Articular mobility in Maori and European New Zealanders

P. Klemp1,2,, S. M. Williams3 and S. A. Stansfield4

1 Dunedin Public Hospital, Dunedin, Departments of
2 Rheumatology and
3 Preventive and Social Medicine, Dunedin School of Medicine, Dunedin and
4 Wellington, New Zealand


    Abstract
 Top
 Abstract
 Introduction
 Subjects and methods
 Results
 Discussion
 References
 
Objectives. To determine the prevalence of hypermobility and of the hypermobility syndrome (HMS) in Maori and European New Zealanders.

Methods. The prevalences of generalized hypermobility (Beighton's score >=4), of hypermobility at individual sites and of HMS were determined in 804 Maori and European subjects. Musculoskeletal system (MSS) manifestations were documented in all subjects by personal interview and an MSS examination. Radiographs were obtained where appropriate.

Results. The percentage of hypermobile subjects was 6.2 for Maori (9.0 for females and 2.2 for males) and 4.0 for Europeans (5.6 and 1.9). Hypermobility was more prevalent in females (P=0.0001). Hypermobility of the elbow was more prevalent in Maori (P=0.003) and hyperextension of the fifth finger and apposition of thumb to forearm were more prevalent in females (P<0.001). HMS was present in two of 41 (4.9%, 95% confidence interval 0.6–17.6%) hypermobile subjects. Both were Maori females and therefore 2/23 hypermobile Maori females (8.7%, 1.1–31.4%) had HMS.

Conclusion. The prevalence of hypermobility in Maori is similar to that in European New Zealanders and Caucasians elsewhere. Larger studies are necessary to determine the prevalence of HMS in Maori, particularly Maori females.

KEY WORDS: Prevalence, Hypermobility, Joint laxity, Hypermobility syndrome, Maori, European, New Zealand.


    Introduction
 Top
 Abstract
 Introduction
 Subjects and methods
 Results
 Discussion
 References
 
There are marked ethnic [17], age [2, 6, 811] and gender [2, 3, 6, 9, 1214] differences in articular mobility. A high prevalence of generalized hypermobility has been demonstrated in Iraqi students (29.8%) [3] and in Nigerians (43%) [7] and comparatively low prevalence in Caucasians (~5%) [6]. Asian Indians are more mobile than South African blacks who, in turn, are more mobile than Caucasians [1]. The difference between Asian Indians and Caucasians was noted in a subsequent study [4]. The majority of hypermobile individuals are asymptomatic. However, a few [5] develop the hypermobility syndrome (HMS) [15, 16], which consists of a number of musculoskeletal system (MSS) and other manifestations, such as marfanoid habitus and skin hyperextensibility. It is important to recognize HMS for several reasons: its recognition prevents unnecessary investigation; the condition may mimic other rheumatic diseases; and patients with HMS can be reassured that it generally follows a benign course. As with hypermobility, there are marked ethnic differences in the prevalence of HMS [3, 7]. Joint symptoms as a manifestation of HMS were documented in 13.3% of Iraqi students [3] compared with none in Nigerians [7]. These differences may be related to differences in pain threshold and attitudes to pain.

There are no prevalence figures for either hypermobility or HMS in New Zealand. Because of the reported ethnic variation, we estimated prevalence for hypermobility and HMS in Maori and European New Zealanders to provide an indication of the role of hypermobility as a cause of MSS and other manifestations in the country.


    Subjects and methods
 Top
 Abstract
 Introduction
 Subjects and methods
 Results
 Discussion
 References
 
