The current prospective descriptive study was done by two operators, a consultant of pain management and radiologist, and conducted primarily on one preserved cadaver then continued on 32 adult patients. The sample size was calculated for agreement study of US for the radiological guidance of trans-foraminal needle placement targeting the lumbar dorsal root ganglion using PRF modulation to relieve patients’ radicular pain [11].
The study protocol was approved by the Ethical Review Board and a written informed consent was obtained from each patient.
All patients fulfilled the inclusion criteria; they all had lumbar CRP for more than 3 months due to a localized herniated disc shown in MRI, not responding and/or intolerant to conservative treatment (visual analogue scale (VAS) of pain measuring more than 4), and reporting no progressive motor weakness.
Patients were excluded if they reported a history of allergy to local anesthetics or radiographic contrast medium, spinal deformity or previous lumbar spinal surgery, psychiatric disorders, local or systemic contraindication to lumbar interventions, and pregnancy.
The primary outcome of the present study was to measure the grade of accuracy of US-guided trans-foraminal PR cannula placement adjacent to the desired DRG; secondary outcomes were pain relief, analgesic consumption, patients’ functionality, and safety of the technique.
The intervention technique
After reviewing Provenzano and Narouze’s study [12] which described 7 sonographic views of lumbar spine injections and the studies published by Gofeld et al. [13] and Galiano et al. [14] which described US-guided lumbar trans-foraminal injection, the current study suggested that axial sonogram of lumbar vertebra below the level of desired transverse process, targeting lateral border of inferior articular process using in-plane needle approach, is the best plane for trans-foraminal DRG modulation.
First stage of the study (cadaveric work)
A preserved whole-body cadaver was placed in prone position on a procedural table at the anatomy laboratory. Personal protective tools were worn and a curved US probe (25 MHz) of US GE machine (logic P5, USA) was covered and placed midline sagittal oblique to view the sacral hiatus, sacrum and lumbar spinous processes, and laminae.
At the selected vertebral level, the US probe was rotated transversely to view the axial sonogram of the spinous process, superior articular process, lamina, and transverse process (TP) (Fig. 1). The US probe was moved slightly down and/or oblique below the level of TP with mild cephalic tilt to visualize inferior edge of lamina, lateral border of inferior articular process, dura, and existing nerve root (Fig. 2). One-finger breadth lateral to the lateral edge of the probe a spinal needle was inserted approximately 70–80° on the cadaver skin and directed from lateral to medial towards the lateral border of the inferior articular process (Fig. 3).
Upon reaching the lateral border of the articular process, the angle of the needle on the cadaver surface decreased (to 60°and less) during the needle advancement anterior, superior. and medial to the articular process to be placed into the intervertebral foramen; then, 1 cc of ionized contrast was injected and only an antero-posterior (A-P) fluoroscopic view was taken to verify the vertebral level (Fig. 4) and the dye spread pattern in the dural sleeve around the nerve root (Fig. 5) FL machine was designed for A-P view only. Five trans-foraminal injections (L1/L2 through L5/S1) were performed bilaterally.
The aim of this stage was to make the best needle probe orientation; determination of the site, direction, tilt, and angle of needle entry; and path into the trans-foraminal space under US guidance.
Second stage of the study (clinical work)
The intervention was done in the block room under complete aseptic technique. The patient asked to be in prone position on the operating table with a pillow under his/her abdomen to eliminate lumbar lordosis. A portable US machine (SonoSite Inc., US) with a curved probe (2–5 MHz frequency) was adjusted and used for vertebral counting to reach the desired vertebral level simulating the technique performed on the cadaver (Figs. 6, 7, 8, and 9).
Fluoroscopic imaging was taken for level verification by fluoroscopy machine, Siemens, Cios Connect. Two milliliters of lidocaine 1% was injected to numb the skin and underlying tissues and a 22-G, 90-mm PRF insulated /curved cannula, with a 10-mm active tip, was inserted into the desired intervertebral foramen using the abovementioned cadaveric technique (Fig. 10).
