Measurement of sagittal intervertebral angle and its influencing factors in normal adult lumbar spine Liu Zhao[1] Shen Huiliang Zhang Qingming Hu Hailiang [Abstract] Objective To measure the sagittal intervertebral angle of normal adult lumbar spine and discuss its influencing factors. Methods From 2006.1 to 2009.1, a total of 672 cases were examined in our physical examination center, and 450 cases, 235 males and 215 females, with an average age of 43 years, obtained complete information, and the intervertebral angle and lumbar curvature (L1-L5 intervertebral angle) of the adjacent segments of the lumbar spine were measured using special measurement software. The mean lumbar interbody angles were L1-L2, 2.52°; L2-L3, 5.33°; L3-L4, 8.15°; L4-L5, 12.11°; L5-S1, 20.14° and L1-L5, 24.96°. There was no statistically significant difference in lumbar spine curvature between sexes and body mass indexes (P<0.05). There was a statistically significant difference in lumbar curvature between different age groups (P<0.05). With increasing age, the lumbar curvature gradually became smaller. Conclusion The lumbar curvature gradually decreases with age, but the smaller lumbar curvature after middle age tends to be stable rather than progressively decreasing. Liu Zhao, Department of Orthopedics, Xuanwu Hospital, Capital Medical University [Keywords] Intervertebral body; Angle formation; Normal adults; Values The Measurement of the Reciprocal Angulation of the Lumbar Spine in Sagittal plane and discuss its effect factors In Normal Adults LIU Zhao, SHEN Hui-liang. Cao Li, Hu Hai-liang, Department of Orthopeadics, BeiJing XuanWu Hospital, Capital Medical University, BeiJing 100053, China 【Abstract】Objective To determine the reciprocal angulation of the lumbar spine in sagittal plane and discuss its effect factors. Method There were about 672 normal adults who experienced body examination from Jan. 2006 to Jan. 2009, 450 patients' data is complete. There were 235 men and 215 women, with the average age 43. Determine the segmental and L1 to L5 reciprocal angulations by using the special measurement Determine the segmental and L1 to L5 reciprocal angulations by using the special measurement tools . Results The angulations are as follows: L1-L2, 2.52°; L2-L3, 5.33°; L3-L4, 8.15°; L4-L5, 12.11°; L5-S1, 20.14°; L1-L5, 24.96°. There were no significant differences between the total lumbar lordosis and the patients' gender and BMI.(P<0.05). The normal adults in different age groups, however , own different total lumbar lordosis(P<0.05) ; the angulations become smaller as the people get older The older , the less lumbar curvature. the lumbar curvature tends to be stable after The lumbar curvature tends to be stable after middle age other than progressive diminished. The number of lumbar spine disorders is on the rise with the aging of the population and the increase of degenerative spine disorders. Currently, the surgical management of lumbar spine deformities includes the correction of radiologically significant coronal, sagittal and horizontal anomalies in the lumbar spine. The coronal and horizontal alignment of the lumbar spine is relatively easy to explain. However, lumbar sagittal alignment is more difficult to determine. Stagnara [1], Korovessis [2], and Ruey-mo Lin [3] have reported on the overall lumbar sagittal alignment in normal French, Greek, and Taiwanese subjects, but there are few literature reports on the factors influencing sagittal alignment in national subjects. The purpose of this study was to obtain the reference values of segmental intervertebral angles and lumbar curvature between adjacent vertebrae in the sagittal plane of the lumbar spine in normal national subjects and to investigate the influencing factors. 1.Materials and methods 1.1 General information Through the approval of our hospital ethics committee, this study collected 672 subjects who underwent physical examination at our medical examination center from 2006.1 to 2009.1. Inclusion criteria: (1) age 18 years or older, no significant lower back pain for at least the last 6 months; (2) exclusion of patients with huge lumbar disc herniation, lumbar spinal stenosis and severe lumbar degeneration, trauma and congenital deformity; (3) exclusion of those who have undergone lumbar spine and spine related surgery; (4) unequal length of both lower limbs; (5) exclusion of patients with hip and knee joint disorders. The total