Bilateral transcutaneous tibial nerve stimulation: a promising treatment for women with postpartum constipation: A randomized controlled trial

Introduction

Constipation, i.e. functional bowel disorder, is a common health issue affecting people of various ages, although it is more commonly observed during pregnancy, after delivery, and following surgery. As bowel habits vary significantly from three bowel motions per day to three per week, normal behavior might be described as fewer than three bowel motions weekly [1]. It is not uncommon for new mothers to report constipation after giving birth, with many complaining of constipation in the first three to six months, and some may even experience it for up to a year after delivery [2].
Such postpartum constipation is more common after a cesarean section (CS) delivery (57%) than after a vaginal delivery (47%) [3]. It has been attributed to the high progesterone levels experienced during pregnancy, which frequently cause constipation; these remain elevated for a few weeks after birth, resulting in hypomotility of the gastrointestinal tract and relaxation of the abdominal muscles, increasing constipation and gas production. Constipation can also be exacerbated by changes in the pelvic floor muscles caused by high intra-abdominal pressure, luminal obstruction from an enlarged uterus, consuming insufficient fiber during delivery, and hemorrhoids that hurt and restrict efficient bowel elimination [4].
Pharmaceutical treatments in the form of laxatives are effective on treating constipation, but their effects fade with the end of their use. Also, their prolonged use is associated with side effects, such as abdominal pain, diarrhea, potentially fatal hyperphosphatemia, hypoalbuminemia, and raised liability for fecal incontinence [5]. Therefore, non-pharmacological therapies are encouraged; these can include abdominal massage, aerobic exercises, and other complementary therapies, such as acupuncture and neurodynamic stimulation [6,7].
One of the most common non-pharmacological methods proven to treat fecal incontinence [8], overactive bladder syndrome [9] and constipation is Percutaneous Tibial Nerve Stimulation (PTNS) [10]. The tibial nerve arises from the nerve roots of Lumbar 4 up to Sacral 3, which also feed the hindgut and the pelvic floor. However, PTNS is expensive and invasive [11]. A non-invasive alternative for stimulating the tibial nerve that does not use needle puncture is Transcutaneous Tibial Nerve Stimulation (TTNS)[12]. TTNS is also less expensive and harmless, and patients can use it at home [13].
Although some previous research indicates that TTNS is effective at treating constipation [7,14,15], no research has investigated its effect on constipation in postpartum women. Therefore, the aim of the present study was to ascertain the effectiveness of TTNS in alleviating the symptoms of constipation and enhancing the quality of life in postpartum women.

