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This was a single-blind, randomized clinical trial with three parallel groups, conducted in a university clinic located in Kermanshah, Iran, following the CONSORT guidelines. The trial protocol received approval from the Ethics Committee of Kermanshah University of Medical Sciences (Approval ID: KUMS.rec.1395.169) and was registered on the Iranian registry of the clinical trial website (www.irct.ir) on 10/01/2017, with the identification number IRCT201604178035N4.
Participants
The positive stretch provocation test of FAIR, combined with tenderness over the piriformis muscle upon palpation, as determined by an expert physiotherapist, served as the basis for diagnosing DGS during the physical examination. Participants eligible for inclusion in the study were individuals aged 18–60 who experienced lower back pain (LBP) within the area between the lower rib cage and gluteal folds. Exclusion criteria were applied to those with other forms of LBP, such as disc herniation or spondylolisthesis, as well as individuals with hip pathology, recent hip or knee injuries, or systemic diseases impacting their overall health, such as severe diabetes and obesity The exclusion process involved a combination of medical history assessment, radiologic imaging, and clinical tests designed to rule out other potential causes of LBP, such as intervertebral disc herniation or spondylolisthesis.
A total of 45 participants (32 females and 13 males) were included in the study. The mean age (SD) of the participants was 41.80 (9.59) years, and the mean (SD) body mass index was 26.48 (3.21). All participants provided written, informed consent to take part in the trial.
Randomization sequences were generated by a statistician who was not involved in the clinical procedures. A randomized block procedure with a block size of 3 was used. All enrolled participants were randomly assigned to either a control group or a treatment group. The principal assessor (MB.Sh) responsible for clinical data collection was kept blind to the assignment of patients.
The sample size was determined using the Pocock formula, employing G-Power software and drawing on primary outcome data from a prior study [11] (m1 = 3.36, SD1 = 1.58, m2 = 3.36, SD2 = 2.06). With a 95% confidence level and 80% power, it was calculated that 15 participants were required for both the control and treatment groups.
Interventions
All participants received a standardized treatment protocol consisting of 15 min of heat therapy (Hot Pack) and 15 min of transcutaneous electrical nerve stimulation (TENS) applied to the low back and buttock area. In addition, the intervention groups received more specific treatments [9].
Compression exercise
Participants in the compression exercise (CE) group assumed a lying position with the ankle of the tested side resting on the other flexed knee to stretch the muscle. A foam roller was placed under the hip, and they gently rolled on the lateral buttock area at the point of tenderness (see Fig. 1).
Stretching exercise (SE): Participants in the stretching exercise (SE) group were positioned supine with their arms at their sides and palms facing downward. Their healthy foot was placed against a wall and maintained in that position. While lying on their back, they placed the ankle of the affected side over the other knee, just above the kneecap, with the leg bent. Participants were asked if they felt a slight stretch in the piriformis muscle (Fig. 2). Both intervention groups performed three sets of two-minute exercises with two minutes of rest between each set. The control group did not receive any additional interventions.
To ensure that the exercises were performed correctly, an experienced physiotherapist closely monitored the participants. Each group received three sessions of physiotherapy treatment per week, totaling ten sessions.
Outcome measures
Primary outcome
The primary outcome measures the difference in sEMG amplitude values between the gastrocnemius and tibialis anterior muscles on the affected buttock side within each group when compared to the other groups.
Secondary outcome
The secondary outcome evaluates differences in pain or disability among the groups, comparing each group to the others.
To gain insights into the pressure on the sciatic nerve, we assessed the electromyographic activity of muscles innervated by the sciatic nerve, specifically the gastrocnemius and tibialis anterior muscles. This assessment was conducted during the “Flexion Adduction and Internal Rotation test (FAIR),” which allowed us to acquire EMG signals from these muscles while stretching the piriformis muscle.
Surface Electromyography (sEMG)
EMG signals were recorded using the Myon 320 device (Myon AG, Switzerland) with pre-gelled self-adhesive surface electrodes made of Ag/AgCl. To reduce skin impedance, the skin was abraded and cleaned with alcohol wipes. Electrode locations were determined following the SENIAM guideline (http://www.seniam.org/).
The placement for each muscle was as follows:
Gastrocnemius: Positioned on the most prominent bulge of the medial muscle.
The equipment had a common mode rejection ratio (CMRR) of 110 dB and a sampling rate of 1,000 Hz. A bandpass filter was applied, with a range between 20 and 450 Hz.
Tibialis Anterior: Placed at a location one-third of the distance between the tip of the fibula and the tip of the medial malleolus. The inter-electrode distance was 2 cm.
The equipment had a common mode rejection ratio (CMRR) of 110 dB and a sampling rate of 1,000 Hz. A band pass filter was applied, with a range between 20 and 450 Hz. sEMG signals from the gastrocnemius and tibialis anterior muscles were recorded while participants performed the Flexion Adduction and Internal Rotation (FAIR) test. Additionally, sEMG of these muscles was recorded while participants made maximal efforts to plantar and dorsiflex their ankle in the supine position, respectively. The root mean squares (RMS) of these sEMG signals were calculated. To normalize the sEMG of muscles during the FAIR test, the RMS of each muscle was divided by the RMS of the Maximum Voluntary Contraction (MVC) signal of the same muscle. The normalized RMS values were used as the outcome measure for assessment.
The pain intensity of participants was measured using the visual analogue scale (VAS), where 0 indicated no pain, and 100 represented pain as severe as possible. Disability was assessed using the Persian-translated version of the Oswestry Disability Questionnaire, with 0 indicating no disability and 100 representing total disability [12].
Statistical analysis
Sample characteristics were presented as mean (SD) and counts (percentage) for continuous, and categorical variables, respectively. One-way ANOVA and Fisher’s exact tests were applied to sample characteristics comparison.
2 times (pre vs. post) × 3 groups (two different types of exercises vs. control) repeated-measures ANOVA was conducted on all outcome measures (EMG signals, pain and disability) to examine the main effects of the time and interaction. The main effect of the group (as a between-subjects factor) was determined by any conspicuous difference in outcome measures observed between the three groups. So, analysis of covariance (ANCOVA) with LSD post hoc test was performed on the outcome measures to explore the between-group differences. Partial eta-squared was used for effect size.
All statistical analyses were performed using SPSS software version 26 and p < 0.05 were considered the significant level.
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