This study was part of an epidemiological survey of rheumatic disease conducted in Rotorua, which has a population of 65 000. The people are predominantly Maori and Europeans in the geothermal region of the North Island, Maori of the Arawa tribe in Whakarewarewa on the outskirts of Rotorua and Maori of the Tuhoe (‘Children of the Mist’) tribe in Ruatahuna, an isolated village with a population of approximately 280, situated 165 km from Rotorua. Random selection of Maori and Europeans aged 5 yr and older living in Rotorua was done by selecting every 40th name in order of appearance in the 1992 Rotorua District Council electoral role and the 1990 Eastern Maori District Habitation Index and from randomly selected schools, classes within these schools and children within these classes. Letters inviting participation in the survey were sent to adults and to parents or guardians of children. Letters of reminder were sent to non-responders. Eight responders who were neither Maori nor European were excluded from the study. The acceptance rate was 380/984 (38.6%) for adults and 73/170 (42.9%) for children, giving an overall acceptance rate of 39.3%. Random selection of Maori of the Arawa and Tuhoe tribes was not possible because traditional beliefs favour participation by all as opposed to random selection. Two senior members of each tribe were therefore elected by the elders to recruit and to interview as many members of the respective tribes as possible. The response rate from the Arawa tribe was 75%, as estimated by the health carers, and 175/280 (62.5%) from the Tuhoe tribe. Informed consent was obtained from each subject, parent or guardian and the following data were documented by personal interview and examination of all subjects, using a standard questionnaire. (i) Demographic details, comprising age, gender and ethnic group. Data from the Arawa and Tuhoe tribes were obtained by the health carers. Individuals were classified Maori if they claimed 25% or more Maori ancestry. (ii) A general medical history and a detailed current and past rheumatological history. Answers were entered as ‘yes’, ‘no’ and ‘don't know’. If an answer was declined, the question was left blank. (iii) A physical examination was made of the MSS and any abnormal findings were recorded. These included evidence of non-articular rheumatism, such as tendinitis, bursitis, enthesopathy and ligamentous instability; synovitis; osteoarthritis; body habitus; skin elasticity and any other extra-articular manifestations. In the analysis, only subjects with manifestations consistent with HMS were included. Subjects with defined rheumatic disorders, such as rheumatoid arthritis, crystal-induced arthropathy and seronegative arthropathy, were excluded. Radiographs were obtained to assist with diagnosis where appropriate. The method of Beighton et al. [2] was used to determine articular mobility. Hypermobility was defined as a score >=4/9. Hypermobility at individual sites was also documented. HMS was diagnosed using earlier clinical descriptions [5, 15], as the study predated the current draft diagnostic criteria for HMS [16].

Statistical methods
The {chi}2 test was used to make simple comparisons between two groups. Logistic regression was used to adjust for age and sex when making comparisons between Maori and Europeans, and for age and ethnicity when making comparisons between males and females. Adjustments for age were made using 5-yr age groups.


    Results
 Top
 Abstract
 Introduction
 Subjects and methods
 Results
 Discussion
 References
 
Demography
Data were complete for 792 (98.5%) of the 804 subjects aged >=5 yr. These 792 subjects comprised 438 Maori (182 males, mean age 30.49 yr, S.D. 20.22; and 256 females, mean age 35.06 yr, S.D. 19.03) and 354 Europeans (159 males, mean age 45.54 yr, S.D. 19.92; and 195 females, mean age 46.10 yr, S.D. 19.93).

Articular mobility
The prevalences of hypermobility in Maori and Europeans and in males and females are shown in Table 1Go. After adjusting for age and gender, there was no ethnic difference in the prevalence of hypermobility (P=0.86) but after adjusting for age and ethnicity the prevalence of hypermobility was significantly higher in females (P=0.0001).


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TABLE 1.  Prevalence of hypermobility in Maori and European males and females

 
Percentage frequencies for each score (0–9) in Maori and Europeans are shown in Fig. 1Go. The majority had a score of 0 (78% of Maori males, 89.9% of European males, 57.8% of Maori females and 76.4% of European females). The curve for each distribution was similar across the four groups apart from a tendency for more Maori women to have a score of 2. No subject scored >7. Comparison of mobility by age group showed that the score fell sharply in both Maori and European males, so that by age 20 yr most scored <=1. The decrease was more gradual in both Maori and European females but after age 30 yr most also scored <=1.



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FIG. 1.  Percentage frequencies of mobility scores 0–9 in Maori and European males and females.

 
Hyperextension of the elbow was significantly more common in Maori (P=0.003) after adjusting for age and gender, and hyperextension of the fifth finger and elbow and apposition of thumb to forearm were significantly more common in females (P<0.001) after adjusting for age and ethnicity. None of the interactions between ethnicity and gender was significant.