number of available data obtained was 450. There were 235 males and 215 females. Age was 18-80 years old, with a mean age of 43 years. Body mass index was weight divided by height squared (kg/m2), and was divided into 3 groups according to our definition of obesity and overweight: BMI<24 for normal group, 2428 for obese group. The different gender and age groupings are shown in Table 1. Table 1 Age distribution of 450 subjects Male Female Grouping Number (pcs) Age (years) Body mass index (kg/m2) Number (pcs) Age (years) Body mass index (kg/m2) Youth group 50 25.2±2.4 23.6±4.6 50 23.6±2.8 25.2±4.1 Middle-aged group 145 44.7± 2.5 24.4±4.0 135 45.1±2.6 24.6±4.2 Elderly group 40 66.0±4.5 26.4±4.4 30 67.0±4.5 26.5±4.7 1.2 Basic method of projection: For lateral projection of the lumbar spine, the examiner lies on the examination bed on the left side, with the coronal axis of the body perpendicular to the examination bed, knees and hips flexed (flexion about 45°), and both upper limbs Both upper limbs are placed naturally on the anterior chest. All radiographs were measured by the authors, and the mean value was taken in each case by repeated measurements three times. Image and data processing methods: The obtained DR images of lumbar spine X-rays were acquired by the PACS system terminal, and the angle between adjacent and non-adjacent vertebral bodies was measured using the Cobb technique using our measurement software, i.e., tangents were drawn on the upper endplate of the upper vertebra and the upper endplate of the lower vertebra, and the angle of intersection of the tangent plumb line was the angle between the two vertebral bodies, (L1-L2, L2-L3, L3-L4, L4-L5, L5-S1,L1-L5) (see Figure 1). All measurements were taken by the investigator himself, and each measurement was averaged three times. Figure 1 Measurement of intervertebral body angulation (L1-L5) 1.3 Statistical processing The collected data were statistically processed using SPSS 11.5 for Windows. For the comparison between two groups of data with sample size >10 and conforming to normal distribution, the independent sample t-test was used; for the comparison of multiple samples, if the data conformed to normal distribution and the variance had chi-square, the ANOVA was used, and if it did not conform to the criteria as above, the rank sum test was used, and P<0.05 was used as the criterion for statistically significant differences. 2. Results The reference values of lumbar spine segmental and overall lumbar spine curvature in normal subjects found in this study are shown in Table 2. Table 2 Intervertebral angle of lumbar vertebrae (unit: degree) 18-30 31-40 41-50 51-60 ≥61 Male Female Male Female Male Female Male Female Male Female Mean L1-L2 3.18 2.43 3.25 2.60 2.62 2.55 2.17 2.19 2.52 2.49 2.52 L2-L3 6.60 7.36 4.48 6.19 4.09 5.80 3.59 4.38 3.33 7.53 5.33 L3-L4 10.00 7.56 9.67 9.05 6.82 7.89 5.91 8.71 6.96 8.87 8.15 L4-L5 14.74 10.68 12.00 11.87 9.00 12.84 13.41 12.28 12.19 12.39 12.11 L5-S1 20.42 20.62 14.62 23.64 15.04 21.63 21.56 16.84 20.24 21.38 20.14 In the total population, lumbar segmental formation angles L1-L2, 2.52°; L2-L3, 5.33° ; L3-L4, 8.55°; L4-L5, 12.11°; L5-S1, 20.14°; L1-L5, 24.96°; and L1-S1, 42.00°. Lumbar curvature occurs mainly in three segments of the lower lumbar spine, namely L3-L4, L4-L5 and L5-S1, with the lowermost three segments causing more than half of the lumbar curvature, and L5-S1 segmental lumbar curvature accounting for about 40% of L1-S1 lumbar curvature. The distribution of the normal value of normal lumbar lordosis shows a typical "bell-shaped" curve (see Figure 2). Figure 2 Distribution of lumbar curvature The lumbar curvature, the angle between the L1-L5 vertebrae, is 25.06° for men and 26.81° for women. There were three groups based on age overall, namely, youth group (18-30 years old), middle-aged group (31-60 years old) and elderly group (61 years old and above). The overall lumbar curvature values for the youth, middle-aged and elderly groups were 29.25°, 24.95° and 24.48°, respectively, which shows that the overall lumbar anterior convexity angle gradually decreased with increasing age. The statistical data were normally distributed and the variance was homogeneous, and the difference between the three groups was statistically significant using ANOVA (P<0.05); further, when compared between the two groups, the difference between the youth group and the middle-aged and elderly groups was statistically significant (P<0.05); the difference between the middle-aged group and the elderly group was not statistically significant (P>0.05). There was no statistically significant difference in the effect of gender and body mass index on the lumbar curvature. 