ABSTRACT:

OBJECTIVE The purpose of the present study was to evaluate the pelvic bone deformities and its correlation with the acetabular center-edge (CE) angle.
METHODS Between August 2014 and April 2015, we prospectively evaluated patients aged between 20 and 60 years old. The exclusion criteria were: metabolic disease, previous hip or spine surgery, radiograph showing hip arthrosis ≥ Tönnis two, severe hip dysplasia, global acetabular overcoverage, acetabular crossover sign, hip deformities from slipped capital femoral epiphysis (SCFE) or Leg-Perthes-Calveé, and bad quality radiographs. At anteroposterior (AP) pelvic radiographs, we have evaluated: the CE angle, the acetabular index (IA), the acetabular crossover sign, the vertical and horizontal superior and inferior pelvic axis (H1: Horizontal line 1, superior pelvic axis; H2: Horizontal line 2, superior pelvic axis; V1: Vertical line, superior pelvic axis; HR: Horizontal line, inferior pelvic axis; VR: Vertical line, inferior pelvic axis). The superior and inferior pelvic axis were considered asymmetric when there was a difference ≥ 5 mm between both sides. Patients were divided into two groups: control and group 1.
RESULTS A total of 228 patients (456 hips) were evaluated in the period. According to the established criteria, 93 patients were included. The mean age was 39.9 years old (20 to 60 years old, standard deviation [SD] = 10,5), and the mean CE angle in the right hip was 31.5º (20 o to 40º), and in the left 32.3º (20 o to 40º). The control group had 38 patients, with asymmetric H1 in 4 cases (10.5%), H2 in 5 (13.1%), V1 in 7 (18.4%), HR in 5 (13.1%) and VR in 1 (2.63%). Group 1 had 55 patients, with asymmetric H1 in 24 cases (43.6%), H2 in 50 (90.9%), V1 in 28 (50.9%), HR in 16 (29.09%) and VR in 8 (14.5%). Comparing both groups, there was statistical significance for H1, H2 and V1 asymmetry (p < 0.001).
CONCLUSION In the present paper, we observed the correlation between variation in the acetabular CE angle and asymmetry of the superior hemipelvis. The present authors believe that a better understanding of the pelvic morphologic alterations allows a greater facility in the diagnosis of hip articular deformities.

Keywords: hip dislocation; acetabulum; femur head.

RESUMO:

OBJETIVOS O objetivo do presente trabalho é avaliar a deformidade dos ossos pélvicos e sua correlação com ângulo centro-borda acetabular (CE).
MÉTODOS Foi realizado um estudo prospectivo caso-controle, entre agosto de 2014 e abril de 2015. Os critérios de inclusão foram pacientes consecutivos com idades entre 20 e 60 anos. Os critérios de exclusão foram: doença metabólica, cirurgia prévia de quadril ou coluna, radiografia evidenciando artrose de quadril ≥ Tönnis 2, displasia do desenvolvimento do quadril (DDQ) severa, sobrecobertura acetabular global, sinal do cruzamento das linhas acetabulares, deformidades decorrentes de epifisiólise ou Legg-Perthes-Calveé, e radiografia sem qualidade adequada. Foram avaliados na radiografia anteroposterior (AP) de pelve: o ângulo CE, índice acetabular (IA), sinal do cruzamento das linhas acetabulares, mensuração do eixo horizontal e vertical da hemipelve superior e inferior (H1: Linha Horizontal 1, hemipelve superior; H2: Linha Horizontal 2, hemipelve superior; V1: Linha Vertical, hemipelve superior; HR: Linha Horizontal, hemipelve inferior; VR: Linha Vertical, hemipelve inferior). As mensurações H1, H2, V1, HR e VR foram consideradas assimétricas quando, na comparação de uma hemipelve em relação ao lado contralateral, evidenciou-se uma diferença > 5 mm. Os pacientes foram separados em dois grupos: controle e grupo 1.
RESULTADOS O total de pacientes avaliados no período foi de 228 (456 quadris). De acordo com os critérios estabelecidos, foram incluídos neste estudo 93 pacientes. A idade média foi de 39,9 anos (20 a 60 anos, desvio padrão [DP] = 10,5), e o ângulo CE médio do quadril direito foi de 31,5º (20º a 40º) e do esquerdo de 32,3º (20º a 40º). Um total de 38 pacientes foi incluído no grupo controle, sendo que com relação à H1, foi constatada aferição assimétrica em 4 casos (10,5%), H2 em 5 (13,1%), V1 em 7 (18,4%), HR em 5 (13,1%), e VR em 1 caso (2,63%). No grupo 1, foram incluídos 55 pacientes, sendo que com relação à H1, foi constatada aferição assimétrica em 24 casos (43,6%), H2 em 50 (90,9%), V1 em 28 (50,9%), HR em 16 (29,09%), e VR em 8 casos (14,5%). Na comparação entre o grupo controle e o grupo 1, observou-se diferença estatisticamente significativa para a assimetria das mensurações H1, H2 e V1 (p < 0,001).
CONCLUSÃO No presente trabalho, evidenciou-se correlação entre variação do ângulo CE acetabular e assimetria da hemipelve superior. Os presentes autores acreditam que o melhor entendimento das alterações morfológicas pélvicas permite uma maior facilidade no diagnóstico das deformidades articulares do quadril.