Of the 41 hypermobile individuals [mean age 23.4 yr, S.D. 16.76; 27 Maori (4 males, 23 females) and 14 Europeans (3 males, 11 females)], 33 (80.5%) had no MSS complaints, past or present. Features consistent with HMS were present in 2/41 (4.9%, 95% confidence interval 0.6–70.6%). One, a Maori female aged 29 yr with mobility score 7, had longstanding polyarthritis with no evidence of an inflammatory or other arthropathy, and the other, a Maori female aged 44 yr with mobility score 4, had polyarthralgia and non-articular rheumatism, including partial rupture of the left Achilles tendon after minor trauma. The prevalence of HMS in Maori females was therefore 2/23 (8.7%, 95% confidence interval 1.1–31.4%). The remaining six (14.6%) hypermobile individuals with MSS manifestations were not considered to have HMS (three had transient, mild arthralgia of knees; two elderly females had generalized osteoarthritis clinically and radiologically; and one male had intermittent lumbar backache with normal lumbosacral radiographs.


    Discussion
 Top
 Abstract
 Introduction
 Subjects and methods
 Results
 Discussion
 References
 
The 6.2% prevalence of hypermobility in Maori was similar to that of European New Zealanders in our study and, allowing for differences in age, gender and methods, similar to that of population studies in Caucasians elsewhere [6] but considerably lower than prevalence figures from Iraq [3] and West Africa [7]. The rapid reduction in mean mobility scores in both Maori and Europeans by age 20 yr [2, 4] and the higher prevalence of hypermobility in females [2, 3, 6, 9, 1214] are well documented. In our discussions with Maori, the higher prevalence of hyperextension of elbows in Maori males and females does not appear to be acquired through an activity specific to the Maori way of life and is therefore likely to be genetic. A possible explanation for the similarity of prevalence figures for hypermobility in Maori and Europeans is genetic admixture. The definition of Maori as having 25% or more Maori ancestry is arbitrary and controversial but is accepted and applied by most investigators in epidemiological studies.

Our demonstration that HMS is uncommon is in agreement with most other studies. Of possible significance is that both subjects in our study with HMS were Maori females, giving a prevalence of 8.7%. This raises the possibility that HMS may be relatively common in Maori females. The numbers are, however, small and larger studies are necessary to investigate this further.

The non-random recruitment imposed by the tribes, which yielded a high response rate, and the random selection, which yielded a low response rate, may be sources of bias. However, having excluded responders who were neither Maori nor European from the study, we believe that our sample is genetically representative of Maori and Europeans living elsewhere in New Zealand. Another possible source of bias is that, as hypermobility is determined genetically [17], members of the same family in the closely-knit tribes may have been included in the hypermobile group and inflated the prevalence figure. As far as we could establish, this did not occur. To determine whether hypermobile subjects from the tribes included at least one family member, we examined the names and addresses of all the hypermobile subjects from the tribes. For reasons of privacy and cultural sensitivity, it was considered inappropriate to question the subjects directly. None of the Arawa tribe had either the same surname or the same address. Of the Tuhoe subjects, two children, aged 5 and 6 yr, had the same surname. It was not possible to determine whether they were related as the elders who obtained the demographic data gave the same postal address for all participants (a post office box number), not the street address of each. We do not believe that exclusion of one of the children on grounds of being either a sibling or cousin would alter the prevalence figures substantially. The analysis included adjustment for the age differences in the two samples. We believe that obtaining data, as we did in our study, by personal interview and physical examination of all subjects whether or not they had MSS complaints has an advantage over the use of self-administered questionnaires. The former method is regarded as appropriate and more accurate than the latter method for demographic data in Maori, particularly with respect to determining ancestry, which was obtained by senior members of the tribe. Beighton's method for determining articular mobility was used because it is simple to perform, is currently the most commonly used method and as such allows comparison in epidemiological studies. Articular mobility is a graded phenomenon [2] and there is no precise cut-off point for determining hypermobility. Most investigators use a score >=4/9 to indicate hypermobility [18].

In conclusion, while we acknowledge that selection bias may be a factor in our study, this will be a factor in any Maori study because of traditional tribal beliefs. On the assumption that our sample is representative of the country as a whole, the study has merit in that it is the first report on hypermobility from New Zealand.


    Acknowledgments
 
The study was funded by the William Barkla Research Fund, Queen Elizabeth Hospital, Rotorua. We thank the nominated members of the Arawa and Tuhoe tribes for recruiting volunteers and for their assistance in obtaining the demographic data.


    Notes
 
Correspondence to: P. Klemp, Department of Medicine, Dunedin School of Medicine, P.O. Box 913, Dunedin, New Zealand. Back


    References
 Top
 Abstract
 Introduction
 Subjects and methods
 Results
 Discussion
 References
 

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Submitted 3 March 2000; Accepted 9 November 2001