HIP
The role of femoral neck anteversion in the development of osteoarthritis in dysplastic hips H. Li, Y. Wang, J. K. Oni, X. Qu, T. Li, Y. Zeng, F. Liu, Z. Zhu From Department of Orthopaedics, Shanghai No. 9th People’s Hospital, Shanghai JiaoTong University School of Medicine, Shanghai, China H. Li, MD, Orthopaedic surgeon, Associate professor Y. Wang, MD, Orthopaedic surgeon, Professor X. Qu, PhD, Orthopaedic surgeon, Surgery Fellow Y. Zeng, MD, Orthopaedic surgeon, Surgery Fellow F. Liu, MD, Orthopaedic surgeon, Associate professor Z. Zhu, MD, Orthopaedic surgeon, Professor Shanghai No. 9th People’s Hospital, Department of Orthopaedics, Shanghai Jiao Tong University School of Medicine, Shanghai 200011, China. J. K. Oni, MD, Orthopaedic surgeon, Adult Reconstructive Surgery Fellow Department of Orthopaedics, Rush University Medical Center, Chicago, Illinois 60612, USA. T. Li, PhD, Biochemistry researcher, Associate professor Department of Biochemistry, Rush University Medical Center, Chicago, Illinois 60612, USA. Correspondence should be sent to Prof Z. Zhu; e-mail: [email protected] ©2014 The British Editorial Society of Bone & Joint Surgery doi:10.1302/0301-620X.96B12. 33983 $2.00 Bone Joint J 2014;96-B:1586–93. Received 15 February 2014; Accepted after revision 10 September 2014
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There have been several studies examining the association between the morphological characteristics seen in acetabular dysplasia and the incidence of the osteoarthritis (OA). However, most studies focus mainly on acetabular morphological analysis, and few studies have scrutinised the effect of femoral morphology. In this study we enrolled 36 patients with bilateral acetabular dysplasia and early or mid-stage OA in one hip and no OA in the contralateral hip. CT scans were performed from the iliac crest to 2 cm inferior to the tibial tuberosity, and the morphological characteristics of both acetabulum and femur were studied. In addition, 200 hips in 100 healthy volunteer Chinese adults formed a control group. The results showed that the dysplastic group with OA had a significantly larger femoral neck anteversion and a significantly shorter abductor lever arm than both the dysplastic group without OA and the controls. Femoral neck anteversion had a significant negative correlation with the length of the abductor lever arm and we conclude that it may contribute to the development of OA in dysplastic hips. Cite this article: Bone Joint J 2014; 96-B:1586–93.
Various morphological abnormalities contribute to acetabular dysplasia. The dysplastic acetabulum has a shallow articulating cavity, an excessively oblique roof and decreased cover of the femoral head.1,2 These abnormalities may cause abnormal joint stresses, leading to degeneration of the labrum and articular cartilage, and the onset of osteoarthritis (OA).3,4 However, the role of acetabular dysplasia in the aetiology of OA in the adult hip remains controversial. Three crosssectional radiographic studies5-7 failed to identify an association between OA and acetabular dysplasia. Two systematic reviews by Lievense et al8,9 concluded that there was limited evidence to support the conclusion that dysplasia increases the incidence of OA of the hip, but neither considered the effect of femoral morphology. In this study we analysed the morphological characteristics of the acetabulum and femur in the dysplastic hips both with and without OA to investigate whether there is an association between the two and to analyse the effect of the shape of the femur shape on the development of OA.
Patients and Methods Between February 2008 and July 2012, standard anteroposterior (AP) radiographs of the pelvis, with the patella situated in the frontal plane, were performed on consecutive adult patients with acetabular dysplasia who had
been admitted either for surgery or for evaluation of dysplasia. The initial inclusion criteria for the study were: 1) Patients with bilateral acetabular dysplasia, defined as a centre–edge (CE) angle < 20° and an acetabular angle (AA) > 45°10 (Fig. 1). 2) Patients who had early or mid-stage OA in one hip without OA and the contralateral hip. OA was evaluated using the qualitative assessments of Croft et al,11 who graded it into five categories (Table I). We included patients who had grade 1, 2 or 3 OA in one hip and a contralateral hip with no articular symptoms and no radiological evidence of OA. Patients with grades 4 and 5 with advanced or end-stage OA were excluded. Patients who had spinal pathology, had undergone osteotomy of the hip, or who had a deformity of the lower limbs, secondary post-traumatic OA, an inflammatory arthropathy, osteonecrosis or an infectious disease were excluded. On the basis of these criteria, 72 dysplastic hips in 36 adult patients (21 women and 15 men) were included in the study. The mean age of the patients was 49.3 years (SD 8.8; 23 to 66). A control group was made up of 200 hips in 100 healthy volunteer Chinese adults (50 women and 50 men) with a mean age of 46.2 years (SD 7.2; 30 to 60) (Table II). CT scans were performed from the iliac crest THE BONE & JOINT JOURNAL
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Table I. The five grades of osteoarthritis according to Croft et al11 Grade
Criteria
Grade 1 Grade 2 Grade 3
Osteophytosis only Joint-space narrowing only Two of the following features: osteophytosis, joint-space narrowing, subchondral sclerosis or cyst formation Three of the following features: osteophytosis, joint-space narrowing, subchondral sclerosis or cyst formation As grade 4, but with deformity of the femoral head.
Grade 4 Grade 5
Table II. Patient demographics
Fig. 1 Radiograph showing the centre–edge (CE) angle, acetabular angle (AA), abductor lever arm (ALA), and the horizontal distance of the femoral head centre (FHC)
to 2 cm below to the tibial tuberosity, using a GE Pro-Speed CT scanner (GE Healthcare, Chalfont St Giles, United Kingdom). In order to reduce exposure to radiation, the femoral cortical area was scanned at intervals of 1.25 mm, whereas we scanned the pelvis, knee and the adjacent area at intervals of 0.625 mm. The CT data were then imported into the Mimics 10.01 medical imaging program (Materialise, Leuven, Belgium) for the creation of a threedimensional (3D) reconstruction. This program allowed us to calculate dimensional and morphological variables twodimensionally including in the axial, coronal and sagittal planes, as well as three-dimensionally. Femoral neck anteversion (FNA) was defined according to Kingsley and Olmsted12 and was measured as previously described.13 Briefly, the FNA is the angle between an imaginary transverse line that runs medially to laterally through the posterior edges of the medial and lateral condyles of the distal femur, and an imaginary transverse line passing through the centre of the femoral head and neck. Other femoral measurements included the length of the abductor lever arm (ALA), the horizontal distance of the femoral head centre (FHC), the neck–shaft angle of the femur, the length of the femoral shaft mechanical axis (LFMA), and the length of the femoral shaft anatomical axis (LFAA). The abductor lever arm is the perpendicular distance from a line tangential to the greater trochanter to the centre of rotation of the femoral head. The tangential line corresponds to the abductor shadow on the radiograph14 (Fig. 1). The FHC is the distance between the centre of gravity of the body to the centre of the femoral head. The magnification of the radiograph was decided by the diameter of the femoral head measured by radiography and CT. For the measurement of neck–shaft angle, LFMA and LFAA, the key anatomical VOL. 96-B, No. 12, DECEMBER 2014
No. of patients (hips) Females/males Mean age (SD) (yrs) Height (cm) (SD) Weight (kg) (SD) BMI (SD)
AD group
Control group
p-value
36 (72) 21/15 49.30 (8.86) 163.44 (7.87) 62.36 (9.92) 23.46 (2.37)
100 (200) 50/50 46.17 (7.25) 165.68 (8.03) 65.62 (9.12) 23.85 (2.68)
0.12 0.02 0.12 0.11 0.45
AD, acetabular dysplasia; BMI, body mass index
landmarks of the lower limb in 3D coordinates were converted into a standard frontal 2D image using Unigraphics NX4.0 software (Siemens PLM Software, Plano, Texas), and the measurements were carried out on the 2D image, as previously described.13 The acetabular anteversion (AcetAV) angle is defined as the acetabular opening direction in the axial plane and is measured on a transaxial reformat through the centres of the femoral heads.15 The combined anteversion (CA) angle was calculated by adding the FNA angle and the AcetAV angle. The acetabular depth (AcetDep), which is the distance from the bottom of the acetabulum perpendicular to the line from the anterior rim to the posterior rim of the acetabulum, was also measured in this plane. Measurements of acetabular cover include the anterior CE angle, the anterior acetabular sector angle (AASA), the posterior acetabular angle (PASA) and the horizontal acetabular sector angle (HASA).15,16 The anterior CE angle, which is an indication of the superior–anterior acetabular cover of the femoral head,17 was measured on a reformatted sagittal image passing through the centre of the femoral head (Fig. 2a). The AASA and PASA, which are indications respectively of the anterior and posterior acetabular cover of the femoral head, were measured on a reformatted axial image passing through the centres of the femoral heads (Fig. 2b). The HASA was calculated by adding the AASA and PASA together. In addition, we measured the pelvic rotation angle (PRA) to assess the rotational deformity of the pelvis.18 In 3D-CT reconstruction imaging, the PRA is formed between the horizontal line and another line connecting the midpoint of the anterior superior iliac spine with the midpoint of the posterior superior iliac spine (Fig. 3).
