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Pain Medicine: Research Report

Lateral Parasagittal Versus Midline Interlaminar Lumbar Epidural Steroid Injection for Management of Low Back Pain with Lumbosacral Radicular Pain

A Double-Blind, Randomized Study

Ghai, Babita, MD, DNB, MAMS; Vadaje, Kaivalya Sadashiv, MD; Wig, Jyotsna, MD, FAMS; Dhillon, Mandeep Singh, MS

Author Information
doi: 10.1213/ANE.0b013e3182910a15

Low back pain with lumbosacral radicular pain is a significant clinical, social, and public health problem affecting people indiscriminately.1 Intervertebral disk herniation with nerve irritation is the common cause of lumbosacral radicular pain.2–5 Various treatment modalities including conservative and surgical interventions are available, but conservative measures with minimal interventions are now preferred in the wake of unsatisfactory surgical outcomes.6–8 Disk herniation releases large amounts of phospholipase A29 which favors the production of prostaglandins10 leading to inflammation and pain generation.11 Epidural steroid injections (ESIs) may reduce the inflammatory response either by inhibiting the synthesis or release of proinflammatory substances11 and are the most commonly performed interventions.1,12 It has been suggested that ESIs would be most effective for pain relief if they are delivered close to the site of the pathology.12,13 ESIs can be accomplished by 2 main approaches: interlaminar and transforaminal. The interlaminar epidural injection has been widely used but its efficacy has been reported to be limited.12–15 This is probably because the drug is delivered mainly in the dorsal epidural space with limited ventral epidural spread.16–18 Recently, the transforaminal route has been reported to be more effective than the interlaminar route.3,12,19,20 This is probably because the transforaminal route allows a high concentration of drug to be delivered precisely at the targeted site of disk herniation, i.e., ventral aspect of the epidural space.3,15 However, the transforaminal route has been associated with various complications such as spinal cord injury, permanent paralysis,21–23 increased incidence of intradiskal injection of the drug24–26 and even death.27 There are concerns regarding the safety of the transforaminal route, and there is a search for a technically better route with fewer complications for drug delivery into the ventral epidural space.

Ventral spread of contrast with the needle in the lateral most part of the interlaminar space has been reported to be 100%.28,29 However, these studies only investigated the pattern of contrast spread and the clinical significance of the findings was not studied. To the best of our knowledge, there are no controlled randomized trials in the literature comparing the lateral parasagittal interlaminar (PIL) and midline interlaminar (MIL) routes for clinical outcome in patients having low back pain with lumbosacral radicular pain. Hence, we conducted this study to compare the therapeutic efficacy of a lateral PIL approach and the MIL approach of ESI in patients with lumbosacral radicular pain not responding to other conservative management. We hypothesized that a lateral PIL approach may produce a better clinical outcome because of the better ventral epidural spread of the drug compared with a MIL approach.


After institutional ethics committee approval, 40 consecutive ASA physical status I and II patients of either gender (18–65 years) with low back pain associated with unilateral lumbosacral radicular pain for at least 3 months duration not responding to medications and physical therapies were assessed for study inclusion from the institute’s pain clinic from September 2009 to October 2010. The diagnostic criteria for lumbosacral radicular pain were defined previously30,31 as pain perceived in the territory innervated by the affected nerve root. As far as possible, somatic referred pain was excluded. Radicular pain was defined as sharp, shooting or lancinating pain perceived in the skin as well as deep in the tissue.30,31 All patients were evaluated before study with magnetic resonance imaging.

Patients with a history of surgery on the lumbar spine, spinal canal stenosis, facet joint arthopathy, cauda aquina syndrome and other unstable neurologic deficits, allergic to contrast or corticosteroids, bleeding diathesis, patients who had received lumbar ESIs in the past 3 months or using systemic corticosteroids for pain relief, and pregnant patients were excluded from the study.

