Introduction

Significant anatomical and physiological changes occur during pregnancy which enables the woman to accommodate, nourish, and cater for the growing fetus. These changes which are hormone mediated, together with sustained increase in intra-abdominal pressure from the growing fetus, facilitate the stretching and flaccidity of the linea alba-a tendinous raphe between the paired rectus abdominis muscles in the anterior abdominal walls causing elongation of the muscles with resultant increase in the distance between its medial borders.[1] The distance between the paired rectus abdominis muscle is referred to as inter-rectus distance (IRD), while an increased IRD, due to abnormally excessive separation between both components of the muscle along the linea alba, is termed diastasis recti abdominis (DRA), rectus abdominis diastasis, or divarication of rectus abdominis muscles.[2,3]

The most common anatomical location for DRA in females is at the level of the umbilicus, although it may extend to the supra/infra-umbilical regions,[4] involving different sites along the linea alba.[4-7]

Several treatment options are available for the management of DRA but physiotherapy has been the most widely utilized conservative measure of DRA management with its effectiveness reported in several studies.[8-12] To facilitate physiotherapeutic intervention, successful diagnosis, and evaluation of outcome measures are dependent on the use of valid and reliable assessment techniques. Therefore, sound clinimetric properties are necessary pre-requisite for the choice of measuring instruments. Available methods for measuring DRA in Physiotherapy and in most health-care practices include the use of calipers, tape measure, computed tomography, magnetic resonance, ultrasound, and the traditional finger width (palpation) method.[4,8,13-21]

These measurement methods are used cross-culturally with each possessing its benefits and limitations. The gold standard instrument for the measurement of IRD is the conventional ultrasound imaging (USI), because it compares favorably to intraoperative surgical compass measurements,[22] while producing consistent results between days.[23] Moreover, it provides a measure of IRD on a continuous scale, increasing its responsiveness. However, its cost is astronomical and requires extensive examiner training and clinical mastery.[24] Furthermore, its availability and accessibility to physiotherapists in developing countries are not guaranteed.

Palpation method, the predominantly used measure in clinical diagnosis,[25] involves the use of fingers to feel the medial borders of the rectus abdominis muscles. Diagnosis is made based on the number of fingers that fit between the medial borders of the rectus abdominis muscles. However, there are no standard guidelines on the positioning of the palpating fingers relative to its distance from the umbilicus as well as the starting position of the client. Nevertheless, this technique is easy to carry out and requires no specialist training. The digital calipers involve placing the inside measurement jaws where the palpating fingers are located at the medial borders of both rectus abdominis muscle bellies, with the values read from the screen. This instrument has the advantage of clarity because of the liquid crystal display screen and has no need for recalibration. However, its utilization of alkaline cell batteries may be an encumbrance, as well as its sensitivity to weather changes.

The most recent innovation for IRD measurement is the diastometer, invented in 2015 by Tupler.[26] It has two components, a distance-measuring component adapted to measure the DRA distance and a depth-measuring component adapted to measure the depth of DRA. Measurement is done by wearing this device as a belt around the abdomen, ensuring that the reference point, a red dot positioned at the center of the measuring strip aligns with the umbilicus. The values are obtained by sliding the indicator loops into the position, marked by the palpating fingers, and are read off from the location of the indication loops with respect to the indicia on the tape.[26] The depth of the IRD is determined by depressing the clad forefinger finger sock component gently into the abdomen with the lower measurement visible on the finger sock determining the depth. This dual property of the diastometer makes it unique among the instruments under review. Despite accreditations to its effectiveness in the assessment of DRA, there are no empirically proven documentations on its validity and reliability, relative to other standardized measurement tools. Previously, some authors have reported validity and reliability results for other measuring tools, including calipers,[17,27,28] palpation technique,[29,30] and ultrasound.[22,23,31] However, considering variations in their study designs and findings, there is still a need to further evaluate the clinimetric properties of these measurement tools, especially in a different geographical location. Furthermore, investigating each instrument’s concurrent validity against the gold standard (USI) is a surefire way of proving their clinical utility. Thus, this study is designed to determine the construct validity of the diastometer, inter- and intra-rater reliability of the diastometer, calipers, and palpation techniques as well as the concurrent validity of all three against conventional USI.

Methods

This study which utilized a methodological design, a variant of observational study designs, was carried out at the Department of Physiotherapy, Enugu State University teaching Hospital Park Lane (ESUTHP) Enugu, Nigeria. Participants included purposively selected parous women (20–45 years of age) who have experienced 1–4 childbirths and presented for postpartum checkup or routine infant immunization at the above-named hospital during the period of this study (April–July 2019). The exclusion criteria included: (1) A history of recent abdominal surgery as the scars may obscure the lines alba, (2) neck and low back pain of ≥3-month duration which may limit the appropriate performance of the testing procedures which involved a head tilt and supine lying position, respectively, and (3) pregnancy which may alter study findings due to hormonal changes.

For a significant Pearson product moment correlation at a 0.05 level of significance, a power of 0.90, and a medium effect size of 0.30, 92 participants were needed for this study.[32]

To control for subject attrition, 97 participants were recruited but only 90 successfully completed this study.

