Are Asian hands more flexible than their Caucasian counterparts?

Abstract

Introduction

Though there is a general perception that Asian hands have an increased range of movements in all their joints, there is very little written in the literature on this topic. Our unit caters to a multiethnic population and it has been our experience that the outcomes after hand surgery are generally better in Asian hands. This study was aimed at comparing the range of movements between two cohorts of volunteers: Asians and Caucasians.

Methods

Data were collected on their ethnicity, gender, age, handedness and any medical conditions. The Beighton score was measured for all subjects and range of movements was measured using a standard goniometer. Totally, 114 subjects were enrolled into the study, which included 53 men (46%).

Results

There were 59 Caucasians and 55 Asians. The range of movements of wrist and hand was greater in Asians and the difference was statistically significant (p < 0.05). Men in general had greater range of movement of the fingers whereas women had greater range of movement of the thumb. There was no difference between Asian men and women with regard to wrist movements. However, Caucasian women had greater wrists movements than Caucasian males. The average Beighton score was the highest in Asian women (7), followed by Asian men (6). Caucasian men and women had an average Beighton Score of 2.

Discussion

Normative data for different ethnic groups are important for hand therapy as they can guide rehabilitation protocols. Our study demonstrates that a difference in hand flexibility between British Asians and their Caucasian counterparts exists.

Keywords

Orthopaedics quantitative research statistics

Introduction

In patients with hand injuries, a successful outcome critically depends on effective, individualized rehabilitation protocols.^1,2 Many flexor and extensor post-injury protocols were based on data from studies of Caucasian patients.^3–9 However, several small studies have indicated that joint mobility depends on a number of factors, including sex and ethnicity.^7–12 Occupation has also been shown to be important in joint mobility.^13–15 Previous studies have demonstrated that ballet dancers have increased levels of flexibility.^13–20 Genetics has also been shown to play a role in joint flexibility.²¹ Hand injuries can have psychosocial as well as physical implications.^22–24 Patient’s cultural or psychosocial perceptions may affect their outcome after tendon rehabilitation. Psychosocial problems may impact on the patient’s work, activities of daily living and ultimately their independence.²⁵ The effect of stress may influence motivation to engage in therapy.²⁶

In our hand surgery unit, which serves a mixed Caucasian and Asian population, there is a perception that patients of Asian origin have increased joint mobility, and that this may lead to better postoperative outcomes and an adjustment of hand protocols to suit.

While the exact reason for this is not clear, it could either be due to the increased pre-operative flexibility of their hands or because the healing mechanisms in these patients are different. A recent study demonstrated a difference in hand grip strength between different ethnic groups.²⁷ However, there has been little published data on the normal range of movement (ROM) of the small joints of the hand in different ethnic subgroups.

Our aim was to compare the range of movement in the hand in healthy Caucasian and Asian subjects and provide normative values.

Methods

British Asian (A) and Caucasian (C) medical students at the local university were invited to participate in the study. For the purpose of this study, ‘Asian’ was defined as those people with ancestry from the Indian subcontinent such as India, Pakistan, Bangladesh and Sri Lanka. Informed consent was obtained. The local hospital governance department approved the study. Other ethnic groups, including non-British Asians, were excluded to minimize any possible geographical variations. Anyone with a history of hand/wrist injury/surgery at any time previously were excluded. Those with current pain symptoms in the hands/wrists were also excluded. Furthermore, those with a connective tissue disorder (e.g. Ehlos-Danlos, Marfan’s, Osteogenesis Imperfecta) were excluded. Benign Joint Hypermobility Syndrome is characterized by an increase in Beighton score and multiple joint pain. Anyone who had painful joints was not invited to participate in the study. These exclusion criteria were chosen to get values for healthy individuals and minimize any confounding factors.

Demographics of the subjects were documented, including age, gender, handedness and participation in sports.

