Prevalence of hip osteoarthritis and acetabular dysplasia in French and Japanese adults

K. Inoue, P. Wicart1, T. Kawasaki, J. Huang, T. Ushiyama, S. Hukuda and J.-P. Courpied2

Department of Orthopaedic Surgery, Shiga University of Medical Science, Otsu, Japan,
1 Chirurgie Orthopédique, Hôpital Saint-Joseph, Paris and
2 Service d'Orthopédie, Hôpital Cochin, Paris, France


    Abstract
 Top
 Abstract
 Introduction
 Subjects and methods
 Results
 Discussion
 References
 
Objective. To determine ethnic variations of acetabular morphology, and to delineate their relationship with hip osteoarthritis (OA).

Methods. Radiographs of 283 French men, 118 French women, 414 Japanese men and 368 Japanese women, aged 20–79 yr, who underwent intravenous urography were assessed by a single observer for morphometric measurement and hip OA scoring.

Results. The standardized morbidity ratio (SMR) for hip OA was highest in French men and lowest in Japanese men, whereas the SMR for acetabular dysplasia was highest in Japanese women and lowest in French men. French men and women had the highest centre–edge angle, followed by Japanese men then Japanese women.

Conclusion. In a large number of subjects assessed by a single observer, this study confirms other previous reports that the relationship between acetabular dysplasia and risk of hip OA is negative.

KEY WORDS: Acetabular morphology, Minimal joint space, Hip osteoarthritis, French, Japanese.


    Introduction
 Top
 Abstract
 Introduction
 Subjects and methods
 Results
 Discussion
 References
 
The prevalence of osteoarthritis (OA) appears to vary widely among ethnic groups. The characteristic differences between Caucasian and Japanese people found in a population-based radiographic study of OA performed in the early 1970s in Kamitonda, Japan, were a lower prevalence of hip OA and first carpometacarpal joint OA [1, 2] in the Japanese population when compared with results of a study in Leigh, UK [3]. Recent studies by British researchers, using radiographs of older adults who underwent an intravenous urogram (U), showed a far lower prevalence of acetabular dysplasia in the UK than in Japan [4, 5]. Subsequently, their co-workers performed similar studies for Hong Kong Chinese men [6], Nigerian men [7] and Japanese men and women [8]. The overall result of these studies does not support a positive relationship between the prevalence of hip OA and that of acetabular dysplasia, which is contrary to the classical concept that insufficient acetabular coverage is a cause of hip OA.

Previous studies on the pelvic morphology of Japanese were based on pelvic radiographs (P) [1, 8], whereas recent studies by British researchers used U [47]. Our previous study, which tested the comparability of pelvic radiomorphometric variables, showed that a direct comparison of some variables between U and P was unjustified. In the present study, a large number of French and Japanese adults, who had undergone U, were examined for the purpose of evaluating the relationship between acetabular morphology and hip OA frequency. To avoid inter-observer errors, all films were assessed by a single observer.


    Subjects and methods
 Top
 Abstract
 Introduction
 Subjects and methods
 Results
 Discussion
 References
 
A consecutive series of subjects aged between 20 and 79 yr, who underwent an intravenous urogram during early 1994 at the urology department of Cochin Hospital in Paris, or between 1992 and 1993 at the first author's hospital in Japan, were examined. The control film taken during urography was used for assessing the hip joints. In some subjects, the hip was not well visualized or in an inappropriate position due to lumbar kyphosis, so these subjects were excluded. Two men with typical findings of ankylosing spondylitis were also excluded. Thirteen subjects had already undergone hip surgery. Eleven of these were included in the study as having hip OA either by reviewing preoperative radiographs or by OA findings in the contralateral hip, while the other two were excluded because they had had either rheumatoid arthritis or tuberculous coxitis. In three Japanese, the femoral head of one side was dislocated, the original acetabulum being hypoplastic and the femoral head deformed. They were included in the study as having both hip OA and acetabular dysplasia. In total, 1183 subjects were included in the present study. The numbers of subjects aged 20–39, 40–59 and 60–79 yr were 42, 102 and 139 respectively for French men, 68, 186 and 160 for Japanese men, 44, 41 and 33 for French women, and 53, 170 and 145 for Japanese women.

