Radiological analysis of finger length ratio and dimensional profile of finger anatomy morphology

Study design

The present study employed an observational descriptive research design, utilizing secondary data from radiological results of hand examinations conducted at Dr. Saiful Anwar General Hospital in Malang, East Java, Indonesia, from June 2023 to July 2023.

Sample

The study included patients who sought medical care at Dr. Saiful Anwar General Hospital and underwent a radiological hand examination (posterior-anterior or oblique) in either the emergency room or outpatient clinics. The inclusion criteria consisted of patients aged 18 years or older with closed growth plates, complete medical records, and willingness to participate. Exclusion criteria included individuals with congenital hand deformities, a history of trauma or malunion, degenerative bone conditions, or bone growth disorders. Excluding these conditions was necessary to ensure the accuracy and consistency of the anatomical measurements. Congenital deformities, trauma, malunion, and degenerative bone conditions are all known to cause significant anatomical variations that could skew the results. These conditions could alter bone length, joint spacing, and other anatomical parameters, making it difficult to obtain standard anatomical data. By excluding individuals with these conditions, the study ensured the sample represented individuals with normal, undistorted finger anatomy, thereby providing more reliable and valid results for hand reconstruction and prosthetic design.

A purposive sampling method was employed to select patients who met the inclusion and exclusion criteria, ensuring the sample was representative of the hospital’s population. Purposive sampling was chosen because it enables targeted selection of patients most likely to provide relevant data for the study’s objectives. The total sample size was 384 patients, calculated using a standard sample size formula for descriptive research (with a 95% confidence level and a 5% margin of error). This sample size was deemed sufficient to yield reliable and valid results, given the expected variability in hand anatomy measurements.

Procedure

Radiological images consisting of routine posterior–anterior and oblique hand radiographs were retrieved from the hospital’s radiology information system (RIS). Morphological measurements were obtained using the digital measurement tools available within the RIS. The evaluated variables included phalangeal length, head diameter, base diameter, isthmus diameter, articular–isthmus distance, and midshaft diameter, with the radiographic projection used for each parameter indicated in the results tables. Coronal alignment at the metacarpophalangeal (MCP), proximal interphalangeal (PIP), and distal interphalangeal/interphalangeal (DIP/IP) joints was recorded as radial or ulnar deviation on radiographs. Because the present study was retrospective and descriptive, the primary analysis focused on generating reference morphometric values for the study population.

Data processing and analysis

Data were compiled and organized using Microsoft Excel for initial verification and summarized using the Statistical Package for the Social Sciences version 29. Descriptive statistics were used to calculate means and standard deviations for the morphological measurements. To improve clinical interpretability, sex-stratified descriptive findings were also summarized for phalangeal length.

Proximal phalanx (PP) morphology

This study examined 399 samples of the PP in the thumb, index, and ring fingers and 398 samples of the PP in the middle and little fingers. Table 1 displays the measurement outcomes for the PP.

Middle phalanx (MP) morphology

This study involved the analysis of 398 samples collected from the MP of the ring finger, 397 samples from the middle and little fingers, and 394 samples from the index finger. Table 2 displays the measurement outcomes for the MP.

Distal phalanx (DP) morphology

This study involved the analysis of 398 samples from the DP of the thumb, 396 samples from the little finger, 395 samples from the ring finger, 392 samples from the middle finger, and 390 samples from the index finger. Table 3 presents the measurement outcomes for the DP.

Sex-stratified descriptive analysis showed consistently larger phalangeal lengths in males than in females across all digits. In the PP, mean male values ranged from 30.57 ± 2.65 mm in the thumb to 44.36 ± 3.44 mm in the middle finger, whereas female values ranged from 28.19 ± 2.82 mm to 42.12 ± 3.44 mm. In the MP, mean male values ranged from 17.56 ± 2.05 mm to 26.17 ± 2.83 mm, whereas female values ranged from 16.01 ± 2.12 mm to 25.04 ± 2.96 mm. In the DP, mean male values ranged from 15.23 ± 2.22 mm to 21.50 ± 1.98 mm, whereas female values ranged from 14.16 ± 1.70 mm to 19.50 ± 1.77 mm.

Alignment on metacarpophalangeal, proximal interphalangeal and distal interphalangeal

The degree of misalignment in MCP, PIP, and DIP to radial and ulnar deviation is shown in Table 4. Radial and ulnar deviation in the MCP, PIP, and DIP joints could have important implications for surgical planning and prosthetic design. For example, if a prosthetic implant is designed assuming perfect alignment, the misalignment observed in this study could result in poor fit, reduced functionality, and potential complications. Understanding these deviations helps clinicians customize implants and plan surgeries more effectively to compensate for anatomical misalignment, potentially improving patient outcomes in hand reconstruction.

Comparison of proximal phalanx, middle phalanx and distal phalanx by sex

A prior investigation elucidating the morphological correlation between the phalanx and sex found that the PP is larger in males than in females across all phalanxes.^[9]This is relevant to the findings of this study. Specifically, the length of the PP in males ranges from approximately 30.57 ± 2.65 on the thumb, 39.88 ± 3.37 on the index finger, 44.36 ± 3.44 on the middle finger, 41.58 ± 3.76 on the ring finger, and 32.43 ± 3.0 on the little finger. Meanwhile, in females, it ranges from 28.19 ± 2.82 on the thumb, 37.74 ± 2.74 on the index finger, 42.12 ± 3.44 on the middle finger, 39.69 ± 3.76 on the ring finger, and 30.65 ± 3.03 on the little finger. The data presented in this study align with prior research by Ash and Unsworth, which reported that the average size in males on the index finger is 44.26 ± 2.21, on the middle finger 48.56 ± 2.62, on the ring finger 45.65 ± 2.43, and on the little finger 36.59 ± 1.92. Meanwhile, in females, it ranges from 42.88 ± 3.23 on the index finger, 46.06 ± 3.79 on the middle finger, 44.04 ± 4.17 on the ring finger, and 35.97 ± 3.74 on the little finger.^[9,10]

