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Humerus

The humerus is the long bone of the upper arm, extending from the shoulder joint to the elbow joint, and serves as the primary structural element of the brachium. As the largest bone in the upper limb, it provides attachment sites for major muscles involved in arm movement and supports the weight-bearing functions of the shoulder and elbow.^[1]^[2] Etymology The word "humerus" derives from the Latin umerus, meaning "shoulder" or "upper arm".^[3] The humerus features a proximal end with a smooth, hemispherical head that articulates with the glenoid fossa of the scapula to form the glenohumeral (shoulder) joint, allowing for a wide range of motion including flexion, extension, abduction, and rotation. Below the head lies the anatomical neck, followed by the greater and lesser tubercles—prominent ridges for the attachment of rotator cuff muscles such as the supraspinatus, infraspinatus, teres minor, and subscapularis—as well as the surgical neck, a common site of fractures due to its narrow structure. The central shaft, or body, is cylindrical proximally with a flattened or triangular cross-section distally; it serves as an attachment for muscles like the deltoid (via the deltoid tuberosity) and provides passage for the radial nerve through the radial groove.^[4]^[5]^[6]^[7] At the distal end, the humerus expands into a flattened structure that articulates with the radius and ulna to form the elbow joint: the capitulum laterally connects with the radius for hinge-like flexion and extension, while the medial trochlea engages the ulna's trochlear notch for stability. Additional features include the olecranon fossa posteriorly (accommodating the ulna during extension) and the coronoid fossa anteriorly (for flexion), along with the medial and lateral epicondyles for ligament and muscle attachments, such as those of the flexor and extensor groups of the forearm. Clinically, the humerus is prone to fractures, particularly at the surgical neck or shaft, often resulting from falls or trauma, which can impair shoulder mobility and nerve function if untreated.^[8]^[9]^[10]

Introduction

Definition and Location

The humerus is the longest and largest bone in the upper limb, forming the structural foundation of the arm between the shoulder and elbow.^[5] It is classified as a long bone, characterized by a central diaphysis (shaft) flanked by proximal and distal epiphyses, which facilitate growth and articulation during development and maturity.^[8] Anatomically, the humerus is positioned in the brachium (upper arm), extending longitudinally from the glenohumeral joint superiorly to the elbow joint inferiorly.^[4] Its proximal end articulates with the glenoid cavity of the scapula, enabling shoulder mobility, while the distal end connects with the radius and ulna, contributing to forearm positioning and elbow flexion-extension.^[1] In adult humans, the humerus typically measures 32–34 cm in length for males and is slightly shorter in females, averaging around 30–31 cm, though these dimensions vary by population, ethnicity, and individual factors such as height and sex.^[11] For instance, anthropometric studies in diverse cohorts report male humeral lengths ranging from 32.4 cm to 33.8 cm and female lengths from 30.3 cm to 31.1 cm.^[12]

Etymology

The term "humerus" derives from the Latin humerus, meaning "shoulder," which underscores the bone's proximity to the shoulder joint in the upper limb.^[3] This Latin word evolved from an earlier form umerus and traces its roots to the Proto-Indo-European om(e)so-, signifying the shoulder region.^[3] The nomenclature reflects the bone's historical association with the broader shoulder area rather than strictly the arm itself. In ancient Greek medicine, the humerus was first described as the upper arm bone in texts attributed to Hippocrates around 400 BCE, particularly in works on fractures and joint articulations, where it was discussed in the context of dislocations and reductions.^[13] Galen, a prominent physician of the 2nd century CE, further formalized its identification using the Greek term ōmōs (shoulder), linking it explicitly to the proximal upper limb structure in his anatomical commentaries.^[14] Related terms include "arm bone" in older English usage, prior to the widespread adoption of Latin-derived nomenclature in the 18th century.^[15] In modern veterinary contexts, "brachium" denotes the upper forelimb region housing the humerus, drawing from Latin brachium for arm.^[16] The evolution of terminology transitioned from descriptive phrases like "shoulder bone" in classical antiquity to standardized anatomical naming during the Renaissance. Andreas Vesalius, in his seminal 1543 work De humani corporis fabrica, employed precise Latin terms such as humerus to describe the bone systematically, correcting earlier inaccuracies and establishing a foundation for modern nomenclature.^[17] This shift emphasized univocal, rule-based naming for clarity in anatomical studies.^[18]

