Effect of ultrasound cavitation on static and dynamic balance in obese postnatal women with diastasis recti: a randomized controlled trial

Introduction

The hormonal, physical, and biomechanical alterations that occur during pregnancy elevate the risk of developing musculoskeletal and postural issues. These problems continue into the postpartum period, and may negatively impact the recovery from pregnancy [1]. One of the most important musculoskeletal problems observed postpartum is an increased transverse inter recti distance (IRD) along the linea alba, defined as diastasis recti abdominis (DRA) [2]. DRA is diagnosed when the space between the two recti exceeds 2 cm in the supraumbilical region, 2.5 cm at the umbilical level, and 3 cm in the infraumbilical area [3].
Ultrasound imaging has demonstrated high accuracy and reliability in measuring the IRD [4]. Though increased IRD can be congenital, it most frequently occurs during pregnancy, and in the first few weeks after giving birth [2]. Pregnant women are more susceptible to DRA due to increased body weight and gravid uterus volume, as well as greater ligament and muscle laxity resulting from increased levels of estrogen and relaxin [5]. Accordingly, the increase in intra-abdominal pressure, along with the anterior stretch over the abdominal muscles, reduces the consistency of the linea alba [5]. Although the likelihood of DRA increases in the late second trimester and reaches its peak after delivery, it may continue for six months after delivery, with a prevalence rate reaching 35 to 39% [6].
Pregnancy causes the abdominal muscles to stretch and separate away from each other, reducing their ability to maintain postural stability and lumbopelvic control [6]. Pregnant women could experience postural instability due to some postural changes associated with abdominal weight gain and increased uterus and breast size [7]. These changes cause a shift in the center of gravity anteriorly and encourage both lumbar hyperlordosis and exaggerated anterior pelvic tilting, which in turn affect postural stability [7]. Moreover, in DRA patients, balance is disturbed during pregnancy due to the transversus abdominis muscle weakening and thus its improper cooperation with other deep core muscles in the central region [3].
Furthermore, women with fetal macrosomia, polyhydramnios, and obesity may develop DRA. Obesity shifts the center of gravity forward, disrupts body balance, raises stress on joints, adversely affects pelvic posture, and causes exaggerated lumbar lordosis. Accordingly, reducing weight may strongly prevent or manage DRA [8-10]. Individuals with higher BMIs may experience greater functional impairments and postural instability, and a higher incidence of falls compared to individuals with normal body weight. The excess amounts of fat modify the geometry of the body, which may affect its biomechanics and movements. As such, following weight-loss regimens or training programs aimed at inducing weight loss could play an important role in improving postural balance [11].
If untreated, in postnatal women, DRA can impact the ability of the trunk to stabilize through the abdominal muscles. Inadequate lumbar stabilization may increase the risk of musculoskeletal dysfunctions that could affect static and dynamic balance, causing a postural imbalance that may increase the incidence of falls, and exacerbate lumbar hyperlordosis and low back pain, thus affecting quality of life [3]. Therefore, there is a need to identify strategies for abdominal obesity management that can aid health professionals in creating a well-organized intervention program aimed at the treatment or prevention of RDA and its subsequent health complications. Such programs may be of great value in supporting women in caring for their health and their children following childbirth.
Ultrasound cavitation (UC) is a promising non-invasive ablative technique used to reduce abdominal obesity by creating cavities in the treated fatty tissues and liberating triglycerides into the interstitial space [12]. Triglycerides are then transferred via the lymphatic system to the liver and undergo metabolism, giving glycerol and free fatty acids and reducing localized adipose tissue volume [12].
Previous studies have found UC to reduce abdominal fats, manifested by a reduction in waist circumference [13,14], waist/hip ratio and blood cholesterol levels [15]. Moreover, it was reported that the UC has a more beneficial effect than radiofrequency in managing abdominal obesity in overweight postpartum women [16].
This study is the first to document how UC affects the static and dynamic postural balance of obese postpartum women with diastasis recti. We hypothesize that UC could reduce the thickness of abdominal subcutaneous fat, serving as a risk factor for rectus diastasis, and thus improve postural stability. Thus, the aim of the study was to determine how a course of UC treatment affects the static and dynamic postural balance of obese postpartum women suffering from diastasis recti.

