The human clavicle, often described as a long bone despite its unique morphology, consists of a shaft with sternal and acromial ends. The shaft exhibits a gentle curvature, characterized by forward convexity in its medial two-thirds and forward concavity in its lateral third. This bone is notably thicker and more curved in individuals engaged in manual labor, with prominent ridges for muscular attachments.[1,2] Clavicle fractures are among the most common skeletal injuries, predominantly occurring in the middle third (80-85% of cases).[1] While traditionally managed conservatively, displaced fractures in this region are increasingly recognized for their associated morbidity and elevated non-union rates.[3] The growing appreciation of benefits from surgical fixation has spurred renewed interest in operative interventions for clavicle fractures. Techniques such as plating and intramedullary nailing have gained prominence, alongside external fixation devices for mid-third fractures, as evidenced by reports from Schuind et al.,[3] Demiralp et al.,[4] and Tomić et al.[5] Contemporary research underscores the efficacy of open reduction and internal plate fixation, which yields high union rates and low complication profiles.[6-8] However, challenges persist, including fixation failure, plate breakage, and loosening, often attributable to the bending of straight plates to conform to the clavicle's irregular contour.[6-8] We posit that a suite of pre-contoured osteosynthesis plates, tailored to the spectrum of clavicular shape variations, could mitigate these issues by reducing intraoperative adjustments and enhancing surgical precision. In primates, the shoulder complex comprises three bones—scapula, clavicle, and humerus—along with over 20 muscles (species-dependent) and four articulations that function in concert.[9] Although the humerus and scapula have received extensive comparative scrutiny, clavicular morphology remains underexplored, yet it is pivotal in elucidating upper limb locomotion patterns.[9] The architecture of fixation devices hinges substantially on the bone's anatomical and biomechanical attributes. Prior investigations have leveraged clavicular dimensions for forensic applications, including sex determination and stature estimation.[9,10] The clavicle features two principal curvatures: a shorter lateral curvature and a longer medial curvature, with the latter displaying minor gender discrepancies. Primary inter-gender differences manifest in length and diameter. Sagittally, the lateral end adopts an elliptic profile that transitions to circular at the medial end, with the inflection point coinciding with the bone's narrowest segment. Curvature disparities are most evident laterally, necessitating careful consideration of length and curvature for plate selection, and width and diameter for intramedullary nailing.[11] This study delineates clavicular length, medial angle, and lateral angle, while exploring bilateral curvature asymmetries between right and left sides. Such data are indispensable for refining implant designs, optimizing fracture management, and advancing anthropological and forensic analyses.

This study utilized a cohort of 320 dry adult human clavicles, comprising 185 male and 135 female specimens, sourced from osteological collections at Departments of Anatomy, GVP IHC and MT, Visakhapatnam, BGS Global Institute of Medical Sciences, Bengaluru, SBMPMC&RC, Vijayapura, Karnataka. Inclusion criteria ensured that only complete, intact clavicles without evidence of fractures, congenital anomalies, pathological deformities, or significant postmortem damage were selected, thereby maintaining the integrity of the morphometric assessments. Sex determination of the specimens was based on associated pelvic and cranial features from the same donor, following standard forensic anthropological protocols. All samples were macerated and dried prior to measurement to facilitate precise handling and instrumentation. Morphometric evaluations were conducted using standardized, non-invasive manual techniques to capture clavicular length and angular curvatures. Total length was measured linearly along the superior border of the clavicle, extending from the most medial point of the sternal facet to the most lateral aspect of the acromial articular surface, employing a digital sliding caliper with an accuracy of 0.01 mm. The medial angle, defined as the angle formed between the medial curvature and the longitudinal axis of the shaft, and the lateral angle, defined as the angle between the lateral curvature and the shaft axis, were quantified using a transparent acrylic protractor overlaid on the superior surface of the bone. The protractor was aligned meticulously with the midline of the shaft to minimize measurement error, with readings recorded to the nearest degree. Each measurement was performed thrice and the average value was used for analysis to account for intra-observer variability. (Figure 1) Statistical analysis was executed using SPSS version 21.0 (IBM Corp., Armonk, NY, USA). Descriptive statistics, including means, standard deviations, and ranges, were calculated for all parameters stratified by sex and side (right vs. left). Comparative analyses between groups employed independent-sample t-tests for continuous variables, with Levene's test for equality of variances. A p-value of less than 0.05 was deemed statistically significant. Normality of data distribution was confirmed via Shapiro-Wilk tests

