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Journal of Clinical Orthopaedics and Trauma logoLink to Journal of Clinical Orthopaedics and Trauma
. 2020 Oct 17;15:117–124. doi: 10.1016/j.jcot.2020.10.015

A comparative radiographic morphometric analysis to assess the normal radiological morphology of the adult hip in indian population

Balaji Zacharia 1,∗, K Mohammed Fawas 1
PMCID: PMC7920144  PMID: 33717925

Abstract

Objective

Our objective is to analyze the normal radiological morphologic parameters of the adult hip joint of the Indian population and compare it with standard measurements and with other populations to assess the variations.

Methods

A prospective analysis of the normal pelvis X-rays of 800 persons (1600 hips) was done. We have calculated the acetabular inclination, acetabular index, lateral center edge angle (LCEA) and neck-shaft angle (NSA), sphericity of the femoral head, congruity of the joint, version of the acetabulum, depth of acetabulum, and lateralization of the femoral head in normal X-rays of the pelvis in adult persons. We used RadiAnt DICOM viewer version 4.6.5.18450 (64bit) for measurement. Statistical analysis and mean values were calculated using SPSS software.

Results

There were 978 X-rays of the male hip and 622 female. The acetabular inclination varied from 1 to 9. The mean acetabular index was 26.5. The LCEA was between 20 and 50. The mean neck-shaft angle was 133. There were 35, hips with an aspherical head. 94.2% X-rays the hip joint was congruent. There was 2.9% of the retroversion of acetabulum, 3.3% lateralization.

Conclusion

Most of the parameters were comparable to standard values the acetabular index was lower. LCEA and NSA were higher. The acetabular angle was lower. There were femoral head asphericity, joint incongruity, and lateralization of the femoral head in a small proportion of our general population.

Keywords: Hip morphology, Acetabular index, Acetabular inclination, Hip radiology, Lateral center edge angle

1. Introduction

There are many diseases of the hip which are due to its abnormal morphology. The various disease of the hip can be diagnosed by measuring the variations in hip morphology. Femoroacetabular impingement and dysplastic hip are associated with abnormalities in the depth, orientation, and diameter of acetabulum.1 There is a gender difference in the morphology of hip. The acetabulum in females is smaller and situated farther apart compared to males.2 There are studies conducted to find out the morphological variations of the hip in different populations. The morphological abnormalities of the hip and osteoarthritis are more common in Caucasians than in Asian populations. Women have more prevalence of dysplastic diseases compared to men.3 The morphometric analysis of the hip is important for designing of prostheses and implants. Anthropometric analysis of the hip joint in the south Indian population showed that there is a significant difference in proximal femoral anthropometry compared to the western population and among different regions of the country.4 To establish normal radiological anatomy is very important for every population. The morphometric analysis is useful for the physical and forensic anthropology of a population. It is also useful for designing of orthopedic implants and prostheses.

Radiography and computerized tomography scan (CT) are the common methods used to assess the hip joint morphology. For evaluation of hip joint pathology an anteroposterior, cross-table lateral view, Dunn view, frog-leg lateral view, and a false profile view can be utilized. Normally most of the information regarding hip morphology can be obtained from an anteroposterior (AP) view except alpha angle for demonstrating cam type of impingement. An AP radiogram is taken with the patient supine on an X-ray table with both lower limbs in 15-degree internal rotation. The X-ray tube is placed perpendicularly at a distance of 120 cms. We have calculated the acetabular inclination, acetabular index, lateral center edge angle and neck-shaft angle, sphericity of femoral head, congruity of the joint, version of the acetabulum, depth of acetabulum, and lateralization of the femoral head in normal X-rays of the pelvis in adult persons.

There is no comprehensive radiological morphometric analysis to find out the radiographic morphology of the adult hip of the Indian population. Our objective is to analyze the normal radiological morphologic parameters of the adult hip joint of our population and compare it with standard measurements and with other populations to assess the variations.