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Fig. 2a
Fig. 2b
CT scans showing a) the superior–anterior angle (ACE angle) that is measured from a sagittal 2D reformat through the centre of the femoral head. The angle is bound by the horizontal line through the most superior point of the acetabular joint surface and the anterior rim of the acetabulum (post, posterior; ant, anterior) and b) showing a transaxial 2D reformat through the centres of the femoral heads which is used for the measurement of AcetAV, AASA and PASA. AcetAV is the angle between a line connecting the anterior and posterior margins of the acetabulum and a line perpendicular to the intercapital centre line. AASA and PASA are the angles between the intercapital centre line and lines connecting the centre points of the femoral heads to the respective anterior and posterior rims of the acetabulum.
parameters between the normal hips and the subgroups of acetabular dysplasia. Spearman’s correlation coefficient was used to assess the relationships between the radiological parameters and OA. Pearson’s correlation coefficient was used to assess the relationships between morphological parameters. The Mantel–Haenszel chi-squared test20 was used to assess relative risk in the subgroups of acetabular dysplasia with and without OA. Differences were considered statistically significant at p < 0.05. Fig. 3 The pelvic rotation angle (PRA) is formed between the horizontal line and another line connecting the midpoint of the anterior superior iliac spine with the midpoint of posterior superior iliac spine.
Statistical analysis. This was performed using SAS Statistics version V8 for Windows (SAS Institute, Cary, North Carolina). The identification and grading of OA in dysplastic hips was performed by two doctors (HL, XQ). Agreement between them was good (Cohen’s unweighted κ = 0.92). In order to minimise errors of measurement, they were made by three doctors (HL, YZ, XQ). LHW and ZYM measured all samples first. Then, 30 samples were randomly selected and measured by QXH to retest reliability. Agreement between LHW and ZYM was good (Cohen’s unweighted κ = 0.91). The agreement between the first measurements and the retest by QXH was also good (Cohen’s unweighted κ = 0.93). All 30 measurements were demonstrated to be reliable (ICC > 0.89). The CT measurements had a precision value = 0.2 mm and < 1.5°. A paired Student’s t-test was used to compare the radiological parameters between subgroups of acetabular dysplasia. Dunnett tests19 were used to compare the radiographic
Results The measurements of the hip in the dysplastic and normal groups are summarised in Table III. The significant difference between the subgroups with and without OA was found in the FNA, CA and ALA. There were no significant differences between the two subgroups in any other measurements. The mean FNA was 14.42° (SD 4.0) in normal hips and 14.91° (SD 9.85) in dysplastic hips, indicating a similar degree of anteversion (p = 0.12). However, when dysplastic hips were divided into subgroups, the mean FNA was 18.41° (SD 9.75) in the dysplastic subgroup with OA and 12.09° (SD 8.02) in the dysplastic subgroups without OA, indicating a significantly larger degree of anteversion in the dysplastic subgroup with OA (p < 0.001) and less anteversion in the dysplastic subroup without OA (p = 0.002) compared with the normal hips (Fig. 4). Similar results were found in the measurements of the CA. There was a significant difference between the ALA in the dyplastic and normal groups (p = 0.001). Dysplastic hips with OA had the smallest ALA, which was significantly different from that in the normal group (p = 0.004) and in the dysplastic subgroup without OA (p = 0.026). There was a significant negative correlation between the CA and the ALA in dysplastic hips (r = -0.51, p = 0.0001) both in hips with OA (r = -0.43, p = 0.034) and those without OA (r = -0.55, p = 0.0043) (Fig. 5a). FNA was THE BONE & JOINT JOURNAL
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Table III. Various parameters in AD hips and normal hips. All values are presented as mean (SD) Dysplastic hips Total (72 hips) Screening indexes CE (°) AA (°) Femoral measurements FNA (°) ALA (mm) FHC (mm) Neck–shaft angle (°) LFMA (mm) LFAA (mm) Acetabular measurements AcetAV (°) CA (°) Acetabular depth (mm) Anterior centre-edge (°) AASA (°) PASA (°) HASA (°) PRA (°)
OA side (n = 36)
Without OA side (n = 36)
Normal hips (n = 200)
p-value
12.73 (3.56)† 47.10 (2.48)†
12.20 (3.66)† 47.48 (2.71)†
13.34 (3.55)† 46.70 (2.23)†
33.02 (7.33) 41.15 (4.66)
0.26 0.27
14.91 (9.85) 41.02 (6.49)† 94.43 (5.01) 131.22 (7.47)† 399.71 (23.18) 373.58 (22.09)
18.41 (9.75)† 39.10 (5.96)† 94.08 (4.86) 131.8 (7.12)† 399.37 (22.49) 373.31 (22.04)
12.09 (8.02)*† 43.15 (6.49)*† 92.88 (5.22) 130.64 (7.87)† 400.03 (22.86) 373.82 (22.14)
14.42 (4.0) 46.9 (3.54) 93.82 (3.74) 126.45 (5.80) 406.90 (24.51) 378.84 (23.12)
0.016 0.026 0.79 0.59 0.92 0.93
17.42 (5.68) 32.11 (10.01) 18.08 (3.26)† 21.62 (6.06)† 50.13 (7.14)† 86.57 (7.67)† 136.70 (10.83)† 28.51 (3.97)
17.74 (5.75) 35.04 (10.74) 17.97 (3.33)† 20.74 (6.83)† 48.27 (7.88)† 85.64 (8.77)† 133.66 (12.00)† 28.79 (4.30)
17.11 (5.71) 29.18 (8.45)*† 18.30 (3.25)† 22.5 (5.16)† 52.0 (5.90)† 87.59 (6.42)† 139.66 (8.49)† 28.24 (3.64)
18.67 (5.67) 33.37 (4.91) 20.23 (2.03) 26.72 (3.53) 67.66 (4.60) 101.32 (5.41) 168.83 (4.33) 28.12 (2.17)
0.70 0.03 0.71 0.12 0.063 0.40 0.05 0.84
* significant difference † significant difference compared with the normal hips group AD, acetabular dysplasia; OA, osteoarthritis; CE, centre–edge angle; AA, acetabular angle; FNA, femoral neck anteversion angle; ALA, abduction lever arm; FHC, the horizontal distance of the femoral head centre; LFMA, the length of the femoral shaft mechanical axis; LFAA, the length of the femoral shaft anatomical axis; AcetAV-angle, acetabular anteversion angle; CA, combined anteversion angle (FNA+AcetAV-angle); AcetDep, acetabular depth; AASA, anterior acetabular sector angle; PASA, posterior acetabular angle; HASA, horizontal acetabular sector angle; PRA, pelvic rotation angle
*
* *
*
50
35 * *
45 30 40 35
* *
CA (°)
FNA (°)
25
20
15
30 25 20 15
10
10 5 5 0
Normal
AD without OA
AD with OA
Fig. 4a
AD total
AD without OA
AD with OA
AD total
Normal
0
Fig. 4b
Graphs showing a) femoral neck anteversion angle (FNA) and b) combined anteversion angle (CA) against acetabular dysplasia (AD). OA, osteoarthritis. * p < 0.05; ** p < 0.01.