Palavras-chave: luxação do quadril; acetábulo; cabeça do fêmur.

FIGURES

Citation: Roos BD, Roos MV, Camisa Júnior A, Lima EMU, Tisatto DL, Argoud MC. Pelvic Bone Deformity and Its Correlation with Acetabular Center-edge Angle*. 55(2):239. doi:10.1055/s-0039-3400516
Note: * Study conducted at the Hip Group of the Hospital Ortopédico de Passo Fundo, Faculdade de Medicina da Universidade de Passo Fundo, Passo Fundo, RS, Brazil.
Conflict of Interests The authors have no conflict of interests to declare.
Received: November 30 2018; Accepted: January 22 2019
 

INTRODUCTION

There is growing evidence in the literature of the association of changes in the morphology of the hip bone and the development of symptoms, as well as the possibility of evolution to chondral joint degeneration. These changes may be related to the femur, the acetabulum, or both.1 On the acetabular side, frequent morphological alterations include overcoverage (Pincer femoroacetabular impingement [FAI]) and coverage deficiency (developmental dysplasia of the hip [DDH]).2,3

Acetabular overcoverage can be global or focal. Global overcoverage is defined by anteroposterior (AP) pelvis radiography of the center-edge angle (CE)4 > 40º associated with excess femoral head coverage by the anterior and posterior wall of the acetabulum.5 Focal overcoverage is defined by the presence of acetabular retroversion, which is a morphological change in which there is structural deviation of the acetabulum in the sagittal plane towards the posterolateral direction. Radiographically, acetabular retroversion is represented by the presence of the sign of the intersection of the acetabular lines.3,6,7 Both changes have been associated with the dynamic impact between the acetabular edge and the femoral head-neck transition, which may result in acetabular lesions of the posteroinferior cartilage and lip, as well as pain.8

In acetabular coverage deficiency, a reduced contact area between the femoral head and the acetabulum generates excessive shear force at the acetabular chondrolabral junction, which may lead to the emergence of symptoms and chondral degeneration in the long run. This deficiency is most commonly anterosuperior in the acetabulum, and the diagnosis of DDH is made when the CE angle4 is < 25º on pelvic AP radiography.4,9

Some authors have proposed that hip development disorders not only affect the proximal femur and the acetabulum, as evidenced by pathologies such as FAI and DDH, but throughout the pelvis.1,10 However, there is no consensus on which pelvic bone deformities correlate with acetabular morphological changes. We believe that pelvic bone structural changes and acetabular abnormalities are not isolated findings but are instead part of a continuum of structural changes in pelvic development.

The aim of the present study is to evaluate the pelvic bone deformity and its correlation with the CE angle.

 

MATERIALS AND METHODS

A prospective case-control study was conducted between August 2014 and April 2015. The study was approved by the Research Ethics Committee, and all of the participants signed the informed consent form.