2. Materials and methods

We have conducted a prospective observational study. We have obtained an institutional research committee and ethics committee approval for our study. The study was conducted in a tertiary care teaching hospital in south India. All pelvis X-rays taken in our department between 2016 and 2018 were collected from the picture archiving and communication system (PACS). Radiographs from inpatient, outpatient, and emergency units were collected. We have included X-rays of persons between ages 20 and 60 years. Both genders were included. Patients with features of the normal hip on both sides were included. Those with evidence of fracture, arthritis, the sequel of old sepsis, skeletal dysplasia, improperly taken x-rays were excluded. Most of the pelvis X-rays were taken for evaluation of low back pain, hip pain, and as a part of the trauma series.

A total of 1324 pelvis X-ray images were collected. 140 films were excluded due to arthritic hips. There were 320 patients with hip fractures, 38 cases of deformed hips due to dysplasia and old sepsis, and 166 improper films which were excluded. So there were 800 pelvis X-rays and 1600 hips for final evaluation (Appendix 1).

The usual parameters used for evaluation hip joint morphology in AP view include the following. Acetabular depth: the distance between the floor of the acetabulum and medial edge of the femoral head (Fig. 1A, Fig. 1BA and B). Acetabular inclination: It is measured by drawing the Tonnis angle. A line is drawn parallel to the inter teardrop line from the most inferior point of the sourcil (I). Another line connecting the point (I) and lateral most margin of the acetabulum is drawn. The angle formed between these two lines is the Tonnis angle (Fig. 2). The lateral center-edge angle of Wiberg: It is the angle between a line drawn perpendicular to the transverse axis through the center of the femoral head and another line connecting the lateral edge of the acetabulum to the center of the femoral head (Fig. 3). Acetabular version: Normally acetabulum is anteverted, if the posterior acetabular margin cross over the anterior acetabular margin it is known as cross over sign or figure of eight sign indicative of retroverted acetabulum (Fig. 4A, Fig. 4BA and B). Head sphericity: it can be measured on gross visual inspection (Fig. 5). Position of the hip center: It is measured as the longitudinal distance between the center of the femoral head and ilioishial line if it is more than 10 mm it indicates a lateralized femoral head (Fig. 6A, Fig. 6BA and B). Congruency is assessed by comparing the lines drawn along the margins of the head and acetabulum (Fig. 7A, Fig. 7BA and B).5 The femoral neck-shaft angle is calculated by measuring the angle between the line joining the center of the femoral head to the midpoint of the femoral shaft and another line passing through the center of the femoral shaft.6

Fig. 1A.

Fig. 1A

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Radiograph showing acetabular depth: the distance between the floor of the acetabulum and medial edge of the femoral head in a normal hip.

Fig. 1B.

Fig. 1B

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Radiograph showing a deep acetabulum the floor of the acetabulum is medial to ilioischial line – coxa profunda.

Fig. 2.

Fig. 2

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Radiograph showing measurement of acetabular inclination. A line is drawn parallel to the inter teardrop line from the most inferior point of the sourcil (I). Another line connecting the point (I) and lateral most margin of the acetabulum is drawn. The angle formed between these two lines is the Tonnis angle.

Fig. 3.

Fig. 3

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Radiograph showing measurement of lateral center edge angle. It is the angle between a line drawn perpendicular to the transverse axis through the center of the femoral head and another line connecting the lateral edge of the acetabulum to the center of the femoral head.

Fig. 4A.

Fig. 4A

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Normally anteverted acetabulum.

Fig. 4B.

Fig. 4B

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A retroverted acetabulum where the posterior acetabular margin cross over the anterior acetabular margin known as cross over sign.

Fig. 5.

Fig. 5

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Radiograph showing an aspherical head.

Fig. 6A.

Fig. 6A

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Radiograph showing the normal position of the hip center measured as the longitudinal distance between the center of the femoral head and ilioishial line.

Fig. 6B.

Fig. 6B

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Radiograph showing a lateralized hip where the distance from the center of the femoral head to the ilioischial line is more than 10 mm.