Structure

Proximal End

The proximal end of the humerus consists of the rounded humeral head and associated structures that facilitate articulation at the glenohumeral joint and provide attachment points for muscles of the rotator cuff. The humeral head forms a smooth, hemispherical articular surface covered by hyaline cartilage, directed medially and superiorly to fit into the shallow glenoid cavity of the scapula, enabling a wide range of shoulder motion.^[2] This ball-and-socket configuration relies on surrounding soft tissues for stability, as the humeral head's articular surface is substantially larger than the glenoid, with studies reporting a bony radius ratio where the humeral head exceeds the glenoid by approximately 67% in curvature radius.^[19] Immediately inferior to the humeral head lies the anatomical neck, a narrow constriction that separates the head from the adjacent tubercles and serves as the primary site for attachment of the glenohumeral joint capsule and glenohumeral ligaments.^[9] Distal to the tubercles is the surgical neck, a metaphyseal region of further narrowing where the proximal humerus transitions into the shaft.^[2] Projecting laterally from the proximal humerus is the greater tubercle, a prominent bony elevation with three distinct flattened facets on its superior, middle, and inferior aspects, providing insertion sites for the supraspinatus, infraspinatus, and teres minor muscles, respectively.^[20] Medially and anteriorly sits the smaller lesser tubercle, which features a smooth impression for the subscapularis muscle tendon. Separating these tubercles is the intertubercular groove (also known as the bicipital groove), a deep, longitudinally oriented sulcus approximately 10-15 mm wide, bounded laterally by a thick ridge from the greater tubercle and medially by a thinner ridge from the lesser tubercle, which guides the tendon of the long head of the biceps brachii.^[1]

Shaft

The shaft, or diaphysis, of the humerus forms the central cylindrical to prismatic portion of the bone, exhibiting a triangular prism shape with distinct anterior, lateral, and medial borders that define its structural framework. The anterior border runs straight along the front, separating the anterolateral and anteromedial surfaces; the lateral border originates as an extension from the intertubercular region proximally and contributes to the overall lateral contour; while the medial border gradually blends into the medial supracondylar ridge toward the distal end. This configuration provides mechanical stability and attachment points, with the proximal half of the shaft being more cylindrical and the distal half flattening into a more triangular profile.^[5]^[9] The diaphysis is composed of compact cortical bone encasing a central medullary cavity, which in adults contains yellow marrow for fat storage and hematopoietic support in earlier life stages. Key surface markings include the deltoid tuberosity, a roughened V-shaped elevation on the lateral mid-shaft that enhances muscle anchorage. Posteriorly, the radial groove (also termed the spiral groove) appears as a shallow, oblique depression traversing the posterior surface, facilitating the passage of neurovascular structures such as the radial nerve and profunda brachii artery as it spirals from near the greater tubercle to the level of the deltoid tuberosity. Additionally, a single large nutrient foramen is typically located on the anterior medial surface, serving as the entry point for the principal nutrient artery to supply the bone's internal vascular network.^[21]^[22]^[5]^[23] Anatomical variations in the shaft are uncommon but notable, including the supracondylar process, a bony spur projecting from the anteromedial aspect approximately 5 cm proximal to the medial epicondyle, with a reported prevalence of 1-2% in the general population. This variant, measuring 2-20 mm in length, represents a phylogenetic remnant and may influence nearby soft tissue relations.^[24]^[25]

Distal End

The distal end of the humerus widens to form the structures that articulate with the radius and ulna, creating the elbow joint. This region features two distinct articular surfaces laterally and medially, separated by fossae that accommodate processes of the forearm bones during movement, as well as epicondyles and ridges for ligament and muscle attachments. The overall configuration allows for hinge-like flexion and extension while providing stability against varus and valgus stresses. The capitulum is a rounded, knob-like eminence located on the anterior and lateral aspect of the distal humerus. It articulates with the head of the radius, facilitating flexion and extension at the humeroradial joint.^[26] Medially, the trochlea presents a pulley-shaped surface with a central groove flanked by medial and lateral lips; the medial lip projects farther distally and is deeper, enhancing joint stability during articulation with the trochlear notch of the ulna. This oblique orientation contributes to the carrying angle of the forearm.^[26] Posteriorly, the olecranon fossa is a large, shallow depression superior to the trochlea that receives the olecranon process of the ulna during full elbow extension, preventing posterior dislocation. Anteriorly and superior to the trochlea lies the coronoid fossa, a smaller depression that accommodates the coronoid process of the ulna during maximum flexion.^[26] The medial epicondyle is a prominent bony projection larger than its lateral counterpart, serving as the primary attachment site for the ulnar collateral ligament and the common flexor tendon of forearm flexor muscles. The lateral epicondyle, smaller and more rounded, provides attachment for the radial collateral ligament and the common extensor tendon of forearm extensor muscles.^[27]^[26] Extending proximally from the epicondyles are the supracondylar ridges, which include anteromedial and anterolateral projections marking the transition to the humeral shaft; these roughened surfaces give attachment to muscles such as the brachialis (anterior compartment) and pronator teres (on the medial ridge).^[28]

