Need for the Study

Lumbar spinal stenosis (LSS) is a progressive, degenerative condition of the aging spine and a leading cause of chronic lower back pain, neurogenic claudication, and radiculopathy. It places a massive burden on the global healthcare system and is a primary indication for lumbar spinal surgery in older adults ^[1]. However, due to age-related comorbidities or patient preference, many individuals are unsuitable for or unwilling to undergo surgical decompression. In these scenarios, epidural steroid injections (ESIs) have become a cornerstone of interventional pain management, utilized to suppress the inflammatory response, alleviate debilitating symptoms, and delay or prevent the need for surgical intervention ^[2].

Accessing the epidural space is primarily achieved through three distinct anatomical routes: the lumbar interlaminar (ILESI), transforaminal (TFESI), and caudal (CESI) approaches ^[3]. Despite the fact that ESIs are performed millions of times annually, a profound clinical dilemma persists regarding which of these three approaches yields the optimal balance of efficacy and safety for adults with LSS ^[4]. Currently, the choice of approach relies heavily on practitioner preference and training rather than a definitive, comparative evidence base, leading to conflicting societal guidelines and highly variable patient outcomes.

The existing literature presents divergent efficacy and safety profiles for these three modalities, generally evaluating only two approaches simultaneously rather than all three. Studies evaluating the interlaminar versus caudal approaches demonstrate that ILESI often yields superior short- and long-term functional recovery and pain reduction for central canal stenosis. This is theoretically due to ILESI's targeted delivery of a highly concentrated steroid directly adjacent to the stenotic segment, whereas the caudal approach is limited by mechanical flow restrictions and the need for larger injectate volumes to achieve adequate cephalad spread ^{[5, 6]}.

Conversely, head-to-head prospective trials comparing TFESI and CESI in patients with radicular symptoms have highlighted transforaminal injections as yielding statistically superior pain relief (up to 90% relief at 6 months compared to 54.5% for caudal groups) ^[7]. However, TFESI carries an elevated and well-documented risk of catastrophic, ischemic neurological complications such as spinal cord infarction particularly if particulate steroids inadvertently enter the vascular system ^[8]. Meanwhile, the caudal approach, while potentially lacking the target precision of TFESI and ILESI, remains the safest route. It carries the lowest risk of inadvertent dural puncture or neural injury, making it highly advantageous for patients with severe central canal stenosis, altered spinal anatomy, or prior surgical interventions ^[9].

Despite an abundance of fragmented data comparing two modalities at a time, there remains a critical void in the current literature: an absence of a large-scale, randomized controlled trial simultaneously comparing the efficacy and safety of all three approaches (ILESI vs. TFESI vs. CESI) in a single, standardized adult LSS cohort. As spine specialists, we require head-to-head comparative data to formulate an evidence-based clinical algorithm that guides specific injection selection. Therefore, this study aims to definitively evaluate the comparative efficacy (pain reduction and functional mobility) and safety profiles of interlaminar, transforaminal, and caudal epidural steroid injections in the management of lumbar canal stenosis in adults.

