ANNALS OF HUMAN BIOLOGY,
1976,
VOL,
3,
NO. 2. 173--179
The relationship of kyphosis to the shape of vertebral bodies
Ann Hum Biol Downloaded from informahealthcare.com by Chulalongkorn University on 12/31/14 For personal use only.
J. S. M I L N E Royal Victoria Hospital, Edinburgh and I. J. L A U D E R M.R.C. Clinical and Population Cytogenetics Unit, Edinburgh [Received 22 January 1975; revised 18 July 1975] Summary. An index which measures the wedge deformity of vertebral bodies in lateral chest radiographs in older people was calculated by dividing the sum of the vertical anterior heights of the lower six thoracic vertebral bodies and discs by the corresponding sum of vertical posterior heights. This index increased with increasing age in a similar manner in men and in women, in contradistinction to an index measuring kyphosis in which the age effect was greater in women. The index of wedging explained 42 per cent and 48 per cent of the variation in kyphosis in men and in women respectively. Additional effects due to age, detected in women only, added a further 4 per cent to the explained variation and may be due to ageing of soft tissues. 1. Introduction Various authors have described methods of measuring the degree of thoracic kyphosis (Takahashi and Atsumi, 1955; Cowan, 1965; Neugebauer, 1970; Milne and Lauder, 1974). Cowan, using what he called the kyphotic angle, demonstrated the expected increase in kyphosis with increasing age. The present authors measured kyphosis using a surveyor's flexicurve. This instrument is a strip of lead covered with plastic 60 cm in length, which can be bent in one plane only and which retains any shape into which it is bent. The flexicurve was placed on the subject's back with one end on the seventh cervical vertebra and closely applied to the mid-line of the back, the subject being asked to stand as erect as possible. The level of the lumbrosacral joint was marked on the flexicurve after which the instrument was laid on a piece of paper and the spinal curve copied by running a pencil along the flexicurve. The resulting curve is shown in figure 1, in
CEPHALIC ENO
Fig. 1. Typical record of kyphosis obtained with a surveyor's flexicurve showing the dimensions used in calculating the index of kyphosis (B/E). A.H.B.
L
Ann Hum Biol Downloaded from informahealthcare.com by Chulalongkorn University on 12/31/14 For personal use only.
174
J. S. Milne and I. J. Lauder
which the ends of the curve have been joined by a straight line. Kyphosis is measured by dimension B. This dimension varies with height and after examination of various possible indices, it was shown that the most appropriate index for describing kyphosis, with the least dependence on height is dimension B divided by dimension E (Milne and Lauder, 1974). In the present paper this is called the index of kyphosis. This index also shows the expected increase with increasing age, particularly in women. Inspection of lateral chest radiographs in older people reveals vertebral bodies many of which are wedge-shaped, rather than rectangular as they are in younger persons. Some authors mention the association between wedging of vertebral bodies and kyphosis (Nicholas and Wilson, 1963; Rowe and Sorbie, 1963). The present paper describes a method of measuring this wedge deformity and of relating it to measurements of kyphosis.
2. Subjects and methods The sample of older people on whom the measurements were made was obtained from the medical lists of 91 doctors in 50 general practices with surgery addresses in a defined area of Edinburgh. A total of 27 000 persons born in 1905 or earlier were available for sampling in January 1968. From this total a simple random sample was examined of 215 men and 272 women aged 62-90 years. Full details of sampling with a comparison of respondents and non-respondents have been given elsewhere (Milne, Maule and Williamson, 1971).
Fig. 2. Dimensions of a lateral chest radiograph to estimate index of wedging (of vertebral bodies)
Ann Hum Biol Downloaded from informahealthcare.com by Chulalongkorn University on 12/31/14 For personal use only.