Function

Articulations and Movements

The humerus articulates proximally with the scapula at the glenohumeral joint and distally with the radius and ulna at the elbow joint, facilitating a wide range of upper limb movements.^[29] The glenohumeral joint is a ball-and-socket synovial joint formed by the head of the humerus articulating with the glenoid cavity of the scapula, enabling multiplanar motion including flexion and extension, abduction and adduction, and medial and lateral rotation.^[29]^[30] This joint's stability is primarily provided by the rotator cuff muscles and the glenohumeral ligaments, which reinforce the joint capsule and prevent excessive translation of the humeral head.^[30] Distally, the humerus forms the elbow joint, a hinge-type synovial joint involving the trochlea and capitulum of the humerus with the trochlear notch of the ulna and the fovea of the radius, respectively.^[31] This articulation primarily permits flexion and extension, with a typical range of motion from 0° (full extension) to 150° (full flexion), while limited pronation and supination occur through the adjacent proximal radioulnar joint.^[31]^[32] Biomechanically, the center of rotation for shoulder movements is located at the geometric center of the humeral head, allowing the humerus to rotate around this point during arm elevation and other motions.^[33] During arm elevation, the torque at the glenohumeral joint can reach up to approximately 50 Nm, reflecting the demands placed on the joint by gravitational and muscular forces.^[34] At the elbow, the carrying angle—a valgus alignment of 5–15° between the humerus and forearm in full extension—positions the hand away from the body for functional activities such as carrying objects.^[35] Ligamentous support enhances joint integrity at both ends of the humerus. Proximally, the coracohumeral ligament extends from the coracoid process of the scapula to the anterior aspect of the humerus, contributing to the superior reinforcement of the glenohumeral capsule, while the transverse humeral ligament spans the intertubercular groove to maintain the long head of the biceps tendon in position.^[36]^[37] Distally, the annular ligament encircles the radial head, binding it to the ulna and stabilizing the proximal radioulnar joint during forearm rotation.^[38]

Muscle Attachments

The proximal end of the humerus provides attachment sites for several muscles that contribute to shoulder stability and motion. The greater tubercle features three distinct facets for the rotator cuff muscles: the supraspinatus attaches to the superior facet, the infraspinatus to the middle facet, and the teres minor to the inferior facet. The subscapularis muscle inserts on the lesser tubercle. Along the bicipital groove, the pectoralis major inserts on the lateral lip, while the latissimus dorsi and teres major both attach to the floor of the groove.^[2]^[39] The shaft of the humerus serves as an origin or insertion for muscles involved in arm flexion, abduction, and stabilization. The deltoid muscle inserts on the deltoid tuberosity located on the lateral aspect of the mid-shaft. The brachialis originates from the anterior surface of the distal half of the shaft. The coracobrachialis inserts along the medial aspect of the shaft. Additionally, the lateral and medial heads of the triceps brachii originate from the posterior surface of the shaft, with the lateral head above the radial groove and the medial head below it.^[2]^[40] At the distal end, the humerus accommodates attachments for forearm muscles that enable elbow flexion, extension, pronation, and supination. The pronator teres originates from the medial epicondyle as part of the common flexor origin. The brachioradialis and extensor carpi radialis longus originate from the lateral epicondyle as part of the common extensor origin. The triceps brachii also originates from the posterior surface of the distal humerus, proximal to the olecranon fossa.^[2]^[41] The rotator cuff muscles—supraspinatus, infraspinatus, teres minor, and subscapularis—attach to the tubercles of the proximal humerus and collectively stabilize the humeral head within the glenoid cavity during arm movements. Flexor and pronator muscles predominate on the medial distal humerus, while extensor and supinator muscles attach laterally, facilitating balanced forearm actions.^[42]