Small joint active movements in the dominant hand were measured in degrees using a standard goniometer, and Beighton scores^22,28 were also recorded. Degrees of flexion and hyperextension of the metacarpophalangeal (MCPJ) and interphalangeal joints (proximal, PIPJ and distal, DIPJ) of the thumb and fingers were recorded. Thumb abduction and hyperextension were also measured using degrees. For opposition, the Kapandji scale²⁹ was utilized. Degrees of wrist flexion, hyperextension, radial and ulnar deviation were recorded. A standard goniometer was used to make all these measurements.

Measurements were taken by the main author (MS) and KB who is a specialist hand therapist using a standard technique.³⁰ Each measurement was done twice and the average was recorded. KB and MS were present in all the measurements to ensure there were no discrepancies. Moreover, they each measured 10 of the same hands separately to ensure there was no statistical difference in the measurements.

Measurements were expressed as medians and 25/75% interquartiles (IQ). Groups were compared using univariate analysis of variance (ANOVA). The p values < 0.05 were considered to be statistically significant. Confidence intervals (95%) were included.

Results

A total of 114 subjects were enrolled into the study, which included 53 men (46%). Mean age was 19 ± 0.7 years. Fifty-five subjects (48%) were Caucasians. For purposes of data analysis, the subjects were divided into four categories: Asian male (AM; N = 28), Asian female (AF; N = 32), Caucasian male (CM; N = 25) and Caucasian female (CF; N = 30). Twelve subjects (11%) were left-handed. One subject performed gymnastics at regional level. Median Beighton scores are presented in Table 1.

Table 1.

Beighton scores.

Asian male	Asian female	Caucasian male	Caucasian female
Beighton score	6 (5,6) [6,7]^a	7 (5,8) [6,8]^a	2 (1,3) [2,3]	2 (1,3) [1,3]

Values show medians (25,75 quartiles) [95% confidence intervals].

Compared to white subjects of the same sex (p < 0.05).

Finger joints

The median degree of hyperextension of all finger joints was significantly higher in Asians compared to Caucasians (men and women) (see Table 2), with the exception of hyperextension of the distal IPJ of the middle, ring and little fingers in women, which were comparable. For example, median hyperextension of the index MCPJ in Asian men was 21° (IQ 18/24) compared to 8° (IQ 5/11) in Caucasian men (p = 0.001). Asians had higher degrees of flexion in the majority of finger joints, except for index MCPJ, ring MCPJ (men), middle/ring/little PIPJ (women) and index DIPJ (women).

Table 2.

Finger joints.