Ethical approval was obtained from both the Research Ethics Committee College of medicine, University of Nigeria, Enugu campus, and the Research, Education, and Training Committee (RET) of ESUTHP, Enugu, Nigeria. All participants gave written informed consent before participation in the study.

Results

The mean age of the participants was 32.71 ± 5.27 [Table 1] while the majority of the women had spontaneous vaginal deliveries (72.2%), were multiparous (63.3%), and within <1-year postpartum duration (50%) as shown in Table 2. The intra and inter-rater reliability of palpation technique for measurement of IRD are presented in Table 3. The intra-rater reliability was excellent at the three points of measurement (ICC2.1: 0.749–0.967) while the inter-rater reliability was good at the umbilicus (ICC2.2: 0.658) and excellent above and below the umbilicus (ICC2.2: 0.874 and 0.917), respectively. The digital calipers technique for measurement of IRD has excellent intra-rater reliability at the three points of measurement (ICC2.1: 0.750–0.955). It has good (ICC 2.2: 0.685) to excellent (ICC2.2: 0.862–0.904) inter-rater reliability as shown in Table 4. The intra-rater reliability for measuring IRD with the diastometer was excellent at all three reference points (ICC2.1: 0.762–0.958), while the depth showed good (ICC2.1: 0.652) at the umbilicus but was excellent (ICC2.1: 0.837 and 0.946) above and below the umbilicus, respectively. The inter-rater reliability of the diastometer for measurement of IRD was fair/moderate (ICC2.2: 0.471) at the umbilicus and excellent (ICC2.2: 0.881 and 0.902) above and below the umbilicus, respectively. It also showed good to excellent (ICC2.2: 0.723–0.906) for depth as shown in Table 5. Table 6 presents the concurrent validity of palpation, digital calipers, and diastometer against USI in IRD measurement. The palpation (ICC2.2: 0.007–0.256), digital calipers (ICC 2.2: 0.035–0.304), and diastometer (ICC2.2: 0.159–0.250) showed poor levels of agreement between the IRD values measured with USI at the three reference points. Comparisons of IRD measurements with palpation, digital calipers, diastometer, and USI showed significant difference (P = 0.000) at the level of the umbilicus only as shown in Table 7. Bland-Altman plot showed a poor level of agreement at all reference points Figures 1-3.

Table 1 Age and anthropometric characteristics of the participants

Table 2 Maternal characteristics of the participants (n=90)

Table 3 Intra/Inter-rater reliability of palpation technique

Table 4 Intra/Inter-rater reliability of calipers technique

Table 5 Intra/Inter-rater reliability of the diastometer

Table 6 Level of agreement between inter-rectus distances measured with palpation, digital calipers, diastometer, and ultrasound imaging

Table 7 Comparisons of inter-rectus distance measurements with palpation, digital calipers, diastometer, and ultrasound imaging

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Figure 1

Bland Altman plots of IRD (mm), comparing palpation technique and USI measurements (a) above the umbilicus, (b) at the umbilicus, and (c) below the umbilicus

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Figure 2

Bland Altman plots of IRD (mm), comparing calipers technique and USI measurements. (a) Above the umbilicus, (b) at the umbilicus, and (c) below the umbilicus

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Figure 3

Bland Altman plots of IRD (mm) comparing diastometer and USI measurements. (a) Above the umbilicus, (b) at the umbilicus, and (c) below the umbilicus

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Discussion

This study investigated the intra- and inter-rater reliability of measures in the diagnosis of DRA i.e. palpation, digital calipers, and diastometer as well as their concurrent validity against USI. Most of the participants were overweight, multiparous women who delivered through spontaneous vagina delivery.

Reliability and Validity of the Palpation Technique:

This study showed that the palpation technique of measuring DRA has excellent intra- and inter-rater reliability. This infers that the palpation technique is a consistent measure for DRA across raters and for a single rater. There were concerns about differences in finger widths, thick abdominal subcutaneous fat, and flaccidity. However, the study findings showed excellent intra- and inter-rater reliability of this technique. These findings corroborate,[30] which similarly showed good intra-rater but moderate inter-rater reliability of this technique. On the contrary, Bursch[29] reported poor inter-rater reliability of this technique among four raters who measured IRD of postpartum women within <4-day post-delivery. The differences in the study findings may be attributed to the number of raters per study as well as their finger anthropometric characteristics.

The IRD values obtained with the palpation technique showed no agreement with the USI values. There were also significant variations between their recorded values. These findings suggest that the palpation technique cannot be considered a valid modality for DRA measurement, relative to the gold standard USI. This is supported by a prior study[29] which reported a similar outcome, showing poor validity of the palpation technique. Interestingly, another study[38] claimed that this technique has good concurrent validity. These variations are hardly surprising given that the measurement system of the palpation technique and USI differ considerably. It should be noted that USI measurement is on a continuous scale in millimeters while the palpation technique is based on finger width estimations.

Conclusion

The palpation, calipers, and diastometer techniques are reliable measures of DRA but not valid substitutes to USI for the assessment of DRA. The use of these instruments for clinical assessment of DRA should be recommended, particularly in scenarios where USI is neither accessible nor affordable.

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