Vascularization and Innervation

Blood Supply

The blood supply to the humerus is provided primarily by branches of the axillary and brachial arteries, ensuring segmental perfusion to the proximal end, shaft, and distal regions. The proximal humerus, including the head and neck, receives its main arterial supply from the anterior and posterior circumflex humeral arteries, which arise from the third part of the axillary artery. The posterior humeral circumflex artery (PHCA) provides the predominant supply (approximately 64%) to the humeral head, perfusing its superior, inferior, and lateral portions via branches that curve around the surgical neck.^[43] The anterior humeral circumflex artery (ACHA) contributes significant additional perfusion (approximately 36%) via its anterolateral branch, which travels medially around the surgical neck and gives rise to the arcuate artery; this vessel enters the humeral head near the bicipital groove, forming an intraosseous arcade that distributes blood to the epiphysis. Retinacular vessels, branching from the circumflex arteries, penetrate the joint capsule to supply the epiphyseal region directly. The PHCA and ACHA often anastomose to form a periarticular network, with possible additional contributions from the suprascapular artery via anastomoses.^[43] The diaphysis of the humerus is supplied by the profunda brachii artery (also known as the deep brachial artery), the largest branch of the brachial artery, which arises proximally and courses posteriorly along the radial groove with the radial nerve. This artery gives off a nutrient branch that enters the medullary cavity through the nutrient foramen, typically located on the anteromedial surface of the shaft in the middle third, providing endosteal circulation to the bone marrow and cortex. Smaller periosteal branches from the profunda brachii and its collaterals, such as the middle and radial collateral arteries, contribute to cortical perfusion along the shaft. Venous drainage of the humerus follows the arterial pathways, with deep venae comitantes accompanying the circumflex humeral and profunda brachii arteries to ultimately join the axillary vein. Medullary veins within the bone drain toward the nutrient foramen, connecting to the nutrient vein that parallels the nutrient artery and exits to the systemic venous system. Anatomical variations in the humeral blood supply occur frequently, with the ACHA and PHCA showing inconsistencies in origin, course, and relative contributions. These variations can influence the risk of avascular necrosis, particularly following fractures at the surgical neck, where disruption of the arcuate artery leads to reliance on retrograde intraosseous flow; such injuries compromise perfusion to the humeral head, resulting in necrosis rates of 10-33% in displaced fractures.^[44]

Nerve Supply

The nerve supply to the humerus region primarily derives from the brachial plexus, a network formed by the ventral rami of spinal nerves C5 through T1, which provides motor and sensory innervation to the upper limb.^[45] This plexus organizes into roots, trunks, divisions, cords, and terminal branches, with several nerves traversing or adjacent to the humerus bone.^[45] The axillary nerve, arising from the posterior cord of the brachial plexus with contributions from C5 and C6 roots, exits the axilla via the quadrangular space and winds posteriorly around the surgical neck of the humerus.^[46] It provides motor innervation to the deltoid and teres minor muscles while its anterior branch courses along the humerus' surgical neck.^[46] Sensory contributions include the superior lateral cutaneous nerve of the arm, which supplies sensation to the lateral shoulder and upper arm skin adjacent to the proximal humerus.^[47] The radial nerve, originating from the posterior cord with fibers from C5 to T1 roots, descends in the arm and passes through the radial groove on the posterior aspect of the humeral shaft alongside the profunda brachii artery.^[48] This path, detailed further in descriptions of the humeral shaft, positions the nerve in close relation to the bone, where it supplies motor innervation to the triceps brachii and extensor muscles of the forearm.^[48] It also gives rise to the posterior cutaneous nerve of the arm, providing sensory innervation to the posterior skin of the upper arm overlying the humerus.^[49] The musculocutaneous nerve, derived from the lateral cord with C5 to C7 root contributions, pierces the coracobrachialis muscle near the proximal humerus and continues distally in the anterior arm compartment.^[50] It supplies motor innervation to the coracobrachialis, biceps brachii, and brachialis muscles, which attach along the humeral shaft.^[50] At the distal humerus, the median and ulnar nerves course without direct contact to the bone but adjacent to the epicondyles at the elbow. The median nerve, formed by contributions from the lateral and medial cords (C6 to T1 roots), travels medially along the distal humerus near the lateral epicondyle before entering the forearm.^[51] The ulnar nerve, from the medial cord (C8 and T1 roots primarily), descends medially and passes posterior to the medial epicondyle of the humerus in the cubital tunnel.^[52]