Materials and methods

Study Design
This is a prospective, randomized, controlled trial study. It was carried out between August 2022 and February 2023.
Ethics
Ethical approval for the study was granted by the Institutional Review Board at the Faculty of Physical Therapy, Cairo University [No. P.T.REC/012/003728]. The study was prospectively registered at ClinicalTrials.gov with the number NCT05455853. The study followed the CONSORT statement adhered to the Principles of the Declaration of Helsinki for the ethical conduct of human research.
Settings
Participant recruitment and treatment procedures were conducted at the Department of Physical Therapy for Women's Health, Quillin General Hospital, Kafr El-Sheikh, Egypt.
Participants
The study included 56 postpartum women. Their age ranged from 20 to 35 years, and their Body Mass Index (BMI) varied from 25 to 33 kg/m2. The inclusion criteria comprised delivery by Cesarean section (CS), constipation occurring during the first week after delivery, meeting the Rome IV criteria for constipation, and approval from an obstetrician to take part. Each participating woman had to fulfill a minimum of two Rome IV diagnostic criteria related to constipation to ensure the diagnosis.
Women who had inflammatory bowel disease, digestive tract disorders, irritable bowel syndrome, genital organ prolapse or anal fissure, congenital anorectal abnormalities, severe distal venous insufficiency, or skin eruption at the stimulation site were excluded from the study. In addition, patients using laxatives or those with diabetes mellitus, an implanted pacemaker or metallic implant, recent lower limb surgery, peripheral neuropathy, and psychological distress were also excluded. An overview of the study protocol is illustrated in Table 1.
Tab. 1. Schedule of enrollment, intervention, and assessment (SPIRIT)
Sample size calculation
The sample size was determined using G*Power software (version 3.0.10) based on the PAC-SYM abdominal symptoms from the pilot study. It had 80% power at α = 0.05 level, two measurements for each of the two groups, and an effect size of 0.41 using the F-test MANOVA repeated measures within and between interactions. The minimal appropriate sample size was 49 subjects, adding seven (15%) subjects as a dropout, making the total sample size 56 subjects (28 in each group).
Randomization and blinding
The women were randomly allocated to either the TTNS group or control group (ratio 1: 1) using an online randomization application (http://www.randomizer.org/), with 28 participants in each of the TTNS group and the control group. The generated random numbers were used to systematically number index cards that included the random group allocations; to guarantee that allocation was blinded, the cards were created by a researcher who did not have a clinical role in this study. A 10-year experienced outcome assessor and the data analyst were blinded to the allocation randomization till the completion of the statistical analysis.
Interventions
All enrolled patients received a thorough explanation of all study procedures before signing a written informed consent; this document acknowledged the security of their data, described the nature and purpose of the study, and informed than that they were free to withdraw from the study at any time without fear of consequences.
In each session, the patients in the TTNS group received bilateral TTNS for 30 minutes, as well as breathing exercises, abdominal muscle training, and behavioral therapy advice. In contrast, patients in the control group received breathing and abdominal exercises with behavioral therapy advice, with no TTNS. All treatment interventions were administered by a physiotherapist with five years experience, three times weekly for four weeks, with the first session commencing in the first week following delivery [3]. No adverse effects were noted throughout the treatment for any participant in either group.
• The transcutaneous nerve was stimulated using an EV-906 device (Taiwan) was used in continuous mode for 30 minutes with a 10 Hz frequency and 200 μs pulse duration. Self-adhesive surface-stimulating electrodes were used for stimulation on both lower limbs. The negative electrode was positioned behind and above the medial malleolus, and the positive electrode was positioned 10 cm above the negative one (Fig. 1). The intensity was steadily increased until a tingling feeling was experienced in the foot, or planter flexion of the ipsilateral toes. The intensity was modified according to the comfort level of the patient. The stimulation was performed in the morning, immediately after breakfast [7, 11].
Fig.1. Application of bilateral TTNS
• For diaphragmatic breathing, the participant lay on her back, putting one hand on her abdomen and the other on her chest. She was advised to inhale deeply, gradually, and slowly for four seconds, hold for two seconds, and then exhale slowly through her pursed lips for six seconds. For successful performance of the exercise, the patient was instructed that the hand above the abdomen should move further than the hand on the chest, with little or no motion by the former [16]. Three series of ten repetitions had been completed with rest in between, and the participant was advised to rest longer if she felt dizzy or lightheaded.
• For isometric training of the abdominal muscles, each participant was instructed to lie supine with the lumbar curvature in a neutral position and the hips slightly abducted. Two distinct isometric contractions of the abdominal muscles were performed: the first was the "Hollowing maneuver," which involves gently drawing the lower abdomen toward the spine. The contraction continued while breathing was maintained. The second was the "Bracing maneuver," in which the participant was instructed to tighten their abdominal wall and increase their lateral waist diameter. Three series of five repetitions of each abdominal maneuver were performed with 5 s of holding time and relaxations for each. All contractions were performed without apparent motion of the rib cage, lumbar spine, or pelvis [17].
• All women received the following behavioral therapy advice throughout the treatment program. Briefly, they should sit on the toilet for 20 minutes following breakfast and dinner, and establish an identical daily bathroom routine. They should sit on the toilet in a proper position, i.e. bending anteriorly with forearms relaxing on thighs, elevating the feet on a tiny block, keeping the feet apart, relaxing the shoulders, not prohibiting the urge to defecate, and relaxing the muscles of the stomach. In addition, they should drink about 2 l of water every day, ensure sufficient fiber intake (20–35 g per day), and avoid any foods or drinks that contain caffeine [18].
Assessment
All participants were instructed to fill out the questionnaires used in the evaluation procedures before the treatment program and four weeks after its end. The therapist provided a thorough explanation of each questionnaire item.
• Assessment of quality of life (primary outcome): The Patient Assessment of Constipation Quality of Life Questionnaire (PAC-QOL) was utilized to evaluate QoL for constipated patients; it is regarded as a global evaluative instrument with validity and reliability in patients with constipation) Cronbach's alpha >0.80; intraclass correlation coefficients (ICCs) >0.70, except for the satisfaction subscale ICC=0.66), comprising 28 items with four subscales (physical discomfort, psychosocial discomfort, worries and concerns, and satisfaction). It assesses how constipation affects daily living, with a lower total score denoting a higher QoL [19].
• Constipation symptoms (secondary outcome measure) were assessed using the Patient Assessment of Constipation Symptom Questionnaire (PAC-SYM). It comprises 12 items, arranged into three symptom subscales: an abdominal subscale with four items, a rectal subscale with three items, and a stool subscale with five items. The scores for each item are given on 5-point Likert scales, varying from 0 to 4 (0 denoting "no symptom," 1 denoting "mild," 2 denoting "moderate," 3 denoting "severe," and 4 denoting "very severe"). The overall score is obtained by dividing the overall score by the number of responses, resulting in a mean between 0 and 4. A lower score indicates a lower symptom burden. According to observational data, the PAC-SYM questionnaire is responsive to change over time and possesses concurrent validity (r= 0.68 for participants and r=0.72 for the researcher), test-retest reliability, and internal consistency (Cronbach’s alpha = 0.89; ICC = 0.75) [20].
• Stool consistency (secondary outcome measure) was measured using the Bristol Stool Form Scale (BSFS), a quick, valid, and reliable measure for evaluating stool consistency: the inter-rater and intra-rater reliability of the BSFS by individual stool type is excellent, with respective ICC of 0.88 (95% CI: 0.86–0.90, p < 0.001) and 0.89 (95% CI: 0.86–0.91, p < 0.001) [21]. It is a standard research tool and an ordinal scale for rating and classifying stools into seven groups according to consistency, i.e. from hard masses as nut feces (type 1) to a completely liquid with no solid pieces (type 7). Constipation is indicated by types 1 and 2; types 3, 4, and 5 reflect consistent normal stools as simple to defecate, while types 6 and 7 have abnormal consistency [21]. This scale provides textual definitions for each stool form to make sure patients can appropriately characterize their stool patterns [22].
Statistical analysis
The demographic data of the TTNS and control groups were compared using an unpaired t-test. The Shapiro-Wilk test was employed to assess the normality of the data distribution. Wilcoxon and Mann-Whitney tests were used to compare the within-group and between-group effects of the measured variables. The scores were subjected to statistical analysis using the Statistical Package for the Social Sciences software (version 20 for Windows; SPSS Inc., Chicago, Illinois, USA). P ≤ 0.05 was considered significant.

