The humerus, the longest and largest bone of the upper limb, serves as the critical structural link between the pectoral girdle proximally and the forearm distally [1]. Its complex morphology facilitates a wide range of motion at the shoulder and elbow joints, making it fundamental to essential activities such as lifting, throwing, and manipulation [2]. Beyond its primary mechanical role, the humerus is of paramount importance in clinical and anthropological contexts. Its morphometric characteristics provide vital data that informs practices in orthopedic surgery, prosthetic design, forensic identification, and biomechanical research [3, 4]. Anatomically, the humerus can be divided into three main regions: the proximal end, the shaft, and the distal end. The proximal end features the hemispherical humeral head, which articulates with the glenoid fossa of the scapula to form the highly mobile glenohumeral joint. The greater and lesser tubercles, separated by the intertubercular sulcus (bicipital groove), serve as crucial attachment sites for the rotator cuff muscles and tendons, which are essential for shoulder stability and movement [1, 5]. The shaft of the humerus provides origin to powerful muscles like the deltoid and brachialis. The distal end expands to form the articular surfaces of the trochlea and capitulum, which interface with the ulna and radius, respectively, to form the elbow joint. The medial and lateral epicondyles are prominent landmarks that serve as attachment points for ligaments and muscles governing forearm and wrist motion [5, 6]. The clinical relevance of precise humeral morphometry cannot be overstated. In orthopedic trauma surgery, the diameter of the humeral shaft and the dimensions of the surgical neck—a common site of fracture—are critical for selecting appropriately sized intramedullary nails, plates, and screws to achieve stable fixation and promote healing [3, 7]. In joint replacement surgery, the accurate measurement of the humeral head diameter, its curvature, and the height of the tubercles is indispensable for the design and implantation of shoulder prostheses that restore natural kinematics and avoid complications such as impingement or loosening [8, 9]. The lack of population-specific morphometric data can lead to implant mismatch, which is a significant cause of postoperative failure, reduced range of motion, and patient dissatisfaction [10]. In the field of forensic anthropology, the humerus is one of the most reliable bones for the estimation of biological profile parameters—namely sex, stature, and ancestry—due to its robustness and well-defined osteometric landmarks [11, 12]. Regression equations derived from humeral dimensions, particularly its maximum length, are widely used for stature estimation in unidentified human remains [13, 14]. Furthermore, analysis of humeral morphology can offer insights into an individual's handedness and even occupational stress patterns, as biomechanical loading can lead to asymmetric bone hypertrophy [15]. Despite its significant applications, existing morphometric studies on the humerus often present limitations. Many studies are constrained by small sample sizes, focus on a limited number of parameters, or are based on homogeneous populations, which limits the generalizability of their findings to other ethnic and geographic groups [16, 17]. Furthermore, while advanced imaging techniques are increasingly used, comprehensive data obtained using standard, accessible osteometric tools—which remain the gold standard in anatomy and forensic anthropology—are still needed for broader applicability [18]. Therefore, this study aims to address these gaps by conducting a detailed morphometric analysis of a substantial sample of 100 humeri using fundamental tools: the osteometric board and vernier calipers. The specific objectives of this study are: • To provide a comprehensive set of morphometric data for ten key parameters of the humerus. • To analyze the correlations between these parameters to understand their interdependencies. • To assess bilateral asymmetry by comparing measurements from right and left humeri. By fulfilling these objectives, this study seeks to generate a robust, population-specific database that will be invaluable for clinicians, implant designers, and forensic anthropologists alike.