Study Design A retrospective observational study was conducted to evaluate the clinical outcomes of different epidural steroid injection techniques in adult patients diagnosed with symptomatic lumbar spinal stenosis. The study was conducted at Nandi Medical College and Research Institute, Chikkaballapur, Karnataka, India. Medical records of eligible patients treated during a six-month enrolment period were reviewed, and each patient was followed for a minimum duration of one year after the index procedure. Follow-up data for patients who subsequently received continued care at other tertiary teaching institutions in Karnataka, including Hassan Institute of Medical Sciences, were incorporated into the analysis using available clinical records and documented follow-up visits. Figure 1 Study Population The study included 143 adult patients with magnetic resonance imaging (MRI)-confirmed lumbar spinal stenosis who presented with neurogenic claudication, radicular pain, or both. The study population predominantly comprised individuals from rural communities engaged in agriculture and other forms of manual labour, where persistent pain and functional limitation had a substantial impact on daily activities and occupational performance. MRI findings demonstrated central lumbar canal stenosis in all included patients, with an average anteroposterior canal diameter of less than 12 mm. Patients with complete clinical records and regular follow-up were included in the final analysis. Patient Groups Patients were categorized according to the epidural steroid injection technique employed during treatment. Based on the anatomical approach, three groups were identified: • Interlaminar Epidural Steroid Injection (ILESI): 55 patients • Transforaminal Epidural Steroid Injection (TFESI): 45 patients • Caudal Epidural Steroid Injection (CESI): 43 patients The choice of injection technique was based on clinical evaluation, radiological findings, and the treating surgeon's judgement. Baseline Assessment Baseline demographic and clinical characteristics were recorded before intervention. These included age, sex, occupation, associated comorbidities such as diabetes mellitus and hypertension, baseline pain intensity measured using the Visual Analogue Scale (VAS), functional disability assessed using the Oswestry Disability Index (ODI), and walking distance before the onset of neurogenic claudication. Injection Technique All epidural steroid injections were performed under image guidance using standard aseptic precautions. Patients undergoing the interlaminar approach received 80 mg of methylprednisolone combined with 5 mL of 0.5% bupivacaine, producing a total injectate volume of approximately 6-7 mL to facilitate adequate spread across multiple lumbar levels. During the one-year follow-up, patients in this group received an average of 1.8 injections. For the transforaminal approach, 10 mg of dexamethasone was administered with 2 mL of 0.5% bupivacaine, resulting in a total injectate volume of 3 mL. A non-particulate corticosteroid was selected to minimise the risk of vascular and neurological complications associated with transforaminal epidural injections. Patients in this group underwent an average of 2.1 procedures during follow-up. The caudal epidural group received 80 mg of methylprednisolone mixed with 15-20 mL of 0.5% bupivacaine and normal saline. The larger injection volume was intended to promote cephalad spread of the medication towards the stenotic lumbar segments. The mean number of injections administered in this group was 2.3 over the study period. Outcome Measures Clinical outcome was evaluated using pain intensity, functional disability, and walking capacity. Pain severity was assessed with the Visual Analogue Scale (VAS), while functional status was measured using the Oswestry Disability Index (ODI). Functional ambulation was assessed by documenting the maximum walking distance before the onset of disabling neurogenic claudication. Patients were reviewed at 6 weeks, 3 months, 6 months, and 12 months following the initial intervention. Treatment success was defined as a reduction of at least 50% in the VAS score together with an improvement of 40% or more in the ODI compared with baseline values. Secondary outcome measures included the requirement for repeat epidural injections, conversion to surgical decompression during the follow-up period, procedure-related complications, and overall patient satisfaction. Statistical Analysis Data were analysed using standard statistical methods. Continuous variables were expressed as mean ± standard deviation, whereas categorical variables were presented as frequencies and percentages. Comparisons between treatment groups were performed at each follow-up interval using appropriate statistical tests. A p-value of less than 0.05 was considered statistically significant. Ninety-five percent confidence intervals were calculated where applicable to estimate the precision of treatment effects.

Baseline Characteristics

A total of 143 patients with MRI-confirmed lumbar spinal stenosis were included in the final analysis. Of these, 55 patients underwent interlaminar epidural steroid injection (ILESI), 45 received transforaminal epidural steroid injection (TFESI), and 43 were treated with the caudal epidural steroid injection (CESI) technique. All patients completed the scheduled clinical follow-up over a period of one year.

The demographic and baseline clinical characteristics of the three groups were comparable. The overall mean age of the study population was 61.1 ± 7.8 years, with males constituting 60.8% of the cohort (87/143). Nearly four-fifths of the participants (79.7%) were engaged in agricultural work or other forms of heavy manual labour, reflecting the predominantly rural population served by the participating institutions.

Diabetes mellitus and hypertension were the most frequently encountered comorbidities, affecting 52 and 66 patients, respectively. Before treatment, pain intensity and disability were severe across all three groups. The mean baseline VAS score was 8.2 ± 0.9, while the mean baseline ODI was 68.3 ± 8.3%. Similarly, walking capacity was markedly restricted, with an average pre-treatment walking distance of 171 ± 45 feet. No statistically important differences were observed in baseline characteristics among the treatment groups, indicating that the study population was reasonably comparable before intervention.

Table 1: Baseline Demographic and Clinical Characteristics of the Study Population

Pain Outcomes

All three treatment modalities produced a clinically meaningful reduction in pain during the early follow-up period. Improvement was greatest within the first six weeks after injection.

Patients treated with the interlaminar approach experienced the largest reduction in pain scores. Mean VAS decreased from 8.2 ± 0.9 at baseline to 3.2 ± 1.1 at six weeks and remained relatively stable throughout the subsequent follow-up visits, measuring 3.5 ± 1.2 at three months, 4.1 ± 1.5 at six months, and 4.6 ± 1.6 at one year.

Table 2: Comparison of Mean Visual Analogue Scale (VAS) Scores During Follow-up

Figure 2: Mean Visual Analogue Scale (VAS) Scores Over Time in the Three Treatment Groups

A comparable early response was observed in the TFESI group, with mean VAS declining to 3.0 ± 1.3 at six weeks. However, pain scores gradually increased during later follow-up, reaching 5.2 ± 1.8 at twelve months.