Development

Ossification

The humerus, as a long bone, undergoes endochondral ossification, in which a cartilaginous template is progressively replaced by bone tissue through the activity of osteoblasts at ossification centers. The primary ossification center emerges in the mid-diaphysis (shaft) during the eighth week of intrauterine development, initiating longitudinal growth and forming the initial bony structure of the humerus.^[9]^[53] Secondary ossification centers develop in the epiphyses, contributing to the expansion of the articular surfaces and tuberosities while maintaining separate growth plates (physes) until fusion occurs later in adolescence.^[2] In the proximal humerus, the main epiphyseal center for the humeral head appears between 1 and 6 months postnatally, followed by the greater tubercle center at 1 to 3 years and the lesser tubercle center between 3 and 5 years. These proximal secondary centers typically fuse with the humeral head epiphysis by 7 to 13 years of age, after which the entire proximal epiphysis unites with the shaft at the metaphyseal physis between 14 and 17 years in females and 16 and 18 years in males, with complete skeletal maturity reached by 18 to 20 years.^[54]^[55] At the distal humerus, secondary ossification centers appear in a sequential manner: the capitellum at around 1 year, the medial epicondyle at 4 to 6 years (often cited as 5 years; earlier in females ~5.8 years, later in males ~8.2 years), the trochlea at 7 to 10 years, and the lateral epicondyle at 10 to 13 years (typically 11 to 12 years; females ~10.4 years, males ~12.2 years). Fusion of these distal centers with the metaphysis occurs progressively, with the capitellum fusing by 10 to 15 years, the trochlea and lateral epicondyle by 12 to 16 years, and the medial epicondyle by 13 to 17 years; overall distal physeal closure aligns with proximal timelines, completing by 14 to 16 years in females and 16 to 18 years in males. Timings may vary by population and sex, with females generally earlier.^[56]^[57] The presence of multiple ossification centers in the growing humerus results in variable fracture patterns in children, as forces may separate or injure specific epiphyseal components rather than propagating through a unified bone structure, influencing treatment approaches such as closed reduction versus surgical pinning.^[58]

Embryological Origins

The upper limb bud, which gives rise to the humerus, begins forming during the fourth week of gestation as a bulge on the lateral aspect of the embryonic trunk, arising from proliferating mesenchymal cells derived primarily from the lateral plate mesoderm.^[59] This process is initiated by fibroblast growth factor 10 (FGF10) expression in the lateral plate mesoderm, which induces the overlying ectoderm to thicken into the apical ectodermal ridge (AER), a structure essential for limb outgrowth.^[59] The progress zone, a region of undifferentiated mesenchyme beneath the AER, interacts with AER signals to maintain proliferation and direct differentiation along the proximo-distal axis; Hox genes, such as those in the HoxA and HoxD clusters, pattern this axis, with the proximal segment corresponding to the humerus (stylopod).^[60] By weeks 6 to 7 of gestation, the cartilaginous model of the humerus develops through chondrification, where mesenchymal condensations from the lateral plate mesoderm differentiate into chondrocytes, forming the first anlage of the long bones in the upper limb.^[61] This precartilaginous template establishes the basic shape of the humerus prior to ossification, marking it as one of the earliest skeletal elements to chondrify in the limb.^[62] Genetic regulation of humeral development involves key signaling pathways that ensure proper outgrowth and polarity. Fibroblast growth factors (FGFs), secreted by the AER, promote proximo-distal elongation by sustaining mesenchymal proliferation in the progress zone and regulating Hox gene expression.^[63] Sonic hedgehog (Shh), expressed in the zone of polarizing activity (ZPA) on the posterior limb bud margin, establishes anterior-posterior polarity, distinguishing flexor from extensor compartments and influencing humeral head orientation.^[60] Disruptions in these early processes can lead to rare anomalies such as humeral agenesis, often associated with phocomelia, a condition historically linked to thalidomide exposure during days 24-29 post-fertilization, with an incidence of approximately 0.6 to 4.2 per 100,000 live births in non-exposed populations.^[64]