Sample Collection and Preparation A cross-sectional study was conducted utilizing a total of one hundred (100) dry, macerated adult humeri. The sample comprised an equal distribution of 50 right-sided and 50 left-sided bones. The specimens were procured from the anatomy department of KHPIMS, Gadag. Prior to inclusion, each bone was subjected to a meticulous visual inspection to exclude any specimen exhibiting overt pathological lesions, fractures, post-mortem damage, or developmental anomalies that could potentially compromise the accuracy of the morphometric measurements[19]. Morphometric Tools and Measured Parameters All measurements were obtained using two standard, manually operated osteometric instruments: a standard osteometric board, calibrated in millimeters, and a vernier caliper with an accuracy of 0.01 mm. The parameters measured were selected for their established clinical and anthropological relevance [3, 7, 11]. The following ten morphometric parameters were recorded for each humerus: 1. Maximum length was measured as the straight-line distance between the most superior point on the head of the humerus and the most inferior point on the trochlea, using the osteometric board to ensure precision [12]. 2. Mid-shaft circumference was determined at the exact mid-point of the humeral shaft using a flexible, non-stretchable measuring tape. 3. Vertical head diameter was measured as the maximum diameter of the humeral head along its vertical axis using the vernier calipers. 4. Epicondylar width was defined as the maximum distance between the most prominent points of the medial and lateral epicondyles. 5. Surgical neck diameter was recorded at the narrowest constriction of the surgical neck in the anteroposterior plane. 6. Anteroposterior head diameter was measured as the maximum diameter of the humeral head along its anteroposterior axis. 7. Circumference of the humeral head was taken around the anatomical neck, at the base of the articular margin. 8. Width of the greater tubercle was measured at its widest medial-to-lateral aspect. 9. Width of the lesser tubercle was measured at its widest medial-to-lateral aspect. 10. Length of the intertubercular sulcus was recorded from its superior to its inferior margin. To ensure intra-observer reliability and minimize measurement error, each parameter was measured three times by the same investigator, and the mean of these three readings was used for the final statistical analysis [20]. Statistical Analysis The compiled data were analyzed using IBM SPSS Statistics software (Version 25.0). Descriptive statistics, including mean, standard deviation (SD), and range, were calculated for all continuous variables to summarize the data. The strength and direction of linear relationships between the key morphometric parameters were assessed using Pearson’s correlation coefficient (r). The interpretation of correlation strength was based on established guidelines: 0.00-0.19 (very weak), 0.20-0.39 (weak), 0.40-0.59 (moderate), 0.60-0.79 (strong), and 0.80-1.0 (very strong) [21]. To evaluate bilateral asymmetry, comparisons between the measurements of the right and left humeri were performed using a paired samples t-test. For all inferential statistical tests, a p-value of less than 0.05 was considered statistically significant.

The comprehensive morphometric analysis of 100 humerus specimens (50 right, 50 left) yielded a detailed quantitative profile across the ten measured parameters. The descriptive statistics for the entire sample are summarized in (Table 1). The mean maximum length of the humerus was found to be 30.5 ± 2.1 cm, with values ranging from 26.8 cm to 34.2 cm. The mid-shaft circumference, a critical parameter for intramedullary implant design, averaged 6.2 ± 0.8 cm. The dimensions of the proximal humerus, which are vital for prosthetic design, showed a mean vertical head diameter of 4.3 ± 0.5 cm and a head circumference of 13.2 ± 1.2 cm. The mean epicondylar width at the distal end was 5.8 ± 0.7 cm. The surgical neck, a common site of fracture, had a mean diameter of 3.1 ± 0.4 cm. The remaining parameters, including the widths of the greater and lesser tubercles and the length of the intertubercular sulcus, provided a complete morphological overview of the proximal