Fig. 7A.

Fig. 7A

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X-ray image of a congruent hip. Congruency is assessed by comparing the lines drawn along the margins of the head and acetabulum.

Fig. 7B.

Fig. 7B

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X- ray image of a incongruent hip.

We used RadiAnt DICOM viewer version 4.6.5.18450 (64bit) for measurement. Statistical analysis and mean values were calculated using SPSS software.

3. Result

There were 978 X-rays of the male hip (61.1%) and 622 female x-rays (38.9%). The acetabular inclination varied from 1 to 9 with a mean of 4.1 (SD 2.4) (Appendix 2). The mean acetabular index was 26.5 (SD 3.4) and varied between 19 and 33 (Appendix 3). The lateral center edge angle was between 20 and 50 with a mean of 35.9 (SD 7.2) (Appendix 4) (Table 1). The normal range for the neck-shaft angle was 125.5 to 140.5 with a mean value of 133 (SD 4.1). There were 35 hips (2.2%) with an aspherical femoral head the rest were having spherical heads. 94.2% X-rays the hip joint was congruent. In 93 normal radiographs (5.8%) there was joint incongruity. The majority of the hips were having an anteverted acetabulum (97.1%, 1554) and retroverted acetabulum in the rest. In 3.3% of hip, radiographs showed lateralization (52). There was a coxa profunda in 49 hips (3.1%) (Table 2).

Table 1.

Shows the minimum, maximum, mean of the age, acetabular inclination, acetabular index, and LCEA of the study population.

Variables Number Minimum Maximum Mean Standard deviation
AGE 800 20 60 38.36 11.785
Acetabular inclination 1600 −15.9000 85.0000 4.161125 4.9119758
Acetabular index 1600 1.3000 38.0000 26.534500 3.4006930
LCEA 1600 3.4000 55.7000 35.890188 7.2377716
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Table 2.

Showing distribution of different variables of radiographic hip morphology in our population.

Male 978 61.1%
Female 622 38.9%
Spherical head 1565 97.8%
Aspherical head 35 2.2%
Congruent hip 1507 94.2%
Incongruent hip 93 5.8%
Anteverted acetabulam 1554 97.1%
Retroverted acetabulum 46 2.9%
Hip center normal 1548 96.8%
Hip center lateralized 52 3.3%
Depth normal 1551 96.9%
Coxa profunda 49 3.1%
Total 1600 100%
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4. Discussion

We have done a radiological morphometric study of the hip in our population using 1600 hip X-rays. Most of the parameter is within the normal ranges. We observed femoral head asphericity, the incongruity of the hip joint, and lateralization of the femoral head in a small percentage of our normal population. We analyzed our results and compare them with the results of other populations.

Morphological abnormalities in the acetabulum and its relation with the femoral head can lead to labral and articular cartilage injury. This can lead to degenerative diseases of the hip. The common conditions causing abnormalities in the morphology of acetabulum are developmental dysplasia of the hip (DDH) and femoroacetabular impingement (FAI).7 The acetabular inclination is a measurement used to assess the coverage of the femoral head by acetabulum. The sharp angle and acetabular roof angle of Tönnis are used to measure inclination. The upper limit for the Tonnis angle is 10°. The higher the inclination there is less coverage for the femoral head as in DDH. When the angle is less there is over coverage of the femoral head like in FAI.8 In our patients, the inclination varied from one to nine with a mean value of 4.1.