Index	Middle	Ring	Little
Hyperextension in °
MCP
AM	−21 (−18,−24) [−19,−23]^a	−25 (−22,−31) [−21,−29]^a,b	−23 (−22,−27) [−20,−26]^a	−25 (−19,−30) [−20,−30]^a
AF	−25 (−24,−30) [−23,−28]^a	−22 (−18,−23) [−20,−24]^a	−24 (−18,−27) [−22,−27]^a	−22 (−18,−25)^a [−21,−24]
CM	−10 (−5,−12) [−7,−13]	−7 (−5,−8) [−6,−8]^b	−14 (−6,−15) [−11,−17]	−10 (−8,−12) [−8,−12]
CF	−10 (−5,−11) [−7,−12]	−11 (−8,−12) [−10,−12]	−13 (−11,−14) [−12,−14]	−11 (−7,−16) [−8,−14]
PIP
AM	−13 (−9,−20) [−7,−19]^a	−12 (−7,−15) [−9,−15]^a	−21 (−8,−22) [−14,−28]^a	−12 (−5,−18) [−5,−19]^a
AF	−16 (−11,−22) [−12,−19]^a	−12 (−10,−16) [−9,−15]^a	−17 (−14,−24) [−12,−21]^a	−9 (−6,−12) [−6,−11]^a
CM	−10 (−8,−12) [−9,−11]^b	−7 (−2,−8) [−5,−9]	−10 (−4,−11) [−7,−13]	−10 (−2,−11) [−7,−13]^b
CF	−3 (−2,−7) [−1,−5]	−8 (−5,−10) [−6,−9]	−11 (−3,−12) [−8,−13]	−1 (0,−5) [0,−2]
DIP				−1 (0,−5) [0,−2]
AM	−16 (−11,−20) [−11,−21]^a	−11 (−10,−15) [−9,−13]^a	−9 (−8,−12) [−7,−11] ^b	−17 (−10,−22) [−12,−22]^a
AF	−15 (−12,−17) [−13,−17]^a	−13 (−12,−16) [−12,−15]	−18 (−14,−24) [−14,−22]	−18 (−12,−22) [−15,−21]
CM	−7 (−6,−11) [−6,−8]	−8 (−6,−10) [−6,−10]^b	−8 (−7,−10) [−7,−9]^b	−6 (−6,−15) [−1,−10]^b
CF	−8 (−8,−10) [−7,−9]	−12 (−6,−16) [−9,−14]	−17 (−12,−22) [−12,−22]	−20 (−9,24) [−14,−26]
Flexion in °
MCP
AM	65 (57,88) [55,75]	83 (−78−88) [78,88]^a	70 (67,88) [66,74]^b	68 (63,70) [65,71]^a,b
AF	74 (58,85) [66,82]	83 (80,90) [78,88]^a	87 (74,94) [80,94]^a	79 (72,90) [72,87]^a
CM	65 (55,70) [58,72]	70 (69,78) [66,74]	68 (60,70) [66,70]^b	59 (55,60) [57,61]^b
CF	60 (55,66) [56,64]	75 (70,80) [72,77]	57 (51,64) [53,61]	55 (53,60) [53,57]
PIP
AM	100 (87,105) [92,108]^a,b	99 (96,101) [98,100]^a,b	101 (99,103) [99,103]^a,b	98 (93,100) [95,101]^a,b
AF	89 (82,98) [93,94]^a	83 (78,96) [78,88]	89 (84,99) [82,96]	88 (78,98) [81,96]
CM	88 (75,88) [84,92]^b	90 (83,100) [82,98]	92 (88,95) [89,95]	84 (80,91) [79,89]^b
CF	77 (58,89) [67,87]	87 (80,90) [83,91]	90 (88,94) [89,91]	80 (76,84) [77,83]
DIP
AM	70 (67,75) [67,73]^a	91 (89,97) [87,94]^a,b	85 (78,88) [81,89]^a	90 (82,95) [86,94]^a
AF	74 (66,82) [66,82]	88 (80,98) [81,96]^a	85 (70,94) [74,96]^a	86 (78,94) [81,92]^a
CM	68 (62,70) [64,72]	80 (70,91) [75,85]^b	68 (65,68) [67,70]^b	70 (59,72) [64,76]^b
CF	63 (51,72) [55,71]	71 (66,77) [66,75]	54 (40,60) [46,62]	53 (46,61) [48,58]

Values show medians, (25,75 quartiles) and [95% confidence intervals].

AM: Asian male; AF: Asian female; CM: Caucasian male; CF: Caucasian female.

Compared to white subjects of the same sex (p<0.05).

Compared to women of the same ethnicity (p<0.05).

There was no difference between Asian men and Asian women in the range of hyperextension in the majority of finger joints, with the exception that Asian men had a greater degree of hyperextension of the middle MCPJ (25° vs. 22°, p < 0.05) and a reduced degree of hyperextension of the ring DIPJ (9° vs. 18°, p < 0.05). Compared to Caucasian women, Caucasian men had reduced hyperextension of the middle MCPJ (7° vs. 11°, p < 0.05), middle DIPJ (8° vs. 12°, p < 0.05), ring DIPJ (8° vs. 17°, p < 0.05) and little DIPJ (6° vs. 20°, p < 0.05). Caucasian men had greater hyperextension of the little PIPJ than Caucasian women (10° vs. 1°, p < 0.05).