Participants were invited to the study voluntarily. Inclusion criteria were consecutive patients aged 20 to 60 years old. The exclusion criteria were: metabolic disease, previous hip or spine surgery, radiograph showing hip arthrosis ≥ Tönnis two, severe DDH (CE angle < 20º),4,9 global acetabular overcoverage (CE angle > 40º and/or acetabular index [AI] < zeroº),5 sign of acetabular lines intersection (suggesting acetabular retroversion), CE angle asymmetry < 5º, hip deformities from slipped capital femoral epiphysis (SCFE) or Leg-Perthes-Calveé, and bad quality radiographs.11

The selected patients underwent pelvic radiography at AP incidence with their feet at 15º of internal rotation, with the tube 120 cm away from the film, and with the radius directed to the center point between the upper edge of the pubic symphysis and a horizontal line connecting both anterosuperior iliac spines. The distance between the coccyx and the pubic symphysis, besides its alignment, were factors considered to evaluate the quality of the radiographs.11

The following radiographic studies were evaluated in both hemipelves: CE angle, AI, sign of intersection of acetabular lines, measurement of horizontal and vertical axis of upper hemipelvis (iliac wings - H1, H2 and V1), measurement of the horizontal and vertical axis of the lower hemipelvis (ischium and ilium pubic branches - HR and VR). The definition of the method for measuring the pelvic axes is exemplified in Figure 1.

Fig. 1. Exemplification of bilateral pelvic axis measurement method. All lines (H1, H2, V1, HR and VR) are referenced to the line between the teardrops. a) H1 and H2 correspond to the measurement of the horizontal axis of the upper hemipelvis. Initially, a line is defined connecting the upper points of the acetabular roofs (supra-acetabular line). H1 is 2cm above it; H2 is 7cm above it. b) V1 corresponds to the measurement of the vertical axis of the upper hemipelvis. It is the measurement from the highest point of the iliac bone to the supra-acetabular line. c) HR corresponds to the measurement of the horizontal axis of the lower hemipelvis, having as reference a midpoint of the pubic symphysis joint. d) VR corresponds to the measurement of the vertical axis of the lower hemipelvis, having as reference a midpoint of the measurement of the HR.

The measurements of the axis of hemipelves (H1, H2, V1, HR and VR) were considered asymmetrical when, in comparing a hemipelvis in relation to its contralateral side, a difference > 5 mm was found.

The selected patients were separated into two groups: control and group 1.

The control group included patients whose hips had a CE angle with a difference of < 5º, with no sign of acetabular line intersection. Group 1 included patients with CE angle asymmetry ≥ 5º, comparing one hip to the contralateral side, with no sign of acetabular line intersection.

The aim of the present study is to evaluate the correlation between CE angle variation and pelvic bone deformity (H1, H2, V1, HR and/or VR asymmetry), comparing both groups.

The hypothesis is that the presence of CE angle variation correlates with the upper hemipelvis asymmetry (suggesting rotational change of the upper hemipelvis).

To assess homogeneity between the groups, the chi-squared test was applied for age, gender, CE angle and AI. The Fisher exact test was used to analyze the intergroup qualitative variables (H1, H2, V1, HR and VR). In the present study, differences were considered statistically significant when p < 0.05. The software PASW Statistics for Windows, Version 18.0 (SPSS Inc. Chicago, IL, USA) was used in the statistical analysis. A total of 50 radiographs were randomly selected to measure the κ coefficient. Two authors, Roos B. D. and Lima E. M. U., evaluated the radiographs at different times, with an interobserver agreement of 0.72.

 

RESULTS

The total number of patients evaluated during the period was 228 (456 hips). According to the established criteria, 93 patients were included in the present study, 49 males and 44 females. The excluded patients are represented in Table 1. The average age was 39.9 years old (ranging from 20 to 60 years old, standard deviation [SD] = 10.52), the mean right hip CE angle was 31.5º (ranging from 20º to 40º, SD = 5.30) and the left was 32.3º (ranging from 20º to 40º, SD = 5.11). The mean AI was 5.14 (ranging from 0 to 10, SD = 2.97) in the right hip and 5.17 (ranging from 0 to 10, SD = 3.09) in the left hip.

