Concurrent Validity of Calipers and Ultrasound Imaging to Measure Interrecti Distance. Cynthia M. Chiarello, J. and Adrienne McAuley. J Orthop Sports Phys Ther 2013;43(7):495-503.

Laura Scheufele PT, DPT, WCS

August 7, 2013
 

Primary Aim: To determine the concurrent validity of digital nylon calipers in comparison to ultrasound imaging (USI) for the measurement of interrecti distance (IRD). Secondary purpose was to describe the IRD seen in typical adult males and females.

Subjects: A sample of convenience of 56 individuals (11 men, 45 women: 22 nulliparous and 23 parous)

Exclusion criteria: If pregnant; had scarring from previous abdominal surgery such that, on observation of the abdomen, the linea alba or umbilicus was obscured or deformed; had rheumatological or connective tissue disease; or had any medical condition that would prohibit active abdominal contraction.

Study Design: Clinical measurement, concurrent validity criterion standard.

Methods: Each subject positioned in hook-lying and two measurement sitesmarked with water-soluble pen: 4.5 cm above the umbilical midpoint and 4.5 cm below the umbilical midpoint. No umbilical measurement taken secondary to technical difficulties with USI (also previously reported in other studies as well). Measurements taken in two positions: 1) the abdominal muscles at rest (arms at side) and 2) with active contraction of the abdominals (arms crossed over chest and head raised only until spine of the scapulae off the table surface.)

Caliber measurements taken first (to avoid marks being distorted by the ultrasound gel) by a single examiner (examiner #1).This examiner palpated for the medial borders of the right and left rectus abdominis muscle bellies at the marked locations. The inside measurement jaws of the caliper were positioned at the locations of the palpating fingers, perpendicular to the direction of the muscles, and adjusted to the perceived IRD width. Examiner #1 would leave the room and examiner #2 would enter to complete the USI measurements. Each examiner was blinded from the other’s findings.

The USI assessmentperformed with the patient still positioned hooklying. A 5-MHz curvilinear transducer perpendicular to the abdominal surface at each marked location. The onscreen image of the IRD was captured and then the measuring feature was used to measure the IRD. The examiner determining the location of the medial borders, using the onscreen cursor to mark the distance between the muscle bellies.

A separate study performed to establish each tester’s own reliability. 8 subjects measured with calipers and 6 with USI. Three measurements for each location both at rest and with abdominal muscle contracted performed on the same day. Intrarater reliability found to be very high for each tool, with intraclass correlation coefficients (ICCs) ranging between 0.90 to 0.99.

Results:

The nulliparous women had the smallest IRD in both locations and with both tools except the rest position below the umbilicus, which was the smallest in the men subgroup.

 

Validity of the measurements taken with the caliper as compared to the USI was different above versus below the umbilicus.

Above umbilicus: No statistical difference (P> .05) in IRD values between the 2 measurement tools in both rest and contracted positions.

Below umbilicus: The IRD measurements using calipers were significantly larger (P< .0001) than when using USI for both rest and contracted positions. Low agreement between the 2 measurement tools below the umbilicus.

 

Table 3 summarizes the mean averages of each subset

Discussion: Ultrasound is considered the best available clinical tool to assess IRD, but it not readily available for most clinicians. A digital nylon caliper is a cost effective clinical tool but previously its use was not validated. The caliper measurements above the umbilicus were comparable to the USI both when at rest and with abdominals contracted (considered good to excellent validity), but not with the measurements below the umbilicus. In this location the measurements were overestimated compared to the USI. Speculation about the cause of this difference may have been due to 1) inaccurate identification of the medial borders using manual palpation with the caliper measurement (possibly related to greater adipose tissue in the area 2) the measurements could have been taken at different depths or 3) the caliper jaws could have produced an outward pressure against the muscle belly, thus increasing the distance.

Significant variances in IRD noted between gender and parity, as well as location above or below the umbilicus. There is no current standard for defining DRA, and thus clinicians need to be careful when interpreting measurements.

Strengths: Examiners blinded from each other’s assessment. Inclusion of males and females.

Weaknesses: Relatively small sample size. Unable to compare measurements at the level of umbilicus. In order to prevent the marking from being wiped off, not able to randomize order of measurement.

Conclusion:Calipers are a valid tool for measuring IRD above the umbilicus in males and females when using USI as the criterion standard, but not for the location below the umbilicus.

 

Impact on practice: This is an important first step towards establishing an inexpensive evaluation tool for DRA that is validated.  Ultimately this may pave the way for additional studies to establish which treatments for DRA is evidence based as well.

Thought questions:

1)     Where do we go from here regarding research?
2)     How are clinicians currently assessing DRA? What parameters do you use as “normal”/abnormal? Does this study change how you are going to assess?
3)     How are clinicians treating DRA?

 

Other notable research:

Mota et al (JOSPT 2012) reported on test-retest reliability of ultrasound measurement of IRD. This study evaluated 24 healthy females at positions 2 cm above and below the umbilicus and assessed during rest, an “abdominal crunch” and with a drawing-in maneuver. Ultrasound found to be a reliable measurement for measuring IRD at rest and during abdominal crunch and drawing in maneuver. The lowest ICC value (0.50) found below the umbilicus during contraction. The test-retest measurements across days showed good reliability during rest and drawing-in maneuver (ICC 0.78 and 0.74) and very good above with rest, abdominal crunch, and drawing in ( ICC 0.87, 0.83, and 0.90).

Mota et al (Manual Therapy 2012) reported on the reliability of IRD measurement by palpation and compared to ultrasound in 20 healthy females. Palpation found to be sufficiently reliable to be used in clinical practice, but ultrasound found to be more accurate and valid.

Beer et al (Clinical Anatomy 2009) investigated the normal width of the linea alba in 150 nulliparous women between the ages of 20 to 45 yo with ultrasound. Chose 3 reference points: level of xiphoid, 3 cm above umbilicus, and 2 cm below the umbilicus. Broad ranges of widths were observed, with the widest reference point 3 cm above the umbilicus. Mean widths as follows: Level of xiphoid 7 +/- 5 mm, 3 cm above umbilicus: 13 +/- 7 mm, and 2 cm below umbilicus 8 +/- 6 mm. Defined the normal width ( 10^th and 90^th percentiles taken) as up to 15 mm level of xiphoid, up to 22 mm 3 cm above umbilicus, and up to 16 mm 2 cm below the umbilicus in nulliparous women.  

Spitznagle (Int Urogynecol J 2007) reported on the prevalence of DRA in an urogynecolgical population, differences in characteristics of patients with and without DRA, and the relationship of DRA to support-related PFD diagnoses. A relationship was noted between the presence of DRA and SUI, FI and POP.