Asian men had greater flexion of the ring and little MCPJs compared to Asian women, whilst Caucasian men had significantly less flexion of these joints than Caucasian women (Table 2). Differences in flexion of the IP joints between genders were also influenced by sex. For example, Asian men had greater flexion of all four MCPJs compared to Asian women, whilst a gender difference was only apparent in Caucasians for index and little MCPJs. By contrast, Caucasian men had greater flexion of the DIPJs in three fingers (middle, ring and little) compared to Caucasian women, whilst a gender difference was only observed in Asians for the middle DIPJ.

Thumb joints

Asians had greater hyperextension of the thumb MCPJ and IPJ, except for the IPJ in Asian men, which had reduced hyperextension compared to Caucasian men (14° vs. 26°, p < 0.05). With regard to flexion, the ethnic difference was influenced by gender. A greater degree of flexion of the thumb MCPJ was observed in women only (58° vs. 45°, p < 0.05), whilst greater flexion of the thumb IPJ was observed in men only (74° vs. 60°, p < 0.05).

There was a greater degree of thumb abduction and hyperextension in Asians compared to Caucasians, whilst there was no such observed difference in the Kapandji scale (Table 3).

Table 3.

Thumb joints.

Asian male	Asian female	Caucasian male	Caucasian female
MCP
Flexion in °	45 (37,50) [42,48]^a	58 (42,68) [51,66]^b	43 (35,45) [38,45]	45 (40,45) [44,46]
Hyperxtension in°	−18 (−16,−21) [−15,−21]^a,b	−30 (−26,−32) [−29, −31]^b	−11 (−4, −13) [−7, −15]^a	−12 (−10, −15) [−11, −13]
IPJ
Flexion in °	74 (71,77) [72,76]^b	71 (55,90) [57,85]	60 (45,60) [53,67]^a	76 (69,80) [71,81]
Hyperextension in °	−14 (−11,−17) [−11,−17]^a,b	−25 (−16,−28) [−21,−28]^b	−26 (−22,−26) [−25,−28]^a	−11 (−7, −16) [−9, −13]
Abduction in °	18 (37,40) [16,20]^b	17 (12,16) [16,18]^b	15 (12,16) [13,17]^a	11 (10,12) [10,11]
Kapandji score	10^a	10	10^a	10

Values show medians, (25,75 quartiles) and [95% confidence intervals].

Compared to women of the same ethnicity (p < 0.05).

Compared to white subjects of the same sex (p < 0.05).

There was a greater degree of hyperextension of the thumb MCPJ and IPJ in women, with the exception that Caucasian men had greater extension of the IPJ than Caucasian women (26° vs. 11°, p < 0.05). Women had a greater degree of flexion of MCPJ in Asians only (58° vs. 45°, p < 0.05) and IPJ in Caucasians only (76° vs. 60°, p < 0.05). A greater degree of hyperextension was observed in Caucasians only (6° vs. 4°, p < 0.05).

Wrist joint

Asians had significantly greater degrees of all wrist movements compared to Caucasians, with the exception of flexion in male subjects (p < 0.05) (see Table 4).

Table 4.

Wrist joints.

Asian male	Asian female	Caucasian male	Caucasian female
Hyperextension in °	−95 (−89,−98) [−90,−100]^a	−90 (−88,−99) [−88,−92]^a	−55 (−54,−72) [−46,−64]^b	−49 (−40,−56) [−44,−54]
Flexion in °	60 (56−64) [58,62]	62 (54,77) [52,72]^a	65 (60,68) [63,67]^b	50 (46,55) [48,52]
Radial deviation in °	29 (23,31) [25,33]^a	29 (25,32) [27,31]^a	21 (20,22) [20,22]^b	16 (15,18) [15,17]
Ulnar deviation in °	45 (43,45) [44,46]^a,b	45 (42,65) [34,56]^a	30 (24,30) [27,33]^b	25 (22,32) [21,29]

Values show medians, (25,75 quartiles) and [95% confidence intervals].

Compared to white subjects of the same sex (p < 0.05).

Compared to women of the same ethnicity (p < 0.05).

Caucasian men had significantly greater degrees of all wrist movements compared to Caucasian women (p < 0.05). There was no difference in wrist movement between Asian men and Asian women (p > 0.05) (Table 4).

