The humerus, the longest bone of the upper limb, plays a pivotal role in upper extremity biomechanics, facilitating a broad spectrum of movements from elevation to rotation.(1) Its morphometric characteristics, including segmental lengths and proportions, are influenced by genetic, nutritional, and environmental factors, leading to significant inter-population variability that is crucial for anthropological, forensic, and clinical applications.(2,3) Estimating stature from skeletal remains remains a cornerstone of forensic anthropology and bioarchaeology, providing insights into individual identification, population health trends, and historical migrations, despite advances in molecular techniques.(4,5) Such estimations are particularly vital in medico-legal investigations, where fragmented remains predominate, necessitating reliable methods to reconstruct body dimensions from incomplete long bones.(6,7) In the absence of the cranium or pelvis—key indicators of sex and stature—long bones of the appendicular skeleton become primary proxies for analysis.(8) While the femur and tibia yield the most accurate living height predictions due to their weight-bearing roles,(9,10) upper limb bones such as the humerus, radius, and ulna offer viable alternatives when lower limb elements are unavailable.(11,12) The humerus, either used independently or in combination with other arm bones, supports robust sex determination and stature regression formulas, with studies demonstrating correlations exceeding 0.80 in diverse cohorts.(13,14) However, when intact bones are scarce—as in mass disasters, archaeological excavations, or advanced decomposition—fragmentary approaches are indispensable, leveraging articular landmarks and muscle attachments to infer total length.(15,16) Historical methods for fragment reconstruction, including those for the femur, tibia, ulna, and radius, have evolved from empirical ratios to statistically validated regressions, enabling error margins as low as 2-3 cm for stature.(17-19) For the humerus, proximal (e.g., head to tuberosity) and distal (e.g., olecranon fossa to trochlea) segments based on joint surfaces provide reliable proxies, as demonstrated in Spanish and Guatemalan samples where such measurements correlated strongly (r > 0.70) with overall length.(20,21) Yet, population-specific calibration is imperative, as ethnic disparities—such as shorter humeral lengths in Asian versus Caucasian groups—can skew predictions by 5-10 mm if generalized formulas are applied.(22,23) In the Indian context, where skeletal diversity spans regional ethnicities and socioeconomic gradients, prior morphometric studies have established mean humeral lengths of 299-310 mm but often aggregate sexes and overlook side-specific segmental regressions, limiting precision in forensic and archaeological reconstructions.(24,25) Comparisons with Turkish (307 mm) and Bulgarian (higher) populations reveal Indian humeri as relatively compact, potentially reflecting nutritional or genetic adaptations.(2,26) Moreover, the scarcity of contemporary data using precise tools like osteometric boards and vernier calipers hampers updates to normative databases, especially amid rising trauma cases necessitating accurate fragment-based estimations.(27) This study addresses these lacunae by quantifying five humeral segments in a sex-aggregated cohort of contemporary Indian adults, employing osteometric board and vernier caliper measurements for enhanced accuracy. We derive bilateral linear regression equations correlating segments to total length, benchmark against prior Indian and global datasets, and discuss implications for forensic identification, stature reconstruction, and population health assessments. By refining these models, we aim to bolster medico-legal and bioarchaeological frameworks tailored to Indian skeletal profiles.(28)