The purpose of the study was explained to all patients, and written informed consent was obtained. Three patients declined to participate hence 37 patients were randomized to 1 of the 2 groups, i.e., PIL group (n = 19) or MIL group (n = 18) (Fig. 1). Randomization was done using computer-generated random numbers using blocks of 6. The random numbers were kept in opaque sealed envelopes and were opened by an anesthesiologist not involved in the study.

Figure 1
Figure 1:
Flow chart of patients who participated in the study. MIL = midline interlaminar; PIL = parasagittal interlaminar; ESI = epidural steroid injection; VAS = visual analog scale; MODQ = modified Oswestry Disability Questionnaire.

Before each intervention, standard monitoring was established after securing an IV cannula. The intervertebral level was determined by clinical examination and the results of magnetic resonance imaging studies. The maximum affected level was selected if multiple disks were involved.


The initial anteroposterior fluoroscopic images were obtained to identify the level of the intervertebral disk and interlaminar space in prone position. Under aseptic conditions and after local infiltration with 2% lidocaine, an 18-gauge, 3.5-inch, Tuohy needle was introduced at the level of disk pathology and advanced from the posterior to anterior direction. In the PIL group, the needle was introduced into the most lateral epidural space of the affected side, using the loss-of-resistance to saline technique, and the parasagittal orientation of the needle was maintained throughout the procedure (Fig. 2). In the MIL group, the needle was introduced at the midpoint between 2 spinous processes at the affected level (Fig. 2). After negative aspiration for cerebrospinal fluid and blood, 0.5 mL Iohexol (300 mg/mL), (OMNIPAQUE™, GE Healthcare, London, UK) was injected to confirm the epidural space. This was followed by further injection of 3.5 mL of contrast under continuous fluoroscopy to confirm the spread of the contrast as well as to verify that no contrast medium reached intravascular, subarachnoid, subdural, or intradiskal spread. Lateral images were taken to evaluate ventral epidural space. Ventral spread was defined as present if the contrast traveled along the posterior longitudinal ligament or abutted the posterior aspect of the contiguous vertebral body at the level of needle insertion on the lateral projection of the fluoroscopy (Fig. 3).32 The perineural spread was defined as nerve root infiltration of contrast (Fig. 4). After epidural space confirmation, 2 mL methylprednisolone acetate (l mL = 40 mg; DEPO-MEDROL™ injection, Pfizer products India Pvt. Ltd, Mumbai, India) with 2 mL sterile normal saline was injected.

Figure 2
Figure 2:
Defining anatomical landmarks for needle placement. MIL= midline interlaminar; PIL = parasagittal interlaminar.
Figure 3
Figure 3:
Parasagittal interlaminar (PIL) approach, ventral epidural contrast spread seen in lateral view.
Figure 4
Figure 4:
Parasagittal interlaminar (PIL) approach, perineural spread of contrast seen in anteroposterior (AP) view.

Fluoroscopy time for each patient was recorded consecutively for scout films at each needle adjustment and during the injection phase and limited to <60 seconds.


Patients were assessed for pain by visual analog scale (VAS) on a horizontal 0 to 100 scale ranging from 0 (no pain) to 100 (worst pain possible) and for disability and impairment using the modified Oswestry Disability Questionnaire (MODQ).32,33 Patients were also assessed for possible neurologic complications including postural headache, motor weakness, paraplegia, paresthesia, and newly developed pain.


The random numbers were kept in opaque sealed envelopes and were opened by an anesthesiologist not involved in the study. One of the 2 investigators (BG/KSV) performed the procedure in an operating room, and the other investigator followed patients in the pain clinic, i.e., if the procedure was done by BG, the patients were followed by KSV and vice versa. The patients and the investigator assessing the patients were unaware of the group allocation.

Primary and Secondary Outcomes

We defined the approach as “effective” when pain relief was ≥50% from baseline. The primary outcome of the study was the incidence of patients achieving effective pain relief at 6 months. The secondary outcomes studied were overall VAS score, presence of anterior spread, number of injections required, and MODQ scores.


