 |
 |
 |
 |
 |
 |
 |
|
 |
 |
 |
 |
 |
 |
 |
 |
PD Dr. Anne Mannion, Schulthess Klinik, Zürich; PD Dr. Haiko Sprott, Rheumaklinik und Institut für Physikalische Medizin, UniversitätsSpital Zürich
Background
Exercise therapy is one of the few evidence-based treatments for non-specific cLBP, although itdoes not elicit a positive response in all patients. The reasons for the widely varying individual responses
are not known, although many believe that it is the result of an inappropriate, “one-sizefits-all” approach to treatment; it is argued that, instead, specific types of exercise should be prescribed for specific patients, determined on the basis of their individual LBP history, signs, symptoms, and functional disturbances. Nonetheless, identifying “the right treatment for the right patient” is far from easy.
Dysfunction in the activation of the deep-lying trunk muscles, measured using intramuscular electromyography (EMG), is one disturbance that has been observed in connection with LBP; it is believed to pose a threat to segmental stability and hence predispose to continuing/future episodes of pain. As such, "spine stabilisation exercises", aimed at restoring deep trunk muscle motor control, have become a popular concept in physiotherapy. However, there are still many “unknowns” in relation to both the extent and nature of the proposed dysfunction and the mechanism of action of the specific exercise treatment. Since intramuscular EMG is invasive, a prerequisite for the in depth investigation of these phenomena is the availability of a reliable, accurate and sensitive means for assessing deep trunk muscle function. The objectives of our study were to develop such a method, based on M-mode ultrasound and tissue velocity information from tissue Doppler imaging (TDI), and use it to examine the trunk muscle function of patients with cLBP compared with healthy controls and compared with themselves after a physiotherapy programme of spine stabilisation exercises.
Methods
Development and validity of the non-invasive ultrasound method.Fourteen healthy subjects made rapid arm movements, in standing, in response to a visual signal indicating the required movement direction. Recordings were made of medial deltoid (MD) surface EMG, and of fine-wire intramuscular EMG and TDI tissue-velocity changes of the contralateral transversus abdominis (TrA), obliquus internus (OI) and obliquus externus (OE) (=the lateral abdominal muscles). Muscle onsets of activity were determined by blinded visual analysis of EMG and TDI data. TDI could not distinguish between the relative activation of the three muscles, so in subsequent analyses only the onset of the earliest abdominal muscle activity was used. The latter occurred <50ms after the onset of medial deltoid EMG (i.e. was feedforward) and correlated significantly with the corresponding EMG-onsets (r=0.47, p<0.0001). The mean difference between methods was 20ms, and was likely explained by electromechanical delay; limits of agreement were wide (-40 to +80ms) but no greater than those typical of repeated measurements using either technique. TDI yielded reliable and valid measures of the earliest onset of feedforward activity within the lateral abdominal muscle group.
Main results
Evaluation of lateral abdominal muscle function in cLBP .In 50 patients with cLBP and 50 matched, pain-free controls, the ability to preferentially activate and increase the thickness of the TrA during an “abdominal hollowing” exercise was examined using M-mode ultrasound; the feedforward activity of the lateral abdominal muscle group during rapid arm movements was also assessed, using the new TDI technique. Patients self-rated their pain and disability in everyday activities.
In both groups, feed-forward activity of the lateral abdominal muscles (<50 ms after MD activation) was recorded during arm movements in all directions. There was a tendency for the onset of the earliest abdominal muscle activity to be slightly earlier in the cLBP group than in the control group, reaching significance for left arm movements (p=0.015). There was no significant relationship between the muscle onsets (mean over all directions and sides) and pain or self-rated disability. The mean TrA contraction ratio (i.e., thickness of the muscle during contraction divided by the thickness at rest) during abdominal hollowing was significantly lower in the cLBP patients than in the controls (p=0.02), although the difference was not great (1.35 ± 0.14 vs 1.44 ± 0.23 respectively). The TrA contraction ratio showed a low but significant negative correlation with selfrated disability (Roland Morris (RM) score) (r=-0.40, p=0.004), i.e., higher disability was associated with a lesser ability to activate the TrA.
Effect of a programme of spine stabilization exercises on lateral abdominal muscle function, pain
and disability in patients with cLBP.
32/37 (86%) patients completed a 9-week physiotherapy programme of spine stabilization exercises (PT-SS). The RM disability score showed a moderate, significant decrease after treatment (from 8.9 ± 4.7 to 6.7 ± 4.3), as did average pain intensity (from 4.7 ± 1.7 to 3.5 ± 2.3) (each p<0.01). The mean TrA contraction ratio increased significantly from 1.34 ± 0.12 to 1.41 ± 0.17 (p=0.04) and improvements were seen in various functional tests simulating everyday activities (p<0.05). However, on an individual level no functional changes bore a significant relationship to the corresponding changes in pain or disability. There was no significant response to therapy in the onset of the earliest lateral abdominal muscle activity during rapid arm movements (p=0.53).
Implications and practice
In contrast to popular belief in physiotherapy practice, the voluntary activation of the TrA has only a minor role, and the anticipatory (feedforward) activity of the lateral abdominal muscles appears to have no role in cLBP, as far as distinguishing between patients and controls, correlating with self-rated pain and disability, responding to specific exercise therapy, and explaining treatment effects are concerned.There is evidence from RCTs for the effectiveness of spine stabiliation exercises as a treatment for cLBP (regardless of their mechanism of action), and our studies hence provide no grounds to discourage their continued use. However, the underlying physiological rationale certainly requires further investigation. The M-mode ultrasound TDI tool developed in the present study could be used to further investigate the phenomenon in large groups of cLBP patients undergoing treatment.
Project period: 51 months
Budget: CHF 743,987
Correspondence:
PD Dr. Anne Mannion
AFM Biomedical Research Consultancy
Bank House
1 Burlington Rd
Bristol, BS6 6TJ, UK
E-mail: anne@annefmannion.com
Further applicants:
PD Dr. Haiko Sprott
Department of Rheumatology and Institute of Physical Medicine, University Hospital Zurich
CH-8091 Zürich
E-mail: haiko.sprott@usz.ch