Thoracic Kyphosis: Range in

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1 979 Downloaded from wwwajronlineorg by on 02/13/18 from IP address Copyright ARRS For personal use only; all rights reserved Thoracic Kyphosis: Range in Normal Subjects Gerald T Fon1 2 Thoracic kyphosis was measured on chest radiognaphs of 31 6 normal subjects by Michael J Pitt1 means of a modification of the Cobb technique for measuring scoliosis Patients were A Cole Thies Jr3 accepted as normal if they had no thoracic or spinal complaints or radiographic abnormalities in the chest including the thoracic spine A total of 1 59 male and 157 female subjects 2-77 years old was studied The relation among age, gender, and kyphosis were determined using least squares fits of first-order linear mathematical models These results were also used to determine the expected ranges of kyphosis for a normal patient of a given age and gender The degree of kyphosis increased with age and the rate of increase was higher in females than in males Clinical explanations for this differential increase are discussed Exaggeration of the normal thoracic curvature is associated with a variety of conditions, such as Scheuerrnann disease, congenital spinal anomalies, and paralytic and metabolic processes, as well as inflammatory or traumatic conditions [1 ] An increased incidence of spinal curvature in patients with cystic fibrosis was recently reported [2] Severe thoracic kyphotic curves may result in pain, cardiopulmonary failure, and even paraplegia, in addition to cosmetic deformities Some degree of thoracic convexity in the saggital plane is normally present and a range of 20#{176}-40#{176} has been suggested from limited studies [3-5] While there has been extensive research on the treatment and prevention of spinal curvatures, we could find no studies specifically on the normal range of thoracic kyphosis, although ranges are assumed in published studies for other purposes [4-6] The purpose of our study was to determine the expected range of thoracic kyphosis in a group of patients of varying age and gender as seen on routine chest radiographs Received June 1 2, 1 979; accepted after revision December 1 8, 1979 Materials and Methods, Department of Radiology, University of Anzona, Health Sciences Center, Tucson, AZ Chest radiographs of 4 patients examined at the University of Arizona Health Sciences Address reprint requests to M J Pitt Center in Tucson from to were selected These radiographs had bean inter- 2 Present address: Department of Radiological pretad as normal by a radiologist at the time of the Sciences, UCLA School of Medicine, Los Angeles, examination and were classified CA according to the American College of Radiology index [7] The patient identification numbers 3 Division of Computer Systems and Biostatis- and the code for a normal chest examination had been stored on microfiche From tics, University of Arizona, Health Sciences Cen- this file 1 cases/year for the years were sampled with about equal numbers ten, Tucson, AZ for each age group and gender AJR 134: , May 1980 Even though the chest radiographs had been classified as normal, they were reviewed X/80/ $0000 again by the senior author (GTF) Hence the films ware evaluated by two radiologists American Roentgen Ray Society over a 1-3 year period Of the 4 patients sampled, only 31 6 were selected for the study

980 FON ET AL AJR:134, May 1980 Downloaded from wwwajronlineorg by 463199 on 02/13/18 from IP address 463199 Copyright ARRS For personal use only; all rights reserved These mat the two important