Patients in each group were followed up for 6 months at intervals of 15 days, 1, 2, 3, and 6 months. Patients who had <50% pain relief from baseline received additional injections with the same approach, drug, and dosage at the same level with a maximum of 3 injections in an individual patient with at least 15 days apart (Fig. 1). Those who had pain relief ≥50% from baseline did not receive further injections. If required, they also received injection with the same approach during the follow-up period when pain increased and decreased within 50% of baseline.

Cointerventions and Postintervention Medications

All participants were receiving conservative management (adjuvant; pregabalin, opioid and non-opioid, and/or a therapeutic exercise program) before joining the study. Participants who showed substantial improvement with the study intervention reduced or stopped their drugs; for the other patients, dosages were increased or continued at the same dosages. Exercises and job attendance continued. No other additional treatments, such as physical therapy (ultrasonic therapy, microwave diathermy, moist heat) or other interventions, other than the assigned study intervention, were offered.

Statistical Analysis

Sample Size Calculation

In the absence of available published data comparing PIL and MIL approaches evaluating clinical outcome for management of chronic low back pain with lumbosacral radicular pain, we performed a pilot study of 20 patients, 10 patients in each group with an intermediate step of analysis. The results of the pilot study suggested that the PIL approach was effective in 80% (8 of 10 patients) compared with 30% (3 of 10 patients) of patients using the MIL approach at 6 months. To detect a change in incidence of an effective injection from 30% to 80% with an α of 0.05 and β of 0.1 (power 90%), 17 patients in each group were required. We assessed 40 patients for possible dropouts. Sample size calculation was done using a test for proportions comparing 2 independent samples.34

Data are presented as mean ± SD. Data were analyzed for normality using Kolmogorov-Smirnov Z test. Demographic data were analyzed using Student “t” test or χ2 test. Categorical data including primary end point were analyzed by χ2 test. Two-way repeated measures analysis of variance was conducted to analyze VAS and MODQ over time. For this, the data were tested for normality, homogeneity, and equal covariance by Kolmogorov-Smirnov Z test, Levene test for equality of error variances, and Box Test of Equality of Covariance Matrices, respectively. The assumption of sphericity was tested by Mauchly test. If the Mauchly test was significant indicating violation of the assumption of sphericity, we used the Greenhouse-Geisser test with adjustment for time × factor, time × group interaction and between-subject effects for VAS and MODQ. If found significant, follow-up analysis was performed with Bonferroni correction for multiple comparisons. The duration of effective pain relief and administration of further ESIs were analyzed by using Kaplan-Meier survival analysis. The Clopper-Pearson Exact method was used to find the upper limit of 95% confidence interval (CI) of complications. Computer statistical software SPSS version 17.0 (SPSS Inc, Chicago, IL) was used for analysis. P < 0.05 was considered significant.


No patient was excluded from the study after randomization, and all patients in each group completed follow-up for the study duration of 6 months. Both groups were comparable with respect to demographic data, duration of symptoms, baseline VAS, MODQ, and level of intervertebral injections (Table 1). Baseline data were normally distributed.

Table 1
Table 1:
Patients’ Demographic and Baseline Data

Primary Outcome (Effective Pain Relief)

With the PIL approach, the number of patients achieving effective pain relief was significantly higher compared with the MIL group at 15 days, 1, 2, 3, and 6 months (Fig. 5). At the 6-month follow-up, a significantly higher relative success of effective pain relief was noted in the PIL group (relative risk, 4.10; 95% CI, 1.40–12.05; P = 0.001). Absolute risk reduction analysis revealed absolute risk reduction of 52% with 95% CI as 19% to 77% and number needed to treat as 1.93 with 95% CI as 1.26 to 4.05.

Figure 5
Figure 5:
Effective pain relief (≥50% from baseline) incidence. PIL = parasagittal interlaminar; MIL = midline interlaminar.

