Research Review By Dr. Shawn Thistle©

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Date Posted:

May 2012

Study Title:

Association Between Changes in Abdominal and Lumbar Multifidus Muscle Thickness and Clinical Improvement After Spinal Manipulation

Authors:

Koppenhaver SL, Fritz JM, Herbert JJ et al.

Author's Affiliations:

Baylor University, San Antonio, Texas; University of Utah, Salt Lake City, Utah; School of Chiropractic and Sports Science, Murdoch University, Perth, Australia; University of Alberta, Alberta, Canada; Glenrose Rehabilitation Hospital, Alberta, Canada.

Publication Information:

Journal of Orthopaedic & Sports Physical Therapy 2011; 41(6): 389-399.

Background Information:

Spinal manipulation (SMT) is one of the most frequently utilized treatments for low back pain (LBP), despite conflicting results from the existing body of clinical research on its efficacy. Results from clinical trials investigating SMT as a treatment for LBP range from very promising, to showing little or no clinical benefit. If the existing literature has shown us anything, it is that SMT does not work for everyone with LBP. Having said that, it works very well for many patients. We all know this and see it every day!

To improve clinical outcomes with SMT, we must grasp important concepts from emerging literature on the underlying mechanisms of action of SMT, as well as ways to target those patients most likely to benefit from this treatment. Both areas of knowledge are expanding, shedding important light on our ‘bread and butter’ intervention.

In recent years, research paradigms have shifted from the traditional bone-out-of-place model to increased investigation of the neurophysiological effects of SMT, including its influence on aberrant function of trunk and abdominal musculature. It is generally accepted that LBP is often accompanied by dysfunction of trunk muscles (such as the erector spinae [2] or multifidii [1]) or abdominal muscles (such as the transversus abdominus or internal oblique [3-5]). Many agree that the lumbar multifidus (LM) is of particular importance in LBP. In addition to having a cross-sectional area that is twice that of the longissimus thoracis and iliocostalis lumborum, the LM is also a vital stabilizing muscle of the lumbar spine. Further, atrophy and fatty infiltration of the LM muscle has been demonstrated in a variety of LBP populations (1).

With this in mind, existing evidence suggests that SMT can affect the musculature of the spine and trunk, but the longevity of these effects and their clinical relevance remain controversial (6). Despite this growing body of research demonstrating physiologic effects following the application of SMT, very few studies have attempted to correlate these changes with clinically relevant outcomes. Therefore, the goal of this study was to examine the relation between improved disability and changes in the LM and abdominal thickness using ultrasound imaging following two SMT treatments, delivered in one week, in patients with LBP.

Pertinent Results:

  • The authors appropriately controlled for the effects of age, sex, and body mass index
  • Overall, change in contracted LM muscle thickness was predictive of improved disability at 1 week (P = 0.02)
  • Further, larger increases in contracted LM muscle thickness at 1 week were associated with larger improvements in LBP-related disability
  • As expected, those who experienced clinical improvement tended to have a shorter symptom duration and less leg pain
  • Contrary to the authors’ hypothesis, significant decreases in both contracted Transversus Abdominus (TrA) and Internal Oblique (IO) muscle thickness were observed immediately following SMT, but these changes were transient and not related to clinical improvements

Clinical Application & Conclusions:

The results of this paper suggest that a major benefit of lumbar SMT is improvement in the ability of the LM muscle to contract, and that this improved contractility remains one week later. Further, this sustained recruitment of the LM was significantly associated with reduced disability scores as determined by the ODI at one-week follow-up in this dataset – this is promising and requires further investigation.

These results suggest that the impact of manipulation on the multifidus may be more than a reflex response, which would disappear quickly after delivery of the manipulative thrust. It seems reasonable that SMT may somehow ‘reset’ the multifidus to a more optimal functional level through alpha-motor-neuron modulation. The duration of this, or other responses is an important research question to be pursued in future trials, and the exact mechanisms involved remain largely speculative at this time.

Regarding the other muscles imaged in this study: The findings regarding the IO are in agreement with previous studies that downplay the role of this muscle in LBP. The results for the TrA on the other hand, contradict previous studies, highlighting the need for further investigation.

From a clinical perspective, since manipulation seems to improve the contractility of the multifidus, it is within reason that this benefit may be further enhanced by incorporating exercise training targeting the trunk musculature and LM. The addition of exercise in general remains a responsible, evidence-informed approach to LBP.

Study Methods:

This was a prospective cohort study designed to examine the relationship between clinical improvement (based on reduced disability scores) and changes in muscle thickness of the transverse abdominis (TrA), internal oblique (IO) and lumbar multifidus (LM) muscles following two SMT treatments in patients with LBP.

