He et al. Insights Imaging (2021) 12:87 https://doi.org/10.1186/s13244-021-01021-6 Insights into Imaging ORIGINAL ARTICLE Open Access Muscle elasticity is diferent in individuals with diastasis recti abdominis than healthy volunteers Kai He1†, Xiuling Zhou2†, Yulan Zhu3, Bo Wang2, Xiaojian Fu1, Qiyuan Yao1, Hao Chen1* and Xiaohong Wang2* Abstract Objective: To determine the value of shear wave elastography (SWE) in assessing abdominal wall muscles, includ- ing rectus abdominis (RA), external oblique muscle (EO), internal oblique muscle, and transversus abdominis (TrA) in patients with diastasis recti abdominis (DRA) and healthy controls. Methods: From October 2018 to December 2019, 36 postpartum DRA patients and 24 nulliparous healthy women were identifed. Inter-rectus distance (IRD) measurements were taken by B-mode ultrasound. Shear wave speed (SWS) values were acquired by one operator at ten specifc locations. Clinical and ultrasound variables, including demo- graphics, IRD, muscle thickness, and muscle SWS, were compared between the two groups using Student’s t test or Fisher’s exact test. Pearson correlation analyses were conducted for the variables of IRD, muscle thickness, and SWS in the 36 DRA patients. Results: The maximum diameter of recti abdominus separation was located at the umbilicus in DRA patients (4.59 1.14 cm). The SWS value was signifcantly lower in the RA (p 0.003) and higher in the TrA muscle (p < 0.001) in DRA± patients compared with the age-matched controls. However,= SWS in both muscles (RA and TrA) showed a sta- tistically positive correlation with IRD (p < 0.05). In addition, the SWS value in EO statistically decreased in DRA patients compared with the healthy controls (1.65 0.15 vs. 1.79 0.14, p 0.001). ± ± = Conclusions: The application of SWE to abdominal wall muscles in DRA patients is feasible. The correlation between SWS value and IRD in RA should be interpreted with caution. Keywords: Sonoelastography, Shear wave speed, Diastasis recti abdominis, Linea alba, Abdominal wall muscle Key points • Imaging assessment using shear wave elastography of abdominal muscle elasticity. • Abdominal muscle elasticity in DRA patients was dif- *Correspondence: [email protected]; [email protected] ferent from healthy volunteers. †Kai He and Xiuling Zhou are co-frst authors and have contributed equally to this work • Abdominal muscle elasticity in DRA patients was 1 Department of General Surgery, Huashan Hospital, Fudan University, 12 correlated with inter-rectus distance. Wulumuqi Road, Shanghai 200040, China 2 Department of Ultrasound, Huashan Hospital, Fudan University, 12 Wulumuqi Road, Shanghai 200040, China Full list of author information is available at the end of the article © The Author(s) 2021. 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Insights Imaging (2021) 12:87 Page 2 of 11 Background internal oblique (IO) muscle, or transversus abdominis Diastasis recti abdominis (DRA) is the enlargement of (TrA), is comparatively higher. the distance between the edges of the recti abdominis Tis study aimed to determine the utility of apply- along the linea alba with no fascial defect [1, 2]. Nor- ing SWE to the evaluation of abdominal wall muscles, mally, the rectus muscles are fused at the midline with including rectus abdominis, external oblique muscle, no more than 1 to 2 cm separation [3]. A signifcant internal oblique muscle, and transversus abdominis, number of women are afected by DRA during the pre- in patients with DRA and healthy controls, to assist in natal and postnatal periods [4], resulting in functional clinical management. No study has been reported on the problems, such as back pain and hernia [5]. SWE of abdominal wall muscles in DRA patients. Clinically, DRA is evaluated by fnger breadth. Te widths of the two recti abdominis muscles are assessed Methods by palpation 4.5 cm above and 4.5 cm below the umbili- Patients cus, along the linea alba [6]. Separation is observed Tis study was reviewed and approved by the Institute most commonly at the umbilicus. A width greater than Ethics Committee of Huashan Hospital (No. KY2018- or equal to the width of two fngers is defned as DRA 438). Informed consent forms were signed by all par- [5]. No separation or a width of less than two fngers is ticipants. Te study protocol was registered in China defned as no DRA. However, in the past twenty years, Clinical Registry Center (No. ChiCTR1900023012). From the reliability of palpation has been debated [1, 3, 4]. October 2018 to December 2019, postpartum women Terefore, prior studies investigated the application of suspected of DRA