A prospective, randomized, controlled study was conducted in pain clinic of Seoul National University Bundang Hospital. This study was approved by the institutional review board of Seoul National University Bundang Hospital (IRB No. E-1412-278-002) and was registered in the Clinical Research Information Service (Registration No. KCT0002614). All participants were provided written and verbal information about the trial before providing written consent. The inclusion criteria were as follows: 1) 18–60 years old patients, 2) patients with low back pain and radicular symptoms, 3) patients diagnosed with lumbar disc herniation using MRI, 4) patients with pain duration of four weeks to three months, and 5) patients with a visual analogue scale (VAS) score of 4 or more. The exclusion criteria were as follows: 1) patients with a history of spinal surgery, 2) patients with a neurological deficit that requires emergency surgery, 3) patients receiving osteoporosis medications, 4) patients with compressed fracture, and 5) patients with malignant tumours. Overall, 60 patients were randomly assigned to each group before NSDT using a computer-generated randomization program. The experimental group (n = 30, decompression group, group D) was treated with decompression treatment, and the control group (n = 30, non-decompression group, group N) was treated with pseudo-decompression treatment.
Non-surgical decompression therapy
Non-surgical spinal decompression therapy was performed with Spine MTK-1 (Shinhwa Medical, Busan, Republic of Korea). The NSDT apparatus has built-in air bladders, disc angle pulls adjustments, and harnesses and can increase the distraction force more slowly in the latter part of the decompression. Three split table designs were used for reducing friction in the lumbar muscles.
Group D received 10 treatment sessions for 30 mins for eight weeks. The sessions were provided twice a week for the first two weeks and once a week for the remaining eight weeks. The distraction force and angle were determined using computer programming that puts the patient’s weight and the target disc level. The distraction force was increased by 1 kg per treatment session, starting from half of the body weight minus 5 kg. If the patient complained of pain during treatment, the distraction force was reduced by 25%. Patients laid in the supine position with a flexed knee with a support on the table. They were fastened to the table using two belts, one below the rib cage and the other one on the iliac crest. Decompression therapy was applied with 60 s of hold and 30 s of rest [8, 14, 15]. A safety button can be pushed at any time by the patient to release tension. Group N underwent NSDT using the same protocol and treatment sessions as group D, but no weight loading (distraction force was zero) was applied.
Both groups received nonsteroidal anti-inflammatory drugs and muscle relaxants. When the patient’s VAS score increased by >20%, the daily dosing frequency was increased. Nevertheless, the patient received a weak opioid, such as tramadol, when the patient’s pain was not controlled; however, the patient was excluded if their pain was persistent or aggravated.
Measurement of herniated disc through MRI
Magnetic resonance imaging was performed before NSDT and three months after all sessions to determine the change in herniated disc following NSDT. T2 weighted axial images were used for calculating the herniation index (HI) of the disc. The HI was measured on the axial plane with maximal herniation of the intervertebral disc on MRI (Fig. 1). MRI images were analysed by two experienced pain clinicians, who were not involved in this study. The maximal anteroposterior disc height (AB, mm), which is the diameter of the herniated disc material extended maximally from the posterior border of the vertebral body, was measured. The width of the herniated disc material at the level of the middle AB distance (CD, mm) of the herniated disc material from the coronal plane of the MRI, the maximal anteroposterior canal length (EF, mm), and mid AB distance (GH, mm) were measured. Then, the HI was calculated using the following formula :
Increased HI means that the herniated disc aggravated.
Pain intensity in the low back and lower extremities with respect to the VAS (0 = no pain and 10 = worst pain) was measured before NSDT (baseline), 1, 2, and 3 months after the last session. Additionally, the Korean Oswestry Disability Index (K-ODI) was employed for evaluating the degree of disability at the same time point. Information regarding age, gender, height, weight, symptom duration, and diagnosis (the type of HIVD) were obtained from each patient.
A total sample size of 54 achieved an effect size of 0.55 and 80% power with a type 1 error of 0.05. Effect size was calculated based on the assumption that 50% of patients in the group D would have 50% reduction in pain intensity. To allow for a 10% dropout rate, the final sample size was 30 patients per group. All measurements were expressed as mean ± standard deviation or standard error of the mean (%). Patients’ age, height, weight, symptom duration, and HI change rate (%) after treatment were compared using the t-test or Mann-Whitney U test. For cases in which a significant time-dependent change in pain intensity (VAS) and K-ODI occurred within the same group, a repeated-measures analysis of variance was performed. Additionally, logistic regression was performed for calculating the adjusted odds ratio with a 95% confidence interval for identifying patient factors associated with a successful NSDT. The Hosmer-Lemeshow goodness of fit was used for testing the estimated logistic regression model. All statistical analyses was performed using SPSS Statistics program version 21.0 (IBM Corp, Armonk, NY, USA). A P-value of <0.05 was considered statistically significant.