Inclusion/Exclusion Criteria:

To be included in this study, participants had to:
  • Have LBP located between the 12th rib and buttocks, that, in the opinion of the screening examiner, was originating from the lumbar region;
  • be between 18 and 60 years of age;
  • have a Modified Oswestry Disability Index (ODI) score of at least 20%; and
  • have the ability, as reported, to lie prone and supine for a minimum of 20 minutes each.
Individuals were excluded from the study if they met any of the following criteria:
  • Prior surgery to the lumbosacral spine;
  • osteoporosis;
  • neurogenic LBP (defined by either a positive ipsilateral or contralateral straight leg raise, or reflex, sensation, or strength deficits in a pattern consistent with nerve root compression);
  • medical “red flags” of a potentially serious condition, including cauda equina syndrome, a major or rapidly progressing neurological deficit, fracture, cancer, infection, or systemic disease; or
  • prior SMT to the lumbosacral spine, or TrA or LM muscle stabilization exercises performed in the previous 4 weeks.
The authors also divided subjects into ‘likely responders’ and ‘likely non-responders’ to SMT based on a Clinical Prediction Rule containing 5 factors (8). Subjects with 4 or 5 out of the 5 factors were classified as ‘likely responders’, those with exactly 3 factors were excluded, and those with 0-2 factors were classified as ‘likely non-responders’.

The study consisted of 3 sessions in one week:
  1. Session 1: after consent, subjects completed the outcome questionnaires and underwent a standard history and physical examination, ultrasound of the trunk muscles, and SMT.
  2. Session 2: occurred 2-3 days after session 1 – second application of SMT and ultrasound imaging of the trunk muscles.
  3. Session 3: occurred one week after the initial visit – repeated questionnaires and ultrasound imaging of the trunk muscles.
Diagnostic ultrasound imaging at rest and during submaximal contractions (a prone upper-extremity lifting task) was used in 78 subjects to measure changes in resting and contracted muscle thickness (LM, IO and TrA) before and after each of two high-velocity, low-amplitude (HVLA) thrust manipulations delivered to the anterior-superior iliac spine in an anterior-to-posterior direction (this was a supine lumbar manipulation which has been used and described in multiple studies to date [ex. 9]). Manipulations were delivered to both sides by a chiropractor who was blinded to the ultrasound imaging results. Subjects were asked to refrain from any trunk strengthening exercises during the course of the study, but were asked to stay active.

Outcome measures employed in this study included the Oswestry Disability Index (ODI), Fear-Avoidance Beliefs Questionnaire, pain drawings, and 11-point numeric pain rating scale (NPRS). Muscle thickness measurements were also made from the diagnostic ultrasound images.

Study Strengths / Weaknesses:

Study Strengths:
  • The authors measured resting and contracted thickness changes in the TrA, IO and LM
  • This was one of, if not the first, study to attempt to correlate changes in abdominal/trunk muscle thickness post-SMT with clinical outcomes
Weaknesses:
  • Timing of muscle contraction via EMG was not measured in this study – further research should examine this variable to further our understanding of the relationship between SMT and trunk muscle function.
  • The use of the Clinical Prediction Rule in the inclusion criteria may limit the external validity of these results. Further, in the results section, no mention was made about whether the status of ‘likely responder’ or ‘non-likely responder’ based on the CPR correlated with outcomes…a strange omission.

Additional References:

  1. Beneck GJ & Kulig K. Multifidus Atrophy Is Localized and Bilateral in Active Persons With Chronic Unilateral Low Back Pain. Arch Phys Med Rehabil 2012; 93: 300-306.
  2. DeVocht JW, Pickar JG, Wilder DG. Spinal manipulation alters electromyographic activity of paraspinal muscles: a descriptive study. J Manipulative Physiol Ther 2005; 28: 465-471.
  3. Hodges PW. Changes in motor planning of feed¬forward postural responses of the trunk muscles in low back pain. Exp Brain Res 2001; 141: 261- 266.
  4. Hodges PW. Is there a role for transversus abdominis in lumbo-pelvic stability? Man Ther 1999; 4: 74-86.
  5. Hodges PW, Richardson CA. Altered trunk muscle recruitment in people with low back pain with upper limb movement at different speeds. Arch Phys Med Rehabil 1999; 80: 1005-1012.
  6. Lehman GJ, Vernon H, McGill SM. Effects of a mechanical pain stimulus on erector spinae ac¬tivity before and after a spinal manipulation in patients with back pain: a preliminary investiga¬tion. J Manipulative Physiol Ther 2001; 24: 402- 406.
  7. Fritz JM, et al. Preliminary investigation of the mechanisms underlying the effects of manipulation: exploration of a multivariate model including spinal stiffness, multifidus recruitment, and clinical findings. Spine 2011; 36(21): 1772–1781.
  8. Flynn T, Fritz J, Whitman J, et al. A clinical prediction rule for classifying patients with low back pain who demonstrate short-term improve¬ment with spinal manipulation. Spine; 2002; 27: 2835-2843.
  9. Childs JD, Fritz JM, Flynn TW, et al. A clinical prediction rule to identify patients with low back pain most likely to benefit from spinal ma¬nipulation: a validation study. Ann Intern Med 2004; 141: 920-928.