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No diffuse osteoporosis in lumbar scoliosis but lower femoral bone density on the convexity
Bone Vol. 18, No. 1 January 1996:15-17 ELSEVIER
No Diffuse Osteoporosis in Lumbar Scoliosis but Lower Femoral Bone Density on the Convexity D. H A N S , 1 B. B I O T , 2 A. M . S C H O T T , 1 a n d P. J. M E U N I E R 1 I INSERM Unit 403, Epidemiology Section, Pavilion F. HOpital Edouard Herriot, Lyon, France 2Centre des Massues, Lyon, France
Materials and Methods
The aims of our study were to find out, in 15 female volunteers with untreated structural lumbar idiopathic scoliosis, through dual-photon X-ray absorptiometry measurements, whether femoral bone mineral density (BMD) was different between the right and the left side and whether this difference was related to scoliosis convexity. We showed that no statistical significant difference between femoral neck BMD measured on both sides of the same patient (p = 0.6). However, neck BMD from the same side as the convexity side was significantly lower than the opposite one. (Bone 18:15-17;
We recruited 15 healthy female volunteers (11 premenopausal and 4 postmenopausal women; mean age 45 _+ 11 years; range 23-58 years of age) with untreated adolescent structural lumbar idiopathic scoliosis (Table 1) (one curve, mean angle 31 _+ 8.4°; range 21°-50°; carelessness of preliminary treatment explains average Cobb angle). All X-rays were examined independently by two rheumatologists: none of these women had posterior spine arthritis and only three of them had mild anterior spine arthritis. Women were excluded when they had a history of osteoporotic fracture, hip prosthesis, Paget's disease of bone, malignant bone disease or renal failure. None of the women received osteotropic drugs. Standing anteroposterior and lateral X-rays, taken at a standard distance, visualized the whole spine, pelvis, both hips, and the upper femoral region. The scoliosis angle was measured by the method of Cobb and convexity side was assessed. Whole body and femoral neck BMD were measured using a DXA DPX-Plus (Lunar Corp., Madison, WI). These techniques permit direct and precise measurements with a very low dose of radiation. For femur measurement, a standardized procedure was used to minimize the positioning error as follows: we ensured that the leg to be examined was rotated inward, abducted, rotated by turning the leg and the foot, and then the foot was placed against the positioning fixture. The in vivo short-term precision of these femur measurements was assessed in 20 healthy volunteers (hospital employees) with the Lunar DPX-Plus; measurements were done twice each with repositioning. The in vivo short-term precision expressed in coefficient of variation (CV) was 1.4% for the femoral neck BMD. As reported by Mazess et al., in vivo short-term precision expressed in CV was 0.8% for total body BMD. 5 To investigate the relationship between D X A and scoliosis parameters we performed simple linear regression analysis. The comparison of the right and left neck BMD was performed with the paired Student's t-test.
1996) Key Words: DXA; Lumbar scoliosis; Osteoporosis.
Introduction Previous studies using X-rays, 9A° bone absorptiometry, s'm or bone histomorphometry 3 have shown that scoliosis of >10 ° is more common in osteoporotic patients than in controls and that the severity of scoliosis is related to osteopenia. For example, Thevenon et al. have shown in 56 patients over 60 years of age (67.9 +_ 5.5 years) that the lumbar scoliosis angle was significantly negatively correlated to the femoral neck bone mineral content (BMC) but not with spine BMC. s Velis et al. noted that patients with unstable scoliosis were more osteoporotic than patients with stable scoliosis and had femoral neck bone mineral density (BMD) 2 6 4 8 % lower than controls, lO In contrast, Robin et al. concluded that there was no basis to assume a causal relationship between scoliosis and osteoporosis. 7 In fact, to date, the links between scoliosis and osteoporosis are still unclear, and the influence of lumbar convexity on lower limb bone mineral density has never been analyzed. The aims of the present included: • To determine, using whole body dual-energy X-ray absorptiometry (DXA) measurements, whether or not scoliotic patients had a lower BMD than a reference population. • To compare femoral B M D measured on both sides of the same patient and to determine whether or not the difference was related to scoliosis convexity.