Total Number of ESIs

Total number of ESIs administered to patients in the PIL group were significantly less, i.e., 29 as compared with the MIL group, i.e., 41 injections (P = 0.043). Mean injections (SD) required over a 6-month duration for the PIL and MIL groups were 1.53 (0.84) and 2.28 (0.90), respectively, with 95% CI of the difference (0.172–1.331) (P = 0.013, t test). Thirteen patients (44.8%) in the PIL group received only 1 injection to achieve effective pain relief compared with 5 (12.19%) in the MIL group. The remaining 6 patients in the PIL group and 13 patients in the MIL group received further injections. Two of 6 patients in PIL and 3 of 13 patients in the MIL group achieved effective pain relief for 6 months after 2 injections. Four (21.1%) patients in the PIL group compared with 10 (55.6%) patients in the MIL group required 3 injections.

Ventral Epidural Spread

In the PIL group, ventral epidural spread significantly higher (89.65%, 26 of 29 injections) as compared with 31.7% (13 of 41 injections) in the MIL group including both first and repeat injections (P = 0.001; Table 2).

Table 2
Table 2:
Characteristics of the Approaches (Ventral Epidural Spread, Perineural Spread, and Total Fluoroscopy Time)

Perineural Spread

The perineural spread was significantly greater in the PIL group, i.e., 44.82% (13 of 29 injections) and only 14.63% (6 of 41 injections) in the MIL group in all injections (P = 0.005; Table 2).

VAS Scores and ODQ Score Over Time

Results of repeated measures analysis of variance revealed time × factor (P < 0.001 for both VAS and ODQ) and time × group interaction (P < 0.001 for VAS and P = 0.035 for ODQ). Between-group effect was also significant (P = 0.003 for VAS and P = 0.002 for ODQ). Follow-up within group pairwise analysis revealed that VAS scores decreased significantly at all time intervals compared with baseline in both groups. Between-group analysis revealed that VAS and ODQ scores were significantly lower in the PIL group compared with the MIL group at different time intervals except baseline (Figs. 6 and 7).

Figure 6
Figure 6:
Visual analog scale. PIL = parasagittal interlaminar; MIL= midline interlaminar. Error bars represents standard deviation. *P value at different time intervals as compared with baseline (within group, pairwise comparisons with Bonferroni correction). #1 P= 0.776, #2 P = 0.009, #3 P = 0.001, #4 P = 0.001, #5 P = 0.01, and #6 P = 0.001, respectively, (for between-group comparisons at specified time intervals with Bonferroni correction)
Figure 7
Figure 7:
Modified Oswestry Disability Questionnaire (ODQ) score. PIL = parasagittal interlaminar; MIL = midline interlaminar. Error bars represents standard deviation. *P < 0.001 at different time intervals as compared with baseline (within group, pairwise comparisons with Bonferroni correction). #1 P = 0.065, #2 P = 0.001, #3 P<0.001, #4 P =0.006, #5 P = 0.013, and #6 P = 0.002, respectively, for between-group comparisons at specified time intervals with Bonferroni correction.

Pain-Free Survival Analysis by Kaplan-Meier Survival Curves

Kaplan-Meier curve was plotted for pain-free survival in each group noting the period of effective pain relief as a clinical outcome after epidural injections. We found from the figure that effective pain relief was less or reoccurrence of pain in a previously pain-free period was more in the MIL approach, whereas pain-free survival period was longer in the PIL group (P = 0.014; Fig. 8).

Figure 8
Figure 8:
Kaplan-Meier graph for effective analgesia period. This figure represents the probability of patients having effective analgesia at different points of time. PIL = parasagittal interlaminar; MIL=midline interlaminar.