In all phalanxes, the average length of the MP is greater in males than in females. The latest data show that the male MP measures 21.45 ± 2.87 on the index finger, 26.17 ± 2.83 on the middle finger, 24.85 ± 3.18 on the ring finger, and 17.56 ± 2.05 on the little finger. Meanwhile, in females, it ranges from 21.1 ± 3.43 on the index finger, 25.04 ± 2.96 on the middle finger, 23.73 ± 2.66 on the ring finger, and 16.01 ± 2.12 on the little finger. Similar to this study, research performed in 1996 has shown a male range MP length from 26.44 ± 1.89 on index finger, 32.28 ± 2.19 on middle finger, 30.82 ± 1.92 on ring finger, and 21.9 ± 1.48 on little finger are bigger than female, which ranges from 26.09 ± 2.57 on index finger, 30.13 ± 3.08 on middle finger, 28.16 ± 3.24 on ring finger, and 21.51 ± 2.98 on little finger.^[8-10] Lastly, in the DP, it has been observed that the length of the DP is greater in males ranging from 21.5 ± 1.98 on thumb, 15.63 ± 2.36 on index finger, 16.61 ± 2.34 on middle finger, 17.1 ± 2.45 on ring finger, and 15.23 ± 2.22 on little finger, compared to females across all phalanxes, with measurements ranging from 19.5 ± 1.77 on thumb, 14.64 ± 2.05 on index finger, 15.46 ± 1.87 on middle finger, 15.69 ± 1.83 on ring finger, and 14.16 ± 1.7 on little finger.

Nevertheless, it should be noted that the phalanx length among Indonesians remains comparatively shorter than that reported in the study for other ethnic groups. Prior research has indicated a disparity in hand size between genders, with women typically exhibiting dimensions approximately 5–10% smaller than those of men.^[11] Empirical data indicate that this sexual dimorphism occurs during the initial stages of prenatal development.^[12] The phenomenon in question manifests at approximately 2 years of age, indicating that the underlying mechanisms contributing to the observed disparity are active during the early stages of human development.^[13]

Exploratory proportional analysis of MC and phalangeal dimensions

The proportional analysis in this study should be interpreted as exploratory. The lack of agreement between the present data and previously proposed Fibonacci-based relationships indicates that such heuristics are not universally transferable across populations. However, invalidating a heuristic is not equivalent to validating a superior predictive model. For that reason, the proportional relationships described in this study are presented only as empirical descriptive approximations, not as validated formulas for clinical prediction. Validation in an independent cohort and formal error analysis would be required before any predictive model could be recommended. This discrepancy may be attributed to variations in ethnicity, measurement techniques, age ranges, and hand positions during radiological examination.^[14-16] The study concludes that the ratio approach to the length of the MC, PP, MP, and DP applies to the index, middle, and ring fingers:

MC = 1.5 × PP, PP = 1.7 × MP and MP = 1.5 DP

And on the little finger:

MC = 1.5 × PP, PP = 1.7 × MP, MP = 1.1 × DP.

Further investigation is advised to examine variations in average differences within each sample across the formulation approach. A new formula can be developed through research that incorporates more precise data, specifically from macroscopic (cadaveric) studies. By doing so, it is anticipated that a more suitable and accurate formula can be established and subsequently applied to the Indonesian population.

Furthermore, the relative proportions of the phalanx in this study were determined by comparing the MC and phalanx proportions, as established by previous studies.^[14-16] These studies examined the variations in finger proportions; the results are presented in Tables 5-7.

The proportions of MC length relative to phalanges in Table 5 are consistent with previous studies that used a difference approach for each MC-phalanx pair, calculated from radiographic measurements. However, previous studies have not reported data on the head and base diameters.^[14-16] Tables 6 and 7 describe the proportions of the diameter of the head and base between the MCs and between the phalanx in measurements using radiographs in this study. These data can serve as an initial reference for determining morphological proportions, with more accurate calculations based on cadaveric measurements and guidelines for finger management to achieve appropriate morphology and optimal hand function.

This study has several important limitations. First, it was a retrospective radiographic study based on routine clinical images rather than a dedicated standardized imaging protocol. Second, formal interobserver and intraobserver reliability analyses were not performed, so measurement reproducibility cannot be quantified from the present dataset. Third, anthropometric variables such as height, body habitus, and hand dominance were not available. Fourth, the study did not include implant templating, implant-fit analysis, or clinical outcomes. Finally, the proportional relationships described here were not validated in an independent cohort. Accordingly, the findings should be interpreted as baseline descriptive radiographic data rather than as evidence of implant performance.

Recommendations

This study suggests developing a more accurate formula for predicting finger anatomy in Indonesians, as the Fibonacci formula does not align with observed proportions. Future research should incorporate cadaveric studies for more precise data. Clinicians should consider these anatomical variations when selecting implants, thereby ensuring a better fit and better outcomes in hand reconstruction. In addition, gender-specific data should be integrated into surgical planning and prosthetic design for more personalized treatment. Future studies should also extend these descriptive findings by incorporating radiographic templating against available fixation devices and small-joint implants, implant-fit analysis, clinical case series, and post-operative outcome correlation. Such work is required to determine whether the morphometric differences observed in the Indonesian population should influence fixation strategy, implant selection, or prosthetic design.