Technical and measurement reportUltrasound transducer shape has no effect on measurements of lumbar multifidus muscle size
Introduction
In recent years ultrasound technology has found widespread application, both in diagnostic use and rehabilitation (Whittaker et al., 2007). Rehabilitative ultrasound imaging (RUSI) can offer a safe, objective and relatively inexpensive means of evaluating muscle and related soft tissue morphology, and can provide visual feedback to aid interventions in research and clinical practice (Whittaker et al., 2007). The RUSI technique has undergone extensive reliability studies, showing high reliability for both taking and interpreting images (Kiesel et al., 2007, Wallwork et al., 2007, Koppenhaver et al., 2009). The validity of RUSI against the gold standard of magnetic resonance imaging (MRI) has also been established for several muscles (Hides et al., 1995, Hides et al., 1996, Lee et al., 2006, O’Sullivan et al., 2009). An area that has received relatively little attention is determining appropriate scanner specifications for imaging muscles and the present study addresses the topic of transducer shape (or configuration).
A curvilinear transducer with an approximate frequency of 5 MHz is commonly used to image lumbar multifidus (Hides et al., 1992, Stokes et al., 2005, Lee et al., 2006, Kiesel et al., 2007), with no justification of transducer choice given. Some guidance based on anecdotal evidence suggested that more sound waves would reach the lateral border of multifidus with a curvilinear transducer (Stokes et al., 2007). It is unknown, however, if the shape of the transducer affects measurements of muscle dimensions. In a recent study, phantom objects were imaged using both curvilinear and linear transducers (Warner et al., 2008). Small differences were found between the two transducer configurations when measuring simulated muscle cross-sectional dimensions using a semi-solid phantom, although these differences were not clinically significant (Warner et al., 2008).
The present study aimed to determine whether there was a difference between measurements made from images of lumbar multifidus muscle obtained using linear and curvilinear transducers. The null hypothesis was that there would be no difference between measurements from images using the two transducers.
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Participants
Fifteen males (aged 21–32 years; mean height 180 cm, weight 81.7 kg and body mass index, BMI, 25.5) were recruited from staff and students at the University of Southampton. Exclusion criteria were: extended history of severe lower back pain, any wound or skin condition in the region to be scanned, any previous spinal or pelvic fractures that may interfere with positioning or any known spinal abnormality (such as scoliosis). Ethical approval for the project was obtained from the School of Health
Comparison of measurements from the linear and curvilinear transducers
The t-test analysis showed no significant differences between transducers (Table 2).
The Bland and Altman plots (Fig. 3) showed minimal between-transducer differences. Confidence intervals for the mean difference (d) between transducers were close to zero (Table 2). For thickness (Fig. 3a), d of 0.01cm showed a clear similarity between transducers. The width measurement (Fig. 3b) showed the largest mean difference (0.14 ± 0.3 cm), indicating a bias towards a larger measurement with the linear
Discussion
The main finding indicates that measurements of all three dimensions of multifidus muscle size (thickness, width and CSA) at L3 were not influenced by whether a linear or curvilinear transducer was used, therefore confirming the null hypothesis that measurements would not differ. Intra-rater reliability of measurements on the same images on different days were good to excellent. Linear measures were highly correlated with CSA but thickness, which is most commonly used in the literature, had the
Conclusions
Measurements of multifidus width, thickness and CSA made from images using linear and curvilinear transducers were not significantly different. However, the curvilinear transducer gave better clarity of the lateral muscle border and is therefore recommended as the transducer of choice for ease of interpreting images of the lumbar multifidus. This study highlights the need for research to determine appropriate scanner specifications for RUSI in different muscles and study populations.
Acknowledgements
The authors thank the participants for giving up their time to take part in the study. There were no conflicts of interest within the present study.
References (18)
- et al.
Multifidus size and symmetry among chronic LBP and healthy asymptomatic subjects
Manual Therapy
(2008) - et al.
Measurement of lumbar multifidus muscle contraction with rehabilitative ultrasound imaging
Manual Therapy
(2007) - et al.
Reliability of rehabilitative ultrasound imaging of the transversus abdominis and lumbar multifidus muscles
Archives of Physical Medicine and Rehabilitation
(2009) - et al.
The relationship between EMG and change in thickness of transversus abdominis
Clinical Biomechanics
(2004) - et al.
The validity of rehabilitative ultrasound imaging for measurement of trapezius muscle thickness
Manual Therapy
(2009) - et al.
Ultrasound imaging of lumbar multifidus muscle: normal reference ranges for measurements and practical guidance on the technique
Manual Therapy
(2005) - et al.
The effect of chronic low back pain on size and contraction of the lumbar multifidus muscle
Manual Therapy
(2009) - et al.
Induced transducer orientation during ultrasound imaging: effects on abdominal muscle thickness and bladder position
Ultrasound in Medicine & Biology
(2009) - et al.
Real-time sonography to estimate muscle thickness: comparison with MRI and CT
Journal of Clinical Ultrasound
(2001)