Monitoring Complications

We did not encounter any intrathecal, intradiskal, intravascular, or subdural placement of contrast in any of the patients. No other complication was noted. The exact 95% Clopper-Pearson CI was 0.0% to 17.6% in the PIL group, 0.0% to 18.5% in the MIL group, and 0.0% to 9.4% for both groups together. No technical difficulty was encountered in any patient. However, relocation of the needle at the desired site was required in both groups. Superficial spread was noted in 1 patient in the MIL group requiring relocation of the needle. Four of 41 injections in the MIL group and 2 of 29 injections in the PIL group were required to relocate the needle in the desired site. No patient in the study group reported any swelling, redness, or persistent pain at the site of injection or sustained paresthesia.


The present study revealed that the PIL approach for ESI was significantly more effective compared with the MIL approach for treatment of chronic low back pain with lumbosacral radicular pain. Ventral epidural contrast spread was significantly more in the PIL approach than the MIL approach. The improvement in disability was significantly better with the PIL approach than the MIL approach. Fewer injections were required in patients treated with the PIL approach than MIL approach, hence reducing economical burden and repeated hospital visits.

Lumbar ESIs with or without fluoroscopy are a commonly performed intervention for the management of lumbosacral radicular pain.1,2,5,12 Most disk herniations are located posterior to vertebrae, hence it is suggested that epidural steroid would be more effective if it is delivered close to this targeted site.12 However, there is no clear consensus on the technical aspects and the ideal method to perform ESI.35 Indeed, there is wide variation among individual practices in almost every technical aspect of ESI.35

Lumbar injection with placement of the needle into the dorsal epidural space under fluoroscopic guidance is easy and safe29 but the efficacy has been limited12–15 probably due to limited delivery of the steroid into the ventral epidural space. Contrast spread in the ventral epidural space is reported to be only 28% to 47% of the time with the interlamminar route.16–18 On the contrary, the transforaminal route of ESI is reported to be more effective than the interlaminar,3,12,19,20,36 as it allows better ventral spread. However, the transforaminal route is associated with many serious complications such as spinal cord injury and paraplegia including higher vascular and intradiskal spread and even death.21–27

One hundred percent ventral epidural spread has been reported when the needle is placed in the lateral most part of the epidural space.28,29 Candido et al.28 evaluated contrast flow pattern with the PIL and transforaminal approach and reported 100% ventral epidural spread with PIL and 75% ventral spread with the transforaminal approach. Choi and Barbella29 investigated lumbar interlaminar ventral epidural injection of contrast with placement of an epidural catheter at the ventrolateral portion of the nerve root in patients with low back and L5 radicular pain. They reported ventral epidural spread in all patients concluding that lumbar interlaminar ventral epidural injections can be an alternative method for ventral epidural injection. However, the clinical significance of these findings was not evaluated in either of these studies.

We compared the PIL approach with the MIL approach for clinical outcome of lumbosacral radicular pain because the MIL approach is more commonly practiced at our institute. We reported a 31.7% incidence of ventral epidural contrast spread with the MIL approach which is in accordance with previous studies.16–18 In the present study, we found that ventral epidural contrast spread with the PIL approach was 89.65% for all injections which is slightly lower than previous studies.28,29 We assume that this may be attributed to performer differences. Better ventral spread of drug with the PIL approach is most probably the reason for better clinical outcomes in this group compared with the MIL group. In fact, our results strengthened the assumption of our hypothesis.

Each patient in our study received 4 mL of contrast which was equal to the volume of the drug used for injection. This volume was used in our study, because it is within the range of the volumes (2–5 mL) used by previous investigators.15,37,38

We performed all interventions under fluoroscopic guidance. Fluoroscopy is a well-established tool for confirming the epidural space and patterns of contrast spread. Previous studies have suggested that ESIs performed blindly have high probabilities of missing the perceived target area 30% to 40% of the time.39 Also, there are few complications associated with fluoroscopic-guided injection compared with blind injections.40