Material and methods

Study Design

This study is a randomized, controlled clinical trial.

Ethical approval statement

Before starting, the Institutional Review Board of the Faculty of Physical Therapy, Cairo University, granted permission for ethical conduct (No: P.T. REC/012/003570). Study planning and recruitment commenced in March 2023. It was recorded in ClinicalTrials.gov (NO: NCT05900856). Detailed explanations of the study's protocol were provided to the participants, who then provided informed consent prior to joining the study. From June 2023 to December 2023, this study was carried out strictly in accordance with the ethical standards for research concerning human participants as stated in the Declaration of Helsinki.

Recruitment and Randomization

In total, 81 obese postnatal women diagnosed with diastasis rectus abdominis demonstrated interest in the study; all had been referred by a gynecologist and recruited from the outpatient clinic of the Obstetrics and Gynecology department, El Minya University Hospital, Egypt. Of these, 21 were excluded: nine declined by choice, and twelve were found to be ineligible. The exclusion criteria comprised a prior cesarean delivery, surgeries involving the abdomen or back, spine disorders, dermatological conditions of the abdomen, or significant health issues, such as cardiac disorders, poorly regulated diabetes, hypertension, autoimmune diseases, cancers, kidney or hepatic failure, or those with contraindications for weight reduction. Finally, 60 participants were included in the study.
The remaining 60 participants were randomly assigned to two groups. All were postnatal women, aged from 25 to 35 years, with a body mass index (BMI) from 30 to 39.9 Kg/m2. All were recruited between two and five months after giving birth: all were multiparous and had been delivered vaginally. The diagnosis of DRA was confirmed by IRD ranging between 2.5 and 4 cm at 2.5 cm in the supraumbilical area, as identified by ultrasound imaging.
The 60 participants were assigned randomly into two equal groups, i.e. control and study; researcher bias was eliminated by following a random assignment protocol based on the usage of computer-generated numbers in SPSS for Windows Version 23 (USA). Cards were put in sealed envelopes, and distributed into two groups by a research assistant. The assistant than drew the enclosed card from each envelope, which specified whether the participant would be allocated to the control or study group at a 1:1 allocation ratio. The outcome evaluators and data analysts were blinded to the randomized allocations until the final statistical analysis was completed. After randomization, no participant dropped out of the study. All women in the control group received a caloric restriction diet, while those in the study group received caloric restriction plus UC.

Outcome measures

The outcome measures were assessed at baseline and two months later. The evaluators were blinded to the groups to which the participants were assigned. Primary outcome measures included the overall stability index (OSI) of static and dynamic postural balance. Secondary outcome measures included abdominal subcutaneous fat thickness and IRD.

Primary outcome measures

Overall stability index (OSI) of static and dynamic postural balance:
The OSI of static and dynamic postural balance represents the number of fluctuations in static and dynamic balance around the zero axes in both the sagittal and frontal planes [17]. Its value was determined using the Biodex Balance System SD (model: TP-3040-15, DC input: 19V-6.32A, software version 4.0.06, 2017, serial number: R712010010, manufactured in Taiwan). The Biodex Balance system showed good to excellent test-retest reliability with an intra-class correlation coefficient (ICC) for the OSI of 0.85 (95% confidence interval).
Two tests were performed for each participant, starting with the static balance test and ending with the dynamic balance test. In the dynamic test, the instability levels were measured using a platform with 12 different stability levels, starting with the highest, i.e. level 12, and ending with the lowest, i.e. level 1 [3]. Level 1 allowed the movable foot platform to be inclined up to 20° in all directions [18]. The machine recorded the degree of inclination from baseline in both the side-to-side (X) and front-to-back (Y) directions during the test, and converted it to OSI, i.e. the cumulative sum of X and Y. A high score in the OSI represented poor balance performance [18].
Each participant received a training test, followed by three consecutive tests in both static and dynamic modes. Each test was 20 seconds long, with 10 seconds of rest between each. Changes were recorded with regard to the platform center, and the mean of three tests representing the postural fluctuations was automatically calculated and displayed on the device screen [6]. In all cases, the participant was directed to stand bilaterally on the locked platform, placing their bare feet on the four areas I. II. III. IV. The toe of the right foot was placed in area I, the toe of the left foot in area II, the left heel in area III, and finally, the right heel in area IV [3].
All women were asked to look in front of the screen that was adjusted according to their heights, where their hands were placed comfortably beside the bodies. During the assessment, all women were instructed to maintain their balance independently, and keep their feet in position until the end of each measurement while focusing on a target displayed on the screen. The aim was to keep a moving dot marker stationary and centered. They were also advised to use the handles of the device in case of loss of balance, in which case they repeated the test from the beginning [6]. During the first assessment, each foot position was recorded based on the coordinates on the platform grid; this allowed more consistent re-assessment, as the foot could be positioned in the same space in a re-assessment [3].