Results The mean whole body BMD of scoliotic women compared with an age-matched z score and a young adult French reference population given by the manufacturer (t score) were -0.1 and -0.5 SD, respectively. The mean femoral neck BMD (mean of both sides), also expressed as z score and t score, were -0.16 and -0.83 SD, respectively.
Address for correspondence and reprints: Dr. D. Hans, Htpital Edouard Herriot, INSERM Unit 403, Epidemiology Section, Pavillon F, 69437 Lyon Cedex 03, France.
© 1996 by Elsevier Science Inc. All rights reserved.
15
8756-3282/96/$15.00 SSDI 8756-3282(95)00421-1
16
D. Hans et al. Influence of scoliosis convexity on DXA measurements
Bone Vol. 18, No. 1 January 1996:15-17
Table 1. Characteristics of the population of 15 healthy female volunteers having untreated adolescent structural lumbar idiopathic scoliosis, including femoral bone mineral density
Patient/
Right neck
Left neck
Weight
age/YSM"
BMD
BMD
(kg)
Scoliosis descriptionb
W.I./23/0 V.C./51/0 P.H.-50-0 M.I.-55-5 M.D.-54-0 L.L.-58-8 G.L.-52-0 G.B.-39-0 G.M.-53-1 D.M.-27-0 C.R.-45-0 B.S.-37-0 A.M.-43-0 C.E.-56-5 D.A.-29-0
0.877 0.796 1.009 0.926 0.821 0.832 0.797 1.015 0.707 0.837 0.899 0.957 0.900 0.920 0.877
0.838 0.835 1.056 0.816 0.861 0.805 0.750 0.977 0.623 0.874 0.850 0.978 0.907 0.983 0.899
48 61 55 60 53 44 51 53 50 67 70 61 54 65 66
Left-25°-lumbar Lefl-48°-lumbar Left 24°-lumbar Left-25 ° lumbar Right-27°-Iumbar Left 33°-lumbar Left-27°-lumbar Left-36°-thoracolumbar Left-50°-thoracolumbar Right-31 °-lumbar Left-35°-Iumbar Right-25°-lumbar Right-21 °-lumbar Right-23°-lumbar Right-35°-lumbar
aYSM: years since menopause, bConvexity side-Cobb angle-location of the curve.
Using a paired t-test, no statistically significant difference was found between the femoral neck B M D measured on both sides of the same patient (p = 0.6). However, a statistically significant difference was found (p = 0.006) when the neck BMD from the same side as the convexity side (CS) was compared to the opposite side (OS): the femoral neck BMD was lower in the CS. The mean difference [formula: (CS - OS)/CS] e x p r e s s e d in p e r c e n t was - 4 . 2 % (range - 1 3 . 5 to +4.7) (Figure 1). Based on the previous results, femoral neck BMD from the convexity side and opposite side were also expressed as z and t scores. The opposite femoral neck BMD (compared to convexity) was -0.4 and -1 SD vs. 0 and -0.7 SD, respectively, for femoral neck B M D corresponding at the convexity side. I.i
•
_
•
.
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.
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,
.
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,
.
,
O a~
.
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•
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.
~
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.