also found to correlate negatively with the ALA in dysplastic hips (r = –0.43, p = 0.002) (Fig. 5b). Other correlations between the various parameters and OA in dysplastic hips VOL. 96-B, No. 12, DECEMBER 2014
are shown in Table IV, and correlations with regard to various parameters in dysplastic hips in Table V. The AcetAv, CA and CE angles were found to correlate with anterior
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AD without OA y = 55.52-0.42x
AD with OA AD without OA
50 AD y = 52.04-0.34x 40 AD with OA 30
AD with OA AD without OA
60 50 ALA (mm)
ALA (mm)
60
y = 47.64-0.24x
20 10
AD without OA y = 45.97-0.23x AD y = 45.43-0.29x AD with OA y = 43.83-0.24x
40 30 20 10
0 0
10
20
30
40
50
60
0 0
10
CA (°)
20
30
40
FNA (°)
Fig. 5a
Fig. 5b
Graphs showing correlation analysis between a) combined anteversion angle (CA) and abduction lever arm (ALA), and b) between femoral neck anteversion angle (FNA) and ALA. AD, acetabular dysplasia.
Table IV. Correlation between the parameters and OA Parameters
Correlation coefficient (rs)
p-value
CE (°) AA (°) Neck–shaft angle (°) FNA (°) AcetAV (°) CA ALA (mm) Anterior centre–edge angle (°) AASA (°) PASA (°) HASA (°)
- 0.33 0.13 0.13 0.31 - 0.07 0.30 - 0.28 - 0.12 - 0.30 - 0.31 - 0.41
0.019 0.36 0.39 0.036 0.62 0.037 0.047 0.43 0.036 0.028 0.002
OA, osteoarthritis; CE, centre-edge angle; AA, acetabular angle; FNA, femoral neck anteversion angle; AcetAV, acetabular anteversion angle; CA, combined anteversion angle; ALA, abduction lever arm; AASA, anterior acetabular sector angle; PASA, posterior acetabular angle; HASA, horizontal acetabular sector angle
acetabular cover of the femoral head. There was a significant negative correlation between the CA and the AASA (r = -0.38, p = 0.006), and also between the AcetAv and the AASA (r = -0.5, p = 0.0002). There was a significant positive correlation between the CE angle and the anterior CE angle (r = 0.34, p = 0.01). According to Mantel–Haenszel estimates of relative risk, in patients who have bilateral acetabular dysplasia the risk of OA occurring in the hip with a larger FNA was five times higher than in the contralateral hip. Similarly, the risk of OA occurring in the hip with a larger CA was three times higher than that of the contralateral hip (p = 0.001). Using the Tönnis and Heinecke classification of FNA,21 16 hips had OA, but in the 22 hips with a FNA < 10° only six had OA (Fig. 6a). The relative risk was 2.93 (p = 0.001). In 12 hips with a CA > 40°, 10 had OA, but in 16 hips with a CA between 20° and 29°, only three had OA (Fig. 6b). The relative risk was 4.44 (p = 0.001). OA occurred mainly in the anterior superolateral area of the hips, although it was also found in the middle superolateral and posterior superolateral aspects of some hips. The anterior superolateral area was found to be
involved in all patients with OA, including 20 in whom only one area was involved (Fig. 7).
Discussion In this study we examined the morphological differences of both the acetabulum and the femur in dysplastic hips with and without OA. Our data strongly suggests that the FNA angle is a significant factor contributing to the development of OA in dysplastic hips. There is still controversy regarding the role of acetabular dysplasia in the causation of OA of the hip in adults. Geometrical measurements of the morphology of the hip taken from radiographs, such as acetabular depth and CE angle, have been investigated previously in OA, with varying results.22 Cross-sectional studies in western European and Japanese populations have supported an association between dysplasia and OA of the hip.23-25 However, Asian, African and Turkish populations appear to have a different prevalence of OA of the hip in relation to acetabular dysplasia, compared with that of western Europeans,26-28 although none of these studies considered the effect of femoral morphology. In our study, THE BONE & JOINT JOURNAL
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Table V. Correlations with regard to various parameters in dysplastic hips AD hips correlation coefficient (p-value) Compared parameters
AD total (72 hips)
AD hips with OA (n = 36)
AD without OA (n = 36)
CE/ AA CE/ Neck–shaft angle CE/ FNA CE/ AcetAV CE/ CA CE/ ALA CE/ Anterior centre–edge CE/ AASA CE/ PASA CE/ HASA FNA/ AcetAV FNA/ ALA FNA/ Anterior centre–edge angle FNA/ AASA FNA/ PASA FNA/ HASA AcetAV-angle/ ALA AcetAV-angle/ anterior centre–edge AcetAV-angle/ AASA AcetAV-angle/ PASA AcetAV-angle/ HASA CA/ ALA CA/ ACE CA/ AASA CA/ PASA CA/ HASA
– 0.44 (0.001) – 0.20 (0.16) – 0.04 (0.77) 0.01 (0.93) – 0.04 (0.79) 0.34 (0.016) 0.34 (0.01) 0.12 (0.42) 0.21 (0.14) 0.22 (0.11) – 0.25 (0.09) – 0.43 (0.002) – 0.05 (0.73) – 0.11 (0.45) – 0.28 (0.05) – 0.27 (0.06) – 0.06 (0.69) – 0.11 (0.45) – 0.5 (0.0002) 0.64 (0.001) 0.12 (0.42) – 0.51 (0.0001) – 0.1 (0.47) – 0.38 (0.006) 0.09 (0.55) – 0.19 (0.19)
– 0.36 (0.07) – 0.37 (0.07) – 0.29 (0.16) – 0.03 (0.89) 0.24 (0.25) 0.35 (0.09) 0.30 (0.14) 0.22 (0.29) 0.26 (0.21) 0.15 (0.40) – 0.17 (0.42) – 0.37 (0.07) 0.12 (0.58) – 0.06 (0.79) 0.1 (0.6) – 0.01 (0.98) – 0.03 (0.87) – 0.11 (0.61) – 0.5 (0.01) 0.57 (0.002) 0.06 (0.77) – 0.43 (0.034) 0.03 (0.9) – 0.35 (0.09) 0.013 (0.95) – 0.01 (0.97)
– 0.51 (0.01) – 0.04 (0.83) – 0.17 (0.42) – 0.03 (0.89) – 0.15 (0.47) 0.19 (0.40) 0.35 (0.08) 0.12 (0.58) 0.02 (0.90) 0.21 (0.30) – 0.29 (0.16) – 0.30 (0.14) – 0.15 (0.46) 0.10 (0.63) – 0.34 (0.06) – 0.30 (0.14) – 0.21 (0.31) – 0.05 (0.81) – 0.61 (0.001) 0.72 (0.001) 0.16 (0.43) – 0.55 (0.0043) – 0.22 (0.28) – 0.30 (0.14) 0.38 (0.06) – 0.2 (0.34)
AD, acetabular dysplasia; OA, osteoarthritis; CE, centre–edge angle; AA, acetabular angle; FNA, femoral neck anteversion angle; AcetAV, acetabular anteversion angle; CA, combined anteversion angle; ALA, abduction lever arm; AASA, anterior acetabular sector angle; PASA, posterior acetabular angle; HASA, horizontal acetabular sector angle
OA hips Without OA hips
OA hips Without OA hips
100
100
75
%
%
75
50
25
0
50
25
0 < 10
15 to 20 10 to 14 FNA (°)
> 20
Fig. 6a
< 20
20 to 29 30 to 40 CA (°)
> 40
Fig. 6b
Graphs showing the ratio of OA hips versus those hips without OA a) when the femoral neck anteversion (FNA) angle was classified as < 10°; 10° to 14°; 15° to 20°; and > 20° and b) when the combined anteversion (CA) angle was classified as < 20°; 20° to 29°; 30° to 40°; and > 40°.
