Normative Values for Thumb Length in Young Adult Population

Normative Values for Thumb Length in Young Adult Population Aim: This study was conducted to identify normal values for thumb length with respect to the index finger. Material and Method: Measurements were taken from dorsal and palmer sides of a totally 164 right and left hands of 82 healthy young adults (47 males and 35 females) aged between 18 and 21 years. Measurements of relative thumb length, girth and nail width were performed with respect to the index finger. Measurement values were classified as Thumb Proximal Phalanx (TPP) index and Thumb Digital Crease (TDC) index. Results: Average values of the TPP and TDC indexes were found 0.82 and 0.59 respectively for right hand and 0.74 and 0.49 respectively for left hand. There is no statistically significant differences indicated between right and left hand averages in terms of gender. Average percentage values of thumb length with respect to proximal phalanx of index finder (AD/AB) were found to be 74% and 77% in right hand for females and males respectively; and 70% and 73% in left hand for males and females respectively. Average percentage values of the thumb length with respect to the length of the whole index finger (AD/AC) were found to be 35% and 34% in right hand and left hand respectively. Comparison of the thumb girth and nail width to index finger girth and nail width indicated the percentage values as 132% and 106% respectively. Conclusion: The provided data could help to the clinician’s as to detect pathologies and analyse aesthetic outcomes of reconstructive surgeries intraoperatively and postoperatively.


Bildirimler/Acknowledgements
Yazar bu makale ile ilgili herhangi bir çıkar çatışması bildirmemiştir. The author declares that she has no conflict of interests regarding content of this article. Yazar bu makale ile ilgili herhangi bir finansal destek bildirmemiştir. The Author reports no financial support regarding content of this article.

INTRODUCTION
The thumb has great functional importance among all digits in the hand. Qualified thumb function depends on finger length and mobility; it is also highly important for the necessary reconstruction activities (1,2). There is no widely accepted, reliable measurement tool for the aesthetic appearance of the thumb. Researchers interested in the reconstruction of congenital thumb anomalies have used subjective assessments due to the inadequacy of these measurement tools.
Various studies have been conducted regarding the size of the index finger and thumb. It is reported that the adducted normal thumb tip length reaches half of the proximal phalanx length of the index finger (3,4). Although the values in these studies do not provide supportive data, the data reported so far have been quite helpful in congenital thumb reconstructions and in pre-operative and post-operative assessments processes. Review of the related literature at both national and international level indicated very few studies on this issue. More detailed information is required for the objective identification of the normal thumb length. Therefore, the present study aims to determine the normative length, girth and nail width of the thumb with respect to the index finger in young adult population.

MATERIALS AND METHODS
This study was conducted with totally 82 volunteer students aged 19± 1.3 (between 18 and 21 (35 females and 47 males) who were enrolled in the Faculty of Health Sciences at Çukurova University. The participants were informed about the purpose of the study, and each participant signed the informed consent form. None of the participants were reported to have hand injuries or disabilities during the time the study was conducted. Morphometric measurements were performed in the participants' right and left hands. Measurements were performed in a standardised way using a digital compass and recorded as mm.
Relative Length of the Thumb from the Dorsal Side: Three measurements were taken from dorsal side of two hands along the longitudinal axis as follows; relative thumb length with respect to the length of the index finger; relative thumb girth with respect to the girth of the index finger; and thumb width with respect to the nail width of the index finger. To calculate the relative thumb length, measurements were performed with the method defined by Goldfarb (2) (Figure 1

Statistical Analyses
The data were statistically analyzed by using Student's t-test and one-way analysis of variance (ANOVA). The descriptive analysis was done to obtain mean, standard deviation and measurement range. ANOVA was used to analyze the differences in TPP and TDC indexes between the male and the female subjects. Difference were deemed statistically significant with P-values < 0.05. The statistical analysis was done using SPSS (Statistical Package for Social Sciences, version 21.0) computer software (SPSS, Inc., Chicago, IL, USA).