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0
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. U u~
Discussion In our scoliotic population, 60% of the patients had a left convexity and 40% a right convexity whereas the left convexity percentage is higher in the literature. Because we did not measure the spine specifically, the following conclusion will be based on our whole body and femoral neck D X A measurements: scoliotic patients did not have a significantly lower BMD than the reference population. In agreement with the World Health Organization's new definition of osteoporosis, 6 our scoliotic patients can be considered normal. This first conclusion does not fit in with previous publications. 3"8'9'm Due to the small sample size in the present work we may not have had sufficient data to obtain results similar to those in previous publications. 3"8'9"~°The other possibility is that investigators usually measure the femoral neck BMD of a systematic side (left or right), whereas we took into account both sides. Thus, by calculating the t score in the femur corresponding to the convexity side our scoliotic patients would be considered osteopenic, because osteopenia corresponds to a t score between -1 and -2.5. 6 Our findings show for the first time that the difference between femoral neck B M D measured on both sides of the same patient is related to scoliosis convexity and that femoral neck BMD is lower on the convexity side. A biomechanical hypothesis could be advanced by supposing that the strengths applied on the femur are different according to the convexity side. Indeed, transfer of trunk gravity line to the convexity side induces additional force on the opposite hip. Such a dynamic mechanism could explain the asymmetrical repartition of bone on the femoral neck. In addition, because the localization of the curve is low and considering that there is no significant subjacent compensation, the curve could have a close and immediate influence over the pelvis. However, Hoppenfeld et al. 4 did not show any difference in terms of static strength between the two sides by using a plantar weight-bearing pattern in idiopathic scoliosis. However, when walking, because of the influence of heel drops on bone femoral bone density, ~ and asymmetrical muscular effort in readjustment, it is possible that the force applied on both feet could be different and could influence femoral bone density on one side. According to Bassett, 2 impact loading produced strain rates and amplitudes in skeletal sites leading to an effect on bone formation. Impact can be attenuated by the attitude of the extremity at the moment of heel contact. It would be of interest to determine whether scoliotic patients have a significantly higher incidence of hip fracture on the same side as their lumbar convexity. In addition, these results are clinically important because the DXA anteroposterior spine measurement in scoliotic patients is usually unreliable and, thus, the femoral site is widely used as the DXA measurement site. Our data suggest areas for future study.
.8
Acknowledgments." This
.7
References
study was supported by a grant from Lyon Mutualit6 Sociale Agricole (president: L. Bortoletto: director: J. P. Garcia).
o=
.6 .6
.
•
.65
-
•
.7
.
,
.75
-
o
.8
-
,
.85
.
•
.9
.
•
.
.95
C o n v e x i t y f e m o r a l neck BMD
•
1
-
0
.
1.05 i.i
(g/cm2)
Figure 1. Correlation between the femoral neck bone mineral density (BMD) of the convexity and femoral neck BMD of the concavity.
1. Bassett, C. A. L. Effects of controlled impact loading on bone mass: a preliminary report. J Bone Miner Res 9 (suppl. 1):A276; 1994. 2. Bassen, C. A. L. Why are the principles of physics and anatomy important in treating osteoporosis? Calcif Tissue lnt 56:515-516; 1995. 3. Healey, J. H. and Lane, J. M. Structural scoliosis in osteoporotic women. Clin Orthop 195:216-223; 1985. 4. Hoppenfeld, S., Lopez, R. A., and Molnar, G. Plantar weight-bearing pattern in idiopathic scoliosis. Spine 16:757-760; 1991.
Bone Vol. 18, No. 1 January 1996:15-17
D. H a n s et al. Influence o f scoliosis convexity on D X A m e a s u r e m e n t s
17
5. Mazess, R. et al. Dual-energy X-ray absorptiometry for total body and regional bone mineral and soft tissue composition. Am J Clin Nutr 51:1106-1112; 1990.
9. Vanderpool, D.W., James, J. 1. P., and Wynne-Davies, R. Scoliosis in the elderly. J Bone Joint Surg 51A:446~-55; 1969.
6. Report of World Health Organization. Assessment of fracture risk and its application to screening for postmennpansal osteoporosis. WHO Technical Report Series 843:5~o; 1994.
10. Velis, K. P., Healey, J. H., and Schneider, R. Osteoporosis in unstable adult scoliosis. Clin Orthop 237:132-t41; 1988.
7. Robin, G., Span, Y., Steinberg, R., Makin, M., and Menczel, J. Scoliosis in the elderly. A follow-up study. Spine 7:355-359; 1982. 8. Thevenon, A., Pollez, B., Cantegrit, F., Tison Muchery, F., Marchandise, X., and Duquesnoy, B. Relationship between kyphosis scoliosis and osteoporosis in the elderly population. Spine 12:744-745; 1987.