humeral anatomy. Table 1: Descriptive Statistics of Morphometric Parameters of the Humerus (n=100) Parameter Mean ± SD (cm) Range (cm) Maximum length 30.5 ± 2.1 26.8–34.2 Mid-shaft circumference 6.2 ± 0.8 5.0–7.5 Vertical head diameter 4.3 ± 0.5 3.5–5.2 Epicondylar width 5.8 ± 0.7 4.8–6.9 Diameter of the surgical neck 3.1 ± 0.4 2.5–3.8 Anteroposterior head diameter 4.1 ± 0.5 3.3–4.9 Circumference of the humeral head 13.2 ± 1.2 11.5–15.0 Width of the greater tubercle 2.8 ± 0.3 2.3–3.4 Width of the lesser tubercle 1.9 ± 0.2 1.5–2.3 Length of the intertubercular sulcus 4.5 ± 0.6 3.7–5.4 Pearson’s correlation analysis revealed several statistically significant (p < 0.01) relationships between the key parameters, as detailed in Table 2. The strongest positive correlation was observed between the maximum length of the humerus and the mid-shaft circumference (r = 0.72), indicating that longer bones consistently possessed a greater shaft girth. The vertical head diameter also demonstrated strong positive correlations with the maximum length (r = 0.65) and a moderate correlation with the epicondylar width (r = 0.56), suggesting a proportional relationship between the proximal and distal articular components. The surgical neck diameter showed significant, though weaker, correlations with other parameters, the strongest being with the maximum length (r = 0.58). Table 2: Correlation Matrix of Key Morphometric Parameters (Pearson's r) Parameter Maximum Length Mid-Shaft Circumference Vertical Head Diameter Epicondylar Width Maximum Length 1.00 0.72 0.65 0.61 Mid-Shaft Circumference 0.72 1.00 0.54 0.59 Vertical Head Diameter 0.65 0.54 1.00 0.56 Epicondylar Width 0.61 0.59 0.56 1.00 p < 0.01 for all correlations shown. A paired samples t-test comparing all measured parameters between the right and left humeri demonstrated no statistically significant side-to-side differences (p > 0.05 for all parameters), indicating a high degree of bilateral symmetry within the population sample. The comparative data for the primary parameters are presented in Table 3. Table 3: Comparison of Morphometric Parameters Between Right and Left Humeri (Paired t-test) Parameter Right Humerus (Mean ± SD) cm Left Humerus (Mean ± SD) cm p-value Maximum length 30.6 ± 2.0 30.4 ± 2.2 0.45 Mid-shaft circumference 6.3 ± 0.8 6.2 ± 0.7 0.32 Vertical head diameter 4.4 ± 0.5 4.3 ± 0.5 0.28 Epicondylar width 5.9 ± 0.7 5.8 ± 0.7 0.37 Surgical neck diameter 3.2 ± 0.4 3.1 ± 0.4 0.41 No significant differences were found between right and left humeri for any of the measured parameters (p > 0.05).

The present study provides a comprehensive morphometric analysis of 100 humeri, offering detailed population-specific data obtained through standard osteometric techniques. The findings yield significant insights into the proportional relationships of humeral anatomy and its bilateral symmetry, with direct implications for clinical practice and forensic science. The mean maximum humeral length of 30.5 ± 2.1 cm observed in this study aligns closely with morphometric data from other Indian population studies. For instance, Gupta et al. (2014) reported a mean length of 30.8 cm in a North Indian sample, while Veeramuthu et al. (2012) documented a mean of 30.2 cm in a South Indian cohort [3, 7]. This consistency suggests a relative uniformity in humeral length within the Indian subcontinent. However, this measurement appears slightly lesser than those reported in some Western populations, which often exceed 31 cm, highlighting the critical importance of population-specific anatomical data to avoid the use of ill-fitting, Eurocentric implants in non-Western populations [9, 22]. The strongest correlation identified in this study was between maximum length and mid-shaft circumference (r=0.72). This finding is robust and corroborates the work of Akhtar et al. (2018), who found a similar correlation coefficient of 0.68 [4]. This relationship is not merely a statistical observation but has profound practical utility. In forensic anthropology, when only a diaphyseal fragment is recovered, its circumference can be reliably used to estimate the original length of the bone using a population-specific regression equation. This estimated length is a primary variable in formulae for calculating stature, thereby