Abstract
BACKGROUND:
The most prevalent neuropathy in the upper extremity is carpal tunnel syndrome (CTS). A variety of related risk factors such as biomechanical exposures, body mass index (BMI), sex and hand shape are reported to be related to CTS.
OBJECTIVE:
We aimed to identify the role of BMI, hand, wrist and finger anthropometric dimensions in the development of CTS, and to compare these measured variables between control and CTS participants.
METHODS:
A cross-sectional, case control study (n = 240, CTS = 120, controls = 120) with participants recruited from a convenience sample diagnosed with CTS and referred for anthropometric measurements. The control participants were matched by age and sex. The body height, weight, hand width, hand length, wrist depth, wrist width, wrist circumference, and finger length were measured. Hand, wrist and finger indices, hand to height ratio, and BMI were calculated. Mean values of all dimensions were compared between cases and controls, and the role of independent risk factors were determined by logistic regression analysis.
RESULTS:
The mean BMI, age, weight, sex and height were not significant between the two groups. Among the measured dimensions and calculated indices the significantly different variables between two groups were the wrist width, wrist depth, wrist circumference, hand index, hand to height index, and wrist index. Regression analysis showed that the wrist index (β=-1.7, p = 0.0001), wrist depth (β=0.25, p = 0.0001) and wrist width (β=0.21, p = 0.0001) were the strongest factors in CTS development in the sample.
CONCLUSION:
Wrist parameters have a strong role in predicting the development of CTS, while BMI was not confirmed as an independent risk factor.
Introduction
Carpal tunnel syndrome (CTS) is the most common neuropathy in the upper limb [1]. The median nerve compression at the level of the carpal tunnel commonly results in symptoms of pain and paresthesia in the hand, with symptoms worsening at night [2]. The prevalence and incidence of CTS in the general population are reported at 1–6% [3–6] and 3.3–3.5 per 1000 person-years, respectively [4], and is more common in working populations (8%) [3, 7]. The direct and indirect costs of CTS was 110 million and 130 million US dollars respectively in 2007 [8] and increased to more than 2 billion US dollars for 500,000 CTS release surgeries in the United States alone in 2016 [9].
The etiology of CTS is multifactorial and associated with a number of individual characteristics in the adult population. These factors can be occupational [6], physical or medical [10, 11]. Specific factors play a major role in the development of CTS [4, 12] and include: repetitive stress, repetitive bending or twisting of the hand and wrist at work, exposure of the hand to vibration [4, 13–15], sex [2], age, race, pregnancy [14, 16], disease conditions such as diabetes [2, 17], hypothyroidism [14], and osteoarthritis [17]. Moreover, there are studies that have investigated the association with anthropometric characteristics such as body weight, height, and body mass index (BMI) as potential factors in CTS development. However, there has been limited simultaneous consideration of the association between specific hand and wrist anthropometric dimensions or indices and CTS in these studies [18, 19]. Some of the previous investigation limitations have included; small sample size (n < 67) [19–21]; lack of adequate matched-controls from the perspective of BMI, age and gender [13, 22]; no control group; insufficient measures of dimensions or indices [19, 23]; and, inadequately reported statistical analysis [13, 22]. In-depth knowledge of CTS risk factors is essential in order to screen for, and prevent the condition. Current research suggests that people with CTS have anatomical differences in the hand/s affected by CTS [24].
There is a clear need for studies to investigate potential anthropometric risk contributors due to the high prevalence of CTS, lack of comprehensive information about related risk factors for CTS, and the lack of consideration of hand dimensions and indices in the examination of people with CTS [25], particularly in studies of adequate sample size [26]. With an improved knowledge of the prominent CTS related risk factors, including those that are anthropometric related, the strategies and treatment programs adopted can be selected more precisely from an evidence-based perspective. For this study, the aim was to identify the influence of various hand anthropometric measures and indices in the development of CTS; and the comparison between CTS and controls in a case-matched cohort.
Methods and materials
Study design and participants
In this cross-sectional case-matched control study, a sample of convenience (n = 240, aged 25-60 years; female = 75.8%, 91 in each group) were recruited with 120 participants in each group of CTS and matched controls. In the CTS group, a total of 90 participants had CTS unilaterally, with 30 participants having bilateral CTS, in which both hands were examined and matched with the control group (right-CTS=86, 57.3%; left-CTS=64).