The acetabular index is used to detect the depth of acetabulum. In children, it is measured as an angle formed between the Hilgenreiner line and another line connecting the lateral most point of the acetabulum to the Hilgenreiner line. It is also called the acetabular angle (AA) or Sharp angle. There is controversy regarding whether to take the lateral edge of the acetabulum or lateral margin of the sourcil. According to Kim et al. lateral edge of the acetabulum on plain X-ray represents the anterolateral portion of the acetabulum and the lateral sourcil represents the lateral margin of the mid superior portion of the acetabulum.9 In our case, we took the lateral edge of the acetabulum and inter-teardrop line for measuring the acetabular index. The sourcil method is better because it represents the area of compressive stress in the hip and better correlates to the extent of the important weight-bearing zone of the roof of the acetabulum.10 The acetabular index will be more in DDH indicating a shallow acetabulum under the coverage of the femoral head. The normal value of the acetabular index is between 33 and 38°. In our study, we found that the acetabular index in our population is between 19 and 33° with a mean of 26.5. This indicates the fewer number of acetabular dysplasia in our population.

Lateral center edge angle (LCEA) is a method to assess acetabular morphology. Wiberg described the LCEA and its importance in the development of osteoarthritis of the hip. Here also a controversy exists regarding the lateral edge of acetabulum or sourcil to be taken for the measurement. It has been found that sourcil LCEA represents anterosuperior acetabular coverage and lateral bone edge LCEA represents superolateral coverage of the femoral head. Computed tomographic measurement of LCEA is always more compared to radiographic measurement. A less than 20-degree LCEA indicates dysplasia and more than 40° indicates femoroacetabular impingement.11 In our series, LCEA varied between 20 and 50° with a mean value of 35.9°. We used the lateral bone edge method for assessing LCEA.

The centrum –collum-diaphyseal angle or neck-shaft angle (NSA) is an important measurement to quantify the inclination between the femoral neck and the shaft. The normal range is between 120 and 140°. In DDH the NSA will be more and called coxa valgum. In bone softening conditions, malunion, and skeletal dysplasias NSA may be less and called coxa varum. There can be variations in the NSA based on gender and age.12 Our cases showed an NSA between 125.5 and 140.5 with a mean value of 133°.

Sphericity of the femoral head is an important factor preventing the development of osteoarthritis of the hip. Diseases like Legg Calve Perthes, Slipped capital femoral epiphysis, and dysplastic hip can produce a loss of sphericity of the femoral head. There is a higher incidence of aspherical femoral head and acetabulum in Caucasians. Cadaveric studies have shown a lower incidence of femoral head asphericity in Chinese and Korean populations.13 Out of 1600 hip X-ray images examined we found only 35 (2.2%) aspherical femoral heads.

The femoral head is almost exactly spherical, and the surfaces of the femoral head and acetabulum are congruent. So that very perfect contact between all parts of cartilaginous surfaces is to be expected in any position of the hip joint (Hammond and Charnley). But the joint surfaces are not spherical so they cannot be congruent. The joint may be congruent in some positions than in others. The acetabulum is more aspherical compared to the femoral head. The incongruity of the joint is another factor for the development of osteoarthritis. Even when the head is spherical there can be joint incongruity.14 On radiological examination of normal hips, we found 5.8% of incongruity in our population.

The normal acetabulum is anteverted. The anteversion of acetabulum increases with age until triradiate cartilage fusion. This is due to the growth of the acetabular posterior wall in its superolateral aspect. An abnormal opening of the acetabulum posteriorly in the sagittal plane is retroversion. Retroverted acetabulum may be seen in 20% of the normal population. It is found out in radiographs using a crossover sign.15 We have 46 cases (2.9%) of the retroverted acetabulum in our study.

Coxa profunda or deep acetabulum indicates the medial wall of the acetabulum is medial to the ilioischial line. Although it is indirect evidence of the pincer type of FAI. It can be seen in asymptomatic persons also.16 We found out coxa profunda in 49 (3.1%) X-ray images.

The position of the hip center is important in normal and after arthroplasty. Lateralization of the femoral center of rotation is not useful as it decreases the abductor lever arm.17 When the distance between the medial margin of the head of the femur and lateral margin of the acetabulum is more than 10 mm then the hip is lateralized. 3.3% of hips (52) in our series were lateralized.

