British Journal of Radiology 75 (2002),536-538 © 2002 The British Institute of Radiology
Supportive cushions produce no practical reduction in lumbar lordosis
V L Murrie, MSc1,
H Wilson, DCR1,
W Hollingworth, PhD2,
N M Antoun, FRCP, FRCR1 and
A K Dixon, MD, FRCR1
1 Department of Radiology, Addenbrooke's NHS Trust and the University of Cambridge, Hills Road, Cambridge CB2 2QQ and 2 Department of Public Health and Primary Care, University of Cambridge, Cambridge CB2 2SR, UK
Correspondence: V L Murrie, Level 5 Radiology, Box 219, Addenbrooke's Hospital, Hills Road, Cambridge CB2 2QQ, UK
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Abstract
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It is common practice to place a pillow or bolster under the knees of patients undergoing lumbar spine CT or MRI. The use of such supportive cushions leads to gentle hip flexion that is thought to ease pain and "reduce lumbar lordosis". It is also thought to facilitate axial imaging through the discs. Observations in seven subjects who underwent lumbar spine MRI with and without such hip flexion showed no appreciable change in the degree of lordosis. As the use of such devices does not produce a practical reduction of lumbar lordosis, the decision to employ them should be made entirely with respect to patient comfort.
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Introduction
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In the early days of lumbar spine CT, when gantry angulation was limited and the quality of sagittal reconstructions was relatively low, it was critical to obtain axial images along the plane of the discs. It became common practice to place a pillow or bolster behind the knees of a patient in order to "reduce lumbar lordosis" to achieve this angle, and such recommendations are still made in current texts of radiographic practice [1]. Indeed, most manufacturers designed specific bolsters for this purpose. Although the need is reduced in MRI because imaging planes can be obtained in any chosen angle, the practice of using pillows and/or bolsters persists in many centres and such devices are still designed and marketed by companies.
During studies on the degree of lordosis in patients with and without back pain in our MRI unit, we have become increasingly interested in the wide variation in the degree of lordosis amongst the normal population [2]. We have confirmed that women have a greater lordosis than men and that lordosis is more prominent in those with greater body mass index. The way in which lumbar lordosis alters with posture, age and in response to disease remains controversial.
In this preliminary study, we were interested to see the extent to which modest hip flexion as a result of a cushion behind the knees altered lumbar lordosis in the supine position. A larger study of this nature would be useful to confirm our findings.
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Methods
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Five patients, who had consented to spinal imaging as part of another study, and two members of staff were imaged with MRI, in accordance with our institutional policy for the examination of volunteers. In all cases an examination was made with and without the use of a standard bolster (45°).
In the two volunteers our standard T2 weighted sagittal sequence was used (Figures 1 and 2
). In the five patients images were obtained from a fast three-dimensional localizer sequence. All imaging was performed on a 1.5 Tesla MR system (GE Medical systems, Milwaukee, WI).
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Figure 1. T2 weighted sagittal images of a 28-year-old woman. Guidelines of angle (white) highlight the little appreciable difference in position (a) without and (b) with a supportive cushion behind the knees. The radiologists, blind to the positioning, found an increase in lordosis of +4° when the support was in place.
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Figure 2. A 53-year-old man with chronic lumbar disc degeneration and previous surgery at L5/S1. Note the almost identical lordosis (a) without and (b) with a supportive cushion. The reduction in lordosis was assessed at-3°.
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Lumbar lordosis was measured by consensus by two experienced radiologists on a workstation using a modified Cobb angle technique [3]. A line was drawn along the superior margin of the L2 vertebral body and a second line was drawn along the superior margin of S1. The angle between these two lines was calculated. The radiologists were unaware which images were obtained with and without hip flexion.
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Results
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In this small group of seven subjects the angle of lordosis ranged from 16° to 70° (Table 1). A positive degree difference indicates an increase in lumbar lordosis with the cushion in place (Table 1). In one volunteer (Figure 1
) and three patients there was slightly greater lordosis with the bolster in place.
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Table 1. The consensus measurement of five patients and two volunteers made by two experienced radiologists, with and without a supportive cushion under the knees
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Discussion
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It is clear that there is a wide range of lordotic angles in the general population, regardless of back pain status [2]. This brief study shows that the angle of lordosis does not change appreciably with modest hip flexion, and the differences are well within the range of variation of such measurements [4]. Certainly the experienced radiologists in this study could not determine which set of images was produced with hip flexion and which without. Indeed, lordosis increased in three patients with the use of a cushion. This is contrary to the suggestion of standard texts [1]. Whilst there were slight changes of angle in nearly all subjects with and without the cushion, it did not affect diagnosis.
The addition of a knee support during imaging of the lower spine should be based on patient comfort alone and should not be considered as a factor that reduces lordosis of the lumbar spine during imaging in the supine position.
Received for publication November 21, 2001.
Accepted for publication February 14, 2002.
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References
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- Whitley AS, Alsop CW, Moore AD, Wright MJ, editors. Special procedures in Diagnostic Imaging. Oxford: Butterworth Heinemann, 1991.
- Murrie VL, Dixon AK, Wilson H, Hollingworth W, Doyle T. Lumbar Lordosis measurement: a study in patients with and without low back pain. Clin Anat 2001;14:298.
- Cobb JR. Outline for the study of scoliosis. In: Thomson JEM, Boount WP, editors. American Academy of Orthopaedic Surgeons. Instructional Course Lectures. Ann Arbor, MI: JW Edwards, 1948:261–75.
- Morrissy RT, Goldsmith GS, Hall EC, Kehl D, Cowie GH. Measurement of the Cobb Angle on radiographs of patients who have scoliosis. Evaluation of intrinsic error. J Bone Joint Surg Am 1990;72:320–7.[Abstract/Free Full Text]
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Abstract
Introduction