The study protocol was approved by the ethics committee of the University of Social Welfare and Rehabililitation Sciences. The CTS participants were recruited from outpatients referred to the Tehran Red Crescent Rehabilitation Clinic, and the control participants from volunteers recruited through the relatives of the CTS participants and staff from the University of Social Welfare and Rehabililitation Sciences. The study was conducted from April to November 2018 in Tehran. All CTS participants had their diagnosis confirmed through a clinical examination and completion of an electrophysiological confirmation (electromyography-EMG and nerve conduction velocity-NCV) [27] by an orthopaedic physician. Participants were then referred for anthropometric measurement to a physiotherapist with extensive experience in this field. Participants were excluded if they had any history of hand surgery, cervical radiculopathy, current pregnancy, diabetes mellitus, or were taking any medications including oral contraception [26]. Recruited participants who formed the control group were evaluated by a physician to exclude the presence of CTS or cervical radiculopathy, and then were matched by age and sex with participants from the CTS group.
Informed consent was obtained from all participants. The study was approved by the Ethical Committee of the University of Social Welfare and Rehabilitation Sciences, Tehran, Iran (IR.USWR.REC.1396.384).
Information on participants’ symptoms, age, weight, height and associated diseases was recorded. All anthropometric measurements were performed by the physiotherapist within the rehabilitation clinic between 9 : 00 AM and 12 : 00 AM in an attempt to ameliorate the influence of daily diurnal changes, such as oedema, which is common in this population. To ensure an appropriate matched selection between the two groups, the symptomatic CTS hands were examined first, and the control participant’s matched hands were then subsequently measured.
Anthropometric measurements
In the CTS group, the anthropometric measures of the affected hand and wrist, as referred by the orthopaedic physician, were used for statistical evaluation. Measurements of the hand and wrist were taken from the palmar side with the fingers extended and abducted on a hard, flat surface [13, 26]. All measurements were performed three times using a standard engineering calliper with the mean of the three recordings used for further analysis. Height and weight were measured by one of the research team, with BMI calculated as weight/height2 (kg/m2) [26, 28].
Hand
Wrist
Fingers
Data analysis
Descriptive statistics for continuous variables are presented as the mean±SD. Normal distribution of the data and equality of variance in standard deviation were assessed. The comparison between the two groups was performed with the independent t-test with no assumptions violated. The correlation between variables was measured by the Pearson correlation (r), and multiple regression analysis was used to evaluate anthropometric risk factors for CTS participants. The diagnosis of CTS was considered as the dependent variable and the anthropometric dimensions as the independent variables when findings and data were entered into the model. Age and sex were used as a group-matching factor and consequently not used in the model. Statistical analysis was performed using SPSS 13.0 and all statistically significant levels were set at p = 0.05. A power of analysis calculation indicated that the minimum sample size required was n = 118 to determine a minimum a statistical difference between the CTS and control groups at the given p = 0.05 level using the formula
Results
This study enrolled 240 participants (CTS = 120, controls = 120) with no statistically significant difference between groups for demographic data on age, weight, height and BMI (see Table 1).
Descriptive data and comparison of CTS and control participants
Descriptive data and comparison of CTS and control participants
BMI=Body Mass Index, Independent t-Test was used.
A variety of anthropometric dimensions and indices were measured and comparisons were made between the two groups (see Table 2). Wrist dimensions included width, depth and circumference and each had statistically significant differences between the CTS and the control participants (see Table 2). Palm length, hand width, hand length and finger length were found to have no significant difference. Hand, hand to height, and wrist indices were significantly different between groups; while the finger index was not significantly different (see Table 2).
The comparison of anthropometric data in CTS (n = 120) and control participants (n = 120)
*p<0.05; **p<0.01, Independent t-Test was used.
A correlation analysis was performed between anthropometric dimensions, indexes and BMI using the data from all 240 hands. The BMI correlated with wrist depth (r = 0.57, p < 0.001), wrist width (r = 0.61, p < 0.001), wrist circumference (r = 0.54, p < 0.001), finger length (r = 0.52, p < 0.001), hand length (r = 0.57, p < 0.001) and palm length (r = 0.55, p < 0.001).
A multiple regression analysis was carried out to investigate whether anthropometric dimensions and indices could significantly predict CTS development (see Table 3). These results indicated the model explained 95.6% of variance; and that the model was a significant predictor of CTS development, F (7,253)=13834.28, p < 0.001. The model demonstrated that the risk factors for CTS are palm length, hand length, wrist depth, wrist circumference, wrist width and finger index. Among the measured parameters the wrist index (β=-1.7, p = 0.0001), wrist depth (β=0.25, p = 0.0001) and wrist width (β=0.21, p = 0.0001) were respectively the strongest factors in the development of CTS.