Date Received: March 17, 1995 Date Revised: September 13, 1995 Date Accepted: September 15, 1995
No Diffuse Osteoporosis in Lumbar Scoliosis but Lower Femoral Bone Density on the Convexity D. H A N S , 1 B. B I O T , 2 A. M . S C H O T T , 1 a n d P. J. M E U N I E R 1 I INSERM Unit 403, Epidemiology Section, Pavilion F. HOpital Edouard Herriot, Lyon, France 2Centre des Massues, Lyon, France
Materials and Methods
The aims of our study were to find out, in 15 female volunteers with untreated structural lumbar idiopathic scoliosis, through dual-photon X-ray absorptiometry measurements, whether femoral bone mineral density (BMD) was different between the right and the left side and whether this difference was related to scoliosis convexity. We showed that no statistical significant difference between femoral neck BMD measured on both sides of the same patient (p = 0.6). However, neck BMD from the same side as the convexity side was significantly lower than the opposite one. (Bone 18:15-17;
We recruited 15 healthy female volunteers (11 premenopausal and 4 postmenopausal women; mean age 45 _+ 11 years; range 23-58 years of age) with untreated adolescent structural lumbar idiopathic scoliosis (Table 1) (one curve, mean angle 31 _+ 8.4°; range 21°-50°; carelessness of preliminary treatment explains average Cobb angle). All X-rays were examined independently by two rheumatologists: none of these women had posterior spine arthritis and only three of them had mild anterior spine arthritis. Women were excluded when they had a history of osteoporotic fracture, hip prosthesis, Paget's disease of bone, malignant bone disease or renal failure. None of the women received osteotropic drugs. Standing anteroposterior and lateral X-rays, taken at a standard distance, visualized the whole spine, pelvis, both hips, and the upper femoral region. The scoliosis angle was measured by the method of Cobb and convexity side was assessed. Whole body and femoral neck BMD were measured using a DXA DPX-Plus (Lunar Corp., Madison, WI). These techniques permit direct and precise measurements with a very low dose of radiation. For femur measurement, a standardized procedure was used to minimize the positioning error as follows: we ensured that the leg to be examined was rotated inward, abducted, rotated by turning the leg and the foot, and then the foot was placed against the positioning fixture. The in vivo short-term precision of these femur measurements was assessed in 20 healthy volunteers (hospital employees) with the Lunar DPX-Plus; measurements were done twice each with repositioning. The in vivo short-term precision expressed in coefficient of variation (CV) was 1.4% for the femoral neck BMD. As reported by Mazess et al., in vivo short-term precision expressed in CV was 0.8% for total body BMD. 5 To investigate the relationship between D X A and scoliosis parameters we performed simple linear regression analysis. The comparison of the right and left neck BMD was performed with the paired Student's t-test.
1996) Key Words: DXA; Lumbar scoliosis; Osteoporosis.
Introduction Previous studies using X-rays, 9A° bone absorptiometry, s'm or bone histomorphometry 3 have shown that scoliosis of >10 ° is more common in osteoporotic patients than in controls and that the severity of scoliosis is related to osteopenia. For example, Thevenon et al. have shown in 56 patients over 60 years of age (67.9 +_ 5.5 years) that the lumbar scoliosis angle was significantly negatively correlated to the femoral neck bone mineral content (BMC) but not with spine BMC. s Velis et al. noted that patients with unstable scoliosis were more osteoporotic than patients with stable scoliosis and had femoral neck bone mineral density (BMD) 2 6 4 8 % lower than controls, lO In contrast, Robin et al. concluded that there was no basis to assume a causal relationship between scoliosis and osteoporosis. 7 In fact, to date, the links between scoliosis and osteoporosis are still unclear, and the influence of lumbar convexity on lower limb bone mineral density has never been analyzed. The aims of the present included: • To determine, using whole body dual-energy X-ray absorptiometry (DXA) measurements, whether or not scoliotic patients had a lower BMD than a reference population. • To compare femoral B M D measured on both sides of the same patient and to determine whether or not the difference was related to scoliosis convexity.