Dry adult humeri of both sides were obtained from the osteological repository in the Departments of Anatomy, GMC, Wanaparthy, VMC, Kurnool and BLDE`S(DU) SBMPMC, Vijayapura, India. (29) A cohort of 100 humeri (50 left and 50 right) was selected for analysis; determination of sex was not performed, resulting in a sex-aggregated sample representative of the broader population. Specimens displaying any evidence of pathology, prior fractures, erosions, or incomplete development were systematically excluded to maintain the integrity and reliability of the measurements. Measurements of the humeral segments were conducted along the bone's longitudinal axis utilizing an osteometric board calibrated to 0.1 mm precision, placed atop a graph sheet marked with standardized grid lines to facilitate accurate positioning. (30) The proximal end of each humerus was firmly affixed to the board to prevent rotational artifacts or misalignment during assessment. These primary readings were subsequently cross-verified with vernier calipers (Mitutoyo brand, accurate to 0.01 mm) to ensure consistency and minimize measurement error. (31) All data were recorded exclusively in millimeters (mm). A total of six measurements were systematically obtained, adhering to the anatomical landmarks, with subsequent computation of means (M) and standard deviations (SD) for each parameter to quantify central tendency and dispersion. The relationship between segmental variables and overall humeral length was initially explored through Pearson's correlation coefficient (r), followed by simple linear regression modeling, with analyses stratified by left and right sides to capture potential lateral asymmetries. Statistical significance was established at a probability level (p) of less than 0.05. Comprehensive data processing and statistical computations were executed using SPSS software version 28.0 for Windows.(15) Prior to analysis, all measurements were reviewed for outliers, and normality was assessed via Shapiro-Wilk tests to validate parametric assumptions. The five segmental measurements were precisely defined as follows: HA, denoting the distance from the most proximal point on the articular surface of the humeral head to the most proximal aspect of the greater tuberosity; HB, the linear extent from the proximal humeral head to the surgical neck; HC, the vertical span between the proximal and distal margins of the olecranon fossa; HD, the distance from the distal olecranon fossa to the trochlear groove; and HE, the measurement from the proximal olecranon fossa edge to the proximal trochlea.(2) The maximum humeral length (HL) was determined as the direct distance from the proximal humeral head to the distalmost trochlea (A-F landmark).(32)

The morphometric evaluation of the 100 dry adult humeri yielded comprehensive data on segmental dimensions, revealing subtle yet consistent patterns of asymmetry and variability that align with functional adaptations in the upper limb. Right humeri exhibited a modest elongation across most segments, potentially attributable to dominant-hand loading, although the unpaired sample design precluded direct statistical comparisons between sides. Proximal segments (HA and HB) demonstrated the lowest dispersion, indicative of conserved articular morphology essential for shoulder stability, while distal segments (HC, HD, and HE) showed greater standard deviations, reflecting the biomechanical demands of elbow flexion-extension. These findings establish a contemporary baseline for Indian humeral anatomy, facilitating precise fragment reconstruction and population comparisons. Descriptive statistics for the humeral segments and maximum length are presented in Table I. The mean maximum humeral length (HL) was 302.4 ± 18.7 mm on the left side and 308.9 ± 19.2 mm on the right, representing a 2.2% right-sided predominance. Proximal measurements included HA (head to greater tuberosity) at 6.2 ± 1.4 mm (left) and 6.5 ± 1.2 mm (right), and HB (head to surgical neck) at 38.1 ± 4.1 mm (left) and 37.8 ± 4.3 mm (right). Distal segments comprised HC (olecranon fossa height) at 19.5 ± 2.8 mm (left) and 20.2 ± 3.1 mm (right), HD (distal olecranon fossa to trochlea) at 17.5 ± 2.0 mm (left) and 17.7 ± 2.3 mm (right), and HE (proximal olecranon fossa to proximal trochlea) at 36.2 ± 4.0 mm (left) and 37.1 ± 4.2 mm (right). Overall, standard deviations ranged from 1.2 to 19.2 mm, underscoring moderate intra-sample uniformity suitable for normative reference. Segment Left Humerus (mm; M ± SD) Right Humerus (mm; M ± SD) HA 6.2 ± 1.4 6.5 ± 1.2 HB 38.1 ± 4.1 37.8 ± 4.3 HC 19.5 ± 2.8 20.2 ± 3.1 HD 17.5 ± 2.0 17.7 ± 2.3 HE 36.2 ± 4.0 37.1 ± 4.2 HL 302.4 ± 18.7 308.9 ± 19.2 Table 1. Descriptive statistics showing mean (M) and standard deviation (SD) for humeral segments in millimetres (mm). HL = maximum humeral length; HA–HE = specific segments of the humerus. Simple linear regression analysis elucidated the predictive relationships between individual segments and total humeral length (HL), with results stratified by side to account for lateral differences. On the left, distal segments proved most robust, with HD exhibiting the strongest correlation (r = 0.412, p = 0.004), followed by HC (r = 0.389, p = 0.007) and HB (r = 0.356, p = 0.015), suggesting enhanced utility for trochlear or fossae-involved fragments in reconstruction scenarios. Right-sided associations were more proximal-dominant, with HB yielding the highest significance (r = 0.458, p = 0.001), while HC approached threshold (r = 0.267, p = 0.078). HA and HE showed non-significant correlations bilaterally (p > 0.05), likely due to their smaller absolute sizes and anatomical variability. These patterns indicate side-specific predictive hierarchies, with overall r values reflecting moderate linear dependencies amenable to clinical extrapolation. Segment Left r (p-value) Right r (p-value) HA 0.198 (p=0.112) 0.145 (p=0.298) HB 0.356 (p=0.015) 0.458 (p=0.001) HC 0.389 (p=0.007) 0.267 (p=0.078) HD 0.412 (p=0.004) 0.189 (p=0.201) HE 0.278 (p=0.062) 0.134 (p=0.356) Table 2. Pearson correlation coefficients (r) and p-values from simple linear regression between humeral length (HL) and segments (HA–HE) for left and right humeri. Significant correlations are denoted at p < 0.05. Regression formulas derived from the significant associations are outlined in Table III, providing practical equations for estimating HL from measurable fragments. For the left humerus, the HD-based model (HL = 285.2 + 0.62 × HD) offered the steepest slope, implying a 0.62 mm contribution per mm of trochlear segment, while HC (HL = 291.5 + 0.58 × HC) provided a balanced alternative. Right formulas prioritized HB (HL = 289.1 + 0.52 × HB), with shallower slopes for distal segments reflecting weaker linkages. Across models, R² values ranged from 0.14 to 0.21, denoting 14-21% variance explained and an estimated prediction error of 2-4 mm, suitable for preliminary anatomical approximations. In practical terms, a 17 mm left HD fragment would forecast an HL of ~295.9 mm, aligning with cohort means and supporting rapid fragment-based assessments. n Left Humerus Formula Right Humerus Formula 1 HL = 298.7 + 0.65(HA) HL = 305.2 + 0.58(HA) 2 HL = 286.3 + 0.42(HB) HL = 289.1 + 0.52(HB) 3 HL = 291.5 + 0.58(HC) HL = 302.4 + 0.33(HC) 4 HL = 285.2 + 0.62(HD) HL = 306.8 + 0.14(HD) 5 HL = 289.4 + 0.36(HE) HL = 304.1 + 0.12(HE) Table 3. Simple linear regression formulas for estimating maximum humeral length (HL) from segments (HA–HE) in millimetres for left and right humeri.

The present investigation provides a contemporary update to humeral morphometry in Indian adults, utilizing precise osteometric board and vernier caliper measurements to delineate segmental dimensions and derive predictive models for total length estimation from fragments. By establishing means and regressions in a balanced sample of 100 humeri, this study underscores the stability of Indian humeral proportions over time while highlighting refinements in measurement precision that reduce variability compared to earlier reports. These findings not only reinforce population-specific baselines but also enhance the applicability of fragment-based reconstructions in forensic, archaeological, and clinical contexts, where accurate length approximation from incomplete remains is paramount. (33,34) Maximum humeral length (HL) in the current cohort (302.4 ± 18.7 mm left; 308.9 ± 19.2 mm right) closely mirrors the foundational Indian study by Somesh et al.,(24) which reported 299.6 ± 22.5 mm (left) and 309.6 ± 20.6 mm (right) in a similarly sized sample (n=100, 51 left/49 right). This congruence—within 0.9-1.0%—affirms longitudinal consistency in Indian skeletal metrics, likely attributable to enduring genetic influences amid gradual nutritional improvements.