Risk factors for CTS in the logistic regression analysis for all patients
CTS: Carpal Tunel Syndrome. *p<0.05; *p<0.01. Logistics regression analysis was used.
A variety of demographic and anthropometric factors have previously been reported to be variably associated with CTS development including age, BMI, sex, wrist and also hand dimensions [26, 34]. This study aimed to determine the role of various anthropometric measures of the hand, wrist and finger dimensions in the development of CTS, and also to compare these measured variables between CTS and control participants in a matched cohort. Among the calculated anthropometric dimensions, the wrist depth, wrist width, wrist circumference, wrist index, hand index, and hand length/height ratio were significantly different between healthy and CTS participants. However, regression analysis showed only wrist index, wrist depth and wrist width as the determinant dimensions in the prediction of CTS development.
One of the key findings of this study was that wrist parameters are major determinants in CTS development [35, 36]. Among these, the wrist index was the strongest determinant, which is consistent with the results of previous studies. Wrist index is the ratio of wrist depth/wrist width which is usually a value < 1.0 and referred to by different authors as “wrist squareness” [37], “squarer” [26] or “square-shaped” [24]. Kamolz et al. [18], Moghtaderi et al. [31], Farmer et al. [30], Kouyoumdjian et al. [38], Trybus et al. [24] and Lim et al. [19] showed that the wrist index, or squareness, in CTS participants was very close to the values obtained in this study. In our study, the wrist index (wrist depth/wrist width) in CTS participants (0.73) were higher than the control participants (0.70). The reported wrist index for control participants was 0.69, 0.68, 0.69, 0.68, 0.69, 0.69 by Kamolz et al. [18], Moghtaderi et al. [31], Farmer et al. [30], Kouyoumdjian et al. [38], Lim et al. [19], and Plave et al. [39], respectively.
It appears that with an increasing wrist index, the wrist shape becomes squarer and higher sensory latencies are reported [18, 39]. Therefore, in participants with this square-shaped wrist, completing a task requires greater wrist flexion and extension during range of motion, which consequently could cause greater pressure in the carpal tunnel [18, 26]. This discrepancy of the wrist index between CTS and control participants has been suggested as being explained by the presence of oedema, tenosynovial hypertrophy, and transient changes in the adjacent soft tissue [18, 40]. There is still no consensus on whether this is a pre-existing physiological anomaly that predisposes individuals to CTS, or whether it is a transient change that develops as a consequence.
Clinically, the wrist index measure can be readily determined and intervention strategies assessed as effective or not in eliminating or reducing the potential for CTS to occur. These interventions include: therapies such as carpal bone mobilisation [41, 42], myofascial mobilisation [43], mobilising the transverse carpal space through self-stretching [44], or the use of a traction device [45], which subsequently affect oedema or hypertrophy. Traditionally, research into carpal tunnel manual therapies has not included anthropometric measurements [46] but clinical practice guidelines [34] have summarised the significant role that measurements have in predicting disposing factors and severity of CTS. Preventative ergonomics should be investigated specific to the square wrist due to the anatomical difference in torque, available active range of motion, and grip loading. To our knowledge no research has been published in regard to ergonomics and the wrist index.
Farmer et al. [30] found no significant difference between the wrist indices of the symptomatic and contralateral wrists of CTS participants with unilateral symptoms, which is in contrast to our findings. In their study, they also reported that participants with bilateral CTS, in which their hands were operated, did not present with a lower wrist index. The authors suggested that any relationship between the wrist index and CTS may be related to the differences in BMI between the two groups. Our findings challenge this finding. We controlled for potential variability in the BMI in the two groups of this study and no significant difference was found. Consequently, BMI cannot be a source of difference which supports the findings of Boz et al, who found that the relationship between CTS and wrist index is independent of BMI [13].