at the outpatient clinic in our insti- advanced imaging technology, like B-mode ultrasound tution were identifed. Eligible subjects were recruited (US), on the evaluation of inter-rectus distance (IRD) based on the following inclusion criteria: 1) age between measurement. Most studies demonstrate the superior 18 and 60 y/o; 2) IRD greater than or equal to 2-fnger accuracy and validity of imaging tools compared to pal- width on palpation, irrespective of the locations along pation [7–9]. the midline, measured in the standard supine crock- Clinical management of DRA is challenging [10]. Based lying position with arms crossed over the chest; and 3) on the pathophysiology described by Baumann et al. [11], full-term fetus. Te exclusion criteria for all postpar- the combination of physiotherapy and surgical repair tum women were as follows: (1) additional history of has the potential to improve the anatomical divarication abdominal surgery or injury (except cesarean section); and the laxity of the ventral abdominal muscles. In other (2) chronic or degenerative pathology of the muscle (e.g., words, the preoperative assessment of DRA is not solely autoimmune myositis); (3) abdominal rehabilitation of a distance measurement problem. Individual preopera- neuromuscular electrical stimulation within the previ- tive evaluation of physiologic tension is important. Up to ous 6 months; and (4) inadequate clinical and ultrasound now, conventional modalities, including B-mode ultra- (US) imaging data. Nulliparous age-matched women sound, computed tomography, and magnetic resonance were recruited from the physicians and nurses at our imaging, have been used to assess the IRD, but no func- institution to participate as healthy controls. Te exclu- tional biomechanical property evaluation was available. sion criteria for the healthy participants were similar to Terefore, an objective imaging assessment of the intrin- that for DRA patients, including age (< 18 and > 60 y/o), sic abdominal muscle characteristics, such as the elastic- surgery, and history. Te clinical variables of age, weight, ity, is needed to predict successful treatment and disease and height were recorded for each subject. progression. In recent years, ultrasound shear wave elastography US data collection (SWE) has been increasingly used to measure physiologic Equipment and pathologic muscle behavior due to its non-invasive- Ultrasound images were obtained using a high-end scan- ness, high accuracy, user-friendliness, and availability in ner (Aixplorer, Supersonic Imagine, France) equipped commercial ultrasound scanners [12–14]. However, to with an SWE mode (general preset). Te scanner was this end, no convincing evidence in the current litera- coupled with a linear array probe (SL10-2, Supersonic ture has established the application of SWE for detecting Imagine, France). Elastography was performed to evalu- muscle properties in DRA patients. Based on our previ- ate tissue elasticity. Elasticity is the tendency of tissue to ous study of SWE in incisional hernia patients [15], we resist deformation against an applied force or to resume hypothesize that the elasticity in rectus abdominis (RA) its original shape after removal of this force. A higher of DRA patients is signifcantly lower than that in healthy elastic modulus correlates with a higher resistance to controls, while the elasticity of lateral abdominal wall deformation and an increased stifness [16]. Shear wave muscles, including the external oblique (EO) muscle, speed is a quantitative measure of tissue stifness and He et al. Insights Imaging (2021) 12:87 Page 3 of 11 can be converted to shear modulus using the following equation: 2 µ = Cs ρ where µ is shear modulus; Cs is shear wave speed (SWS) in this equation; and ρ is density, which can be assumed to be 1000 kg/m3 for all soft tissues [17]. Higher speed values are associated with increased tissue stifness. A senior radiologist (XW.: with 10 years of experience in abdominal and musculoskeletal ultrasound imaging) per- formed the IRD measurement on B-mode US and SWS measurement on SWE. IRD measurement Te DRA patients underwent B-mode US examination of their anterior rectus abdominis sheath to evaluate the width of rectus diastasis. To standardize the position of the transducer, each measurement location was marked on the skin when the participant was resting in the supine position, with their arms across their chests. Addition- ally, special attention was paid to the pressure imposed on the probe to avoid refexive responses from the par- ticipants. A thick gel layer was applied to replace the air Fig.