Discussion

This study has demonstrated that in normal subjects, Asians have a higher flexibility in general indicated by their high median Beighton score. The ROMs of wrist and hand was greater in Asians and the difference was statistically significant (p < 0.05). The gender difference in these groups was variable between hand and wrist. Men in general had a greater ROM of the fingers whereas women had greater ROM of the thumb. There was no difference between Asian men and women with regard to wrist movements, whereas Caucasian women had a greater ROM of their wrists compared to their male counterparts. This study demonstrates that Asian hands have a greater ROM than Caucasian hands.

In our region, there are a wide variety of different ethnic groups which utilize our hand service. We have taken the two most common groups (Caucasian and Asian) and demonstrated that there are variations in small joint hand movements. There are a number of possible reasons for this.

A study in 1949 looked at the variation in extension of the MCPJ and IPJ of the thumb in different ethnic groups.³¹ They did find that those from the Indian subcontinent had a more mobile hand than their European counterparts. From the radiographs, they concluded that there was no difference in the bony anatomy between the measured groups. They thought that the differences in thumb hyperextension were due to changes in the soft tissues (capsule, ligaments and tendons) whether genetic or developmental. Our study methods are different as we used clinical methods as opposed to radiographs. Furthermore, we looked at more joints.

Similar results were found in a study in Cape Town.³² Again they found no difference in osseous anatomy and skin tension between the different racial groups and attributed the increase in extension to a lax volar plate and flexor tendons.

Other studies have also demonstrated that hypermobility is more prevalent in some racial groups.^{11,12,16–18,33–35} However, only two of the studies were controlled which clearly showed hypermobility in Igloolik Eskimos compared to Native Americans³²and no difference between Caucasian and Maoris.³⁴

There is evidence that hypermobility is age and sex related with younger children having higher scores as do females compared with age matched men.^11,13,14,33 All of our subjects were very young and of similar age. This reduced the confounding effects of age in our results.

Occupation and sport can also affect hypermobility. American music students and Swedish Industrial workers also had a high prevalence of hypermobility.^13,15 Ballet dancers have been shown to have higher mobility compared to controls. However, it was also shown that hypermobility was evident in some joints not exposed to stretching exercises which might indicate the influence of a genetic component.^16,20 In our study, we had one subject who was a gymnast at regional level. She had higher than average scores for flexibility compared to her cohort.

The COL5A1 gene and its variants code for a component of Type V collagen. Mutations of this gene have been implicated in Ehlers Danlos syndrome. This study factored the subjects’ weight and age and demonstrated that the COL5A1 gene was associated with lower limb range of motion in the Caucasian population.²¹

Genetic influences as well as environmental and behavioural factors have been proposed as determinants of differences in spinal range of motion between individuals but this has not been investigated in different racial groups. Interestingly, in a study of differences in lumbar movements in adult male twin pairs, it was found that lumbar flexion movements was primarily determined by genetic influences while lumbar extension was influenced to a greater extent by environmental and behavioural factors.³⁶

There are limitations to the study. Studies have demonstrated that when measuring joint movements, there is a scope for intra and interobserver variability.^37,38 KB and MS were present in all the measurements to ensure there were no discrepancies. Moreover, they each measured 10 of the same hands separately and there was no statistical difference in the measurements. However, we acknowledge that there is still scope for measurement error and that higher numbers would be needed to create normative tables for hand joint range of motion for age, gender, ethnicity, etc.

Hand rehabilitation protocols exist to improve hand function after injury and it is imperative to appreciate that there is a variation in ethnicity and normal ranges of motion. We have demonstrated that there is indeed a difference in the flexibility of the normal hand in Asians and the Caucasian population. We believe more research should be done in this area. What would be interesting is looking at patients with hand injuries from different ethnic groups. They can then be assessed to look at the difference in post injury/operative ROM. If there is a difference we can try and identify the causes of this. This may aid in future rehabilitation protocols.

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