Secondary Outcome measures

Abdominal subcutaneous fat thickness at the umbilical level:
An ultrasonic imaging unit (Mindary DP10, linear probe, with 10 MHz frequency, serial number: bn-75013216, manufactured in China) was used to assess abdominal subcutaneous fat thickness at the umbilical level for all women in both groups. Ultrasound imaging is known for accurate, reproducible, and quick analysis of abdominal fat. It facilitates a regional, uncomplicated, and immediate analysis of subcutaneous and visceral fat [19].
Prior to the measurement, air bubbles were eliminated by immersing the probe tip in saline and delicately massaging it with a swab. Each woman was instructed to recline in a supine position, and then a layer of thick ultrasound gel was applied to the abdomen to enhance near-field visualization and to prevent any errors while measuring tissue thickness. The linear probe was oriented perpendicular to the skin at the umbilical level to avoid any errors or obliquity during the assessment. The space between the epidermis and Camper's fascia, i.e. the superficial fascial layer delineating the boundary between superficial and deep subcutaneous fat, was measured at the umbilical level. Each measurement was scanned by the same ultrasonography specialist before and after treatment [15]. The measurements were executed at identical locations, with applying consistent and light pressure for optimal ultrasound image clarity. Finally, these measurements were displayed on the monitor screen [15].
The inter recti distance (IRD) at 2.5 cm above the umbilicus:
Ultrasound imaging represents a reliable technique for measuring the IRD in postpartum women with DRA [20]. It has very good reliability with an ICC for IRD of 0.83 (95% confidence interval) [21]. The transverse distance between the medial margins of the two abdominal recti were also measured.5 cm superior to the uppermost part of the umbilicus in all participants. Each woman was directed to adopt a crock lying position, and a suitable amount of KY gel was placed on the abdomen. The convex probe of the device was placed transversely and perpendicular to the linea alba (2.5 cm superior to the umbilicus). All ultrasound images in B mode (brightness mode) were captured at the normal exhalation end, to minimize the impact of breathing and ensure uniformity in imaging across the participating women [4]. Using an on-screen caliper, the transverse linear distance was measured between the medial aspect of the right rectus abdominis muscle and its corresponding point on the left rectus abdominis muscle; all measurements were taken to the closest 0.1 cm [4]. Each measurement was performed by the same ultrasonography specialist before and after treatment. The measurements were executed at identical locations, applying consistent and light pressure to ensure optimal ultrasound image clarity. Finally, these measurements were displayed on the monitor screen [15].