3.Discussion Stagnara [1] et al. reported segmental and global lumbar curvature values in normal French subjects (20-29 years old) without lumbar spine disorders: L1-L2, -2°; L2-L3, -7°; L3-L4, -11°, L4-L5, -15°; L5-S1, -21°; L1-S1, -56°. Korovessis [2] et al. the overall lumbar spine curvature (T12-S1) of 99 normal Greeks aged 20-79 years with a mean age of 52.7±15 years: 83°±16°. In the present study, the lumbar curvature L1-L5: 24.96°. This shows that the national population has a smaller lumbar curvature angle than the European and American population. Although there are significant differences in overall and segmental pronation between individuals, the proportion of overall pronation that is specific to each individual and each segment is relatively constant. 3.1 Factors affecting lumbar spine curvature 3.1.1 Errors in measurement The choice of subject position and the end vertebrae for overall lumbar spine curvature varies among studies. Some authors believe that sagittal measurements of the spine in the standing position are more accurate because this position is weight-bearing and closer to the normal physiological state of the subject, while others choose to perform the measurements in the lateral recumbent position. However, regardless of the position, most of the variation in lumbar spine angle is still present between L5 and S1 and in relation to pelvic rotation; and since the normal supra-sacral end plate is not easily visible on radiographs due to the influence of the iliac bone, this study tends to use two stages from L1 to L5 to evaluate the overall lumbar lordosis, with a mean of 24.95°±7.09° and a range of 10.30°- 50.05°, we agree with the suggestion of numerous authors [1,2,3] that normal lumbar curvature fluctuates over a wide range and that its mean value is only a reference value and cannot be considered “normal”. In the present study, the subjects were placed in a lateral recumbent position with the knee and hip flexed at approximately 45° during the X-ray projection. Although the measurement of this angle was not precise in each subject, the results of Fernand’s [4] study showed that there was no statistically significant difference in lumbar curvature between the two groups of subjects with the hip and knee simultaneously flexed at 45° and fully extended to 0° in the lateral recumbent position. At the same time, most hospitals in China use the lateral recumbent position when performing projections of lumbosacral spine X-rays, and this measurement method would benefit many medical centers. In addition, the difference in measurement tools directly contributes to the accuracy of the measurements and the magnitude of the errors. However, the method in the literature [1,2,4] has a large measurement error due to the clarity of the radiographs and the errors generated between the measurers. In this study, digital measurement software was used to measure the collected radiographs directly, reducing the errors arising from these factors. Voutsinas [5] reported measuring the sagittal plane curvature of the thoracic and lumbar spine using the Cobb method and found an error of approximately 2° (SD ± 1°) from the observer itself. To further reduce intra- and interobserver errors, all measurements in this study were measured uniformly by the authors, and the values measured were averaged three times and then averaged. The accuracy and reliability of the data obtained within the observer were not included in this study, and the angle of lumbar segmental angulation may change if this study is repeated. For methodological reasons, the values obtained using the standard Cobb angle technique and averaging will not fluctuate greatly; also we did not attempt to define a normal lumbar curvature, but rather a distribution of lumbar curvature. Even though the lumbar segmental angulation may change slightly, the relationship between them will not change essentially. 