Hand index or hand shape (hand length/hand width), usually a value in the order of 2.0 is another parameter which was considered in previous research with some studies reporting a significant difference in hand index between the CTS and control participants [18, 20]. Previous studies have also shown that the hand length is shorter and the palm width is larger in a CTS group than control participants [20]. Our results confirmed this with a significant difference (p < 0.001) in the hand index found between control participants at 2.20, compared to the lower value of those with CTS at 2.04. These findings are further supported in CTS studies where the control participants versus CTS has been shown to be lower with respective values of 2.23 and 2.03 by Chroni et al. [20] and 2.20 and 2.0 by Kamolz et al. [18]. Sharifi-Mollayousefi et al. [47] and Boz et al. [13] used an alternative hand index measurement methodology (hand width (mm)/hand length (mm)×100, which usually provides a value in the order of 40-45, but the CTS was lower than the control) and respectively demonstrated a higher index in the CTS group (44.9, 44.84) than in the control participants (42.87, 42.30). The suggested mechanism for the effect of a lower hand index on the development of CTS can be the increased exerted force by a hand with higher length for a given repetitive hand motion. There is only one older study with some recognised methodological limitation such as low sample size (18 case, 18 control) and no electrophysiological confirmation of CTS, where the results were in contrast to the current study [48].
We also found that finger index can be an independent risk determinant for CTS, which is in accordance with the findings of Boz et al. [13] and Chroni et al. [20]. Boz et al. found a significant difference between finger index in control participants and CTS female participants [13], but showed no relationship between the finger index and CTS severity. Another study by Sgarifi et al. [47], failed to show the role of the digit index as a risk determinant. We are unaware of any previous studies that have investigated the finger index relationship with CTS. Consequently, future research will be required for greater clarification.
Lastly, we also found a significant difference in hand length/height ratio between the two groups but logistic regression analysis did not confirm it as a risk factor for CTS, suggesting that the ratio of hand to body height is not related to the development of CTS. Furthermore, this result supports similar findings by Boz et al. [13], and Sharifi et al. [47]. We are not aware of any other published studies that considered this relationship of hand length/height ratio and the presence of CTS. Consequently, from both our results and that of previous research findings it is indicative that the presence of a square-shape wrist and hand, as quantified by shorter lengths (palm, finger, hand length) and larger widths (palm, wrist, fingers width), are risk factors for CTS. This square-shape may compound a predisposition for a greater requirement for a fulcrum and torque increase due to the shorter lever arm mechanical deficiency when compared to the more stretched hand [49, 50]. A recommendation from this study would be that individuals with this square-shape wrist and hand would potentially require altered fulcrum lever length for work settings (such as the use of pliers) in the presence of increased torque load.
A major strength is that this is the first study in an Iranian population on this aspect of the links between anthropometrics and CTS. Additional strengths are that the study has matched the participants based on the age, sex, height and weight to control the BMI as a cofounding parameter. We have employed an adequate sample size in both the CTS and control participants to find the optimal contributed indices and dimensions related to CTS development. There are some limitations in this study such as categorised participants based on the severity of involvement and evaluating the relation between severity of CTS and hand/wrist parameters, and that differences in indices by sex were not determined. Furthermore, the total sample size was skewed toward female participants, which may limit the generalisability of the results. Future research must consider a higher proportion of male participants, and other dimensions and indices to thoroughly determine the full series of CTS risks related to the hand and wrist. This may include parameters such as grip strength and further investigation into hand shape. A longitudinal study may be required to determine whether the wrist index or “squareness” is a risk factor for or a consequence of CTS.
Conclusion
The aim of our study was to compare the hand anthropometric measures and indices in CTS and healthy control participants, and to investigate their role in the presence of CTS. Our results suggest that the wrist index, sometimes referred to as “squareness”, is more strongly associated with CTS than the hand index or hand shape. We also found hand length, hand palm, and finger index are independent risk factors for CTS. Controlling for BMI in both groups did not demonstrate it as an independent risk factor. The overall findings from our study indicate that wrist parameters are among the most critical and useful parameters in the research of CTS prevalence; and anthropometric measurements, which can be rapidly and accurately determined within the clinical practice setting, can highlight an individual’s potential risk for CTS, or in the presence of CTS it can explain the causal presence of CTS. Consequently, integrating this assessment knowledge with manual interventions may provide an evidence base to therapeutic and preventative opportunities. Longitudinal studies investigating these indices in asymptomatic participants or people with mild-moderate CTS may clarify these different relationships, the ability of interventions to mitigate CTS severity, or whether the anthropometric change is a consequence.
Funding
This study was financially supported by the Rofideh Rehabilitation Hospital, University of Social Welfare and Rehabilitation Sciences, Iran, Tehran (Grant no. 1896).
Conflict of interest
All authors declare that they have no conflicts of interest.
Footnotes
Acknowledgment
The authors appreciate the financial and technical support from Rofideh Rehabilitation Hospital Clinical Research Development Center. Also, the authors are grateful to the volunteers for their participation.