Interventions

The study group consisted of 30 obese women with postpartum diastasis recti, who were treated by UC on the abdominal area for 30 minutes, twice weekly, in addition to a caloric restriction diet (1600 to 2000 Kcal/day, for 2 months). The control group consisted of 30 obese women with postpartum diastasis recti, who were treated by the same caloric restriction diet only (1600 to 2000 Kcal/day, for 2 months).
The caloric restriction diet
The caloric restriction diet was designed by a nutritionist. It consisted of the following: between 20 and 35% of total calorie count consisted of fats, 10 to 35% of protein, and 45 to 65% of complex carbohydrates, with a greater focus on fruits, vegetables, fiber-rich whole grains, and cereals [22]. All women in both groups met the nutritionist at the beginning of the study to collect information such as height, weight, age, type of obesity (general and/or localized obesity), eating habits, and appetite to obtain the appropriate treatment course. Based on the taken information, the nutritionist provided the participant with a suitable diet program. The adjustment to the diet took about two weeks, and then weekly follow-up visits were performed at the clinic. To ensure adherence to the caloric restriction diet, all women were taught to keep a daily food diary to record dietary intake, which was revised at each clinic visit. Additionally, they had access to a dedicated phone line to contact the nutritionist with any questions or issues related to their diet, providing immediate feedback and continuing support.
The ultrasound cavitation (UC)
The participants in the study group also received ultrasound treatment to reduce abdominal fats. For this purpose, a Dae Yang Mabel 6 UC device was used: frequency (50 to 60 Hz), power consumption 150 Watt, power input AC (100 to 230 Volt), hand probe diameter 8.0 cm (Daeyang Medical Company, Korea). The UC technique was explained briefly to all participants to give them confidence and encourage cooperation throughout the treatment.
All participants were advised to empty her bladder prior to the start of treatment to ensure comfort and relaxation throughout the session. Additionally, they were advised to consume 1 liter of water before and after each session to enhance fat removal by the kidneys. At the start of the session, each woman was asked to stand upright. The abdominal region was divided vertically into two symmetrical right and left segments by two lines: one was drawn bilaterally from the midpoint under the armpit to the iliac crest, and the other anteriorly from the diaphragmatic center to the point midway between the two iliac crests [16].
The participants then adopted a relaxed posture lying on her back. The skin of the anterior abdominal skin was sterilized with alcohol, and a conductive gel was applied to the cavitation head. The machine was then switched on at an intensity of 50%; this level was maintained for the first eight sessions, and increased to 75% for the subsequent eight sessions. The cavitation head was applied to each abdominal segment for 15 minutes using a slow, minimal circular movement with a vertical rhythm; thus, the entire abdominal area was covered in one 30-minute session. At the end of the session, the skin was cleaned with cotton. This protocol was applied biweekly for eight weeks [16].

Sample Size Calculation

The sample size was computed using data from a pilot study. The calculation was based on the significant change in the mean difference in static balance OSI between the control group (calorie restriction diet only) (0.13 ± 0.07) and the study group (UC plus calorie restriction diet) (1.37 ± 0.48), using a two-tailed unpaired t-test, with α = 0.05, a power of 80%, and an effect size of 0.74. The findings indicated that a sample size of 30 patients was required for each group (G-Power 301). A flow diagram of the participants throughout the study is given in Figure 1. No adverse effects or complaints were reported by the participants either during or after the treatment period.

Statistical analysis

The results were presented as mean ± standard deviation (SD). The Kolmogorov-Smirnov test was performed to examine the distribution of the pre-treatment data. An unpaired t-test was used to compare variables with a normal distribution between groups. The analysis of covariance (ANCOVA) test was used to compare the pre-treatment values of the two groups, and the post-treatment values while controlling the effect of pre-treatment values. A paired t-test was used to compare pre-treatment and post-treatment data within each group. The data analysis was performed using Statistical Package for Social Sciences (SPSS) software (version 19 Windows). P value ≤ 0.05 was regarded as significant.

Results

Table 1 presents the baseline characteristics of all participants in both groups, viz. age, weight, height, and body mass index. All values are given as mean ± SD. Statistically insignificant differences can be seen between groups for all baseline characteristics.
The inter-group comparisons post-intervention and the intra-group comparisons are given in Table 2. Although significantly improved values were noted after treatment for all outcome variables in both the study and control groups, the study group demonstrated a greater improvement in static OSI (by 64.53%), dynamic OSI (by 33.33%), abdominal fat thickness (by 32.44%), and IRD (by 32.65%); the respective values for the control group were 24.83, 16.56, 1.62, and 1.34%. At baseline, no significant differences were found between both groups in terms of static OSI, dynamic OSI, abdominal fat subcutaneous thickness, and IRD. However, following the intervention, significant differences were found between the groups regarding the mean difference (MD) in static OSI (MD = 0.51; p = 0.001), dynamic OSI (MD = 0.18; p = 0.007), subcutaneous fat (MD = 1.01; p = 0.001), and IRD (MD = 0.98; p = 0.001). In all cases, the more favorable value was noted for the UC group compared to the control group.