Clinical Significance

Fractures and Injuries

Fractures of the humerus are common skeletal injuries, with an annual incidence of approximately 50-75 per 100,000 population, predominantly affecting the proximal region and showing higher rates among elderly females due to osteoporosis.^[65] The risk of nonunion is estimated at 5-10% for humeral shaft fractures, influenced by factors such as fracture location and patient comorbidities.^[66] Proximal humerus fractures often result from low-energy falls in osteoporotic individuals, with surgical neck fractures accounting for 70-80% of cases in this category.^[67] These fractures occur just distal to the humeral head and are typically two-part injuries involving displacement of the shaft. Greater tuberosity avulsion fractures, another proximal subtype, frequently associate with rotator cuff tears, arising from forceful contraction of the attached supraspinatus or infraspinatus muscles during trauma.^[67] Humeral shaft fractures arise from direct or indirect trauma, classified by pattern: transverse fractures from high-energy direct blows, and spiral fractures from twisting mechanisms such as falls or assaults.^[68] The Holstein-Lewis variant, a spiral fracture in the distal third of the shaft, carries a 10-20% risk of associated radial nerve palsy due to the nerve's proximity in the spiral groove.^[68] Distal humerus fractures vary by age group; supracondylar fractures predominate in children, often from hyperextension injuries during falls, with about 60% presenting as displaced.^[69] In adults, intercondylar fractures of the T or Y configuration result from high-energy axial loading, involving separation of the medial and lateral condyles along the trochlea.^[70] Initial management of humerus fractures emphasizes closed reduction to restore alignment, followed by immobilization with a sling, cast, or functional brace to promote healing.^[71] Potential acute complications include fat embolism syndrome, particularly in shaft fractures from intramedullary fat release, and compartment syndrome in distal injuries due to swelling in the forearm flexors.^[72]

Surgical and Pathological Considerations

Surgical approaches to the proximal humerus commonly utilize the deltopectoral interval, which provides access to the humeral head, shaft, and tuberosities for fracture reduction and fixation, while minimizing disruption to the deltoid and pectoralis major muscles.^[73] For humeral shaft fractures, a posterior approach is frequently employed, allowing exposure of the mid-to-distal humerus while protecting the radial nerve.^[68] Open reduction and internal fixation (ORIF) with plates and screws is a standard treatment for displaced humeral shaft fractures, achieving union rates of approximately 93.5% across various patterns.^[68] Prosthetic replacement options include hemiarthroplasty for complex proximal humerus fractures in elderly patients, which replaces the humeral head to restore function and alleviate pain, particularly when fixation is unreliable due to poor bone quality.^[74] In cases of rotator cuff deficiency or severe tuberosity comminution, reverse shoulder arthroplasty is preferred, as it relies on deltoid function rather than cuff integrity and has become the standard for displaced three- or four-part fractures in patients over 70 years.^[75] Pathological conditions affecting the humerus include osteoporosis-related fragility fractures, which are common in older adults and warrant dual-energy X-ray absorptiometry (DEXA) screening to assess bone mineral density, especially following low-energy trauma such as falls from standing height.^[76] Primary bone tumors like osteosarcoma predominantly occur during adolescence, with peak incidence between ages 10 and 20, and affect long bones such as the humerus in approximately 10-15% of cases.^[77] Avascular necrosis of the proximal humerus can develop post-trauma, with reported rates of 15-30% in fractures involving the humeral head, often leading to collapse and necessitating further intervention.^[78] Surgical complications of humeral fracture management include malunion in about 10-20% of cases, particularly with conservative or unstable fixation, resulting in altered shoulder mechanics and potential need for corrective osteotomy.^[79] Postoperative infection rates range from 2-5%, influenced by factors such as surgical timing and soft tissue handling, and may require debridement or implant removal.^[80] Heterotopic ossification, occurring in up to 20% of proximal humerus trauma cases, can limit range of motion and is more prevalent after surgical intervention.^[81] As of 2025, bioabsorbable implants, such as biocomposite plates made from degradable polymers, are emerging for proximal humerus fixation, offering reduced reoperation rates by eliminating hardware removal and promoting natural bone healing through gradual load transfer.^[82] Stemless humeral implants in shoulder arthroplasty demonstrate improved longevity, with 13-year survivorship rates exceeding 89% for revisions, due to enhanced bone preservation and decreased stress shielding compared to stemmed designs.^[83]