3.1.2 Subjects’ own factors In terms of gender, this study found no statistically significant differences in overall lumbar curvature between males and females (P>0.05). This is similar to the results obtained in the studies of Stagnara [1] and Farfan [6].The results of Fernand [4] et al. showed greater lumbar curvature in women than in men. This coincides with our study where we found that the lumbar spine curvature was significantly greater in women compared to men in all age groups except the >60 years group, but the difference between the two was not statistically significant.Eileen [7] et al. conducted a comparative comparison of 25 black women and 27 white women and found that although the former showed a greater lumbar spine curvature in appearance curvature was greater, there was no significant difference in lumbar anterior lordosis and lumbosacral angle between the two. Black women appeared to have greater lumbar curvature because they had more soft tissue in their hips, making their hips fuller and thus giving the subjective illusion of greater lumbar curvature. It is thus hypothesized that the subjective illusion of greater lumbar curvature in women may be due to the excess fatty tissue in their hips. In terms of body mass index, Guo JM [8] studied 98 middle-aged and elderly women with lower back pain and found that patients with BMI > 24 kg/m2 had increased lumbar lordosis and sacral tilt angle. This study found that BMI had no significant effect on lumbar curvature in normal adults, and the values of overall lumbar curvature were similar in the normal, overweight, and obese groups (26.43°, 25.43°, and 25.32°, respectively), with no statistically significant differences between the three (P>0.05). In terms of age, some studies demonstrated a corresponding decrease in lumbar spine curvature with increasing age. Korovessis [2] found that the lumbar curvature decreased significantly with increasing age in people over 60 years of age. However, Ruey-mo Li [3] found a gradual increase in the lumbar anterior lordosis angle with increasing age; the differences were statistically significant between adults >60 years of age and those <35 and 35-60 years of age. According to Ruey-mo Li [3], the size of the anterior lumbar convexity angle depends on the strength of the vertebral body and the support of the surrounding soft tissues, bone mass peaks at 35 years of age, and older adults >60 years of age are usually considered to be at high risk of osteoporotic fractures, so this experiment divided the patients into three groups in terms of age i.e., youth group (18-30 years); middle-aged group (31-60 years); and elderly group (> 60 years). It was found that the overall lumbar spine curvature values gradually decreased with increasing age, and the difference between the youth group and the middle-aged and elderly groups was statistically significant (P<0.05); the difference between the middle-aged and elderly groups was not statistically significant (P>0.05) (Figure 3). This illustrates that the lumbar curvature was greatest in the youth group, and although the value of lumbar curvature decreased slightly with increasing age, the smaller lumbar curvature after middle age tended to be stable rather than progressively decreasing, which may be a mechanism of self-protection of the lumbar spine. REFERENCES 1. Stagnara P, DeMauroy JC, Dran G, et al. Reciprocal angulation of vertebral bodies in a sagittal plane: Approach to references in the evaluation of kyphosis and lordosis[J].Spine, 1982,(7):335-342. 2. Korovessis, Panagiotis, Stamatakis, et al. Reciprocal Angulation of Vertebral Bodies in the Sagittal Plane in an Asymptomatic Greek Population [J].Spine, 1998, 23(6): 700-704. 3. Ruey-mo Lin, I-Ming Jou, Chin-Yin Yu. Lumbar Lordosis: Normal Adults [J]. Formosan Med Assoc,1992,91(3):329-333. 4. Robert Fernand, Daniel E. Fox. Evaluation of lumbar lordosis: a prospective and retrospective study [J]. Spine,1984,10:799-803. 5. Voutsinas SA, MacEwen GD . Sagittal profiles of the spine. [J].Clin Orthop 1986;210:235-242. 6. Farfan HF,Huberdeau RM,Dubow HI. Lumbar interveratebral disc degeneration [J]. Bone Joint Surg,1972,54:492-509. 7. Eileen A. Monster,Jean M.Bryan,Margaret A.Stull,et al. A comparison of actual and apparent lumbar lordosis in black and white adult femals [J].Spine,1989,14(3):310-314. 8. Guo JM, Zhang GQ. Effect of BMI and WHR on lumbar lordosis and sacrum slant angle in middle and elderly women [J]. Zhongguo Gu Shang ,2008, 21(1):30-31. [1] Contact Author: Liu Zhao M (1981-) M.S. Research Interests: Spine Surgery Xuanwu Hospital, Capital Medical University Tel: 15811217429 e-mail: [email protected]