FNA was significantly greater in the dysplastic group with OA than in both the dysplastic group without OA and the control group. In addition, the dysplastic group without OA had a significantly smaller FNA than the control group, VOL. 96-B, No. 12, DECEMBER 2014
whereas the CE was the same in both the dysplastic group with OA and the group without OA groups. Based on our data, we suggest that an abnormal CE alone will probably not influence the occurrence of OA without an increase in
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Fig. 7 CT scans showing osteoarthritis was present in the anterior superolateral aspect of the hip. L, lateral; M, medial; A, anterior; P, posterior.
FNA. It is possible that a decreased ALA and AASA is the mechanism by which a CA angle contributes to the occurrence of OA. It has been established that the load on the hip during gait is inversely proportional to the length of the ALA.18,29 Therefore, the shorter the ALA, the greater the load on the hip. We found that the dysplastic group with OA group had a significantly smaller ALA and larger FNA angle than the other two groups. So, it is likely that a hip with dysplasia and OA, with its larger CA angle, will have increased pressure on the anterior superolateral surface of the hip where most of the OA was found. Conversely, the dysplastic group without OA had a significantly longer ALA and smaller FNA than the dysplastic group with OA. This longer ALA, and the consequently decreased load across the respective hips, would account for the absence of OA in these hips, despite the presence of dysplasia. The horizontal distance of the FHC was similar in all three groups. This eliminates the influence of the lateral shift of the femoral head on anteversion of the femoral neck. The correlation results showed that FNA had a significantly negative correlation with the ALA, and that AcetAv had a significantly negative correlation with anterior acetabular cover of the femoral head. There have also been various studies on the association between FNA and OA in non-dysplastic hips. Some of these have supported the hypothesis that a persistent increase in FNA leads to a predisposition for OA of the hip.30-32 We suggest that the influence of FNA on OA will be more apparent in dysplastic hips owing to the smaller CE angle, which we found had a significant association with
decreased anterosuperior cover of the femoral head. This finding was similar to that reported in previous studies.1,33,34 In dysplastic hips, deficient anterosuperior cover of the femoral head caused by a decreased CE angle could lead to increased loads across this aspect of the acetabulum if subjected to increased FNA and decreased ALA. Our data suggest that a CA anteversion angle > 40° or FNA > 20° is a valuable reference when contemplating prophylactic pelvic osteotomy. In addition, when dysplastic hips were divided into subgroups, the mean FNA was higher in the dysplastic group with OA and lower in the dysplastic group without OA, but the difference between the two subgroups was small. This suggests that the margin of error for displacement of an osteotomy could pose a significant challenge to surgeons performing joint preservation surgery. Also, in patients in whom a pelvic osteotomy is being considered because of bilateral dysplasia, our results suggest that it should be performed first on the hip with the larger FNA, because the risk of OA developing on this side was five times higher than on the contralateral side. A shortcoming of this study is that only 36 patients from a large number of those with dysplasia of the hip met the selection criteria. However, the comparison of both hips in the same patients helped eliminate many confounding factors and lessened the potential detrimental impact of the small sample size. In addition, in the patients who did not have OA of the hip and whose mean age was 49 years at the time of the study, there is no guarantee that the hips will never develop OA. Furthermore, we are unable to explain why the FNA is different bilaterally in patients with dysplasia. However, these shortcomings do not affect the fact that the FNA significantly influenced the onset of OA in dysplastic hips. This study was supported by National Natural Science Foundation of China (Grant No. 81171729) and Sectors Fund Project of the Ministry of Health of the People’s Republic of China (Grant No. 201302007). No benefits in any form have been received or will be received from a commercial party related directly or indirectly to the subject of this article This article was primary edited by S. Hughes and first proof edited by G. Scott.
References 1. Jacobsen S, Rømer L, Søballe K. Degeneration in dysplastic hips; a computer tomography study. Skeletal Radiol 2005;34:778–784. 2. Kosuge D, Yamada N, Azegami S, Achan P, Ramachandran M. Management of developmental dysplasia of the hip in young adults: current concepts. Bone Joint J 2013;95-B:732–737. 3. Tamura S, Nishii T, Shiomi T, et al. Three-dimensional patterns of early acetabular cartilage damage in hip dysplasia; a high-resolutional CT arthrography study. :Osteoarthritis Cartilage 2012;20:646–652. 4. Klaue K, Durnin CW, Ganz R. The acetabular rim syndrome; a clinical presentation of dysplasia of the hip. :J Bone Joint Surg [Br] 1991;73-B:423–429. 5. Croft P, Cooper C, Wickham C, Coggon D. Osteoarthritis of the hip and acetabular dysplasia. Ann Rheum Dis 1991;50:308–310. 6. Smith RW, Egger P, Coggon D, Cawley MI, Cooper C. Osteoarthritis of the hip joint and acetabular dysplasia in women. Ann Rheum Dis 1995;54:179–181. 7. Lane NE, Nevitt MC, Cooper C, et al. Acetabular dysplasia and osteoarthritis of the hip in elderly white women. Ann Rheum Dis 1997;56:627–630. 8. Lievense AM, Bierma-Zeinstra SM, Verhagen AP, Verhaar JA, Koes BW. Influence of hip dysplasia on the development of osteoarthritis of the hip. Ann Rheum Dis 2004;63:621–626. 9. Lievense AM, Bierma-Zeinstra SM, Verhagen AP, Verhaar JA, Koes BW. Prognostic factors of progress of hip osteoarthritis: a systematic review. Arthritis Rheum 2002;47:556–562. THE BONE & JOINT JOURNAL
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10. Cooperman D. What is the evidence to support acetabular dysplasia as a cause of osteoarthritis? J Pediatr Orthop 2013;33(Suppl1):S2–S7. 11. Croft P, Cooper C, Wickham C, Coggon D. Defining osteoarthritis of the hip for epidemiologic studies. Am J Epidemiol 1990;132:514–522. 12. Kingsley PC, Olmsted KL. A study to determine the angle of anteversion of the neck of the femur. J Bone Joint Surg [Am] 1948;30-A:745–751. 13. Wang Y, Zeng Y, Dai K, Zhu Z, Xie L. Normal lower-extremity alignment parameters in healthy Southern Chinese adults as a guide in total knee arthroplasty. J Arthroplasty 2010;25:563–570. 14. McGrory BJ, Morrey BF, Cahalan TD, An KN, Cabanela ME. Effect of femoral offset on range of motion and abductor muscle strength after total hip arthroplasty. J Bone Joint Surg [Br] 1995;77-B:865–869. 15. Anda S, Terjesen T, Kvistad KA. Computed tomography measurements of the acetabulum in adult dysplastic hips: which level is appropriate? Skeletal Radiol 1991;20:267–271. 16. Anda S, Svenningsen S, Dale LG, Benum P. The acetabular sector angle of the adult hip determined by computed tomography. Acta Radiol Diagn (Stockh) 1986;27:443–447. 17. Milcan A, Yildiz A, Oztuna V, et al. The anterior center edge angle: a study of 102 volunteers. Joint Bone Spine 2004;71:221–223. 18. Jia J, Zhang L, Zhao Q, Li L, Liu X. Does medial rotational deformity of the whole pelvis universally exist in unilateral DDH? Arch Orthop Trauma Surg 2011;131:1383–1388. 19. Dunnett CW. New tables for multiple comparisons with a control. Biometrics 1964; 20:482–491. 20. Mantel N, Haenszel W. Statistical aspects of the analysis of data from retrospective studies of disease. J Natl Cancer Inst 1959;22:719–748. 21. Tönnis D, Heinecke A. Acetabular and femoral anteversion: relationship with osteoarthritis of the hip. J Bone Joint Surg [Am] 1999;81-A:1747–1770. 22. McWilliams DF, Doherty SA, Jenkins WD, et al. Mild acetabular dysplasia and risk of osteoarthritis of the hip: a case-control study. Ann Rheum Dis 2010;69:1774–1778.