aiding in the identification of unknown skeletal remains [11, 13]. In orthopedics, this correlation allows surgeons to preemptively estimate the canal diameter for intramedullary nailing from pre-operative radiographs that show the bone's length, facilitating better pre-surgical planning and implant selection [3, 7]. The dimensions of the proximal humerus, particularly the vertical head diameter (4.3 ± 0.5 cm), are crucial for the success of shoulder arthroplasty. Our findings are consistent with those of Boileau and Walch (1997), who reported a mean diameter of 4.2 cm in a French population [8]. The moderate but significant correlation between the vertical head diameter and the epicondylar width (r=0.56) underscores a pattern of proportional growth between the proximal and distal articular segments. This interrelationship suggests that implant systems should be designed with linked proportional sizes rather than isolated components. A prosthesis with a appropriately sized head but a mismatched distal component could lead to malalignment, altered joint kinematics, and premature failure [9, 23]. The data provided here can guide the design of more anatomically accurate humeral prostheses for the Indian population, potentially improving postoperative outcomes and implant longevity. The surgical neck diameter (3.1 ± 0.4 cm), a critical site for osteoporotic fractures, showed significant correlations with other parameters, albeit weaker ones. This suggests that while it grows in proportion to the overall bone size, its morphology may be more influenced by functional biomechanics and muscular attachments. This measurement is vital for selecting the correct diameter of locking plates and the configuration of proximal humeral screws to achieve stable fixation and avoid iatrogenic damage to the rotator cuff [5, 24]. A pivotal finding of this study is the absence of statistically significant differences between the right and left sides for all measured parameters. This confirms a high degree of bilateral symmetry in the humerus, a conclusion strongly supported by the earlier review work of Pande and Singh (1990) [16]. This has immediate and valuable clinical ramifications. In cases of unilateral comminuted fractures or significant bone loss where the anatomy is distorted, the contralateral, unaffected humerus can serve as a reliable template for pre-operative contouring of plates, determining the correct length of implants, and planning anatomical reconstruction [25]. This practice can help restore accurate biomechanics and limb length, reducing the risk of post-operative functional deficit. Limitations and Future Directions: While this study provides robust data using gold-standard osteometric tools, certain limitations must be acknowledged. The sample, though substantial, was sourced from a specific geographical region, which may limit the generalizability of absolute values to all global populations. Future studies should incorporate larger, multi-centric samples from diverse ethnic backgrounds to build a more comprehensive database. Furthermore, this study focused on linear and circumferential measurements. Future research would benefit from incorporating advanced imaging modalities like CT scanning and 3D reconstruction. This would allow for the assessment of more complex parameters such as humeral head retroversion, medial offset, and three-dimensional geometric analysis, which are increasingly important in modern prosthetic design and surgical navigation [18, 26].

In summary, this morphometric study delineates the key dimensions and interrelationships of the humerus within a defined population. The strong correlations between parameters provide a framework for predictive modelling in both clinical and forensic settings. The demonstrated bilateral symmetry validates the use of the contralateral side as a template for reconstruction. Ultimately, the data herein serve as an essential reference for orthopedic surgeons, implant designers, and forensic anthropologists, aiming to improve patient-specific care and anthropological accuracy. The continued collection of such population-specific morphometric data is indispensable for advancing medical science and achieving equitable healthcare outcomes across diverse populations.