All films were assessed by a single observer (K.I.). Radiographic OA was defined by the conventional Kellgren and Lawrence (K-L) scale [9]. Subjects with grade 3 or higher in at least one hip were defined as having OA. The 11 subjects who had already undergone joint surgery for hip OA and three additional subjects with a dislocated hip were also defined as having hip OA.

After assessing OA, minimal joint space (MJS) was measured. MJS was defined as the shortest distance between the femoral head margin and the acetabulum, and was measured to the nearest 0.1 mm using callipers. Tracing paper was placed over the film; the points were marked, lines were drawn, the margin of the femoral head was traced, and the centre–edge (CE) angle and acetabular depth were measured [4]. In cases of acetabular dysplasia, the CE angle and acetabular depth are low. When determining the lateral margin of an acetabulum showing enthesial ossification, if there was osteophytosis, the margin of the osteophyte was regarded as the lateral margin of the acetabulum. Because of previous joint surgery, dislocated hip, marked osteoarthritic change or other reasons, radiomorphometric variables were not measured for some hips (19 hips for MJS, 48 hips for CE angle and 51 hips for acetabular depth).

Hips showing a CE angle of <25° were defined as having acetabular dysplasia. The prevalence of hip OA was calculated with respect to subject and that of acetabular dysplasia with respect to the hip joint.

To evaluate within-observer errors, radiomorphometric variables were assessed by the same observer (K.I.) reading a subset of 50 Japanese hips at an interval of 12 months.

Student's t-test, Pearson's {chi}2 test and Fisher's exact probability test were used for comparison between the two groups. Pearson's correlation coefficients were calculated when appropriate. To adjust for age distribution, a standardized morbidity ratio (SMR), standardized to the age distribution of Japanese men, was calculated for hip OA and acetabular dysplasia, with age stratified by 5-yr intervals.


    Results
 Top
 Abstract
 Introduction
 Subjects and methods
 Results
 Discussion
 References
 
The prevalence of hip OA by ethnicity and sex is shown in Table 1Go. The crude prevalence was highest in French men (5.7%), followed by Japanese women (3.5%), French women (2.5%) and Japanese men (1.4%). The difference between ethnic groups was significant for men (P = 0.002). SMR was 389 (95% confidence interval 199–580) for French men, 100 for Japanese men, 168 (0–357) for French women and 254 (116–392) for Japanese women. SMR was significantly higher for French men (P < 0.001) and Japanese women (P < 0.001) than for Japanese men.


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TABLE 1. Crude prevalence and SMR of hip osteoarthritis and acetabular dysplasia

 
The prevalence of acetabular dysplasia by ethnicity and sex is also shown in Table 1Go. The crude prevalence was highest in Japanese women (11.6%), followed by French women (5.6%), Japanese men (5.1%) and French men (1.8%). The difference between ethnic groups was significant for both genders, and that between genders was significant for both ethnic groups. SMR was 37 (95% confidence interval 14–60) for French men, 100 for Japanese men, 79 (36–122) for French women and 231 (181–281) for Japanese women. SMR for French men was significantly lower (P < 0.001) and that for Japanese women significantly higher (P < 0.001) than that for Japanese men.

An analysis of radiomorphometric variables was made separately for the right and left hips and for both hips combined. The results were essentially similar, hence only data for both hips combined are shown in Table 2Go by ethnicity and sex. For both men and women, French subjects showed a significantly higher MJS than Japanese. In French subjects a sex difference was not obvious, whereas Japanese men had a significantly higher MJS than Japanese women. For both genders, French subjects had a significantly higher CE angle than Japanese. In the French subjects there were no sex differences, whereas Japanese men had a significantly higher CE angle than Japanese women. Thus, the mean CE angle was highest in French men and women, followed by Japanese men, and lowest in Japanese women. Similarly, French subjects had a significantly higher acetabular depth than Japanese for both sexes. A higher acetabular depth in men than in women was seen for both French and Japanese.


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TABLE 2. Radiomorphometric variables and correlation coefficients

 
Pearson's correlation coefficients between MJS and CE angle were invariably negative, regardless of ethnicity and sex, all P values being <0.001. The correlation coefficients between MJS and acetabular depth were also negative in all subgroups. However, the relationship between them was not as strong as that between MJS and CE angle (Table 2Go). To exclude the possible effects of acetabular osteophytosis in determining CE angle, we analysed separately the hips of subjects aged <60 yr, which had a K-L grade of 0. There was a significant inverse relationship between MJS and CE angle regardless of ethnicity and sex (data not shown).