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23. Jacobsen S, Sonne-Holm S, Søballe K, Gebuhr P, Lund B. Hip dysplasia and osteoarthrosis: a survey of 4151 subjects from the Osteoarthrosis Substudy of the Copenhagen City Heart Study. Acta Orthop 2005;76:149–158. 24. Reijman M, Hazes JM, Pols HA, Koes BW, Bierma-Zeinstra SM. Acetabular dysplasia predicts incident osteoarthritis of the hip: the Rotterdam study. Arthritis Rheum 2005;52:787–793. 25. Okano K, Yamaguchi K, Ninomiya Y, et al. Femoral head deformity and severity of acetabular dysplasia of the hip. Bone Joint J 2013;95-B:1192–1196. 26. Inoue K, Wicart P, Kawasaki T, et al. Prevalence of hip osteoarthritis and acetabular dysplasia in french and japanese adults. Rheumatology (Oxford) 2000;39:745–748. 27. Ali-Gombe A, Croft PR, Silman AJ. Osteoarthritis of the hip and acetabular dysplasia in Nigerian men. J Rheumatol 1996;23:512–515. 28. Goker B, Sancak A, Haznedaroglu S. Radiographic hip osteoarthritis and acetabular dysplasia in Turkish men and women. Rheumatol Int 2005;25:419–422. 29. Tauber C, Ganel A, Horoszowski H, Farine I. Distal transfer of the greater trochanter in cox vara. Acta Orthop Scand 1980;51:661–666. 30. Reikerås O, Høiseth A. Femoral neck angles in osteoarthritis of the hip. Acta Orthop Scand 1982;53:781–784. 31. Terjesen T, Benum P, Anda S, Svenningsen S. Increased femoral anteversion and osteoarthritis of the hip joint. Acta Orthop Scand 1982;53:571–575. 32. Kitaoka HB, Weiner DS, Cook AJ, Hoyt WA Jr, Askew MJ. Relationship between femoral anteversion and osteoarthritis of the hip. J Pediatr Orthop 1989;9:396–404. 33. Maxian TA, Brown TD, Weinstein SL. Chronic stress tolerance levels for human articular cartilage: two nonuniform contact models applied to long-term follow-up of CDH. J Biomech 1995;28:159–166. 34. Hadley NA, Brown TD, Weinstein SL. The effects of contact pressure elevations and aseptic necrosis on the long-term outcome of congenital hip dislocation. J Orthop Res 1990;8:504–513.
The role of femoral neck anteversion in the development of osteoarthritis in dysplastic hips H. Li, Y. Wang, J. K. Oni, X. Qu, T. Li, Y. Zeng, F. Liu, Z. Zhu From Department of Orthopaedics, Shanghai No. 9th People’s Hospital, Shanghai JiaoTong University School of Medicine, Shanghai, China H. Li, MD, Orthopaedic surgeon, Associate professor Y. Wang, MD, Orthopaedic surgeon, Professor X. Qu, PhD, Orthopaedic surgeon, Surgery Fellow Y. Zeng, MD, Orthopaedic surgeon, Surgery Fellow F. Liu, MD, Orthopaedic surgeon, Associate professor Z. Zhu, MD, Orthopaedic surgeon, Professor Shanghai No. 9th People’s Hospital, Department of Orthopaedics, Shanghai Jiao Tong University School of Medicine, Shanghai 200011, China. J. K. Oni, MD, Orthopaedic surgeon, Adult Reconstructive Surgery Fellow Department of Orthopaedics, Rush University Medical Center, Chicago, Illinois 60612, USA. T. Li, PhD, Biochemistry researcher, Associate professor Department of Biochemistry, Rush University Medical Center, Chicago, Illinois 60612, USA. Correspondence should be sent to Prof Z. Zhu; e-mail: [email protected] ©2014 The British Editorial Society of Bone & Joint Surgery doi:10.1302/0301-620X.96B12. 33983 $2.00 Bone Joint J 2014;96-B:1586–93. Received 15 February 2014; Accepted after revision 10 September 2014
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There have been several studies examining the association between the morphological characteristics seen in acetabular dysplasia and the incidence of the osteoarthritis (OA). However, most studies focus mainly on acetabular morphological analysis, and few studies have scrutinised the effect of femoral morphology. In this study we enrolled 36 patients with bilateral acetabular dysplasia and early or mid-stage OA in one hip and no OA in the contralateral hip. CT scans were performed from the iliac crest to 2 cm inferior to the tibial tuberosity, and the morphological characteristics of both acetabulum and femur were studied. In addition, 200 hips in 100 healthy volunteer Chinese adults formed a control group. The results showed that the dysplastic group with OA had a significantly larger femoral neck anteversion and a significantly shorter abductor lever arm than both the dysplastic group without OA and the controls. Femoral neck anteversion had a significant negative correlation with the length of the abductor lever arm and we conclude that it may contribute to the development of OA in dysplastic hips. Cite this article: Bone Joint J 2014; 96-B:1586–93.
Various morphological abnormalities contribute to acetabular dysplasia. The dysplastic acetabulum has a shallow articulating cavity, an excessively oblique roof and decreased cover of the femoral head.1,2 These abnormalities may cause abnormal joint stresses, leading to degeneration of the labrum and articular cartilage, and the onset of osteoarthritis (OA).3,4 However, the role of acetabular dysplasia in the aetiology of OA in the adult hip remains controversial. Three crosssectional radiographic studies5-7 failed to identify an association between OA and acetabular dysplasia. Two systematic reviews by Lievense et al8,9 concluded that there was limited evidence to support the conclusion that dysplasia increases the incidence of OA of the hip, but neither considered the effect of femoral morphology. In this study we analysed the morphological characteristics of the acetabulum and femur in the dysplastic hips both with and without OA to investigate whether there is an association between the two and to analyse the effect of the shape of the femur shape on the development of OA.
Patients and Methods Between February 2008 and July 2012, standard anteroposterior (AP) radiographs of the pelvis, with the patella situated in the frontal plane, were performed on consecutive adult patients with acetabular dysplasia who had
been admitted either for surgery or for evaluation of dysplasia. The initial inclusion criteria for the study were: 1) Patients with bilateral acetabular dysplasia, defined as a centre–edge (CE) angle < 20° and an acetabular angle (AA) > 45°10 (Fig. 1). 2) Patients who had early or mid-stage OA in one hip without OA and the contralateral hip. OA was evaluated using the qualitative assessments of Croft et al,11 who graded it into five categories (Table I). We included patients who had grade 1, 2 or 3 OA in one hip and a contralateral hip with no articular symptoms and no radiological evidence of OA. Patients with grades 4 and 5 with advanced or end-stage OA were excluded. Patients who had spinal pathology, had undergone osteotomy of the hip, or who had a deformity of the lower limbs, secondary post-traumatic OA, an inflammatory arthropathy, osteonecrosis or an infectious disease were excluded. On the basis of these criteria, 72 dysplastic hips in 36 adult patients (21 women and 15 men) were included in the study. The mean age of the patients was 49.3 years (SD 8.8; 23 to 66). A control group was made up of 200 hips in 100 healthy volunteer Chinese adults (50 women and 50 men) with a mean age of 46.2 years (SD 7.2; 30 to 60) (Table II). CT scans were performed from the iliac crest THE BONE & JOINT JOURNAL
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Table I. The five grades of osteoarthritis according to Croft et al11 Grade
Criteria
Grade 1 Grade 2 Grade 3
Osteophytosis only Joint-space narrowing only Two of the following features: osteophytosis, joint-space narrowing, subchondral sclerosis or cyst formation Three of the following features: osteophytosis, joint-space narrowing, subchondral sclerosis or cyst formation As grade 4, but with deformity of the femoral head.