Recently, 2 studies evaluated the therapeutic efficacy of fluoroscopically guided epidural steroids with an interlaminar approach.38,41 Furman et al.38 evaluated the effect of epidural triamcinolone (80 mg) using the paramedian approach for lumbar radicular pain in a prospective, single-arm pilot study of 21 patients and demonstrated that subjects had improved pain for at least 3 months. However, the authors did not mention the final needle position. Manchikanti et al.41 evaluated the effectiveness of a single injection of lumbar interlaminar local anesthetics with or without steroids for managing chronic pain of disk herniation or radiculitis in a double-blind randomized controlled manner. In this study, the epidural space was entered at the L5/S1 level or at a level below the pathology to direct the flow of contrast toward the herniated disk side in case of unilateral pain and bilaterally in case of bilateral lower extremity pain. The authors reported significant pain relief (>50%) at 12months in 74% of patients treated with local anesthetics and 86% of patients treated with local anesthetics and steroids. However, in this study, final needle placement and contrast pattern were not mentioned.

The total number of ESIs required in an individual patient has not been clearly defined in the literature, but some patients may improve only after 2 or 3 injections.15,42 Ackerman and Ahmad15 reported that patients treated with repeated injections using interlaminar and caudal routes had increased efficacy. They hypothesized that increased efficacy could be related to repeated systemic uptake from the epidural veins in the posterior epidural space and blood vessels in the subarachnoid space after passive diffusion of steroid across dura.15 We used a maximum of 3 epidural injections in patients. Indeed, there is no additional benefit of >3 injections in an individual patient.43 Similarly, if 1 injection reduces pain effectively, there is no need for a repeat injection.43

In the present study, we did not encounter contrast spread to intravascular, intradiskal, subarachnoid, and subdural spaces. Complications with lumbar ESIs were comprehensively reviewed by Goodman et al.44 They concluded that complications with lumbar ESIs are extremely rare and most of the complications can be avoided by accurate needle placement, sterile techniques, and fluoroscopic-guided injections.44

One of the limitations of our study is that we compared the PIL with the MIL approach rather than the transforaminal approach because the MIL approach is most commonly used at our institution. We are presently conducting a double-blind randomized study comparing PIL and transforaminal approaches. Second, this is a preliminary study of 37 patients without a placebo group. However, this is justifiable because no randomized study is available in the literature evaluating the clinical outcome of a PIL approach. In addition, patients enrolled in the study were presented with significant pain, hence it would be unethical to have a placebo group. Another limitation is that the follow-up and assessment of our study were for only 6 months and should have been longer for assessing long-term effectiveness. Also, detailed information comparing medication intake and physical therapy regimens after ESI between the 2 groups was not available.


Epidural steroid administration under fluoroscopic guidance with a lateral PIL approach was significantly more effective compared with a MIL approach for management of chronic low back pain with lumbosacral radicular pain. Patients in our PIL group required fewer ESIs for the study period. The improvement in disability in patients treated with the PIL approach was significantly better than the MIL approach over a period of 6 months. These differences between the 2 approaches are most probably because of better ventral spread using the PIL approach. The administration of ESI was without complication for both PIL and MIL approaches.


Name: Babita Ghai, MD, DNB, MAMS.

Contribution: This author helped design and conduct the study, analyze the data, and write the manuscript.

Attestation: Babita Ghai has seen the original study data, reviewed the analysis of the data, approved the final manuscript, and is the author responsible for archiving the study files.

Name: Kaivalya Sadashiv Vadaje, MD.

Contribution: This author helped design and conduct the study, analyze the data, and write the manuscript.

Attestation: Kaivalya Sadashiv Vadaje has seen the original study data, reviewed the analysis of the data, and approved the final manuscript.

Name: Jyotsna Wig, MD, FAMS.

Contribution: This author helped design and conduct the study and write the manuscript.

Attestation: Jyotsna Wig has seen the original study data, reviewed the analysis of the data, and approved the final manuscript.

Name: Mandeep Singh Dhillon, MS.

Contribution: This author helped design and conduct the study, analyze the data, and write the manuscript.

Attestation: Mandeep Singh Dhillon has seen the original study data, reviewed the analysis of the data, and approved the final manuscript.

This manuscript was handled by: Spencer S. Liu, MD.


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