During needle progression, each patient was asked to be alert and to report immediately if they experienced any shooting pain or tingling in the leg that denoted touching nerve root. If this scenario happened the needle withdrawn 2–3 mm and redirected up and pain checked again.
Sensory stimulation of the DRG of the desired nerve root was tested by eliciting paresthesia in the dermatomal distribution of the affected nerve using an RF probe of neurotherm NT 2000 machine at 50 Hz and 0.4–0.6 V. Fine adjustment of the PRF probe position might be done at this point. Motor stimulation was tested at 2 Hz and at voltage double that of the sensory threshold but at least at 1 V.
Once satisfactory positive sensory stimulation, negative motor stimulation, and negative aspiration for blood or CSF were obtained; a lateral FL image was taken to confirm the cannula placement at the desired foraminal level. One milliliter of iohexol (Omnipaque) was injected under FL imaging to exclude intravascular injection and show distribution of the dye around nerve root. PRF wave was applied reaching 42 °C and a pulse width of 20 ms for 4 min.
After the procedure, the patient was transferred to the recovery room for monitoring, observation, and management of any side effects. Any complication was reported and managed accordingly.
Measurements
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1.
The accuracy and time consumed during an ultrasound-guided DRG modulation
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(a)
The accuracy of pulsed radiofrequency cannula placement in a specific lumbar intervertebral space, adjacent to DRG guided with ultrasound and verified by fluoroscopy, was divided into 3 grades:
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1
Grade II. Correct vertebral level, right cannula position in the intervertebral foramen, and positive sensory stimulation from a single entry trial.
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2
Grade I. Correct vertebral level, right cannula position in the intervertebral foramen, and positive sensory stimulation with multiple trials; Ia = three trials, and Ib = two trials.
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3
Grade 0. Incorrect vertebral level
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(b)
The procedure time consumed was measured in minutes.
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1
Time needed for counting to the desired vertebral level.
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2
Time needed for visualization of the sonoanatomy of the vertebra.
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3
Time needed to direct the cannula into intervertebral foramina, adjust the PRF cannula towards the DRG and stimulation and modulation of DRG.
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2.
Patients’ radicular pain was measured at 2 weeks, 1 month, and 3 months post-intervention and compared to pre-intervention values using visual analogue scale of pain which is a 0–10 cm scale where 0 means no pain and 10 is the worst imaginable pain.
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3.
Patients’ functionality was measured at 2 weeks, 1 month, and 3 months post-intervention and compared to pre-intervention values using Oswestry Low Back Pain Disability Questionnaire which is a ten-item scale; each item is rated from 0 to 5 (minimum to maximum impairment).On completing the test, the collected points are added, divided by 50, and multiplied by 100 to obtain the percentage of disability or index. The higher the ODI index, the greater the disability (0 to 20%, minimal disability; 21–40%, moderate disability; 41–60%, severe disability; 41–60%, severe disability; 81–100%, bed-bound).
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4.
Analgesic consumption reduction was calculated at 1 month post-intervention.
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(a)
If patient reported ≥ 75 pain relief at the first meeting post-intervention, the analgesics reduced gradually through the next 2 weeks by 100%.
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(b)
If the reported pain relieved ≥ 50%, the analgesics reduced gradually within 2 weeks by 50%.
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(c)
If the reported pain relieved less than 50%, the analgesics continued without dose reduction.
Statistical methodology
Data were collected and entered to the computer using SPSS (Statistical Package for Social Science) program for statistical analysis (ver. 21) [15]. Data were described using minimum, maximum, mean, standard deviation, and 95% CI of the mean [16]. Comparisons were carried out between more than two independent normally distributed subgroups using one-way analysis of variance (ANOVA) test [17]. Post hoc multiple comparisons [18] was carried out using Games-Howell test [19]. Repeated measures analysis of variance was used [20]. Pair-wise comparison was done with Bonferroni correction. Diagnostic test evaluation was carried out using MedCalc Software version 14 [21]. An alpha level was set to 5% with a significance level of 95% (p value = 0.05).