Table 1. Description of patients excluded from the study
Exclusion Criteria Excluded
Previous hip or spine surgery 6
Arthrosis ≥ Tönnis 2 12
Severe DDH 8
Global acetabular overcoverage 14
Sign of intersection of acetabular lines 60
Asymmetry of CE angle 1º or 2º 11
Asymmetry of CE angle + unilateral acetabular retroversion 9
SCFE or Legg-Perthes-Calveé 3
Radiography without adequate quality 12
Total 135

Abbreviations: CE, CE angule; DDH, Developmental Dysplasia of the Hip; SCFE, slipped capital femoral epiphysis.

Table 1. Description of patients excluded from the study

There were 38 patients included in the control group, with mean axes measurements of H1, H2, V1, HR and VR presented in Table 2. Regarding H1, asymmetric measurement was found in 4 cases (10.5%), 5 cases in H2 (13.1%), 7 cases in V1 (18.4%), 5 cases in HR (13.1%), and 1 case in VR (2.63%).

Table 2. Description of measurement values H1, H2, V1, HR and VR in gontrol group
Groups H1 R H1 L H2 R H2 L V1 R V1 L HR R HR L VR R VR L
Control 1 71 71 94 93 101 102 67 67 67 68
2 57 65 91 92 92 91 96 92 55 51
3 55 58 85 87 103 100 90 88 80 79
4 51 52 86 89 95 98 93 91 58 57
5 43 43 90 80 115 115 80 88 55 55
6 49 49 97 98 112 112 90 90 57 57
7 66 67 88 88 110 110 76 76 68 69
8 55 61 92 100 126 124 91 100 66 68
9 50 50 111 113 134 134 83 84 60 60
10 73 75 108 106 133 131 91 91 65 67
11 88 88 106 106 131 139 81 90 77 77
12 64 62 100 99 131 133 85 85 53 53
13 72 72 102 100 126 121 76 78 88 90
13 58 60 105 105 137 137 90 88 51 53
15 57 60 110 115 105 107 87 85 75 73
16 55 57 85 87 133 134 85 83 52 50
17 78 78 108 109 132 127 91 90 69 67
18 62 60 126 124 137 143 88 87 60 61
19 72 70 100 100 142 142 80 82 80 80
20 57 55 105 105 151 141 96 97 59 59
21 60 60 103 102 112 112 84 82 77 76
22 58 59 94 92 110 110 94 86 67 66
23 56 56 98 97 97 98 89 89 77 77
24 51 53 102 101 110 110 98 98 78 78
25 50 50 98 98 111 112 89 91 57 56
26 56 57 88 88 110 110 76 76 69 69
27 65 68 86 88 104 101 89 88 81 80
28 50 52 87 90 95 97 93 93 58 56
29 50 50 112 113 134 134 83 83 60 61
30 64 65 108 108 132 131 90 89 66 67
31 64 63 99 98 132 133 85 86 54 53
32 58 60 105 105 137 137 82 84 53 54
33 55 57 85 86 130 131 85 85 52 51
34 82 82 100 100 140 138 81 82 77 77
35 56 55 103 102 112 112 82 80 76 76
36 55 54 99 100 97 96 90 90 77 77
37 63 64 102 101 107 109 95 95 75 75
38 80 80 100 99 140 142 80 80 82 82
Mean 60.68 61.53 99.05 119.89 119.84 86.34 86.55 66.61 66.45 98.89
Standard Deviation 10.212 10.01 9.291 16.256 16.045 6.671 6.5 10.612 10.84 9.282

Abbreviations: L, Left Hip; R, Right Hip.

Table 2. Description of measurement values H1, H2, V1, HR and VR in gontrol group

In group 1, 55 patients were included. The average axis measurements of H1, H2, V1, HR and VR are presented in Table 3. Regarding H1, asymmetric measurement was found in 24 cases (43.6%), 50 cases in H2 (90.9%), 28 cases in V1 (50.9%), 16 cases in HR (29.09%), and 8 cases in VR (14.5%) (Figure 2).