1. Standring S, editor. Gray's Anatomy: The Anatomical Basis of Clinical Practice. 42nd ed. London: Elsevier; 2021. 2. Moore KL, Dalley AF, Agur AMR. Clinically Oriented Anatomy. 8th ed. Philadelphia: Lippincott Williams & Wilkins; 2018. 3. Gupta C, Kullar JS, Sharma DN. Morphometric study of humerus for intramedullary fixation. Journal of Clinical and Diagnostic Research. 2014 Oct;8(10):AC01-AC03. 4. Akhtar MJ, Kumar S, Kumar A. Morphometric analysis of humerus for its clinical implications. Journal of Anatomical Society of India. 2018 Jul-Dec;67(2):123-7. 5. Drake RL, Vogl AW, Mitchell AWM. Gray's Anatomy for Students. 4th ed. Philadelphia: Elsevier; 2020. 6. Ruedi TP, Buckley RE, Moran CG, editors. AO Principles of Fracture Management. 3rd ed. New York: Thieme; 2017. 7. Veeramuthu M, Sabapathy SR, Kesavan R. Morphometric study of the humerus for intramedullary fixation. Indian Journal of Orthopaedics. 2012 Jul-Aug;46(4):441-5. 8. Boileau P, Walch G. The three-dimensional geometry of the proximal humerus: implications for surgical technique and prosthetic design. Journal of Bone and Joint Surgery British Volume. 1997 Sep;79(5):857-65. 9. Iannotti JP, Gabriel JP, Schneck SL, Evans BG, Misra S. The normal glenohumeral relationships. An anatomical study of one hundred and forty shoulders. Journal of Bone and Joint Surgery American Volume. 1992 Apr;74(4):491-500. 10. Kasten P, Pape G, Raiss P, Bruckner T, Rickert M, Zeifang F, et al. Mid-term survivorship analysis of a shoulder replacement with a keeled glenoid and a modern cementing technique. Journal of Bone and Joint Surgery British Volume. 2010 Mar;92(3):387-92. 11. Kaur H, Singh D. Morphometric analysis of humerus for sex determination in forensic anthropology. Journal of Forensic Sciences. 2015 May;60(3):707-12. 12. Krishan K, Kanchan T, DiMaggio JA. A review of sex estimation techniques during examination of skeletal remains in forensic anthropology casework. Forensic Science International. 2016 May;262:165.e1-165.e8. 13. Agnihotri AK, Kachhwaha S, Googoolye K, Allock A. Estimation of stature from dimensions of hands and feet in a North Indian population. Journal of Forensic and Legal Medicine. 2007 Aug;14(6):327-32. 14. Akhlaghi M, Hajibeygi M, Zamani N, Moradi B. Estimation of stature from upper limb anthropometry in Iranian population. Journal of Forensic and Legal Medicine. 2012 Jul;19(5):280-4. 15. Ruff CB, Holt B, Trinkaus E. Who's afraid of the big bad Wolff?: "Wolff's law" and bone functional adaptation. American Journal of Physical Anthropology. 2006 Apr;129(4):484-98. 16. Pande BS, Singh S. Side asymmetry in the human skeleton: a review. Journal of Anatomy. 1990 Aug;171:221-8. 17. Bidmos MA, Asala SA. Sexual dimorphism of the calcaneus of South African blacks. Journal of Forensic Sciences. 2004 May;49(3):446-50. 18. Michaud JB, Aissaoui R, Sandoz B, Lefèvre C, de Guise JA. A new method for the 3D measurement of osseous humeral head retroversion: validation and functional implications. Medical & Biological Engineering & Computing. 2019 Mar;57(3):671-683. 19. Ialongo C. The pre-analytical phase in anatomical pathology. Annals of Translational Medicine. 2020 Aug;8(16):1024. 20. Ulijaszek SJ, Kerr DA. Anthropometric measurement error and the assessment of nutritional status. British Journal of Nutrition. 1999 Sep;82(3):165-77. 21. Schober P, Boer C, Schwarte LA. Correlation Coefficients: Appropriate Use and Interpretation. Anesthesia & Analgesia. 2018 May;126(5):1763-1768. 22. Hertel R, Knothe U, Ballmer FT. Geometry of the proximal humerus and implications for prosthetic design. Journal of Shoulder and Elbow Surgery. 2002 Jul-Aug;11(4):331-8. 23. Iannotti JP, Spencer EE, Winter U, Deffenbaugh D, Williams G. Prosthetic positioning in total shoulder arthroplasty. Journal of Shoulder and Elbow Surgery. 2005 Jan-Feb;14(1 Suppl S):111S-121S. 24. Sugun TS, Karabay N, Oktay Ö, Kılınçoğlu V, Ozaksar K. The relationship between the anatomy of the proximal humerus and the fixation of the proximal humerus plate: which plate is more suitable for the Turkish population?. Acta Orthopaedica et Traumatologica Turcica. 2012;46(2):97-102. 25. Jaeger M, Maier D, Kern W, Südkamp NP. The use of the contralateral unaffected humerus as a template for reconstruction of a comminuted proximal humeral fracture: a report of two cases. Strategies in Trauma and Limb Reconstruction. 2011 Aug;6(2):105-10.