A little knowledge of the morphogenesis of the hip joint is important to understand various morphological parameters. The ectoderm, endoderm, and mesoderm are formed by the third week of gestation. The mesoderm alongside the paraxial mesoderm divides into 38 paired somites after the formation of the notochord. This is primordial for the future development of the axial skeleton and muscles. Lower limb buds appear by 28 days. The hip joint begins as a solid mass of chondroblasts. By the 6th week, the cartilage model of femoral diaphysis appears. Undifferentiated mesenchymal blastema cell appearing in the trochanteric region forms the apophysis. An Interzone appears differentiating two sides of the hip joint by the 7th week. Acetabulum appears as a shallow depression later deepen from 65 to 180°. Meanwhile, the femoral head and articular cartilage are forming and the Interzone deepens and separates the two structures. At this stage, the transverse acetabular ligament is not developd. So hip is not protected inferiorly against dislocation. The secondary center of ossification for ilium appears and blastemal cells near the acetabulum condense to form the acetabular labrum. There is an elongation of the femur but no secondary ossification center is present. From 8 weeks onwards ossification, vascularisation, and maturation occur. Ossification of the femur proceeds from proximal to distal. The lower limb bud begins to internally rotate so the knee moves from lateral to anterior. By the 11th week a 2 mm femoral head with 10° of anteversion which progressively increases to 45° by 36 weeks. The neck-shaft angle is in valgum in early development and decreases from 145° in the 15th week to 130° at 36 weeks. From the time of formation until birth the femoral head loses its sphericity and the acetabulum becomes shallower. The coverage of the femoral head is lowest at birth.18 Postnatal various factors affect the development of the hip. Mechanical loading is an important factor in determining normal development. The triradiate cartilage formed from the ilium, ischium, and pubis is orthogonally loaded during growth until its fusion by the age of 15–18 years. Premature fusion of triradiate cartilage leads to abnormalities in the size and shape of the hip joint and early osteoarthritis. The diameter of the acetabulum is controlled by the growth of acetabulum and depth by mechanical loading by the femoral head.19

The morphometric parameters of the hip joint vary in different populations. The mean center- edge angle of the Swedish population is 35° (SD6.60), of Americans is 36.20° (SD 6.90), of the Japanese population is 30 (SD 6.4), and that of Koreans was 32.60 (SD 5.7). So compared to Europeans and Americans East Asian populations have a lower center –edge angle. Similarly, the mean acetabular angle of Japanese is 37.30 for males and 38.60 for females, for white men 32.20 and 32.10 for white women. In the Korean population AA were 37 (SD 3.7) and 36.5 (SD 3.8) respectively for men and women. In a study conducted among Singaporeans, the mean LCEA was 31.25 (SD 7.98) and the mean AA for males was 39.46 (SD 6.04) and 38. 25 (SD 5.98) in females. The values were higher than those of the Asian population.20 Our results were similar to Caucasian LCEA. But the mean acetabular index (AA) was 26.5 (SD 3.4) which is lower than Caucasians and Asian populations. Acetabular depth is directly correlated to an individual’s height and leg length whereas the center-edge angle correlates inversely with horizontal dimensions like pelvic width. In a normal population, the narrowest joint space width of the hip joint is inversely correlated with the CE angle.21 In a study to analyze the acetabular depth and its relationship with the racial difference in the prevalence of slipped capital femoral epiphysis (SCFE), in asymptomatic adults, the CE angle, or Shaps angle variability did not follow the racial prevalence of SCFE.22

