Background: Epidural injections are the most common minimally invasive intervention used to manage
low back pain with lumbosacral radicular pain. It can be delivered through either transforaminal (TF),
interlaminar, or caudal approaches. The TF approach is considered more efficacious than the interlaminar
approach probably because of ventral epidural spread. However, catastrophic complications reported
with the TF approach have raised concerns regarding its use. These concerns regarding the safety of the
TF approach lead to the search for a technically better route with lesser complications with drug delivery
into the ventral epidural space. The parasagittal interlaminar (PIL) route is reported to have good ventral
epidural spread. However, there is a paucity of literature comparing the effectiveness of PIL with TF.
Objectives: To compare effectiveness of PIL and TF epidural injections for managing low back pain
with lumbosacral radicular pain.
Study Design: Randomized, double-blind, active-control study.
Setting: Interventional pain management clinic in a tertiary care center in India.
Methods: Sixty-two patients were randomized to receive fluoroscopically guided epidural injection
of methylprednisolone (80 mg) either through the PIL (n = 32) or TF (n = 30) approach. Patients were
evaluated for effective pain relief (≥ 50% from baseline) by 0 – 100 visual analogue scale (VAS) and
functional improvement by Modified Oswestry Disability Questionnaire (MODQ) at 2 weeks, 1, 2, 3,
6, 9, and 12 months. Patients who failed to respond to the treatment or when the patient’s response
deteriorated received additional injection of same injectate, dose, and approach. Only if the pain
returns should there be a maximum of 3 injections. Other outcome measures were overall VAS and
MODQ, number of injections, and presence of ventral and perineural spread.
Results: Effective pain relief (≥ 50% pain relief from baseline on VAS) was observed in 76% (90%
CI 60.6 – 88.5%) of patients in the TF group and 78% (90% CI 62.8 – 89.3%) of patients in the
PIL (P = 1.00) group at 3 months. The pain relief survival period was comparable in both groups (P =
0.98). Significant reduction in VAS and improvement in MODQ were observed at all time points postintervention compared to baseline (P < 0.001) in both groups. On average, patients in the PIL group
received 1.84 and patients in the TF group received 1.92 procedures annually. The majority received
injection at L4-L5 intervertebral level (24 in TF and 23 in PIL). Ventral epidural spread was comparable in
both groups (PIL – 91.6% and TF – 89.6%). No major complications were encountered in either group;
however, initial intravascular spread of contrast was observed in 3 patients in the TF group.
Limitations: Limitations included lack of documentation of adjuvant analgesic drug therapy and
procedures performed by a single experienced interventionalist.
Conclusions: Epidural injection delivered through the PIL approach is equivalent in achieving effective
pain relief and functional improvement to the TF approach for the management of low back pain with
lumbosacral radicular pain. The PIL approach can be considered a suitable alternative to the TF approach
for its equivalent effectiveness, probable better safety profile, and technical ease.
Trial registration: CTRI/2012/08/002938.
Key words: Low back pain, lumbosacral radicular pain, interlaminar, parasagittal, transforaminal,
epidural steroid injection, epidural steroids, equivalence clinical trial
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