Grade 4 Grade 5
Table II. Patient demographics
Fig. 1 Radiograph showing the centre–edge (CE) angle, acetabular angle (AA), abductor lever arm (ALA), and the horizontal distance of the femoral head centre (FHC)
to 2 cm below to the tibial tuberosity, using a GE Pro-Speed CT scanner (GE Healthcare, Chalfont St Giles, United Kingdom). In order to reduce exposure to radiation, the femoral cortical area was scanned at intervals of 1.25 mm, whereas we scanned the pelvis, knee and the adjacent area at intervals of 0.625 mm. The CT data were then imported into the Mimics 10.01 medical imaging program (Materialise, Leuven, Belgium) for the creation of a threedimensional (3D) reconstruction. This program allowed us to calculate dimensional and morphological variables twodimensionally including in the axial, coronal and sagittal planes, as well as three-dimensionally. Femoral neck anteversion (FNA) was defined according to Kingsley and Olmsted12 and was measured as previously described.13 Briefly, the FNA is the angle between an imaginary transverse line that runs medially to laterally through the posterior edges of the medial and lateral condyles of the distal femur, and an imaginary transverse line passing through the centre of the femoral head and neck. Other femoral measurements included the length of the abductor lever arm (ALA), the horizontal distance of the femoral head centre (FHC), the neck–shaft angle of the femur, the length of the femoral shaft mechanical axis (LFMA), and the length of the femoral shaft anatomical axis (LFAA). The abductor lever arm is the perpendicular distance from a line tangential to the greater trochanter to the centre of rotation of the femoral head. The tangential line corresponds to the abductor shadow on the radiograph14 (Fig. 1). The FHC is the distance between the centre of gravity of the body to the centre of the femoral head. The magnification of the radiograph was decided by the diameter of the femoral head measured by radiography and CT. For the measurement of neck–shaft angle, LFMA and LFAA, the key anatomical VOL. 96-B, No. 12, DECEMBER 2014
No. of patients (hips) Females/males Mean age (SD) (yrs) Height (cm) (SD) Weight (kg) (SD) BMI (SD)
AD group
Control group
p-value
36 (72) 21/15 49.30 (8.86) 163.44 (7.87) 62.36 (9.92) 23.46 (2.37)
100 (200) 50/50 46.17 (7.25) 165.68 (8.03) 65.62 (9.12) 23.85 (2.68)
0.12 0.02 0.12 0.11 0.45
AD, acetabular dysplasia; BMI, body mass index
landmarks of the lower limb in 3D coordinates were converted into a standard frontal 2D image using Unigraphics NX4.0 software (Siemens PLM Software, Plano, Texas), and the measurements were carried out on the 2D image, as previously described.13 The acetabular anteversion (AcetAV) angle is defined as the acetabular opening direction in the axial plane and is measured on a transaxial reformat through the centres of the femoral heads.15 The combined anteversion (CA) angle was calculated by adding the FNA angle and the AcetAV angle. The acetabular depth (AcetDep), which is the distance from the bottom of the acetabulum perpendicular to the line from the anterior rim to the posterior rim of the acetabulum, was also measured in this plane. Measurements of acetabular cover include the anterior CE angle, the anterior acetabular sector angle (AASA), the posterior acetabular angle (PASA) and the horizontal acetabular sector angle (HASA).15,16 The anterior CE angle, which is an indication of the superior–anterior acetabular cover of the femoral head,17 was measured on a reformatted sagittal image passing through the centre of the femoral head (Fig. 2a). The AASA and PASA, which are indications respectively of the anterior and posterior acetabular cover of the femoral head, were measured on a reformatted axial image passing through the centres of the femoral heads (Fig. 2b). The HASA was calculated by adding the AASA and PASA together. In addition, we measured the pelvic rotation angle (PRA) to assess the rotational deformity of the pelvis.18 In 3D-CT reconstruction imaging, the PRA is formed between the horizontal line and another line connecting the midpoint of the anterior superior iliac spine with the midpoint of the posterior superior iliac spine (Fig. 3).
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Fig. 2a
Fig. 2b
CT scans showing a) the superior–anterior angle (ACE angle) that is measured from a sagittal 2D reformat through the centre of the femoral head. The angle is bound by the horizontal line through the most superior point of the acetabular joint surface and the anterior rim of the acetabulum (post, posterior; ant, anterior) and b) showing a transaxial 2D reformat through the centres of the femoral heads which is used for the measurement of AcetAV, AASA and PASA. AcetAV is the angle between a line connecting the anterior and posterior margins of the acetabulum and a line perpendicular to the intercapital centre line. AASA and PASA are the angles between the intercapital centre line and lines connecting the centre points of the femoral heads to the respective anterior and posterior rims of the acetabulum.
parameters between the normal hips and the subgroups of acetabular dysplasia. Spearman’s correlation coefficient was used to assess the relationships between the radiological parameters and OA. Pearson’s correlation coefficient was used to assess the relationships between morphological parameters. The Mantel–Haenszel chi-squared test20 was used to assess relative risk in the subgroups of acetabular dysplasia with and without OA. Differences were considered statistically significant at p < 0.05. Fig. 3 The pelvic rotation angle (PRA) is formed between the horizontal line and another line connecting the midpoint of the anterior superior iliac spine with the midpoint of posterior superior iliac spine.