Results The mean whole body BMD of scoliotic women compared with an age-matched z score and a young adult French reference population given by the manufacturer (t score) were -0.1 and -0.5 SD, respectively. The mean femoral neck BMD (mean of both sides), also expressed as z score and t score, were -0.16 and -0.83 SD, respectively.
Address for correspondence and reprints: Dr. D. Hans, Htpital Edouard Herriot, INSERM Unit 403, Epidemiology Section, Pavillon F, 69437 Lyon Cedex 03, France.
© 1996 by Elsevier Science Inc. All rights reserved.
15
8756-3282/96/$15.00 SSDI 8756-3282(95)00421-1
16
D. Hans et al. Influence of scoliosis convexity on DXA measurements
Bone Vol. 18, No. 1 January 1996:15-17
Table 1. Characteristics of the population of 15 healthy female volunteers having untreated adolescent structural lumbar idiopathic scoliosis, including femoral bone mineral density
Patient/
Right neck
Left neck
Weight
age/YSM"
BMD
BMD
(kg)
Scoliosis descriptionb
W.I./23/0 V.C./51/0 P.H.-50-0 M.I.-55-5 M.D.-54-0 L.L.-58-8 G.L.-52-0 G.B.-39-0 G.M.-53-1 D.M.-27-0 C.R.-45-0 B.S.-37-0 A.M.-43-0 C.E.-56-5 D.A.-29-0
0.877 0.796 1.009 0.926 0.821 0.832 0.797 1.015 0.707 0.837 0.899 0.957 0.900 0.920 0.877
0.838 0.835 1.056 0.816 0.861 0.805 0.750 0.977 0.623 0.874 0.850 0.978 0.907 0.983 0.899
48 61 55 60 53 44 51 53 50 67 70 61 54 65 66
Left-25°-lumbar Lefl-48°-lumbar Left 24°-lumbar Left-25 ° lumbar Right-27°-Iumbar Left 33°-lumbar Left-27°-lumbar Left-36°-thoracolumbar Left-50°-thoracolumbar Right-31 °-lumbar Left-35°-Iumbar Right-25°-lumbar Right-21 °-lumbar Right-23°-lumbar Right-35°-lumbar
aYSM: years since menopause, bConvexity side-Cobb angle-location of the curve.
Using a paired t-test, no statistically significant difference was found between the femoral neck B M D measured on both sides of the same patient (p = 0.6). However, a statistically significant difference was found (p = 0.006) when the neck BMD from the same side as the convexity side (CS) was compared to the opposite side (OS): the femoral neck BMD was lower in the CS. The mean difference [formula: (CS - OS)/CS] e x p r e s s e d in p e r c e n t was - 4 . 2 % (range - 1 3 . 5 to +4.7) (Figure 1). Based on the previous results, femoral neck BMD from the convexity side and opposite side were also expressed as z and t scores. The opposite femoral neck BMD (compared to convexity) was -0.4 and -1 SD vs. 0 and -0.7 SD, respectively, for femoral neck B M D corresponding at the convexity side. I.i
•
_
•
.
,
.
|
.
•
,
.
•a
,
.
,
O a~
.
/
•
/
.
~
,
.