Comparative Anatomy

In Non-Human Mammals

In non-human mammals, the humerus exhibits diverse adaptations reflecting locomotor demands and phylogenetic history. In quadrupedal species such as dogs and horses, the humerus adopts a more vertical orientation relative to the scapula to facilitate weight-bearing on the forelimbs, with a robust diaphysis that withstands compressive forces during terrestrial locomotion. This configuration contrasts with the more horizontal positioning in humans, emphasizing stability over extensive rotation, and features a prominent deltoid tuberosity for enhanced muscle attachment supporting limb protraction.^[84] Among primates, the humerus is often elongated to support suspensory locomotion, particularly in brachiating species like gibbons, where the bone's length facilitates arm-swinging and hook-like grasping at the distal end for stable suspension from branches.^[85] This adaptation includes a relatively thick cortical bone in the proximal humerus to resist torsional stresses during overhead movement, differing from the more spherical humeral head in humans that enables greater overhead reach and rotation.^[86] Non-human primates generally show less humeral head sphericity than humans, prioritizing flexibility for arboreal suspension over precise throwing or manipulative precision.^[87] In aquatic mammals such as whales and other cetaceans, the humerus is markedly shortened and integrated into a paddle-like pectoral fin, with a flattened diaphysis that enhances hydrodynamic efficiency and reduces drag during swimming.^[88] The bone lacks a medullary cavity and exhibits enlarged epiphyses with a twisted humeral head, adaptations for undulatory propulsion rather than terrestrial support, and the deltoid tuberosity is reduced or absent due to the atrophy of associated shoulder muscles.^[89]^[88] Variations across mammalian orders further highlight functional specialization; for instance, carnivores like felids and canids possess pronounced supracondylar crests on the distal humerus, providing robust attachments for powerful extensor muscles such as the triceps brachii to enable forceful paw strikes and digging.^[90] In rodents, the humerus is miniaturized (micro-humerus) with early epiphyseal fusion, reflecting their small body size and burrowing or scrambling lifestyles, where the bone's compact structure supports rapid, agile movements without extensive elongation.^[91]^[92]

Evolutionary Aspects

The humerus first appeared as a distinct skeletal element during the fin-to-limb transition in early tetrapods approximately 375 million years ago in the Late Devonian period, evolving from the stylopod (proximal segment) of the pectoral fin in lobe-finned fishes. This transformation enabled greater weight-bearing and propulsive capabilities on land, with fossils such as Tiktaalik roseae revealing a humerus with a rounded proximal head serving as a precursor to the ball-and-socket glenohumeral joint, facilitating body propping and rudimentary locomotion.^[93]^[94] Comparative analyses of Devonian humeri indicate that this joint precursor arose in aquatic environments, allowing fin-like appendages to support terrestrial transitions while retaining flexibility for swimming.^[95] In the synapsid lineage leading to mammals, significant modifications occurred during the Triassic period (approximately 252–201 million years ago), where increased humeral torsion marked the shift from sprawling limb postures to more upright, parasagittal gaits for efficient terrestrial movement. Therapsids, key transitional forms, displayed notable shaft elongation in the humerus, enhancing stride length and stability as they adapted to diverse habitats post-Permian extinction.^[96]^[97] This torsion, measured as the twisting angle between proximal and distal articular surfaces, progressively increased in advanced therapsids like cynodonts, optimizing muscle leverage for mammalian-like postures.^[98] Primate evolution during the Miocene epoch (23–5.3 million years ago) featured arboreal adaptations, including enlargement and protrusion of the humeral head to improve glenohumeral mobility for suspensory locomotion such as below-branch hanging and arm-swinging. This configuration, seen in early catarrhines, prioritized joint instability for extensive range of motion over stability, contrasting with earlier mammalian forms.^[99] By around 2 million years ago, in the emergence of Homo sapiens and antecedents like Homo erectus, the glenohumeral joint evolved greater articular congruence and retroversion, maximizing throwing efficiency through enhanced torque and precision during overhead motions.^[100] Fossils from Australopithecus afarensis, dated to about 3.2 million years ago, illustrate intermediate stages in hominin humeral evolution; the proximal humerus of specimen A.L. 288-1 (Lucy) is shorter in absolute length relative to body size and exhibits less retroversion of the humeral head compared to modern humans, reflecting retained arboreal climbing capabilities alongside emerging bipedalism.^[101] This morphology blends ape-like flexibility with human-like proportions, as joint surface areas align more closely with those of Homo than great apes.^[102] Specialized adaptations further diversified the humerus across mammals; in bats, flight evolution reduced the humeral shaft's relative mass while elongating and reinforcing the proximal end to anchor the wing membrane and pectoral muscles for powered aerial locomotion.^[103] Conversely, in cursorial ungulates such as horses, the humerus shortened proximally relative to distal elements, with slender shafts promoting high-speed running by minimizing rotational inertia and enhancing stride efficiency.^[104]