There are variations in the morphology of proximal femur in different populations. Presently the sizing and technique of insertion of the femoral prosthesis are based on osteometric measurements of the western population. In a comparative study to assess the difference in morphology of proximal femurs of Turkish and Caucasians, there was a marked difference in the morphology of proximal femur. Typically in Turkish femurs, the neck-shaft angle is in valgus position and straighter compared to Caucasians.23 In a Korean study to assess the morphology of the proximal femur, they found there was some major difference with Caucasians. They are having lager anteversion of neck, larger canal flare index, and shorter distance between the lesser trochanter and isthmus.24 The neck-shaft angle of the femur varies in different populations. The NSA of Brasilian (132.1 ± 7.2), Chinese (135), England(36), Norwegian (127.7 ± 7.60), and 121.09 ± 7.17° in Malaysians.25 A radiographic study to analyze the geometry of proximal femur the average NSA in males and females was 1310 & 130.370 respectively among the people of the eastern part of India.26 NSA is in valgus at birth which progressively decreases during growth until skeletal maturity. Variations in NSA is associated with an increased incidence of certain diseases. Coxa valga is associated with an increased incidence of proximal femur fractures, genu varum, and medial compartment osteoarthritis. Whereas coxa vara is associated with genu valgum and greater trochanteric pain syndrome. In another study among people of northwest India, the mean NSA was 127.45 ± 2.using the digital radiography method and 126.90 ± 2.50 using dry bone measurement.27 In our population, the mean NSA was 133°. This shows a variation of NSA among different parts of our country.

During the normal movement of the hip joint, there can be joint translations due to aspherical head and acetabulum. The CE angle is negatively correlated with sphericity in the acetabular bone surface.28 The articular surface of the femoral head and acetabulum are usually parallel indicating that the joint is congruous and if not it is incongruous.29 Even if the shape of the head is not spherical the joint can be congruous. This is seen in certain pediatric hip diseases like Perthes disease. It is called incongruous incongruity which can delay the onset of osteoarthritis of the hip joint.30 We found that in a small percentage of our normal population shows an aspherical femoral head and incongruous hip joint. They were asymptomatic. We found no study in the literature for comparison we expect further studies will give an insight into it.

There is a six percentage incidence of acetabular retroversion in the general population. The retroverted acetabulum is commonly associated with diseases like osteoarthritis of the hip,femoroacetabular impingement, Perthes disease, and dysplastic hip.31 Coxa profunda is also prevalent in the normal population. It should not be misinterpreted as evidence of the pincer type of FAI unless associated with abnormalities of LCEA, the cross over sign, and the acetabular index.32 Our study also demonstrated the prevalence of these radiological findings in the general population. In about 3.3% of our population, there was radiographic evidence of lateralization of the femoral head. We don’t know the implication of this finding as there are no previous studies.

Our study is not without limitations. The measurements are based on radiographs so there can be observer variability. The sample size is small. Certain measurements can vary in the position of the pelvis and leg. We have not included the gender variations in our study. We think future studies with the inclusion of multiple images like X-ray, CT scan, and MRI scan give a better assessment of the radiographic morphology of the hip joint in various populations.

5. Conclusion

There are variations in the radiological morphology of the hip joint in different populations. Our analysis showed most of our morphological parameters are within the normal range. The acetabular index was lower compared to normal. LCEA and NSA were on the higher side of normal. There was a radiographic prevalence of retroverted acetabulum and coxa profunda in the normal population. The LCEA was similar to Caucasians but the acetabular angle was lower than Caucasians and other Asian populations. There was radiographic evidence of femoral head asphericity, joint incongruity, and lateralization of the femoral head in a small proportion of our general population.

Contributions

Contributions of the Corresponding author; Conceiving the idea, collecting data, analysis, writing, and editing the manuscript.

Coauthor; Collecting data, analysis, writing, and editing the manuscript.

Declaration of competing interest

We have no conflict of interest for this manuscript and we have not accepted any financial assistance from within or outside of our institution for collecting data, writing the manuscript, and for its publications.

Contributor Information

Balaji Zacharia, Email: balaji.zacharia@gmail.com.

K. Mohammed Fawas, Email: mfawas101@gmail.com.

Appendix.

Appendix 1: Selection of hip X-rays for our study.

Image 1

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Appendix 2: Scattered plot showing the distribution of acetabular inclination in our population.

Image 2

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Appendix 3: Scattered plot showing the distribution of the acetabular index in our population.

Image 3

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Appendix 4: Scattered plot showing the distribution of the lateral center edge angle in our population.

Image 4

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