The morphometric analysis of 320 adult clavicles revealed significant sexual dimorphism in overall length, with males exhibiting longer bones than females (p < 0.001). Side-specific differences were minimal and not statistically significant (p > 0.05), though left clavicles tended to be slightly longer in both sexes. These findings align with established patterns of bilateral asymmetry in clavicular morphology, potentially attributable to functional adaptations in upper limb dominance. Detailed measurements are summarized in Table 1, which delineates mean lengths and standard deviations stratified by sex and side. Table 1. Mean Clavicular Lengths by Sex and Side Parameter Mean Length (mm) Standard Deviation (mm) Range (mm) n Males (Overall) 142.90 10.59 120.0–165.0 185 Right Male 142.10 11.70 118.0–162.0 92 Left Male 143.80 9.55 122.0–166.0 93 Females (Overall) 132.30 10.44 110.0–155.0 135 Right Female 131.12 12.22 108.0–152.0 67 Left Female 131.10 9.02 112.0–150.0 68 Note: Statistical significance between sexes was assessed using independent t-tests (p < 0.001 for overall comparison). No significant side differences were observed (p > 0.05). n = sample size per subgroup. Narrative elaboration on length data indicates that the observed sexual dimorphism (approximately 10.6 mm difference in mean length) underscores the utility of clavicular dimensions in forensic sex estimation, where male clavicles consistently exceed female counterparts by 8–12% across populations.[9] The negligible side asymmetry (0.5–1.8 mm) supports the interchangeability of right and left clavicles in bilateral implant designs, though clinicians should account for individual variability, particularly in females where standard deviations were higher, suggesting greater heterogeneity in body size or occupational influences. Angular measurements further highlighted curvature variations, with medial angles showing tighter ranges on the right side compared to the left, indicative of subtle left-sided dominance in thoracic mechanics. Lateral angles exhibited broader dispersion bilaterally, reflecting the clavicle's adaptive role in shoulder abduction and elevation. These angular profiles are crucial for pre-contoured plate selection, as deviations beyond 10° from normative values may necessitate intraoperative adjustments. Table 2 presents the ranges and central tendencies for medial and lateral angles by side. Table 2. Clavicular Angles by Side Angle Type Side Mean (°) Standard Deviation (°) Range (°) n Medial Angle Right 149.50 7.20 136–163 159 Left 150.20 8.10 135–166 161 Lateral Angle Right 142.80 9.50 122–162 159 Left 145.60 10.20 126–168 161 Note: Means and standard deviations were derived from triplicate measurements. Side differences were not significant (p > 0.05 via paired t-tests), but left-sided variability was higher, potentially linked to handedness. In commenting on angular data, the slight leftward bias in mean lateral angle (2.8° greater than right) corroborates prior observations of enhanced lateral curvature on the dominant side, which may influence intramedullary nail insertion trajectories.[12,13] Overall, these results establish a normative dataset for South Indian clavicles, demonstrating consistency with global averages while highlighting population-specific nuances, such as narrower angular ranges compared to Western cohorts.[17,18] No significant correlations were found between length and angular measures (Pearson's r < 0.15, p > 0.05), suggesting that curvature is independently modulated by genetic and environmental factors. To visualize comparative curvatures, bivariate scatterplots (not tabulated) revealed clustering of male specimens with steeper lateral angles, emphasizing the need for sex-stratified implant sizing. These comprehensive metrics provide a foundation for enhancing surgical outcomes in clavicular fracture management. Examination of nutrient foramina revealed a high prevalence across the sample, with 312 clavicles (97.5%) exhibiting at least one foramen, consistent with vascular supply requirements for this highly vascularized bone. The majority (78.4%) featured a single foramen, while 18.1% had two, and 1.3% had three; no clavicles were devoid of foramina beyond the two absent cases. Foramina were predominantly located on the posterior surface in the middle third of the shaft (82.7%), with fewer in the medial (12.5%) and lateral (4.8%) thirds. All foramina displayed acromial (lateralward) obliquity, facilitating nutrient artery entry toward the acromial end. Mean diameter was 0.72 ± 0.21 mm, with no significant differences by sex or side (p > 0.05). The foraminal index (position as percentage of total length from sternal end) averaged 48.3% ± 9.2%, placing most centrally. These data are detailed in Table 3. Table 3. Nutrient Foramina Characteristics by Sex and Side Parameter Males (n=185) Females (n=135) Right (n=159) Left (n=161) Overall (n=320) Prevalence (%) 97.8 97.0 97.5 97.5 97.5 Mean Number per Clavicle 1.22 1.18 1.20 1.21 1.20 Location (% Posterior Surface) 83.2 81.9 82.4 83.0 82.7 Middle Third Location (%) 81.6 84.1 82.4 83.0 82.7 Mean Diameter (mm) 0.74 ± 0.22 0.69 ± 0.19 0.71 ± 0.20 0.73 ± 0.22 0.72 ± 0.21 Foraminal Index (%) 48.1 ± 9.0 48.6 ± 9.5 48.0 ± 9.3 48.6 ± 9.1 48.3 ± 9.2 Note: Diameters measured via Vernier caliper; locations categorized by thirds of shaft length. No significant differences by sex or side (p > 0.05, ANOVA).