2 980 FON ET AL AJR:134, May 1980 Downloaded from wwwajronlineorg by on 02/13/18 from IP address Copyright ARRS For personal use only; all rights reserved These mat the two important criteria of: (1 ) no abnormality of heart, lungs, or thoracic skeleton and (2) proper positioning and suitable radiographic technique For study purposes, patients were accepted as normal if no thoracic or spinal complaints were noted in the request for radiologic examination and no radiologic abnormalities in the chest including the thoracic spine were identified Medical charts were not reviewed All patients were ambulatory Most ofthe radiographs selected were of patients who had the examination as a preoperative routine for elective surgery or preemployment While the general health status of some of these patients was not optimal, it was assumed that the patients were sufficiently fit to be amublatory and to meet the other criteria required for positioning as described below During the second review of the radiographs by the senior author, changes in the lungs or thoracic spine that could be considered normal in the initial interpretation but might affect the thoracic kyphotic curve were specifically sought Changes that increase the curvature of the spine include atelectasis, hyperaeration, or airtrapping Bony changes such as pectus excavatum, spinal deformities, Schauermann disease, and scoliosis of the spine were axcluded It is well known that the musculature may be affected by systemic diseases with resultant effect on spinal curve By excluding the radiographs that showed any scoliosis patients with significantly weak musculature were presumably excluded because it would be very unusual for poor muscular support to affect the kyphotic curve only without associated scoliosis The recognition of osteoporosis or loss of mineral content of bones especially in the milder forms from simple films is notably difficult However, by excluding any patients with secondary changes in the spine resulting from demineralization, the effect of the loss of mineral content on spinal curvature would be reduced to a minimum Such secondary changes as biconcave depressions of the vertebral end plates resulting in fish vertebrae, vertebral collapse, and significant vertebral wedging were reasons for exclusion For those patients over, mild degenerative changes in the spine consisting of minor marginal osteophytes ware accepted as normal For all selected patients these changes were not mentioned in the initial report and presumably were considered to be within the norm It is obvious that the degree of kyphosis is related to patient Fig 1 -Method of measuring kyphosis positioning To minimize positioning variations, the radiographs included in this study met the following criteria: (1 ) they were made with the patient standing and with a focal-film distance of 1 8 m; (2) the patient s rrms were above the shoulders in the lateral view, with neither humerus below the horizontal position (this would help reduce any increase in the thoracic curve due to positioning); and (3) patients under 3 years of age were excluded since most of these patients were supine or strapped to the Brat Board (the only exception was a 2-year-old whose radiograph was made erect) The degree of kyphosis was measured by a modification of the Cobb technique [8] as used for scoliosis The upper and lower vertebral bodies defining the curve were selected and lines were drawn, extending along the superior border of the upper end vertebra as well as along the inferior border of the lower end vertebra Perpendiculars were drawn from these two lines and the angle was measured at the intersection (fig 1 ) An angle rule was used to draw the perpendiculars and measure the angles The measurements were done on one set of films per patient and in most cases that was the only available set to fall within our definition of normal For each patient, one measurement of the thoracic kyphotic curve was made To test measurement error, a sample of 30 cases out of the 31 6 was drawn, and the cases remeasured The maximum difference between first and second readings was, It should be noted that this is only one aspect of total measurement error Another source of error is the patient s positioning at the time the radiographs were taken A prospective study would be necessary to control this more completely than in this study Statistical analysis Whether a relation existed between age of patient and degree of kyphosis was determined by testing the statistical significance of the slope of a straight line (ie, first-order linear) model fitted separately for males and females by linear regression The adequacy of each straight line model was determined by visual inspection of fits and by statistical tests The difference of slopes between males and females was also tested, using an analysis of covarianca procedure Confidence regions for kyphosis based on age and gender were then determined, using the linear regressions [9] Finally, a descriptive analysis of kyphosis by age and gender was performed, computing means and standard deviations for each age-gender group The results of the descriptive analysis were used to further investigate the adequacy of the firstorder linear model Results The composition of the patient population according to age and gender is shown in table 1 Linear regression of kyphosis on age for both males and females resulted in an adequate fit in the age range 6-75 years and a poor fit in the range 0-3 years Only at age 6 and over did each model indicate an equal likelihood of over- or underprediction of kyphosis For this reason, further regression analysis was limited to the age range of 6-75 years for males and females Results of that analysis are shown in figures 2 and 3 In each figure, the middle line represents the predicted value of kyphosis, and the outer lines delineate a 95% confidence region for an observation of kyphosis for a patient of a given age (parameters of both models are shown in table 2) For both males and females the slopes of these lines were significantly different from zero (p < 001 ) indicating that

3 AJR:134, May 1980 THORACIC KYPHOSIS 981 TABLE 1 : Distribution of Patients by and Gender Downloaded from wwwajronlineorg by on 02/13/18 from IP address Copyright ARRS For personal use only; all rights reserved Totals (years) Male Female Totals No Patients Mean No Patients Mean No Patients Mean r kyphosis was related to the age of the patient The ability of age to predict kyphosis is indicated by two measures in table 2, standard error of the estimate and r2 Standard error of the estimate is a measure of the model s average maccuracy of prediction The percentage of overall variation of kyphosis explained by the model is measured by r2 (the square of the product-moment correlation coefficient r) Analysis of residual values (difference between observed and predicted kyphosis) indicated equal likelihood of underor overprediction across the entire age ranges Parameters of the straight line models are shown in table 2 Analysis of covariance indicated that females showed a statistically significantly greater slope (parameter b in table 2) than males (p < 005) Descriptive profiles of kyphosis are shown in tables 3 and 4 (these tables include patients of ages 3-5 years, who were not included in the linear regression models) The adequacy of the linear model can be further investigated by comparing: (1 ) the male-female differences at each age range and (2) the patterns of standard deviation across age groups The latter comparison indicates no immediate pattern for females, but there exists a suggestive decrease in standard deviation of kyphosis as age increases for male patients This decrease suggests that confidence bounds in figure 2 may be slightly too wide for older patients and slightly too narrow for younger patients The former cornparison is depicted in figure 4, where mean kyphosis for each age group is plotted against mean age within each age group for males and females An unpaired t test of differences between group means (males versus females) is performed at each age group and the results of each test displayed as significance (p)levels in figure 4 An interesting result of this analysis is the similarity of males and females until about age 40, after which females exhibit significantly higher kyphosis for each group (the highest age group, years, included a very small number of cases and did not indicate statistical significance) These results may indicate a subtle departure from the straight line model for female patients that is not immediately apparent in figure 3 I a) (Years) Fig 2-Linear regression of kyphosis on age, including prediction and 95% confidence regions, for male patients (See text) (Years) Fig 3-Linear regression of kyphosis on age, including prediction and 95% confidence regions, for female patients (See text) Discussion This study shows that the normal range of kyphosis is related to both age and gender of a patient The degree of kyphosis increases with age and the rate of increase is higher in females than in males; this appears to be more obvious after age 40 In a limited study of a group of patients years old, Cowan [1 0] also found an increase in the

