Feasibility study of ultrasound-guided percutaneous laser discectomy for cervical radicular pain
Study design and participants
This was a retrospective, single-center, observational study conducted by the Pain Department of Xiangya Third Hospital. Medical records of nine patients with cervical root pain who underwent ultrasound-guided PLD were retrospectively reviewed. Inclusion criteria included the following: (1) patients who were diagnosed with cervical radicular pain based on history, physical examination, and imaging test; (2) pain intensity was greater than 4 out of 10 on the visual analogue scale (VAS) after conservative treatment; (3) patients who were ready to undertake the minimally invasive procedure. Exclusion criteria included: (1) cervical vertebral instability; (2) severe spinal stenosis; (3) calcification of the annulus fibrosus; (4) ossification of the posterior longitudinal ligament.
All nine patients were informed of the details of the interventional treatment before the procedure, and all consented to undergo the surgery and signed the informed consent. The study was conducted in accordance with the Declaration of Helsinki, and the protocol for this study was approved by the Ethics Committee of Xiangya Third Hospital, Central South University (2016-S240).
A preoperative evaluation is necessary to determine the targeted cervical level, and symptomatic discs can be confirmed by MRI before the procedure. Previous study supports the use of provocation discography in cervical perfusion14. However, the role of discography in the PLD remains unclear. Thus, the discography is not systematically carried out before the surgery according to the recommendation of our center.15. The patient was required not to eat or drink on the day of the procedure, and a sedative is administered during the procedure if necessary. A single prophylactic course of cefuroxime was applied intravenously 30 min before surgery. Local anesthesia is performed with a 1% lidocaine infiltration solution into the skin and subcutaneous tissue.
The patient is placed in the supine position with the shoulder slightly elevated to allow better visualization of the lower cervical disc space (C6/C7). A high-frequency linear probe (Fujifilm, SONOSITE, USA) is used to scan the cervical region (Fig. 1a) and the scan depth is set to approximately 4–5 cm. A 19-G cannula with an internal stylet was inserted under ultrasound guidance, the cannulation device is shown in Fig. 1b. In-plane ultrasound guidance is used to insert the cannula (Fig. 1c).
It is important to identify the cervical structures before the puncture. The detail of the sonoanatomy at different cervical levels is described as before16. The first step is to identify the transverse process of C6 and its corresponding tubercles. Indeed, the ultrasound probe is placed in an axial position at the level of the cricoid cartilage. The anterior (Chassaignac tubercle) and posterior tubercle are easily identified by the characteristic U-shape, as shown in Fig. 2a. To avoid damage to the internal jugular vein and carotid artery (Fig. 2b), we move the probe to the midline to scan the cannulation space. In Fig. 2c, the path between the puncture entrance and the anterior surface of the vertebral body is designed to effect cannulation of the C5/6 disc.
Following the initial identification of the C6 vertebral body, we can gradually scan the C7 levels by moving the probe downward. C7 can easily be distinguished from other cervical levels by its right transverse process (Fig. 3a). When performing cannulation at this level, care should be taken to avoid inserting the needle into the vertebral artery (Fig. 3b). The pathway of the C6/7 interverbal disc is given in Fig. 3c.
Similarly, the upper cervical level can be identified later when placing the probe in headache. The intertubercular groove becomes vertical at the level of C5 (Fig. 4a), and smooth and superficial for the C4 nerve root (Fig. 4c). The transition of the transverse process and the perforating access at the C4 and C5 levels is given in Fig. 4, respectively.
Low power discectomy
Once the cannula is placed in the interverbal space and stable, we can insert the cannula gradually under the guidance of fluoroscopy with a C-arm unit. The tip of the cannula should be placed at the level of the distal third segment of the disc, confirmed by the lateral fluoroscopic view (Fig. 5a). Meanwhile, the tip is slightly beyond the midline in the anterior-posterior view (Fig. 5b). An optical fiber (200 μm in diameter) is inserted into the cannula and the distal end of the fiber is connected to a laser generator (Alaude-01; Keheng, Heilongjiang, China). We apply a low power laser (2 W, 1 s pulse width) in the procedure. Low power laser can prevent potential tissue damage by thermal radiation, compared to conventional laser therapy (more than 10W). During laser decompression, a small volume of saline solution (1-2ml) is injected into the disc, and we can see several air bubbles through the cannula due to the vaporization effect. The total laser power is set at around 150-200 J for the first cycle. Then we remove the cannula and the fiber to perform the second cycle, the tip of the cannula should be positioned in the middle of the disc during the second cycle (Fig. 5c). Total laser output was not greater than 350 J for a cervical disc to avoid overshooting degenerate changes.
Flurbiprofen (100 mg daily) is routinely administered within two days of surgery to provide analgesic and anti-inflammatory effect. The patient is advised to stay in bed for at least two days and a rigid collar should be worn the following month after discharge due to potential instability of the cervical spine.
The VAS is used to assess pain intensity in patients, rating from 0 (“no pain”) to 10 (“worst pain imaginable”) before and after treatment. Modified Macnab criteria and Neck Disability Index (NDI) were used to examine pain relief and functional improvement after PLD therapy17. Routine follow-up is scheduled at 1, 3 and 6 months after discharge. All patients completed the first two follow-ups by an independent researcher (XZ), who did not perform the procedure. Patients were asked to rate their current pain at each follow-up. All patients were followed at least 5 months after PLD surgery, with a median duration of nine months (ranging from 5 to 13 months).
A descriptive analysis was used to present the clinical characteristics of the enrolled patients. Pain scores were presented as mean ± standard deviation, and NDI values were given as median with its range respectively. The Shapiro-Wilk test was applied to determine the normality value of each variable. Since the data did not fit a Gaussian distribution, we compared pain intensity and functional index between baseline and different follow-up points using nonparametric one-way ANOVA with repeated measures (test of Friedmann). Statistical significance was assumed for a P value less than 0.05.