Kyphosis and shape of vertebral bodies
175
Left lateral chest radiographs were taken at a tube-film distance of 183 cm with the subject standing with the upper limbs parallel to the ground. The shape of vertebral bodies was measured from the lateral chest radiograph by measuring two distances along the spine in the lower thoracic region with a "Curvimetre" map measurer. This instrument has a toothed wheel geared to a pointer on a dial so that running the wheel along a curved line records the length of the line on the dial. One revolution of the pointer is equivalent to 10 cm. A digital counter in a window in the dial sums decimetres. The dial is graduated in centimetres and millimetres. The anterior distance measured extended from the upper end of the anterior border of the seventh thoracic vertebra to the lower end of the anterior border of the twelfth thoracic vertebra. The posterior distance was measured along a line immediately anterior to the intervertebral foramina extending from the upper border of the seventh to the lower border of the twelfth thoracic vertebra, i.e. along the posterior aspect of the vertebral bodies. The lines have been drawn in white on the lateral chest radiograph in figure 2. If the posterior measurement in expressed as a percentage of the anterior, the more this index exceeds 100, the greater is the degree of wedge deformity in the six vertebrae measured. The six vertebrae measured were chosen because in 50 lateral chest radiographs selected at random from the 447 films exposed in the study, only two were found in which fewer than six vertebrae were clearly visible. The lower seven dorsal vertebrae were clearly visible in only 18 of the 50 films. Kyphosis was measured with a surveyor's flexicurve as described above and elsewhere (Milne and Lauder, 1974).
Reproducibility and validity of methods The technique for estimating wedge deformity in vertebral bodies was tested by four comparisons of paired measurements. These were : 1. Using one radiograph in each person the index was calculated in ten persons on two occasions of measurement. 2. Using two radiographs in each person, exposed on separate occasions the index was calculated in ten persons for each occasion. 3. Using one radiograph in each of ten persons the index was calculated from two measurements, the first using six vertebrae as described above and the second using the greatest number of visible vertebrae (maximum nine). 4. Using one radiograph for each of ten persons the index was calculated from six vertebrae, firstly from measurement along continuous lines as in figure 2 and Paired measurement (as numbered 1st in text) mean
2nd mean
Mean diff.
SD diff.
SE diff.
N
t
1
112"5
111"8
0"7
1-20
0-40
10
1"75
2
116"0
115'7
0-3
1"68
0.56
10
0'54
3
115'7
115'5
0"2
1"47
0-49
10
0"41
4
110"9
112"2
1"3
4"73
1.58
10
0"82
Table 1. Comparison of paired measurements used in studying the index of wedging (of vertebral bodies).
J. S. Milne and I. J. Lauder
176
Ann Hum Biol Downloaded from informahealthcare.com by Chulalongkorn University on 12/31/14 For personal use only.
secondly b y s u m m i n g the a n t e r i o r a n d posterior heights of i n d i v i d u a l vertebrae, the intervertebral disc being excluded f r o m the measurements. A different g r o u p of ten persons was used f o r each of the f o u r comparisons. F o r each of the four sets of p a i r e d m e a s u r e m e n t s , the m e a n difference was calc u l a t e d (table 1). N o n e of these m e a n differences differs significantly f r o m zero. T h e c o m p a r i s o n s suggest that the index is reproducible. T h e f o u r t h c o m p a r i s o n suggests that even with intervertebral discs i n c l u d e d in the m e a s u r e m e n t s the index estimates wedge d e f o r m i t y of vertebral bodies. T h e r e p r o d u c i b i l i t y of the index of k y p h o s i s has b e e n d e s c r i b e d elsewhere (Milne a n d L a u d e r , 1974).
3. Results M e a n values with s t a n d a r d deviations are given for the i n d e x of kyphosis in table 2 a n d for the index of wedging in table 3. B o t h variables show age effects.
Age group Men (N=213) 62-64 65-69 70-74 75-79 80-90
Mean
SD
N
0"105 0-111 0' 117 0-122 0"122
0.025 0"030 0.029 0'036 0'035
46 75 38 34 20
0"107 0"118 0"127 0-I 39 0" 160
0.023 0'028 0"029 0"039 0"050
42 93 55 45 30
Women (N= 265) 62-64 65-69 70-74 75-79 80-90
Table 2. Mean values with standard deviations of the index of kyphosis (B/E) in men and women aged 62-90 years. Age group Men ( N = 200) 62-64 65-69 70-74 75-79 80-90
Mean
SD
N
111 "2 110"7 112"8 113"4 114"3
4'02 4'66 6"21 5'88 5"85
45 68 37 31 19
110"3 111'8 113"5 114'5 114"0
4"03 4"59 4"88 6"75 5"07
40 90 53 39 25
Women ( N = 247) 62-64 65-69 70-74 75-79 80-90
Table 3. Mean values with standard deviations of the index of wedging (of vertebral bodies) in men and women aged 62-90.