982 FON ET AL AJR:134, May 1980 TABLE 2: Parameters of Least Squares Fit For Mathematical Models of Form Kyphosis = b (age) + a TABLE 4: Degree of Kyphosis in Females By Downloaded from

4 982 FON ET AL AJR:134, May 1980 TABLE 2: Parameters of Least Squares Fit For Mathematical Models of Form Kyphosis = b (age) + a TABLE 4: Degree of Kyphosis in Females By Downloaded from wwwajronlineorg by on 02/13/18 from IP address Copyright ARRS For personal use only; all rights reserved Gender No Cases b a SE r r Male Female TABLE 3: Degree of Kyphosis in Males By (years) No Kyphosis (1 Cases Mean SD Minimum Maximum kyphotic angle with age, even though he used a different method for measurement The increase in the kyphotic curve with age is not unexpected, because of the associated changes in the soft tissues and mineral content of the bones with the progression of years An association of progressive increase in spinal curvatures with gradual compression wedging of the vertebrae and its narrowing of the intervertebral discs have been described [1 1, 1 2] The difference in the rate of increase in the degree of kyphosis between genders in the older age groups is interesting It is significant in that the higher rate of increase in kyphosis females as shown in this study where the measurements were done on radiographs is in agreement with the findings of Milne and Lander [13] who used a surveyor s flexicurve and did the measurements on the subjects themselves They used an entirely different method and the kyphosis was measured indirectly by calculation of an index of kyphosis These authors later showed that the difference in kyphosis between the two genders in the older population was not due to a difference in the degree of wedging in the vertebral bodies as one might expect [1 4] There were other variables related to age that were contributory to the thoracic kyphosis in females They postulated the possibility of poor posture and aging of soft tissues with resultant loss of muscle tone leading to increased kyphosis in older females It is also reasonable to postulate that the relative physical inactivity in females, probably related to occupation, may decrease the tone on the spinal ligaments and muscles The dependent breasts may further accentuate the kyphotic curve in these older females The association of kyphosis with age and gender darnonstrated in our study clearly shows that the range of 20#{176}- 40#{176} that has been reported [1, 2, 6] as a reasonable normal range for thoracic kyphosis is inadequate because this range of values in our population would have resulted in false normals in the younger age groups and false (years) 60 females : : males pp16 p69 P-79 p79 pa05 p04 poo7 a 10 No Cases Mean (Years) Kypho sis () Mean SD Minimum Maximum Fig 4-Mean kyphosis for males and females by 1 0-year age intervals, (See text) abnormals in the older age groups As is the case for any sample of patients from one location the results of this study cannot be strictly applied to the general population However, in the absence of any control study where the sample is a true random sample from the general population, these results should serve as useful guidelines for prediction of normal thoracic kyphosis ACKNOWLEDGMENT We thank Janet Quinones for manuscript preparation REFERENCES 1 Keim H Kyphosis and lordosis in the adolescent spine New York: Grune & Stratton, 1976: Erikkila JC, Warwick WJ, Bradford DS Spinal deformities and cystic fibrosis Clin Orthop 1978;1 31 : Bosekar EH The determination of the normal thoracic kyphosis; a roentgenographic study of the spines of 1 21 normal children Presented at Gillete Children s Hospital, St Paul, Minn, Bradford DC, Moe JH, Winter AR Kyphosis and postural roundback deformity in children and adolescents Minn Med 1973;56:

AJR:124, May 1980 THORACIC KYPHOSIS 983 Downloaded from wwwajronlineorg by 463199 on 02/13/18 from IP address 463199 Copyright ARRS For personal use only; all rights reserved 5 Roaf A Vertebral

5 AJR:124, May 1980 THORACIC KYPHOSIS 983 Downloaded from wwwajronlineorg by on 02/13/18 from IP address Copyright ARRS For personal use only; all rights reserved 5 Roaf A Vertebral growth and its mechanical control J Bone Joint Surg (Br] 1 960;42 : Bradford D Editorial comment-kyphosis Clin Orthop 1977;1 28:2-4 7 American College of Radiology Index for roentgen diagnoses, 3d ad Baltimore: Waverly, Cobb AJ Outline for the study of scoliosis Am Acad Orthop Surg 1948;5: Draper N, Smith H Applied regression analysis New York: Wiley, 1966: Cowan NA The frontal cardiac silhouette in older people Br HeartJ 1965;27: Nicholas JA, Wilson PD Osteoporosis of the aged spine Clin Orthop 1 963; : Rowe CA, Sorbie C Fractures of the spine in the aged Clin Orthop I 963; : Milne JS, Lander lj affects in kyphosis and lordosis in adults Ann Hum BioI 1974;1 : Milna JS, Lander IJ The relationship of kyphosis to the shape of vertebral bodies Ann Hum Biol 1976;3:

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Author's response to reviews Title: Scoliotic posture as the initial symptom in adolescents with lumbar disc herniation: its curve pattern and natural history after lumbar discectomy Authors: Zezhang Zhu