte was not found to affect patient-reported outcome measures in those undergoing TLIFs or ALIFs at the L5-S1 level. In addition, no instances of revision surgery or symptom exacerbation were captured in their study. We reconcile the divergence between their conclusion and ours with a few possible hypotheses. First, the study may have been underpowered as the authors searched for this morphology within their already collected cohort. As we demonstrate in this review, several cases are documented to result from this specific variant with both imaging demonstration of nerve tethering against this osteophyte, as well as clinical response to direct decompression.^15,16,23 Second, this morphology relies on distraction to cause nerve tethering, perhaps not enough disc space distraction occurred in this cohort to induce symptoms. Third, the authors do not take into consideration other aspects of foraminal morphology that may affect its behavior with indirect decompression, this serves as further impetus for more studies into this topic. While our classification highlights recurring morphological patterns and mechanisms of indirect decompression failure, the suggested surgical considerations (Table 2) are based on the available evidence and provides a conceptual framework rather than a prescriptive treatment guide.

Regarding the optimal management of these cases, strategies varied across studies. Early surgical intervention appears appropriate in the setting of motor deficits. In cases of pain without neurological compromise, an initial period of observation and medical management, including epidural steroid injections, may reduce the need for surgery. Additionally, in select cases such as Variant 1, incorporating prophylactic transforaminal endoscopic decompression may help mitigate the risk of symptomatic IND and reduce the likelihood of requiring more extensive open surgery.

Limitations

First, this is a fragmented under-recognized topic with a lack of unifying terminology across multiple surgical techniques. As such, there is a possibility of missed studies. Second, only one study reported the prevalence of osteophytes in their surgical cohorts. However, that study did not encounter any failures and therefore no odds ratio of failure could be calculated. Third, this study does not directly determine the proportion of patients experiencing failure of indirect decompression who exhibited one of the foraminal morphologies we reported. We suggest that future research should focus on a cohort of patients who have undergone indirect decompression to assess the prevalence of these morphologies and their correlation with postoperative outcomes. This approach will help minimize potential selection bias and also provide more definitive conclusions about the extent of the role that these foraminal pathologies play in IND failure.

Conclusion and Future Research Direction

The aim of this work is to highlight this understudied component of spinal osseous anatomy and foraminal imaging appearance. We hope that by pooling these cases and presenting them to the reader, we demonstrate the rationale for further study of what role foraminal morphology has to play in case of failure despite achieving disc height restoration or segmental lordosis targets. In future studies, the reproducibility of this classification could be validated through interobserver reliability testing. Additionally, incorporating quantitative imaging thresholds: such as foraminal height, osteophyte dimensions, or superior articular process area could further enhance the objectivity and consistency of variant identification and facilitate broader clinical application. Our findings and proposed classification are intuitive, simple and serve to stimulate further research in the field.

Footnotes

ORCID iDs

Rakan Bokhari

Mohamad Bakhaidar

Abdulrahman Alnaseem

Rodrigo Navarro-Ramirez

Author Contributions

Rakan Bokhari: Conceptualization, Data Curation, Formal Analysis, Methodology, Project Administration, Supervision, Visualization, Writing – Original Draft Preparation, Writing – Review & Editing.

Mohamad Bakhaidar: Conceptualization, Methodology, Project Administration, Supervision, Visualization, Writing – Original Draft Preparation, Writing – Review & Editing.

Abdulrahman Alnaseem: Data Curation, Formal Analysis, Methodology, Writing – Review & Editing.

Khalid Bajunaid: Data Curation, Formal Analysis, Methodology, Writing – Review & Editing.

Omar Aljohani: Data Curation, Formal Analysis, Methodology, Writing – Original Draft Preparation, Writing – Review & Editing.

Mohamed Alwadai: Data Curation, Methodology, Project Administration, Visualization, Writing – Review & Editing.

Saman Shabani: Project Administration, Writing – Original Draft Preparation, Writing – Review & Editing.

Rodrigo Navarro-Ramirez: Conceptualization, Project Administration, Writing – Review & Editing.

Christoph P. Hofstetter: Conceptualization, Project Administration, Writing – Original Draft Preparation, Writing – Review & Editing.

Muhammad Abd-El-Barr: Conceptualization, Methodology, Project Administration, Supervision, Writing – Original Draft Preparation, Writing – Review & Editing.

Funding

The authors received no financial support for the research, authorship, and/or publication of this article.

Declaration of Conflicting Interests

The authors declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

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