Discussion

Diastasis rectus abdominis (DRA) frequently occurs during the prenatal and postnatal phases and could result in numerous health issues, including lower back discomfort, decreased functionality, impaired balance, and an increased likelihood of falls [3, 23]. This research aimed to ascertain how UC affected the static and dynamic postural balance of obese postpartum women suffering from diastasis recti. Our findings reveal significant differences in post-treatment mean values of static OSI, dynamic OSI, abdominal fat subcutaneous thickness, and IRD between the two groups of participants; a more substantial reduction was observed in the study group receiving UC and a diet compared to the controls receiving the diet alone.
Elevated BMI and excess abdominal fat are both influential factors for DRA, possibly due to the presence of larger omental/mesenteric fat deposits, which increase intra-abdominal content and anterior wall pressure, and thus widen the inter-recti distance. As such, abdominal obesity management is one of the most important approaches for preventing or treating DRA [9]; one primary strategy involves adopting a balanced, low-calorie diet, particularly for women with a BMI of 25 Kg/m² or higher [24].
Our findings also confirm that reducing abdominal obesity could improve postpartum DRA and postural instability, as reported by Yalfani et al. [3], who stated that fats accumulating around the stomach are a potential predisposing factor for increasing DRA. They are also in line with those of Suyardi et al. [25], who found a low-calorie diet to have a positive effect on reducing both body weight and waist to hip ratio.
Regarding the efficacy of UC on abdominal fat thickness, our results agree with those of Taha et al. [26], who report that combining focused UC with aerobic exercises yielded greater efficacy in reducing both localized abdominal and intrahepatic fats in non-alcoholic fatty liver patients. El Keblawy et al. [27] also found UC to be more effective than low-level laser therapy in reducing abdominal fat thickness measured by ultrasonography. Moreover, Maher et al. [28] documented that a combination of UC with low-caloric balanced diet and treadmill exercises achieved better efficacy for treating pre-diabetic obese women than a low-caloric balanced diet and treadmill exercise alone. Kiedrowicz et al. [29] propose that UC acts by generating mechanical stress, which disrupts the adipose tissue and generates heat. It also causes enhanced microcirculation, faster metabolism, activated enzymatic reactions, heightened collagen fiber elasticity, and increased cell membrane permeability.
Our results also indicate that UC may improve balance via reducing obesity. This is similar to Handrigan et al. [30], who found overweight individuals to sway more than those of normal weight, and propose that training programs aiming to improve balance control should primarily target weight loss. Their results indicated that the decrease in body mass caused by a weight loss program was accompanied by a reduction in the speed of the center of foot pressure, signifying greater balance control. This improvement may be attributed to an increase in relative muscle strength, which is needed for balance regulation in obese persons.
Interestingly, a few studies have reported that UC no effect on abdominal fat thickness. Shek et al. [31] found that focused UC lacked efficacy in body contouring for Southern Asians compared to Caucasians; in the former, abdominal fat thickness measured using diagnostic ultrasound remained approximately the same after three sessions. A reasonable explanation may be attributed to the slimmer physical features and smaller fat cells of the studied subjects, as a reduction in fat cell volume would be noted in more voluminous adipocytes. Another explanation may arise from the measurement bias caused by abdominal skin laxity after lipolysis.

Strengths and limitations

The present study reveals many valuable strengths. It represents the first blinded randomized study assessing the impact of UC on the static and dynamic postural balance of obese postpartum women with diastasis recti. A major strength of the study is that it measures the OSI of static and dynamic postural balance using the Biodex balance system, and IRD and abdominal subcutaneous fat thickness by ultrasonography, both of which are valid and reliable tools. It also employs a correct sample size and obtains objective data with significant findings without undesirable outcomes. Such an approach improves the reliability and validity of its findings. However, the study also has some limitations. The study intervention was relatively short, and long-term investigations are needed to evaluate the impact of UC on static and dynamic balance in obese postpartum women with diastasis recti. Moreover, the studied women might not be entirely representative of the general population, as they were specifically recruited from an outpatient clinic.

Clinical implications

Our findings are of great benefit to the field of physical therapy, and UC may be of great value to programs dedicated to treat obesity and improve balance in obese postpartum women with diastasis recti.

Conclusions

An eight-week program of ultrasound cavitation on the abdominal area was effective in improving static and dynamic postural balance. It also reduced abdominal subcutaneous fat thickness and rectus diastasis abdominis in obese postnatal women with diastasis recti.

Funding

This research received no external funding.

Conflicts of interest

The authors declare no conflict of interest.

References