Ann Hum Biol Downloaded from informahealthcare.com by Chulalongkorn University on 12/31/14 For personal use only.
Kyphosis and shape of vertebral bodies
177
T h e effects are m o r e m a r k e d in w o m e n c o m p a r e d with m e n for the index of k y p h o s i s b u t this is not so for the index of wedging where values in c o r r e s p o n d i n g age groups are similar in the sexes (tables 3 a n d 5). T h e larger n u m b e r of missing values in table 3 c o m p a r e d with table 2 reflects films u n s u i t a b l e for m e a s u r e m e n t , persons u n a b l e to attend h o s p i t a l who were e x a m i n e d at h o m e a n d persons w h o could n o t stand for r a d i o g r a p h s to be exposed. L i n e a r a n d multiple regression techniques were used, with the index of wedging a n d age as the i n d e p e n d e n t variables, to e s t i m a t e the extent to which v a r i a t i o n in the index of k y p h o s i s is e x p l a i n e d b y the i n d e x of wedging a n d other age effects. T h e results, presented in table 4, show t h a t in m e n a n d in w o m e n the p r i n c i p a l c o n t r i b u t i o n to the regression is m a d e b y the index of wedging which explains 42 p e r cent of the v a r i a t i o n in men a n d 48 per cent in women. A d d i t i o n a l effects due to age, detected in w o m e n only, a d d a further 4 p e r cent to the v a r i a t i o n e x p l a i n e d b y the index of wedging.
Sex
N
Men
200 200
Women
Dependent Independent Regression variable variables coefficient
B/E B/E
SE
R
W W
0'0037
0.0003
0"64
0"0037
0"0003
--
A
0.0002
0"0003
0.65
0.0044
0.0003
0.69
247
B/E
W
247
B/E
W
0"0041
0"0003
--
A
0"0021
0"0003
0"72
Partial F test (on inclusion of age in the regression)
0"65
22"2 **
**P
1976,
VOL,
3,
NO. 2. 173--179
The relationship of kyphosis to the shape of vertebral bodies
Ann Hum Biol Downloaded from informahealthcare.com by Chulalongkorn University on 12/31/14 For personal use only.
J. S. M I L N E Royal Victoria Hospital, Edinburgh and I. J. L A U D E R M.R.C. Clinical and Population Cytogenetics Unit, Edinburgh [Received 22 January 1975; revised 18 July 1975] Summary. An index which measures the wedge deformity of vertebral bodies in lateral chest radiographs in older people was calculated by dividing the sum of the vertical anterior heights of the lower six thoracic vertebral bodies and discs by the corresponding sum of vertical posterior heights. This index increased with increasing age in a similar manner in men and in women, in contradistinction to an index measuring kyphosis in which the age effect was greater in women. The index of wedging explained 42 per cent and 48 per cent of the variation in kyphosis in men and in women respectively. Additional effects due to age, detected in women only, added a further 4 per cent to the explained variation and may be due to ageing of soft tissues. 1. Introduction Various authors have described methods of measuring the degree of thoracic kyphosis (Takahashi and Atsumi, 1955; Cowan, 1965; Neugebauer, 1970; Milne and Lauder, 1974). Cowan, using what he called the kyphotic angle, demonstrated the expected increase in kyphosis with increasing age. The present authors measured kyphosis using a surveyor's flexicurve. This instrument is a strip of lead covered with plastic 60 cm in length, which can be bent in one plane only and which retains any shape into which it is bent. The flexicurve was placed on the subject's back with one end on the seventh cervical vertebra and closely applied to the mid-line of the back, the subject being asked to stand as erect as possible. The level of the lumbrosacral joint was marked on the flexicurve after which the instrument was laid on a piece of paper and the spinal curve copied by running a pencil along the flexicurve. The resulting curve is shown in figure 1, in
CEPHALIC ENO
Fig. 1. Typical record of kyphosis obtained with a surveyor's flexicurve showing the dimensions used in calculating the index of kyphosis (B/E). A.H.B.