Patients managed with the caudal approach demonstrated comparatively smaller reductions in pain throughout the study period. Mean VAS improved to 4.6 ± 1.2 at six weeks but progressively increased to 6.5 ± 1.3 by the end of one year.

Between-group analysis demonstrated significantly lower pain scores in the ILESI group compared with the CESI group at every follow-up interval (p<0.05).

Functional Disability

Functional improvement closely paralleled the reduction in pain scores. The mean ODI decreased substantially in all three treatment groups after intervention.

Table 3: Comparison of Mean Oswestry Disability Index (ODI) scores during follow-up

Figure 3: Mean Oswestry Disability Index (ODI) Scores Over Time in the Three Treatment Groups

Patients in the ILESI group demonstrated the greatest improvement, with ODI declining from 68.4 ± 8.2% at baseline to 31.5 ± 7.2% at six weeks. Although a gradual increase in disability scores was observed during later follow-up, the functional gains remained superior to those achieved with the other treatment techniques throughout the study period.

The TFESI group also exhibited considerable improvement during the early postoperative period, whereas patients receiving caudal epidural injections consistently recorded higher disability scores at every follow-up assessment.

The differences between the interlaminar and caudal groups remained statistically significant at all evaluation intervals (p<0.05).

Walking Capacity

Walking distance improved markedly after epidural steroid injection in every treatment group.

Patients undergoing interlaminar epidural injection achieved the greatest functional recovery, with mean walking distance increasing from 172 ± 45 feet before treatment to 610 ± 120 feet at six weeks. Although a gradual decline was observed over time, walking capacity remained substantially better than baseline, measuring 440 ± 140 feet at one year.

Patients treated with the transforaminal approach demonstrated a similar but less sustained improvement, while those in the caudal group experienced comparatively modest gains throughout follow-up.

At every assessment, the interlaminar group demonstrated significantly greater walking distances than the caudal group (p<0.05).

Figure 4: Mean Walking Distance Over Time in the Three Treatment Groups

Secondary Outcomes

Repeat epidural injections were required in 14 patients (25.4%) in the ILESI group, 16 patients (35.5%) in the TFESI group, and 19 patients (44.1%) in the CESI group, indicating a greater tendency for symptom recurrence following the caudal approach.

During the one-year follow-up, 32 patients underwent surgical decompression. Conversion to surgery occurred in 9 patients (16.3%) treated with ILESI, 10 patients (22.2%) in the TFESI group, and 13 patients (30.2%) in the CESI group.

Figure 5: Percentage of Patients Who Underwent Lumbar Surger During 1-Year Follow-up

Procedure-related complications were uncommon. One inadvertent dural puncture occurred in the interlaminar group and was managed conservatively without long-term sequelae. No procedure-related infections were encountered. No catastrophic neurological complications were observed following transforaminal injections, and no dural punctures or nerve injuries occurred in the caudal group. Patient-reported satisfaction at six months was highest in the interlaminar group, where 78% of patients reported being satisfied or highly satisfied with treatment. Satisfaction rates were 71% in the TFESI group and 52% among patients who underwent caudal epidural steroid injection.

Figure 6: Patient Satisfaction at 1 Year After Epidural Steroid Injection

Figure 6: Patient Satisfaction Following Epidural Steroid Injection Among the Three Treatment Groups

