Comparison of the sonographic features of the abdominal wall muscles and connective tissues in individuals with and without lumbopelvic pain

Whittaker JL, Warner MB, Stokes M. JOSPT 2013; 43(1):11-19.

Ann Dunbar PT, DPT, MS, WCS

June 3, 2015

Introduction

• Muscles of the abdominal wall, multifidii, pelvic floor, and respiratory diaphragm function to pressurize the abdominopelvic cavity for load transfer.
• Researchers have identified functional deficits in abdominal mm in persons with lumbopelvic pain (LPP) however, most studies consider only the transverse abdominis and internal oblique.  Morphologically the 4 layers are different.

Primary Aim: “ to measure and compare the resting thickness of the 4 abdominal wall muscles and their perimuscular connective tissue (PMCT) planes, as well as interrecti distance (IRD) in persons with and without lumbopelvic pain, using ultrasound imaging.

Study Design:  Cross-sectional, case controlled.

Methods:

Definition of LPP: pain not proximal to iliac crest and not distal to popliteal fossa

Sample of convenience, 50 subjects with unilateral LPP greater than 6 weeks and with a positive Active Straight Leg Raise test (ASLRt). Exclusion criteria listed.

Data Gathered:

• Outcome Measures: Oswestery Disabiity Index (ODI) and numberic pain rating scale.
• Demographic information, Nijmegen questionnaire (assesses for dysfunctional breathing patterns) and Urogenital Distress Inventory (UDI)
• Clinical exam details listed in study pg. 12.

US Imaging: Specifications for imaging listed in study including equipment used, settings, and probe location (to image #1—EO, IO, TA and PMCT; #2—RA muscle and associated PMCT; #3—image of IRD.  Images were measured from R side in controls and symptomatic side in those with LPP.  Three images were taken at the end of the exhalation phase of breathing per site (without moving probe).  Authors describe methods for measuring muscle and PMCT thickness and IRD. Data processed in a way that assured examiner blinded from information.

Statistical Analysis: see details in article.

Capnography testing: assesses concentration of CO₂ in the respiratory gases; used to identify abnormal breathing patterns

Results

• Subject characteristics:  see Table 1.  LPP cohort was older (P=.02); scored higher on Nijmegen (p<.001) and UDI (p<.001).
• Descriptive data for m. and PMCT plane thickness in Table 2. They were not correlated with age or parity. Total m. thickness was correlated with BMI (r=0.43; p<.001) and gender (r=0.52; p<.001) whereas PMCT correlated with BMI (r=0.60; p<.001). IRD not correlated with any variables. LPP cohort had less total abdominal m thickness (p=.03) and thicker PMCT (p=.007) and wider IRD (p=.005). No difference found in individual thickness in 4 abdominal mm however after adjusting for BMI and gender, LPP cohort had thinner RA muscle (p<.001).
• Authors provide data in intrarater within- and between-day measurements, see Table 3,4
• Symptom characteristics: pain correlated moderately with IRD (r =0.51, p<.001) and weakly with PMCT (r =0.36; p=.01) and muscle thickness (r=-0.28; p<.05). Numeric pain rating correlated moderately with total PMCT (r =0.54, p<.001).  ODI correlated moderately with PMCT thickness (r =0.58, p<.001) and IRD (r =0.43, P=.02).