Statistical analysis. This was performed using SAS Statistics version V8 for Windows (SAS Institute, Cary, North Carolina). The identification and grading of OA in dysplastic hips was performed by two doctors (HL, XQ). Agreement between them was good (Cohen’s unweighted κ = 0.92). In order to minimise errors of measurement, they were made by three doctors (HL, YZ, XQ). LHW and ZYM measured all samples first. Then, 30 samples were randomly selected and measured by QXH to retest reliability. Agreement between LHW and ZYM was good (Cohen’s unweighted κ = 0.91). The agreement between the first measurements and the retest by QXH was also good (Cohen’s unweighted κ = 0.93). All 30 measurements were demonstrated to be reliable (ICC > 0.89). The CT measurements had a precision value = 0.2 mm and < 1.5°. A paired Student’s t-test was used to compare the radiological parameters between subgroups of acetabular dysplasia. Dunnett tests19 were used to compare the radiographic
Results The measurements of the hip in the dysplastic and normal groups are summarised in Table III. The significant difference between the subgroups with and without OA was found in the FNA, CA and ALA. There were no significant differences between the two subgroups in any other measurements. The mean FNA was 14.42° (SD 4.0) in normal hips and 14.91° (SD 9.85) in dysplastic hips, indicating a similar degree of anteversion (p = 0.12). However, when dysplastic hips were divided into subgroups, the mean FNA was 18.41° (SD 9.75) in the dysplastic subgroup with OA and 12.09° (SD 8.02) in the dysplastic subgroups without OA, indicating a significantly larger degree of anteversion in the dysplastic subgroup with OA (p < 0.001) and less anteversion in the dysplastic subroup without OA (p = 0.002) compared with the normal hips (Fig. 4). Similar results were found in the measurements of the CA. There was a significant difference between the ALA in the dyplastic and normal groups (p = 0.001). Dysplastic hips with OA had the smallest ALA, which was significantly different from that in the normal group (p = 0.004) and in the dysplastic subgroup without OA (p = 0.026). There was a significant negative correlation between the CA and the ALA in dysplastic hips (r = -0.51, p = 0.0001) both in hips with OA (r = -0.43, p = 0.034) and those without OA (r = -0.55, p = 0.0043) (Fig. 5a). FNA was THE BONE & JOINT JOURNAL
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Table III. Various parameters in AD hips and normal hips. All values are presented as mean (SD) Dysplastic hips Total (72 hips) Screening indexes CE (°) AA (°) Femoral measurements FNA (°) ALA (mm) FHC (mm) Neck–shaft angle (°) LFMA (mm) LFAA (mm) Acetabular measurements AcetAV (°) CA (°) Acetabular depth (mm) Anterior centre-edge (°) AASA (°) PASA (°) HASA (°) PRA (°)
OA side (n = 36)
Without OA side (n = 36)
Normal hips (n = 200)
p-value
12.73 (3.56)† 47.10 (2.48)†
12.20 (3.66)† 47.48 (2.71)†
13.34 (3.55)† 46.70 (2.23)†
33.02 (7.33) 41.15 (4.66)
0.26 0.27
14.91 (9.85) 41.02 (6.49)† 94.43 (5.01) 131.22 (7.47)† 399.71 (23.18) 373.58 (22.09)
18.41 (9.75)† 39.10 (5.96)† 94.08 (4.86) 131.8 (7.12)† 399.37 (22.49) 373.31 (22.04)
12.09 (8.02)*† 43.15 (6.49)*† 92.88 (5.22) 130.64 (7.87)† 400.03 (22.86) 373.82 (22.14)
14.42 (4.0) 46.9 (3.54) 93.82 (3.74) 126.45 (5.80) 406.90 (24.51) 378.84 (23.12)
0.016 0.026 0.79 0.59 0.92 0.93
17.42 (5.68) 32.11 (10.01) 18.08 (3.26)† 21.62 (6.06)† 50.13 (7.14)† 86.57 (7.67)† 136.70 (10.83)† 28.51 (3.97)
17.74 (5.75) 35.04 (10.74) 17.97 (3.33)† 20.74 (6.83)† 48.27 (7.88)† 85.64 (8.77)† 133.66 (12.00)† 28.79 (4.30)
17.11 (5.71) 29.18 (8.45)*† 18.30 (3.25)† 22.5 (5.16)† 52.0 (5.90)† 87.59 (6.42)† 139.66 (8.49)† 28.24 (3.64)
18.67 (5.67) 33.37 (4.91) 20.23 (2.03) 26.72 (3.53) 67.66 (4.60) 101.32 (5.41) 168.83 (4.33) 28.12 (2.17)
0.70 0.03 0.71 0.12 0.063 0.40 0.05 0.84
* significant difference † significant difference compared with the normal hips group AD, acetabular dysplasia; OA, osteoarthritis; CE, centre–edge angle; AA, acetabular angle; FNA, femoral neck anteversion angle; ALA, abduction lever arm; FHC, the horizontal distance of the femoral head centre; LFMA, the length of the femoral shaft mechanical axis; LFAA, the length of the femoral shaft anatomical axis; AcetAV-angle, acetabular anteversion angle; CA, combined anteversion angle (FNA+AcetAV-angle); AcetDep, acetabular depth; AASA, anterior acetabular sector angle; PASA, posterior acetabular angle; HASA, horizontal acetabular sector angle; PRA, pelvic rotation angle
*
* *
*
50
35 * *
45 30 40 35
* *
CA (°)
FNA (°)
25
20
15
30 25 20 15
10
10 5 5 0
Normal
AD without OA
AD with OA
Fig. 4a
AD total
AD without OA
AD with OA
AD total
Normal
0
Fig. 4b
Graphs showing a) femoral neck anteversion angle (FNA) and b) combined anteversion angle (CA) against acetabular dysplasia (AD). OA, osteoarthritis. * p < 0.05; ** p < 0.01.
also found to correlate negatively with the ALA in dysplastic hips (r = –0.43, p = 0.002) (Fig. 5b). Other correlations between the various parameters and OA in dysplastic hips VOL. 96-B, No. 12, DECEMBER 2014
are shown in Table IV, and correlations with regard to various parameters in dysplastic hips in Table V. The AcetAv, CA and CE angles were found to correlate with anterior
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AD without OA y = 55.52-0.42x
AD with OA AD without OA
50 AD y = 52.04-0.34x 40 AD with OA 30
AD with OA AD without OA
60 50 ALA (mm)
ALA (mm)
60
y = 47.64-0.24x
20 10
AD without OA y = 45.97-0.23x AD y = 45.43-0.29x AD with OA y = 43.83-0.24x
40 30 20 10
0 0
10
20
30
40
50
60
0 0
10
CA (°)
20
30
40
FNA (°)
Fig. 5a
Fig. 5b
Graphs showing correlation analysis between a) combined anteversion angle (CA) and abduction lever arm (ALA), and b) between femoral neck anteversion angle (FNA) and ALA. AD, acetabular dysplasia.
Table IV. Correlation between the parameters and OA Parameters
Correlation coefficient (rs)
p-value
CE (°) AA (°) Neck–shaft angle (°) FNA (°) AcetAV (°) CA ALA (mm) Anterior centre–edge angle (°) AASA (°) PASA (°) HASA (°)
- 0.33 0.13 0.13 0.31 - 0.07 0.30 - 0.28 - 0.12 - 0.30 - 0.31 - 0.41
0.019 0.36 0.39 0.036 0.62 0.037 0.047 0.43 0.036 0.028 0.002
OA, osteoarthritis; CE, centre-edge angle; AA, acetabular angle; FNA, femoral neck anteversion angle; AcetAV, acetabular anteversion angle; CA, combined anteversion angle; ALA, abduction lever arm; AASA, anterior acetabular sector angle; PASA, posterior acetabular angle; HASA, horizontal acetabular sector angle
acetabular cover of the femoral head. There was a significant negative correlation between the CA and the AASA (r = -0.38, p = 0.006), and also between the AcetAv and the AASA (r = -0.5, p = 0.0002). There was a significant positive correlation between the CE angle and the anterior CE angle (r = 0.34, p = 0.01). According to Mantel–Haenszel estimates of relative risk, in patients who have bilateral acetabular dysplasia the risk of OA occurring in the hip with a larger FNA was five times higher than in the contralateral hip. Similarly, the risk of OA occurring in the hip with a larger CA was three times higher than that of the contralateral hip (p = 0.001). Using the Tönnis and Heinecke classification of FNA,21 16 hips had OA, but in the 22 hips with a FNA < 10° only six had OA (Fig. 6a). The relative risk was 2.93 (p = 0.001). In 12 hips with a CA > 40°, 10 had OA, but in 16 hips with a CA between 20° and 29°, only three had OA (Fig. 6b). The relative risk was 4.44 (p = 0.001). OA occurred mainly in the anterior superolateral area of the hips, although it was also found in the middle superolateral and posterior superolateral aspects of some hips. The anterior superolateral area was found to be
involved in all patients with OA, including 20 in whom only one area was involved (Fig. 7).