FINDINGS
Average values of the measurements performed in hand are demonstrated in Table 1 and Table 2. Comparative results Descriptive statistics of our study in comparison with study by other authors presented in Table 3 and Table 4. The mean values of TPP index value on right and left hands were 78.8±8.3 and 73.3±9.4, respectively, in females. The mean TDC (Thumb Digital Crease) index were calculated on the right and left hands were 60.18±14 and 52.8±14 respectively, in males. The mean TDC index on the right and left hands were 58.2±16 and 46.3±13 respectively, in females. Sex differences were not statistically significant (p>0,05). Average percentage value of thumb length with respect to the proximal phalanx length of the index finger (AD/ AB) was found 72% (SD = 11%; range, 33%-123%); average percentage of thumb length with respect to the length of the whole index finger (AD/AC) was found 34% (SD = 6%; range, 16%-66%). AD/AB average percentages were found 74% and 77% in right hand for females and males respectively and 70% and 73% in left hand for females and males respectively; mean scores were not statistically significant (p>0.05).  Thumb length with respect to the length of the whole index finger (AD/AC) average percentage values were 35% and 36 % in right hand for females and males respectively; it was 32% and 34% in left hand for females and males respectively. Comparisons between the (AD/AB) and (AD/ AC) ratio averages in right and left hands indicated no statistically significant differences according to gender. Average width of the thumbnail was calculated as 106%. This value was found 109% and 106% in right hand for females and males respectively and 107% and 104% in left hand for females and males respectively. Comparison of the length averages of the thumb nail width indicated 132% percentage value in right and left hands. AD/AB:Thumb length relative to proximal phalanx of index finger, AD/AC: Thumb length relative to entire length of index finger.

DISCUSSION
This study evaluated 164 hands of 82 young adult participants in order to determine the normative thumb length, girth and nail width with respect to the index finger. Average percentage of adducted thumb length with respect to proximal phalanx of the index finger (AD/AB) was found 73% while average percentage of thumb length with respect to the length of the whole index finger was found 34%. In their study conducted with pediatric population aged between 1 and 18, Goldfarb et al. also indicated similar results. They reported that the relative size of thumb remained notably constant during growth (2). In a similar vein, Jain A et al. (2017) assessed 482 hands of 241 children in India in order to provide normative data for relative thumb length, girth and nail width in paediatric population (7). The study reported that these percentages remained constant from babyhood to adulthood and did not indicate significant differences between the ages of 1 and 18 (7). Our study also indicated that, these ratios did not demonstrate significant differences in young adult population. Moreover, our results are similar with other studies and support their observations although, they have performed in paediatric population.
Average value of the TPP index was found 0.78 (SD=18) in the present study. This means that the tip of a normal adducted thumb extends to % 78 of the length of the proximal phalanx in index finger. And average value of the TDC index was 0.54 (SD=15); the tip of adducted thumb represents %54 of the distance between the two proximal creases of the index finger. Sunil recently measured the relative length of the adult thumb compared with the length of the index finger in adults. In his study, the calculated thumb length using TPP and TDC indexes values has been reported as 0.69 and 0.41 respectively (5). He also claims that; using the estimated index finger length for calculating the TPP index was better anatomically. Accordingly, to Sunil the TDC index is likely to be more variable hence this index uses skin creases which are likely more variable, as reference points. He also reported that in situation when there is an amputation of the index finger distal to the proximal interphalan-geal crease, the TDC index could be used.
Findings of the present study showed that the average percentages of the measurements obtained from the proportions of TPP indexes, ratios of thumb girth and nail width to index finger girth and nail width displayed similarity in different proportions (1)(2)(3)(4)(5)(6)(7)(8) (table 3 and table 4). But the TDC index values were significantly higher in our study compared to other studies (table 4).
Anthropometric measurements taken from dorsal and palmer sides of hand, using different methods for the calculation of relative thumb length also has shown similar results.
We believe that our work has some limitations these are as follows: Our study was not supported radiologically and further studies are needed in larger populations.
We think that TPP index can be used in cases when proximal phalanx length cannot be identified; for instance, in the amputation of the index finger from distal to proximal interphalangeal crease. In conclusion, these approximate values calculated are considered to be helpful for the reconstruction of the congenital thumb anomalies at both preoperative and postoperative period.