L
Ann Hum Biol Downloaded from informahealthcare.com by Chulalongkorn University on 12/31/14 For personal use only.
174
J. S. Milne and I. J. Lauder
which the ends of the curve have been joined by a straight line. Kyphosis is measured by dimension B. This dimension varies with height and after examination of various possible indices, it was shown that the most appropriate index for describing kyphosis, with the least dependence on height is dimension B divided by dimension E (Milne and Lauder, 1974). In the present paper this is called the index of kyphosis. This index also shows the expected increase with increasing age, particularly in women. Inspection of lateral chest radiographs in older people reveals vertebral bodies many of which are wedge-shaped, rather than rectangular as they are in younger persons. Some authors mention the association between wedging of vertebral bodies and kyphosis (Nicholas and Wilson, 1963; Rowe and Sorbie, 1963). The present paper describes a method of measuring this wedge deformity and of relating it to measurements of kyphosis.
2. Subjects and methods The sample of older people on whom the measurements were made was obtained from the medical lists of 91 doctors in 50 general practices with surgery addresses in a defined area of Edinburgh. A total of 27 000 persons born in 1905 or earlier were available for sampling in January 1968. From this total a simple random sample was examined of 215 men and 272 women aged 62-90 years. Full details of sampling with a comparison of respondents and non-respondents have been given elsewhere (Milne, Maule and Williamson, 1971).
Fig. 2. Dimensions of a lateral chest radiograph to estimate index of wedging (of vertebral bodies)
Ann Hum Biol Downloaded from informahealthcare.com by Chulalongkorn University on 12/31/14 For personal use only.
Kyphosis and shape of vertebral bodies
175
Left lateral chest radiographs were taken at a tube-film distance of 183 cm with the subject standing with the upper limbs parallel to the ground. The shape of vertebral bodies was measured from the lateral chest radiograph by measuring two distances along the spine in the lower thoracic region with a "Curvimetre" map measurer. This instrument has a toothed wheel geared to a pointer on a dial so that running the wheel along a curved line records the length of the line on the dial. One revolution of the pointer is equivalent to 10 cm. A digital counter in a window in the dial sums decimetres. The dial is graduated in centimetres and millimetres. The anterior distance measured extended from the upper end of the anterior border of the seventh thoracic vertebra to the lower end of the anterior border of the twelfth thoracic vertebra. The posterior distance was measured along a line immediately anterior to the intervertebral foramina extending from the upper border of the seventh to the lower border of the twelfth thoracic vertebra, i.e. along the posterior aspect of the vertebral bodies. The lines have been drawn in white on the lateral chest radiograph in figure 2. If the posterior measurement in expressed as a percentage of the anterior, the more this index exceeds 100, the greater is the degree of wedge deformity in the six vertebrae measured. The six vertebrae measured were chosen because in 50 lateral chest radiographs selected at random from the 447 films exposed in the study, only two were found in which fewer than six vertebrae were clearly visible. The lower seven dorsal vertebrae were clearly visible in only 18 of the 50 films. Kyphosis was measured with a surveyor's flexicurve as described above and elsewhere (Milne and Lauder, 1974).
Reproducibility and validity of methods The technique for estimating wedge deformity in vertebral bodies was tested by four comparisons of paired measurements. These were : 1. Using one radiograph in each person the index was calculated in ten persons on two occasions of measurement. 2. Using two radiographs in each person, exposed on separate occasions the index was calculated in ten persons for each occasion. 3. Using one radiograph in each of ten persons the index was calculated from two measurements, the first using six vertebrae as described above and the second using the greatest number of visible vertebrae (maximum nine). 4. Using one radiograph for each of ten persons the index was calculated from six vertebrae, firstly from measurement along continuous lines as in figure 2 and Paired measurement (as numbered 1st in text) mean
2nd mean
Mean diff.
SD diff.
SE diff.
N
t
1
112"5
111"8
0"7
1-20
0-40
10
1"75
2
116"0
115'7
0-3
1"68
0.56
10
0'54
3
115'7
115'5
0"2
1"47
0-49
10
0"41
4
110"9
112"2
1"3
4"73
1.58
10
0"82
Table 1. Comparison of paired measurements used in studying the index of wedging (of vertebral bodies).