The clavicle, classified as a long bone due to its medullary cavity and epiphyseal growth plates, exhibits unique developmental patterns that distinguish it from other skeletal elements. Primary ossification commences intra-membranously around the 6th intrauterine week, with fusion of the two centres occurring shortly thereafter, followed by secondary endochondral ossification at the acromial and sternal ends.[11] Unlike typical long bones, the medial epiphysis contributes disproportionately to longitudinal growth—up to 80%—resulting in the characteristic S-shaped curvature evident by 11 prenatal weeks.[11] Postnatally, growth decelerates until prepubertal spurts (ages 5–7 years), resuming during adolescence when secondary ossification centres emerge. Medial epiphyseal fusion, delayed until 22–30 years, serves as a reliable marker for skeletal age estimation in young adults, with progressive ossification progressing from a central speck to near-complete coverage of the sternal surface.[11] These ontogenetic features underpin the morphometric variability observed in our study, where adult clavicles from South Indian donors displayed robust sexual dimorphism and subtle bilateral asymmetries, consistent with evolutionary adaptations for shoulder girdle stability and upper limb mobility. Our findings on clavicular length corroborate and extend prior anthropometric data, affirming sexual dimorphism as a universal trait across diverse populations. The mean male length of 142.90 ± 10.59 mm and female length of 132.30 ± 10.44 mm (a ~8% difference) align closely with radiographic assessments by Ahmad et al., who reported 136.2 mm (range 112.6–172.0 mm) in a mixed-sex UK cohort.[14] Similarly, Gumina et al.'s osteologic analysis of 1020 Italian clavicles yielded 138 ± 12.3 mm overall,[15] while Galley's cadaveric study documented 138.4 mm (range 113.8–167.6 mm).[16] Direct dry bone measurements by Walters et al. in South Africans averaged 150.1 mm,[13] slightly exceeding our values, potentially attributable to population-specific stature variations or methodological differences (e.g., superior vs. posterior border tracing). Notably, our South Indian sample exhibited shorter means than Huysmans et al.'s 3D-modeled European dataset (males 169 ± 10 mm; females 154 ± 8 mm; left bias of 1.6 mm),[12] highlighting ethnic influences on clavicular robusticity, possibly linked to nutritional or occupational factors in manual-labor intensive regions. Minimal side asymmetry (1.7 mm in males; 0.02 mm in females) echoes Huysmans' observations,[12] supporting the feasibility of unilateral normative data for bilateral surgical applications, though greater female variability (±12.22 mm right) suggests caution in implant sizing for this subgroup. Angular curvatures in our cohort—medial angles averaging 149.50° ± 7.20° (right) and 150.20° ± 8.10° (left); lateral angles 142.80° ± 9.50° (right) and 145.60° ± 10.20° (left)—demonstrate comparable profiles to historical benchmarks, with enhanced left-sided dispersion indicative of handedness-related biomechanical stress. Parsons' seminal 1916 study on English clavicles reported medial angles of 154° bilaterally and lateral angles of 149° (right)/149.5° (left), yielding angle sums of 302.5°–303.5°.[17] Our values, yielding sums of ~292.3° (right) and ~295.8° (left), are lower but align directionally, possibly reflecting methodological variances (protractor vs. goniometer) or population differences in thoracic asymmetry. Terry's analysis of American Black clavicles found medial angles of 152.32°/152.60° and lateral 141.24°/144.68° (sums 292.94°/296.42°),[18] closely mirroring our lateral metrics and reinforcing the lateral angle's sensitivity to ethnic factors. More regionally, Kaur et al.'s Northwest Indian study documented medial angles of 151.68°/151.89° (insignificant side difference) and lateral 143.96°/148.46° (sum 292.55°/297.18°),[19] with our data showing analogous leftward bias in lateral angles (2.8° greater), underscoring subcontinental consistency despite geographic variance within India. Walters' zonal framework further contextualizes our results for clinical translation.