Discussion In this study we examined the morphological differences of both the acetabulum and the femur in dysplastic hips with and without OA. Our data strongly suggests that the FNA angle is a significant factor contributing to the development of OA in dysplastic hips. There is still controversy regarding the role of acetabular dysplasia in the causation of OA of the hip in adults. Geometrical measurements of the morphology of the hip taken from radiographs, such as acetabular depth and CE angle, have been investigated previously in OA, with varying results.22 Cross-sectional studies in western European and Japanese populations have supported an association between dysplasia and OA of the hip.23-25 However, Asian, African and Turkish populations appear to have a different prevalence of OA of the hip in relation to acetabular dysplasia, compared with that of western Europeans,26-28 although none of these studies considered the effect of femoral morphology. In our study, THE BONE & JOINT JOURNAL
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Table V. Correlations with regard to various parameters in dysplastic hips AD hips correlation coefficient (p-value) Compared parameters
AD total (72 hips)
AD hips with OA (n = 36)
AD without OA (n = 36)
CE/ AA CE/ Neck–shaft angle CE/ FNA CE/ AcetAV CE/ CA CE/ ALA CE/ Anterior centre–edge CE/ AASA CE/ PASA CE/ HASA FNA/ AcetAV FNA/ ALA FNA/ Anterior centre–edge angle FNA/ AASA FNA/ PASA FNA/ HASA AcetAV-angle/ ALA AcetAV-angle/ anterior centre–edge AcetAV-angle/ AASA AcetAV-angle/ PASA AcetAV-angle/ HASA CA/ ALA CA/ ACE CA/ AASA CA/ PASA CA/ HASA
– 0.44 (0.001) – 0.20 (0.16) – 0.04 (0.77) 0.01 (0.93) – 0.04 (0.79) 0.34 (0.016) 0.34 (0.01) 0.12 (0.42) 0.21 (0.14) 0.22 (0.11) – 0.25 (0.09) – 0.43 (0.002) – 0.05 (0.73) – 0.11 (0.45) – 0.28 (0.05) – 0.27 (0.06) – 0.06 (0.69) – 0.11 (0.45) – 0.5 (0.0002) 0.64 (0.001) 0.12 (0.42) – 0.51 (0.0001) – 0.1 (0.47) – 0.38 (0.006) 0.09 (0.55) – 0.19 (0.19)
– 0.36 (0.07) – 0.37 (0.07) – 0.29 (0.16) – 0.03 (0.89) 0.24 (0.25) 0.35 (0.09) 0.30 (0.14) 0.22 (0.29) 0.26 (0.21) 0.15 (0.40) – 0.17 (0.42) – 0.37 (0.07) 0.12 (0.58) – 0.06 (0.79) 0.1 (0.6) – 0.01 (0.98) – 0.03 (0.87) – 0.11 (0.61) – 0.5 (0.01) 0.57 (0.002) 0.06 (0.77) – 0.43 (0.034) 0.03 (0.9) – 0.35 (0.09) 0.013 (0.95) – 0.01 (0.97)
– 0.51 (0.01) – 0.04 (0.83) – 0.17 (0.42) – 0.03 (0.89) – 0.15 (0.47) 0.19 (0.40) 0.35 (0.08) 0.12 (0.58) 0.02 (0.90) 0.21 (0.30) – 0.29 (0.16) – 0.30 (0.14) – 0.15 (0.46) 0.10 (0.63) – 0.34 (0.06) – 0.30 (0.14) – 0.21 (0.31) – 0.05 (0.81) – 0.61 (0.001) 0.72 (0.001) 0.16 (0.43) – 0.55 (0.0043) – 0.22 (0.28) – 0.30 (0.14) 0.38 (0.06) – 0.2 (0.34)
AD, acetabular dysplasia; OA, osteoarthritis; CE, centre–edge angle; AA, acetabular angle; FNA, femoral neck anteversion angle; AcetAV, acetabular anteversion angle; CA, combined anteversion angle; ALA, abduction lever arm; AASA, anterior acetabular sector angle; PASA, posterior acetabular angle; HASA, horizontal acetabular sector angle
OA hips Without OA hips
OA hips Without OA hips
100
100
75
%
%
75
50
25
0
50
25
0 < 10
15 to 20 10 to 14 FNA (°)
> 20
Fig. 6a
< 20
20 to 29 30 to 40 CA (°)
> 40
Fig. 6b
Graphs showing the ratio of OA hips versus those hips without OA a) when the femoral neck anteversion (FNA) angle was classified as < 10°; 10° to 14°; 15° to 20°; and > 20° and b) when the combined anteversion (CA) angle was classified as < 20°; 20° to 29°; 30° to 40°; and > 40°.
FNA was significantly greater in the dysplastic group with OA than in both the dysplastic group without OA and the control group. In addition, the dysplastic group without OA had a significantly smaller FNA than the control group, VOL. 96-B, No. 12, DECEMBER 2014
whereas the CE was the same in both the dysplastic group with OA and the group without OA groups. Based on our data, we suggest that an abnormal CE alone will probably not influence the occurrence of OA without an increase in
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H. LI, Y. WANG, J. K. ONI, X. QU, T. LI, Y. ZENG, F. LIU, Z. ZHU
Fig. 7 CT scans showing osteoarthritis was present in the anterior superolateral aspect of the hip. L, lateral; M, medial; A, anterior; P, posterior.
FNA. It is possible that a decreased ALA and AASA is the mechanism by which a CA angle contributes to the occurrence of OA. It has been established that the load on the hip during gait is inversely proportional to the length of the ALA.18,29 Therefore, the shorter the ALA, the greater the load on the hip. We found that the dysplastic group with OA group had a significantly smaller ALA and larger FNA angle than the other two groups. So, it is likely that a hip with dysplasia and OA, with its larger CA angle, will have increased pressure on the anterior superolateral surface of the hip where most of the OA was found. Conversely, the dysplastic group without OA had a significantly longer ALA and smaller FNA than the dysplastic group with OA. This longer ALA, and the consequently decreased load across the respective hips, would account for the absence of OA in these hips, despite the presence of dysplasia. The horizontal distance of the FHC was similar in all three groups. This eliminates the influence of the lateral shift of the femoral head on anteversion of the femoral neck. The correlation results showed that FNA had a significantly negative correlation with the ALA, and that AcetAv had a significantly negative correlation with anterior acetabular cover of the femoral head. There have also been various studies on the association between FNA and OA in non-dysplastic hips. Some of these have supported the hypothesis that a persistent increase in FNA leads to a predisposition for OA of the hip.30-32 We suggest that the influence of FNA on OA will be more apparent in dysplastic hips owing to the smaller CE angle, which we found had a significant association with
decreased anterosuperior cover of the femoral head. This finding was similar to that reported in previous studies.1,33,34 In dysplastic hips, deficient anterosuperior cover of the femoral head caused by a decreased CE angle could lead to increased loads across this aspect of the acetabulum if subjected to increased FNA and decreased ALA. Our data suggest that a CA anteversion angle > 40° or FNA > 20° is a valuable reference when contemplating prophylactic pelvic osteotomy. In addition, when dysplastic hips were divided into subgroups, the mean FNA was higher in the dysplastic group with OA and lower in the dysplastic group without OA, but the difference between the two subgroups was small. This suggests that the margin of error for displacement of an osteotomy could pose a significant challenge to surgeons performing joint preservation surgery. Also, in patients in whom a pelvic osteotomy is being considered because of bilateral dysplasia, our results suggest that it should be performed first on the hip with the larger FNA, because the risk of OA developing on this side was five times higher than on the contralateral side. A shortcoming of this study is that only 36 patients from a large number of those with dysplasia of the hip met the selection criteria. However, the comparison of both hips in the same patients helped eliminate many confounding factors and lessened the potential detrimental impact of the small sample size. In addition, in the patients who did not have OA of the hip and whose mean age was 49 years at the time of the study, there is no guarantee that the hips will never develop OA. Furthermore, we are unable to explain why the FNA is different bilaterally in patients with dysplasia. However, these shortcomings do not affect the fact that the FNA significantly influenced the onset of OA in dysplastic hips. This study was supported by National Natural Science Foundation of China (Grant No. 81171729) and Sectors Fund Project of the Ministry of Health of the People’s Republic of China (Grant No. 201302007). No benefits in any form have been received or will be received from a commercial party related directly or indirectly to the subject of this article This article was primary edited by S. Hughes and first proof edited by G. Scott.
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