The means of the differences within the observer were 0.2 mm for MJS, 1.7° for CE angle and 0.7 mm for acetabular depth.


    Discussion
 Top
 Abstract
 Introduction
 Subjects and methods
 Results
 Discussion
 References
 
The present study showed that hip OA is commoner in French than Japanese populations, while acetabular dysplasia is commoner in women than men and commoner in Japanese than French. In a large number of subjects evaluated by a single observer, our results confirmed other previous findings that acetabular dysplasia does not seem to be a risk factor for hip OA [48].

If a shallow acetabulum is not a risk factor, then it could logically be considered either irrelevant or a protective factor. In the present study, MJS was inversely related to CE angle. A similar inverse relationship between MJS and CE angle in older people has been described in previous reports [4, 5, 8]. One possible explanation for this phenomenon is that changes in hip joint geometry as a result of OA may be responsible, as suggested by Smith et al. [5]. In the present study, in which a number of younger and middle-aged adults were included, an inverse relationship was also seen in their hips, in which OA had a K-L score of 0. This could lead to another explanation: that a low CE angle is a favourable factor for articular cartilage. Physiologically, nutrition for the articular cartilage could be received more efficiently by the cartilage of individuals having a smaller concave facet in a relatively congruent joint such as the hip. However, this postulation is contradictory to the evidence that hip OA is more common in Japanese women, who have a shallow acetabulum than in Japanese men. Although the reason why the CE angle is inversely related to MJS is uncertain at present, it would be reasonable to speculate that a shallow acetabulum is not a protective factor but is irrelevant for the development of hip OA. Factors other than acetabular shape need to be considered in order to explain the varied prevalence of hip OA


    Acknowledgments
 
We would like to thank Professor B. Debere of Cochin Hospital and Professor T. Tomoyoshi and Professor Y. Okada of Shiga University of Medical Science Hospital, who kindly permitted our review of the radiographs. This study was supported in part by grants-in-aid for scientific research from the Ministry of Education, Science, and Culture of Japan (10671356) and by the Société Franco-Japonnaise d'Orthopédie (SOFJO).


    Notes
 
Correspondence to: K. Inoue, Department of Orthopaedic Surgery, Shiga University of Medical Science, Setatsukinowa-cho, Otsu, Shiga, 520–2192, Japan. Back


    References
 Top
 Abstract
 Introduction
 Subjects and methods
 Results
 Discussion
 References
 

  1. Ota H. Prevalence of osteoarthritis of the hip and other joints in Japanese population. J Jpn Orthop Assoc1979;53:165–80.
  2. Inoue K, Shichikawa K, Ota H. Prevalence of hip osteoarthritis and acetabular dysplasia in Kamitonda: from a longitudinal population-based epidemiological study of rheumatic diseases in Japan. Rheumatology1999;38:793–4.[Free Full Text]
  3. Kellgren JH, Lawrence JS. Osteoarthrosis and disc degeneration in an urban population. Ann Rheum Dis1958;17:388–97.[ISI]
  4. Croft P, Cooper C, Wickham C, Coggon D. Osteoarthritis of the hip and acetabular dysplasia. Ann Rheum Dis1991;50;308–10.[Abstract]
  5. Smith RW, Egger P, Coggon D, Cawley MID, Cooper C. Osteoarthritis of the hip joint and acetabular dysplasia in women. Ann Rheum Dis1995;54:179–81.[Abstract]
  6. Lau EMC, Lin F, Lam D, Silman A, Croft P. Hip osteoarthritis and dysplasia in Chinese men. Ann Rheum Dis1995;54:965–9.[Abstract]
  7. Ali-Gombe A, Croft PR, Silman AJ. Osteoarthritis of the hip and acetabular dysplasia in Nigerian men. J Rheumatol1996;23:512–5.[ISI][Medline]
  8. Yoshimura N, Campbell L, Hashimoto T, Kinoshita H, Okayasu T, Wilman C et al. Acetabular dysplasia and hip osteoarthritis in Britain and Japan. Br J Rheumatol1998;37:1193–7.[ISI][Medline]
  9. Kellgren JH, Lawrence JS. Radiological assessment of osteoarthritis. Ann Rheum Dis1957;16:494–502.[ISI]
Submitted 28 July 1999; revised version accepted 10 January 2000.



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