Table 3. Description of measurement H1, H2, V1, HR and VR in group 1
Groups   H1 R H1 L H2 R H2 L V1 R V1 L HR R HR L VR R VR L
Acetabular inclination 1 45 45 90 80 100 99 105 105 68 66
2 84 81 90 92 170 170 76 76 72 70
3 60 50 110 100 100 100 80 80 72 74
4 50 45 100 94 100 105 96 96 64 63
5 62 62 107 100 113 115 87 87 72 72
6 55 50 104 100 102 104 88 88 77 75
7 53 58 72 89 105 109 75 73 63 70
8 60 54 92 86 112 110 88 86 67 66
9 56 57 110 117 110 115 97 107 64 62
10 50 50 90 98 100 100 70 74 67 65
11 73 64 107 97 112 112 69 70 65 65
12 57 51 92 93 107 107 80 79 70 68
13 50 58 92 97 128 123 90 92 47 47
13 82 73 114 110 134 139 93 90 77 77
15 69 69 120 124 138 143 90 80 84 75
16 55 60 118 128 146 145 88 87 52 50
17 52 58 76 80 127 124 89 89 59 59
18 70 70 112 119 135 138 90 90 58 60
19 55 48 115 100 128 108 85 83 40 42
20 67 83 116 120 136 136 75 66 55 53
21 61 62 118 109 135 143 85 75 87 72
22 51 40 85 92 124 127 83 86 57 57
23 49 49 148 123 144 146 95 93 60 60
24 80 82 104 97 119 120 73 75 85 83
25 47 46 82 88 118 116 86 84 57 55
26 53 53 101 96 109 132 82 84 75 73
27 69 69 102 98 138 129 92 90 60 58
28 62 60 95 94 134 135 95 94 62 61
29 42 42 94 102 144 149 102 95 72 67
30 55 55 98 90 145 153 94 92 85 84
31 60 60 75 81 113 112 82 83 85 73
32 62 55 104 94 98 104 70 62 66 64
33 57 61 102 108 108 104 86 88 77 77
34 60 61 96 102 102 102 68 68 72 72
35 44 44 83 91 97 97 77 76 65 65
36 72 72 119 124 137 143 90 82 83 81
37 55 61 120 128 145 145 87 87 51 45
38 52 59 75 80 127 123 89 89 72 71
39 67 67 113 119 135 139 92 90 58 60
40 56 48 110 100 128 108 85 83 41 42
41 66 83 116 121 136 136 71 67 54 44
42 61 63 117 109 136 143 85 76 74 72
43 51 41 86 92 124 127 82 86 60 60
44 49 48 140 123 144 144 95 95 58 58
45 80 82 104 96 119 121 73 74 85 83
46 48 46 82 89 118 116 87 84 55 58
47 54 53 101 95 109 132 82 84 74 73
48 70 69 102 98 138 129 92 91 59 58
49 44 42 94 101 143 149 98 92 65 66
50 50 50 98 89 145 153 94 93 70 69
51 60 61 76 81 113 113 83 83 75 73
52 62 55 104 93 98 104 70 62 62 61
53 57 62 101 108 108 104 86 86 72 72
54 61 61 96 101 103 103 68 66 60 63
55 45 44 83 92 97 96 77 77 60 59
Mean 58.49 58.04 100.51 122.44 123.62 84.85 83.45 66.8 64.29 100.93
Standard Deviation 10.011 11.41 13.179 17.359 18.27 9.093 9.867 11.453 10.544 15.608

Abbreviations: L, Left Hip; R, Right Hip.

Table 3. Description of measurement H1, H2, V1, HR and VR in group 1
Fig. 2. Case example of group 1. a) Asymmetry of the measurements of the horizontal axis of the upper hemipelvis (H1 and H2) is evinced. b) Asymmetry of the vertical axis measurement of the upper hemipelvis (V1) is evdenced. c) Symmetry of the measurements of the horizontal and vertical axes of the lower hemipelves (HR e VR) is evinced.