The principal finding of this study is that the lumbar interlaminar approach provides the most robust and sustained relief of pain and functional disability in adults with symptomatic central spinal stenosis. Transforaminal injections yield excellent early analgesic effects that attenuate more rapidly over the one-year follow-up period. Caudal epidural steroid injections demonstrate the most favourable procedural safety profile yet consistently produce inferior long-term clinical outcomes. This lack of sustained efficacy in the caudal group translates directly to higher rates of repeat interventions and eventual surgical decompression. Effective management of neurogenic claudication requires the adequate delivery of anti-inflammatory medication directly to the site of neural compression [1, 10]. The present findings indicate that interlaminar epidural steroid injections achieve superior longitudinal pain reduction compared to both the transforaminal and caudal routes. These results closely mirror prospective trials by Manchikanti et al. [6] and Akram et al. [5], which established the clinical superiority of the interlaminar approach for diffuse central canal stenosis. Central stenosis is largely driven by posterior column structures, including ligamentum flavum hypertrophy and bilateral facet arthropathy [2, 3]. The interlaminar technique allows for the direct deposition of a high-volume, concentrated corticosteroid bolus into the dorsal epidural space adjacent to the primary compressive pathology [3]. Caudal injections suffer from distinct mechanical flow restrictions in this patient population. Severe central canal narrowing acts as a physical barrier, preventing sufficient cephalad spread of the injectate from the sacral hiatus to the targeted upper lumbar segments [5, 6]. Transforaminal injections, while highly precise for ventral neural targeting, are anatomically better suited for unilateral radiculopathy and frequently fail to adequately bathe the diffuse, bilateral neurovascular structures affected by central stenosis [7, 11]. Reductions in pain intensity translated directly to measurable functional gains across all cohorts. Patients undergoing the interlaminar procedure reported the greatest improvements in the Oswestry Disability Index and maximum walking distance at twelve months. Mechanical neural compression in spinal stenosis induces microvascular congestion and ischemia of the cauda equina, leading to the classic symptom of neurogenic claudication [11, 12]. The robust anti-inflammatory washout effect provided by the interlaminar injectate helps dilute accumulated noxious metabolites, restoring localized microvascular perfusion [12, 13]. Enhancing walking capacity from severely restricted baseline levels to over 600 feet at early follow-up provides a critical therapeutic window. As noted by Srivastava et al., this functional improvement allows patients to engage in active physical rehabilitation [13]. The clinical significance of this finding is profound in the present cohort of rural agricultural labourers, where restored mobility equates to the resumption of daily livelihood and financial independence. The necessity for repeat interventions and ultimate conversion to surgical decompression reflects the durability of each procedural approach. The caudal group exhibited the highest requirement for subsequent injections and the highest rate of surgical conversion at one year. Because the caudal route frequently fails to achieve adequate local drug concentrations at the stenotic level, the resultant analgesic effect is often short-lived [14, 15]. Patients with severe central stenosis facing rapid symptom recurrence after caudal blocks are consequently driven toward operative solutions [14]. Selecting the interlaminar approach for diffuse central pathology can effectively delay or entirely prevent the need for open surgical decompression in a substantial proportion of patients, mitigating surgical morbidity and decreasing healthcare expenditures [16, 17]. While transforaminal injections perform better than caudal approaches in delaying surgery, they remain inferior to interlaminar injections for patients presenting primarily with axial pain and claudication rather than isolated unilateral radiculitis [18, 19]. Interventional spine procedures carry inherent anatomical risks that dictate clinical decision-making. The caudal approach resulted in zero dural punctures or nerve injuries, reinforcing its status as the safest anatomical route [3, 15]. This technique is particularly advantageous for patients with severe deformity or prior lumbar surgery [5]. The interlaminar approach resulted in a single, conservatively managed dural puncture. Notably, the transforaminal group experienced zero catastrophic ischemic neurological complications. The transforaminal approach carries a well-documented risk of spinal cord infarction if particulate steroids inadvertently embolize the radicular medullary arteries [8, 20]. The absence of such events in this study validates the strict utilization of non-particulate dexamethasone for transforaminal injections. Current guidelines strongly advocate for non-particulate agents during transforaminal injections to prioritize patient safety without completely sacrificing analgesic efficacy [21, 22]. Patient satisfaction scores predictably mirrored the efficacy profiles, with the interlaminar group reporting the highest overall satisfaction at six months [23]. A primary strength of this study is the direct, head-to-head comparison of all three epidural approaches within a single, demographically uniform cohort of patients with MRI-confirmed central spinal stenosis. This design provides valuable comparative effectiveness data often lacking in existing literature [13, 16]. Genuine methodological limitations must be acknowledged. The retrospective observational design introduces inherent selection biases, as treatment allocation was not randomized. The absence of a true placebo or saline-only control arm precludes the ability to isolate the specific pharmacological effect of the corticosteroid from the mechanical washout effect of the local anesthetic. Follow-up was restricted to twelve months, limiting conclusions regarding long-term disease progression. Reliance on retrospective medical record review may also result in the underreporting of minor, transient procedural complications. Epidural steroid injections remain a cornerstone of conservative spine care, but their application should not be uniform. The selection of the epidural approach must be meticulously tailored to the patient's specific pathoanatomy. The interlaminar route represents the optimal primary intervention for bilateral central spinal stenosis, offering the best trajectory for sustained functional recovery and pain reduction. In conclusion, this study demonstrates that the interlaminar approach is the optimal primary epidural intervention for adults with symptomatic central lumbar spinal stenosis. It provides the most robust, sustained improvements in pain and functional mobility over a full one-year period. While transforaminal injections yield excellent short-term analgesia, their clinical efficacy diminishes more rapidly. Conversely, the caudal approach boasts the most favorable procedural safety profile but produces inferior long-term clinical outcomes, resulting in significantly higher frequencies of repeat injections and surgical conversions. Interventional spine care must therefore be anatomically tailored, prioritizing interlaminar delivery to maximize therapeutic durability and delay surgical decompression. Author Contributions The first and second authors conducted the primary study. The third & corresponding author assisted with data collection, interpretation, and manuscript preparation.

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