Results

Sixty-five patients were initially screened for eligibility; following screening, 56 were accepted into the study and randomized into two groups. No participants withdrew after randomization (Fig. 2). The normality assumption, variance homogeneity, and presence of extreme scores were checked in the data. The results of the Shapiro-Wilk test for normality indicated that the BSS variables, PAC-QOL scores, and PAC-SYM scores were not normally distributed.
  Fig. 2. CONSORT flow chart of the study
No significant difference was found between the mean age, weight, height, and BMI of the two groups (p > 0.05; Table 2). Also, no significant difference was found between two groups in parity (p > 0.05; chi-square test).
Tab. 2. Demographic data of the participants in both groups.
Impact of physical therapy program on PAC-QOL score:
Both groups demonstrated a statistically significant reduction in physical discomfort, psychosocial worries and concerns, and total PAC-QOL score, and a significant increase in satisfaction after treatment compared with baseline (p = 0.001; Table 3). Significant differences were found between groups in terms of physical discomfort (p = 0.005), psychosocial factors (p = 0.012), worries and concerns (p = 0.001), level of satisfaction (p = 0.002), and total PAC-QOL score (p = 0.001); in each case the TTNS group demonstrated a better result.
Impact of a physical therapy program on BSFS
Both groups demonstrated a statistically significant improvement in post-treatment BSFS compared to pre-treatment (p = 0.001); however, no statistically significant difference was found between groups (p = 0.463) (Table 3).
Tab. 3. Comparison of PAC-QOL and BSFS pre- and post-treatment for both groups
Impact of the physical therapy program on the PAC-SYM score
Statistically significant reductions in abdominal, stool, rectal symptoms, and total PAC-SYM score was found in both groups following therapy compared with baseline (p = 0.001; Table 4). No significant differences in abdominal symptoms were found between groups following therapy (p = 0.612); however, stool, rectal symptoms, and total PAC-SYM score after therapy (p = 0.001) were significantly more favorable in the TTNS group.
Tab. 4. Comparison of pre and post-treatment PAC-SYM for both groups