The groups were considered homogeneous, since they did not differ in relation to gender, age, CE angle and AI (p = 0.086). In the comparison between the control group and group 1 (Table 4), a statistically significant difference was observed for the asymmetry of the measurements in H1 (p < 0.001), H2 (p < 0.001) and V1 (p = 0.005). For the measures HR and VR, no statistically significant difference was observed (p = 0.082; p = 0.077).

Table 4. Description of the results of the comparison of symmetric and asymmetric measurements of H1, H2, V1, HR and VR, in control group versus group 1
  H1 H2 V1 VR HR  
Asymmetry Yes No Yes No Yes No Yes No Yes No Total
Inclination 24 31 50 5 28 27 0 0 16 39 55
Acetabular 85.70% 47.70% 90.90% 13.20% 77.80% 47.40% 0.00% 0.00% 76.20% 54.20% 59.10%
Control 4 34 5 33 8 30 0 0 5 33 38
14.30% 52.30% 9.10% 86.80% 12.20% 52.60% 0.00% 0.00% 13.80% 45.80% 40.90%
Total 28 65 55 38 36 57 0 0 21 69 88
100% 100% 100% 100% 100% 100% 100% 100% 100% 100% 100%
Significance p = 0.001 p < 0.001 p = 0.005 p = 000 p = 0.82
Table 4. Description of the results of the comparison of symmetric and asymmetric measurements of H1, H2, V1, HR and VR, in control group versus group 1
 

DISCUSSION

There is growing evidence in the literature of the association of bone morphological changes in the hip region and the development of symptoms, as well as the possibility of evolution to joint chondral degeneration. These changes may be related to the femur, the acetabulum, or both.1 Considering the acetabulum, as frequent morphological alterations we can find the overcoverage (FAI) and poor coverage (DDH).2,3

Some authors have proposed that hip development disorders not only affect the proximal femur and the acetabulum, as evidenced by pathologies such as FAI and DDH, but throughout the pelvis.1,10 However, there is no consensus on which pelvic bone deformities correlate with acetabular morphological changes. We believe that a better understanding of these dysmorphisms may lead to easier diagnosis of hip joint pathologies.

Fujii et al12 performed a study evaluating the axial plane rotational alignment of the iliac bone in CT scans of patients with DDH, and questioned whether rotational deformity was present in the DDH; whether rotation angles were correlated with acetabular version and inclination; and whether the rotation angles were correlated with the acetabulum deficiency region. The results showed that the internal rotation (IR) of the upper third of the hemipelvis (from upper part of the iliac bone to the anterior inferior iliac spine [AIIS]) correlates with the diagnosis of DDH.12 Iliac bone IR in patients with DDH was also observed by authors as Kumeta et al13 and Suzuki,14 and it is believed that, with this deformity, the acetabulum tends to rotate anterosuperiorly, resulting in decreased anterosuperior coverage and increased posterior coverage.

Also, Fujii et al12 correlated external rotation of the lower third of the hemipelvis (between the iliac bone and the ischiopubic branch) with acetabular retroversion in patients with DDH. This finding is corroborated by Kalberer et al.,15 who observed the prominence of the ischial spine in patients with acetabular retroversion.

These observations suggest that pelvic bone structural changes and acetabular abnormalities are not isolated findings, but are instead part of a continuum of structural developmental changes.

In our study, correlation between CE angle variation and upper hemipelvis asymmetry was found. Like Fujii et al,13 we can see that upper hemipelvis dysmorphisms, resulting from bone development disorders, may influence acetabular morphology. However, we sought to analyze these findings in a group of patients without severe DDH (CE angle < 20º).

To our knowledge, this is the first study that seeks to establish correlations between pelvic dysmorphisms and variation of the CE angle, in the 90th percentile, for the CE angle of the general population (20-40º).16

 

CONCLUSION

In the present study, a correlation between CE angle variation and upper hemipelvis asymmetry was found. These findings suggest that upper hemipelves dysmorphism due to bone development disorders may influence acetabular morphology.

 

REFERENCES

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