J. S. Milne and I. J. Lauder
176
Ann Hum Biol Downloaded from informahealthcare.com by Chulalongkorn University on 12/31/14 For personal use only.
secondly b y s u m m i n g the a n t e r i o r a n d posterior heights of i n d i v i d u a l vertebrae, the intervertebral disc being excluded f r o m the measurements. A different g r o u p of ten persons was used f o r each of the f o u r comparisons. F o r each of the four sets of p a i r e d m e a s u r e m e n t s , the m e a n difference was calc u l a t e d (table 1). N o n e of these m e a n differences differs significantly f r o m zero. T h e c o m p a r i s o n s suggest that the index is reproducible. T h e f o u r t h c o m p a r i s o n suggests that even with intervertebral discs i n c l u d e d in the m e a s u r e m e n t s the index estimates wedge d e f o r m i t y of vertebral bodies. T h e r e p r o d u c i b i l i t y of the index of k y p h o s i s has b e e n d e s c r i b e d elsewhere (Milne a n d L a u d e r , 1974).
3. Results M e a n values with s t a n d a r d deviations are given for the i n d e x of kyphosis in table 2 a n d for the index of wedging in table 3. B o t h variables show age effects.
Age group Men (N=213) 62-64 65-69 70-74 75-79 80-90
Mean
SD
N
0"105 0-111 0' 117 0-122 0"122
0.025 0"030 0.029 0'036 0'035
46 75 38 34 20
0"107 0"118 0"127 0-I 39 0" 160
0.023 0'028 0"029 0"039 0"050
42 93 55 45 30
Women (N= 265) 62-64 65-69 70-74 75-79 80-90
Table 2. Mean values with standard deviations of the index of kyphosis (B/E) in men and women aged 62-90 years. Age group Men ( N = 200) 62-64 65-69 70-74 75-79 80-90
Mean
SD
N
111 "2 110"7 112"8 113"4 114"3
4'02 4'66 6"21 5'88 5"85
45 68 37 31 19
110"3 111'8 113"5 114'5 114"0
4"03 4"59 4"88 6"75 5"07
40 90 53 39 25
Women ( N = 247) 62-64 65-69 70-74 75-79 80-90
Table 3. Mean values with standard deviations of the index of wedging (of vertebral bodies) in men and women aged 62-90.
Ann Hum Biol Downloaded from informahealthcare.com by Chulalongkorn University on 12/31/14 For personal use only.
Kyphosis and shape of vertebral bodies
177
T h e effects are m o r e m a r k e d in w o m e n c o m p a r e d with m e n for the index of k y p h o s i s b u t this is not so for the index of wedging where values in c o r r e s p o n d i n g age groups are similar in the sexes (tables 3 a n d 5). T h e larger n u m b e r of missing values in table 3 c o m p a r e d with table 2 reflects films u n s u i t a b l e for m e a s u r e m e n t , persons u n a b l e to attend h o s p i t a l who were e x a m i n e d at h o m e a n d persons w h o could n o t stand for r a d i o g r a p h s to be exposed. L i n e a r a n d multiple regression techniques were used, with the index of wedging a n d age as the i n d e p e n d e n t variables, to e s t i m a t e the extent to which v a r i a t i o n in the index of k y p h o s i s is e x p l a i n e d b y the i n d e x of wedging a n d other age effects. T h e results, presented in table 4, show t h a t in m e n a n d in w o m e n the p r i n c i p a l c o n t r i b u t i o n to the regression is m a d e b y the index of wedging which explains 42 p e r cent of the v a r i a t i o n in men a n d 48 per cent in women. A d d i t i o n a l effects due to age, detected in w o m e n only, a d d a further 4 p e r cent to the v a r i a t i o n e x p l a i n e d b y the index of wedging.
Sex
N
Men
200 200
Women
Dependent Independent Regression variable variables coefficient
B/E B/E
SE
R
W W
0'0037
0.0003
0"64
0"0037
0"0003
--
A
0.0002
0"0003
0.65
0.0044
0.0003
0.69
247
B/E
W
247
B/E
W
0"0041
0"0003
--
A
0"0021
0"0003
0"72
Partial F test (on inclusion of age in the regression)
0"65
22"2 **
**P