Discussion

The aim of the current study was to determine the effect of TTNS on quality of life and on constipation symptoms in postpartum women. As it is important to carefully consider holistic symptoms when studying functional bowel disease, it was decided to include the PAC-QoL tool as the primary outcome measure as it is the most thoroughly-validated constipation-specific quality of life scale. Furthermore, the PAC-QoL is the benchmark for reporting constipation trials [7]. Also, TTNS was used bilaterally because unilateral application allows the sacral plexus to exhibit asymmetrical dominance, with one side controlling its designated areas more than the other. In addition, bilateral nerve stimulation activates more ascending afferent pathways [14]. Also, neuromodulation was administered in the morning immediately after breakfast as intestinal activity is highest at this time [23].
Our findings indicate significant improvements in all outcome measures in both groups following therapy (p < 0.05). The mechanical and neurological effects of abdominal muscle training and diaphragmatic breathing in the control group may help to explain the significant improvement in all outcome measures. The mechanical impact includes promoting muscle coordination, fecal propulsion, and abdominal muscle tone and activating colonic movements. In addition, its neurological impacts involve activating the sympathetic nervous system to calm anxiety, activating the parasympathetic nervous system to enhance motility, and elevating endogenous serotonin to lessen pain and discomfort [24].
The significant improvement observed in the control group over the course of therapy agrees with Abd El-Aziz et al. [25], who found that strengthening the abdominal muscles reduced the severity of long-lasting constipation. These findings are supported by Silva and Motta [24] who used abdominal and respiratory exercises as well as abdominal massage to cure chronic functional constipation in children. They report that a six-week course of treatment resulted in more frequent bowel movement, and concluded that physical therapy could be used as an alternative therapy for constipation.
The between-group comparison revealed no significant difference between the groups post-treatment regarding BSFS (p > 0.05). However, the TTNS group demonstrated significant improvements in total PAC-SYM and PAC-QOL scores compared to controls (p < 0.05). Zhang et al. [26] attribute the superior improvement observed for peripheral neuromodulation, i.e. TTNS, to its effect on promoting activation of the parasympathetic and inhibiting sympathetic nervous systems, leading to improved intestinal peristalsis and reduced constipation symptoms. It may also enhance excretion by increasing the frequency of both antegrade and retrograde colonic propagation sequences [27]. Our present findings are consistent with those of Iqbal et al. [7] who investigated the impact of bilateral TTNS on chronic constipation. They discovered that daily bilateral TTNS sessions lasting 30 minutes at home for six weeks significantly improved psychosocial well-being, anxiety, and concern for constipation-related manifestations.
Madbouly et al. [14] demonstrated that bilateral TTNS could provide symptom relief in patients with obstructed defecation without any anatomical obstruction. A group of 36 patients (25 women and 11 men) received 30-minute TTNS sessions, three times weekly, for six weeks. They reported a significant enhancement in their PAC-QoL score and stopped using assistive methods of defecation in >75% of their excretion attempts. These findings were also supported by Gokce and Gokce [15], who examined the effectiveness of bilateral TTNS on constipation severity in elderly patients with functional constipation. They found TTNS treatment to be associated with a significant improvement in symptoms, with a considerably shorter duration spent in the bathroom and a reduction in the requirement for laxative or softener use. Additionally, Stundienė et al. [28] reported that TTNS might be efficacious in patients with constipation, i.e. slow transit constipation (STC) and obstructive defecation, who have not responded to most conservative therapies. Stool frequency significantly increased, and abdominal pain, bloating, and laxative use were decreased. Our current findings were also confirmed by Van Wunnik et al. [10] in a study of adolescent patients with chronic refractory constipation. All patients significantly increased the frequency of their bowel motions and significantly decreased their abdominal pain following Sacral Nerve Stimulation (SNS), with no symptoms being observed at six-month follow-up.
In contrast, the current findings contradict those of Dinning et al. [27], who found that three weeks of SNS application could not enhance the frequency of bowel motility in patients with STC. No significant improvement was noted in response rate or outcome measures (stool frequency, QoL, global satisfaction, bothersome scores, number of defecations that correlated with straining or a sensation of complete evacuation, days/week laxative use). They also differ from those of Kumar et al. [29], who studied the impact of PTNS in treating cases with refractory constipation who did not respond to maximal laxatives and biofeedback therapy. Their findings reveal no significant variation in the mean Wexner score and no variation in colonic transit time between the whole population after 12 sessions of PTNS.
To the author’s knowledge, this study is the first to use bilateral TTNS, a non-invasive treatment with no significant adverse effects, to treat postpartum constipation. Two key strengths of this study are its randomized design and calculated sample size. However, the study only lasted for four weeks with no patient follow-up. Therefore, further research aimed at determining how bilateral TTNS will affect postpartum constipation should aim to observe the patients over a longer term with follow-up.

Clinical implications

Bilateral TTNS is a simple, non-expensive, and non-invasive therapeutic modality that can be suggested for both physiotherapists and patients as a treatment for postpartum constipation without adverse effect. It can be administered as an incorporated approach together with traditional physiotherapy in the form of diaphragmatic and abdominal strengthening exercises, as well as behavioral therapy advice.

Conclusions

Among postpartum women with constipation, bilateral TTNS integrated with traditional physical therapy, in the form of diaphragmatic and abdominal strengthening exercises combined with behavioral therapy advice, provides a greater improvement in constipation symptoms and quality of life compared to traditional physiotherapy alone.

Funding

This research did not receive any external funding.

Conflict of interest

There are no conflicts of interest.

References