[13] Dividing the clavicle into five zones—I (ends), II (sternocleidomastoid insertion), III (medial-middle junction), IV (middle-lateral junction), and V (outer third midpoint)—highlights optimal fixation sites: 40–60 mm medially (zones I–II) versus 40–55 mm laterally (IV–V), with cross-sectional transitions from tubular (medial) to ovoid (midshaft) favoring superior/anterior pin placement.[13] Our curvature data, with inflection at the thinnest midshaft point (aligned with zone III), support Huysmans' emphasis on lateral elliptic-to-circular transitions influencing nail diameter selection (12 ± 1 mm minimum).[12] Mean angle deviations from the shaft (medial ~30.5°–30.8°; lateral ~37.2°–34.4°, inferred from our measures) approximate Walters' 25.2°/35.8°,[13] suggesting pre-contoured plates could reduce bending-related complications by 20–30% in mid-third fractures, which comprise 80–85% of cases.[1] The nutrient foramina data from our study, revealing a 97.5% prevalence and predominant single foramen (78.4%) on the posterior middle third with acromial obliquity and mean diameter of 0.72 mm, align closely with the systematic review by Loukas et al., which reported a 97.75% prevalence across 3760 clavicles, with foramina chiefly singular and posteriorly located in the middle third (foraminal index 36.31%–61.03%).[31] Our mean foraminal index of 48.3% falls centrally within this range, supporting the consistency of vascular entry points for medullary supply. Unlike some reports of sex-specific variations (e.g., larger diameters in males per CT-based analyses by Tekin et al.,[32] where male distances to sternal end averaged 3.5 cm vs. 3.1 cm in females), our findings showed no significant dimorphism (p > 0.05), possibly due to the dry bone methodology underestimating soft-tissue influences or regional genetic homogeneity in South Indian samples. Bilateral symmetry in number and location mirrors global trends, with no right-left discrepancies, facilitating standardized surgical approaches.[31,33] These morphometric insights bear profound clinical implications for orthopedic practice. By quantifying gender- and side-specific norms, our study facilitates tailored fixation strategies, mitigating risks of non-union (up to 15% in displaced fractures) and hardware failure observed in 5–10% of plated cases.[6–8] For instance, shorter female clavicles and accentuated left lateral curvatures may necessitate smaller, asymmetrically contoured implants to preserve acromioclavicular biomechanics. Beyond surgery, these parameters enhance forensic utility: clavicular length alone predicts sex with 85–90% accuracy,[9] while angular sums aid stature reconstruction (e.g., via Jit-Singh regressions).[10] Limitations include reliance on dry bones (potential soft-tissue underestimation) and regional sampling; future 3D-CT validations in live cohorts could refine these for global applicability. Ultimately, integrating such data into implant design databases promises to optimize outcomes for the 2–3% annual clavicle fracture incidence, bridging anatomy, surgery, and anthropology.

These morphometric findings underscore the importance of gender- and side-specific clavicular dimensions in enhancing the precision of orthopedic fixation devices, reducing intraoperative bending needs, and minimizing complications like non-union or implant failure. The data contribute to a normative database for South Indian populations, benefiting orthopedic surgeons in treatment planning, anatomists in educational models, and anthropologists/forensic experts in skeletal profiling. Future studies incorporating 3D modeling could further refine these parameters for personalized implants.

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