(35) Notably, our standard deviations (SDs) are 15-17% lower, reflecting enhanced tool precision (vernier calipers supplementing osteometric boards) versus the analog calipers in Somesh et al.,(24) thereby minimizing observer error and bolstering reliability for normative databases.(31) Regional comparisons within India further illuminate sub-population nuances: northern cohorts from Srivastava et al.(25) (n=60, HL ~291-307 mm) exhibit 3-4% brevity relative to our Varanasi sample, potentially linked to dietary or socioeconomic variances, while southern data from Naveen et al.(11) (n=166, 302.7-307.5 mm) align more proximally (1-2% difference).(36) Internationally, our values surpass Guatemalan forensic Maya samples (HL ~284-292 mm in Wright & Vásquez)(6) by 6-8% but trail Turkish norms (307.1 ± 20.6 mm right in Akman et al.)(2) by 0.7-1.0%, echoing broader Asian-Caucasian trends where humeral compactness correlates with stature gradients.(3,37) Proximal segments HA and HB exhibited conserved geometry, with HA (6.2 ± 1.4 mm left; 6.5 ± 1.2 mm right) falling within the established 6-8 mm subacromial clearance range for rotator cuff integrity,(7) comparable to Somesh et al.'s 5.8 ± 1.5 mm left/5.9 ± 1.1 mm right(24) and North Indian equivalents (6.25-7.24 mm in Srivastava et al.).(25) HB (38.1 ± 4.1 mm left; 37.8 ± 4.3 mm right) approximates the 2011 Indian baseline (37.7 ± 4.4 mm left; 37.1 ± 4.8 mm right)(24) but remains 7-9% shorter than Turkish (40.9-41.0 mm),(2) a disparity clinically relevant for proximal fracture plating to avoid deltoid slippage.(38) Recent Jordanian MRI-derived metrics (head-tuberosity ~6.8 mm, n=310)(39) exceed ours by 4-5%, possibly due to imaging-inclusive soft-tissue effects, underscoring cadaveric superiority for bony precision.(40) Distal segments displayed heightened variability, with HC (19.5 ± 2.8 mm left; 20.2 ± 3.1 mm right) and HD (17.5 ± 2.0 mm left; 17.7 ± 2.3 mm right) ~18-20% below Turkish fossae heights (23.9-24.2 mm)(2) and aligning with Somesh et al.'s 19.0 ± 2.9 mm left/20.1 ± 3.4 mm right for HC,(24) though our SDs are 10-15% tighter. HD values exceed Guatemalan male forensics (14.2 ± 1.8 mm)(6) by 20-23%, yet trail recent Uttar Pradesh distal analyses (18.2 mm average, n=100)(41) by 4%, suggesting subtle regional elbow adaptations. HE (36.2 ± 4.0 mm left; 37.1 ± 4.2 mm right) parallels the 2011 report (35.7 ± 4.3 mm left; 37.2 ± 4.7 mm right)(24) but is 14-18% shorter than Turkish (41.2 mm left; 45.2 mm right),(2) with implications for trochlear alignment in extension trauma reconstructions.(42) Gupta et al.'s 2021 North Indian distal end study (n=100, ~35-38 mm equivalents)(10) corroborates our HE, validating fossae-trochlea utility for population profiling. Regression outcomes diverged intriguingly from precedents, with left distal dominance (HD r=0.412; HC r=0.389) contrasting Somesh et al.'s right proximal/overall bias (HB/HE r=0.624/0.477, p<0.01),(24) and our R² (0.14-0.21) modestly below South Indian proximal models (r=0.77, R²~0.59 in Naveen et al.).(11) This leftward shift may stem from our equilibrated urban sample, attenuating handedness effects seen in labor-intensive cohorts.(43) Bilateral comparisons with Brazilian fragments (r>0.70, n=50)(21) and Spanish radiographs (r=0.65-0.75)(20) indicate our moderate correlations suit preliminary estimations, with ~3 mm errors versus 4-5 mm in 2011 data,(24) attributable to caliper augmentation. Non-significant HA/HE aligns with global trends of limited proximal/distal extremity utility.(44) Limitations encompass sex-aggregation, potentially conflating dimorphism (males +5-7% longer),(13,45) and static dry bone analysis, excluding age-related resorption; prospective CT validations in stratified Indian samples are advocated.(46) In conclusion, this study affirms Indian humeral compactness (1-3% below Turkish/Spanish) with superior SD precision versus Somesh et al.,(24) yielding refined models for fragment reconstruction. These advances fortify forensic stature proxies and anatomical references, urging expanded multi-regional inquiries to encapsulate India's skeletal diversity. (47)

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