•
0
m
. U u~
Discussion In our scoliotic population, 60% of the patients had a left convexity and 40% a right convexity whereas the left convexity percentage is higher in the literature. Because we did not measure the spine specifically, the following conclusion will be based on our whole body and femoral neck D X A measurements: scoliotic patients did not have a significantly lower BMD than the reference population. In agreement with the World Health Organization's new definition of osteoporosis, 6 our scoliotic patients can be considered normal. This first conclusion does not fit in with previous publications. 3"8'9'm Due to the small sample size in the present work we may not have had sufficient data to obtain results similar to those in previous publications. 3"8'9"~°The other possibility is that investigators usually measure the femoral neck BMD of a systematic side (left or right), whereas we took into account both sides. Thus, by calculating the t score in the femur corresponding to the convexity side our scoliotic patients would be considered osteopenic, because osteopenia corresponds to a t score between -1 and -2.5. 6 Our findings show for the first time that the difference between femoral neck B M D measured on both sides of the same patient is related to scoliosis convexity and that femoral neck BMD is lower on the convexity side. A biomechanical hypothesis could be advanced by supposing that the strengths applied on the femur are different according to the convexity side. Indeed, transfer of trunk gravity line to the convexity side induces additional force on the opposite hip. Such a dynamic mechanism could explain the asymmetrical repartition of bone on the femoral neck. In addition, because the localization of the curve is low and considering that there is no significant subjacent compensation, the curve could have a close and immediate influence over the pelvis. However, Hoppenfeld et al. 4 did not show any difference in terms of static strength between the two sides by using a plantar weight-bearing pattern in idiopathic scoliosis. However, when walking, because of the influence of heel drops on bone femoral bone density, ~ and asymmetrical muscular effort in readjustment, it is possible that the force applied on both feet could be different and could influence femoral bone density on one side. According to Bassett, 2 impact loading produced strain rates and amplitudes in skeletal sites leading to an effect on bone formation. Impact can be attenuated by the attitude of the extremity at the moment of heel contact. It would be of interest to determine whether scoliotic patients have a significantly higher incidence of hip fracture on the same side as their lumbar convexity. In addition, these results are clinically important because the DXA anteroposterior spine measurement in scoliotic patients is usually unreliable and, thus, the femoral site is widely used as the DXA measurement site. Our data suggest areas for future study.
.8
Acknowledgments." This
.7
References
study was supported by a grant from Lyon Mutualit6 Sociale Agricole (president: L. Bortoletto: director: J. P. Garcia).
o=
.6 .6
.
•
.65
-
•
.7
.
,
.75
-
o
.8
-
,
.85
.
•
.9
.
•
.
.95
C o n v e x i t y f e m o r a l neck BMD
•
1
-
0
.
1.05 i.i
(g/cm2)
Figure 1. Correlation between the femoral neck bone mineral density (BMD) of the convexity and femoral neck BMD of the concavity.
1. Bassett, C. A. L. Effects of controlled impact loading on bone mass: a preliminary report. J Bone Miner Res 9 (suppl. 1):A276; 1994. 2. Bassen, C. A. L. Why are the principles of physics and anatomy important in treating osteoporosis? Calcif Tissue lnt 56:515-516; 1995. 3. Healey, J. H. and Lane, J. M. Structural scoliosis in osteoporotic women. Clin Orthop 195:216-223; 1985. 4. Hoppenfeld, S., Lopez, R. A., and Molnar, G. Plantar weight-bearing pattern in idiopathic scoliosis. Spine 16:757-760; 1991.
Bone Vol. 18, No. 1 January 1996:15-17
D. H a n s et al. Influence o f scoliosis convexity on D X A m e a s u r e m e n t s
17
5. Mazess, R. et al. Dual-energy X-ray absorptiometry for total body and regional bone mineral and soft tissue composition. Am J Clin Nutr 51:1106-1112; 1990.
9. Vanderpool, D.W., James, J. 1. P., and Wynne-Davies, R. Scoliosis in the elderly. J Bone Joint Surg 51A:446~-55; 1969.
6. Report of World Health Organization. Assessment of fracture risk and its application to screening for postmennpansal osteoporosis. WHO Technical Report Series 843:5~o; 1994.
10. Velis, K. P., Healey, J. H., and Schneider, R. Osteoporosis in unstable adult scoliosis. Clin Orthop 237:132-t41; 1988.
7. Robin, G., Span, Y., Steinberg, R., Makin, M., and Menczel, J. Scoliosis in the elderly. A follow-up study. Spine 7:355-359; 1982. 8. Thevenon, A., Pollez, B., Cantegrit, F., Tison Muchery, F., Marchandise, X., and Duquesnoy, B. Relationship between kyphosis scoliosis and osteoporosis in the elderly population. Spine 12:744-745; 1987.
Date Received: March 17, 1995 Date Revised: September 13, 1995 Date Accepted: September 15, 1995