Discussion

• First study to consider thickness of all 4 abdominal mm together with their PMCT planes and IRD in people with LPP.
• LPP cohort had less total abdominal m thickness, thinner RA, thicker PMCT and wider IRD whereas there were no differences found in thicknesses of EO, IO, TA (see Figure 3).
• Authors discuss study by Rankin et al 2006 who publishing normative values for individual abdominal m. thicknesses providing relative contribution to total abdominal thickness (RA, EO, IO, TA were 35%, 23%, 28%, 14% of total respectively). Current authors found variance in RA (45%) and EO (16%) and suggested reasons for differences may have been diversity of ages and sample size as well as imaging site (Rankin et al used a site more cephalad).
• Other previous investigations of cohorts with LBP or pregnancy related pelvic girdle pain studies examined only TA and IO mm. Several studies discussed found no difference in resting thickness of these mm.
• One study examined RA m thickness and IRD in both controls and case cohort of post-partum (PP) women. Authors found the RA to be significantly thinner and IRD wider than controls. These findings are similar with current study however, because these subjects were PP so “comparison was not practical.”
• Current authors discuss scientific basis for increased thickness of PMCT in LPP cohort. They cite one study finding PMCT thickness in chronic LBP cohort. Histological investigations show that connective tissue fibrosis occurs due to inflammation and microtrauma from increased load on the tissues or due to absence of load resulting in atrophy, adhesions, and architectural disorganization.
• Results of current study (thinner RA, thicker PMCT, increased IRD in LPP cohort) suggest similar pathogenesis, that the adaptive PMCT and linea alba remodeling may be due to altered motor control strategies from decreased contribution of RA (leading to atrophy) and increased role of connective tissue (linea alba and PMCT) to contain intra-abdominal pressure and dissipate loading on the trunk. Authors caution that currently, this explanation is speculative though note that the correlation between the duration of pain and the width of IRD also supports this suggestion of adaptive loading response.
• This study is a first to consider the pattern of contribution of all mm of abdominal wall and related connective tissues and to document differences between cohorts using US imaging.  With these findings, current authors further hypothesize that altered m. function in LPP cohort led to insufficient contribution from RA which resulting in increased load on PMCT and linea alba and increased thickness.
• Current study also differs from others in the methodology where many prior studies excluded PMCT in measurement of m. thickness.
• Limitations
• Measured only 1 side of abdominal wall
• LPP cohort was slightly older (abdominal m. thickness is independent of age and gender however, impact of age on PMCT is unknown however, none of sonographic measures were found to correlate with age)

Summary

Individuals with LPP demonstrate thinner RA, wider IRD, and thicker PMCT than controls and these differences were associated with pain duration, intensity and self reported measures of function.

Other References to Consider

• Coldron et al, 2008: “Postpartum characteristics of rectus abdominis on US imaging findings”
• RA thickness and width and the IRD did not return to normal values by 12 months post-partum; authors suggest that wider and thinner RA impacts strength and fascial support predisposing these women to a ‘mechanical disadvantage.’
• Pascoal et al, 2014: “Inter-rectus distance in postpartum women can be reduced by isometric contraction of the abdominal muscles: a preliminary case-control study”
• Used US imaging to study effect of isometric contraction of abdominal mm on IRD in PP women (measured IRD at rest and during isometric contraction where subjects were in hooklying and were asked to lift head and scapulae off table
• IRD significantly wider in PP group compared with controls
• IRD was significantly lower during isometric contraction of abdominal mm suggesting this exercise could be effective for PP women in narrowing the gap

Clinical Application:  

1)  The TA is known to produce a corseting action on the abdominal wall and has been shown to stiffen the SI joint contributing to pelvic stability.  This study found the RA to be thinner and correlated with LPP. Are these results surprising to you?

2) Do you include RA strengthening in your exercise prescription? If so, what is your exercise of choice? 

3) DRA is shown to be present in some 50% of the urogynecological population.   How would you consider RA strengthening for this population?

 

Other References

Coldron Y, Stokes MJ, Newham DJ, Cook K: Postpartum characteristics of rectus abdominis on ultrasound imaging. Manual Therapy. 2008; 13(112-121).

Pascoal AG, Dionisio S, Cordeiro F, Mota P: Inter-rectus distance in postpartum women can be reduced by isometric contraction of the abdominal muscles: a preliminary case-control study. Physiotherapy. 2014; 100(344-348).

Additional Reading

Marchetti PH, Kohn AF, Duarte M: Selective activation of the rectus abdominis muscle during low-intensity and fatiguing tasks. J Sports Sci Med. 2011, Jun 1:10)2):322-7.

On 6/3/15, 6:56 PM, Susan Weedall, PT, WCS wrote:  

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Hi, Beth, We missed you tonight!  Great lead by Ann.  I was asked to provide info on the Las Vegas 2014 CSM lecture that I cited during our discussion  related to "Comparison of the Sonographic Features of the Abdominal Wall Muscles...."  The presentation at CSM 2014 was "Mind the Gap, A comprehensive approach for the evaluation of and intervention of diastasis recti abdominis."  Power point lists presenters Cynthia Chiarello, PT and Adrienne McAuley, PT.  My memory is fuzzy, but I believe one of them was not present.  The power point did not list the intervention I mentioned during tonight's discussion, but my notes read:  "consider releasing the lateral margins of the rectus abdominis with the thought of releasing tension from obliques."  Hope this makes some sense in terms of posting related to the article.  Thanks!