References

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Humerus: Anatomy, Bone markings, Labeled diagrams
Jul 27, 2023 · It is a long bone that extends from the shoulder to the elbow. Proximally, it articulates with the scapula to form the shoulder (glenohumeral) ...Proximal End · Body · Distal End
[6]
Humerus - Physiopedia
Articulation at the Glenohumeral Joint:- The head of the humerus forms the proximal articular surface, articulating with the glenoid fossa of the scapula, ...
[7]
Humerus | Radiology Reference Article - Radiopaedia.org
Aug 27, 2025 · The humerus (plural: humeri) is a tubular bone of the arm that articulates proximally at the shoulder with the glenoid of the scapula, and distally at the ...
[8]
Humerus: What Is It, Location, Function, and More | Osmosis
Aug 28, 2025 · The distal humerus articulates at the elbow joint to the radius and ulna, the two arm bones that make up the forearm. What is the function of ...
[9]
Sex determination and estimation of stature from the long bones of ...
The following measurements were taken: maximum humeral length (mean: 33.4cm in males; 30.7cm in females), vertical humeral head diameter (mean: 5.0cm in males, ...
[10]
Sex identification and reconstruction of length of humerus from its ...
On sex differentiation, our study revealed that the mean humeral length on the right side was 32.42 ± 0.81 cm for males and 30.32 ± 0.81 cm for females. Our ...
[11]
Humerus - Etymology, Origin & Meaning
Humerus, from Latin humerus (shoulder), PIE *om(e)so- "shoulder," means the upper arm bone; originally referred to the shoulder area.
[12]
The Classic: On the Articulations: Hippocrates as... - LWW
Hippocrates was familiar with the problem of dislocation of the shoulder. ... humerus naturally inclines forward, but the rest of the bone is turned outward.
[13]
Omos - Simon Online
May 10, 2016 · Omos is Greek for Latin humerus {"shoulder"}. Commentary: Greek ὦμος ... It means "the bone of the upper arm" as well as the "shoulder".Missing: word | Show results with:word
[14]
humerus, n. meanings, etymology and more | Oxford English ...
The earliest known use of the noun humerus is in the early 1700s. OED's earliest evidence for humerus is from 1706, in Phillips's New World of Words. humerus ...
[15]
The Forelimb - Veterian Key
Apr 25, 2023 · The humerus forms the bone of the arm or brachium. It is a very strong and robust bone in both cattle and horses. There are minor ...
[16]
Historical evolution of anatomical terminology from ancient to modern
In the second stage, Vesalius in the early 16th century described the anatomical structures in his Fabrica with the help of detailed magnificent illustrations.
[17]
The emergence of modern muscle names - PubMed
This investigation revealed the types of contributions they made: Vesalius was an originator of rule-governed muscle terminology with a univocal naming method, ...
[18]
The glenohumeral joint - a mismatching system? A morphological ...
May 13, 2014 · The mean ratio between the radii of the glenoid cavity and the humeral head was 0.6 ± 0.1 for bone, whereas the mean ratio in cartilaginous ...
[19]
Greater tubercle of humerus: location, muscle attachments - Kenhub
The superior aspect of the greater tubercle is marked by three impressions that serve as attachment points for the supraspinatus, infraspinatus and teres minor ...
[20]
Anatomy, Bone Markings - StatPearls - NCBI Bookshelf
May 6, 2024 · Diaphysis: Refers to a long bone's shaft. Examples of long bones include the femur, humerus, and tibia. Epicondyle: A prominence superior to a ...
[21]
Deltoid tuberosity of humerus: Anatomy and function - Kenhub
Mar 7, 2024 · The deltoid tuberosity is a rough, triangular area on the humerus's lateral shaft, serving as the distal attachment for the deltoid muscle.
[22]
An Anatomical Study of the Nutrient Foramina of the Human ... - NIH
The humeri had one or two main nutrient foramina located in a small area between the coracobrachialis and brachial muscles and oriented toward the elbow.
[23]
Fracture of the supracondylar process of the humerus in an ... - NIH
The supracondylar process of the humerus is an uncommon anatomic variant with a reported incidence of 0.8%-2.7% of the general population.Missing: prevalence | Show results with:prevalence
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Supracondylar process of the humerus: study on 375 Caucasian ...
The supracondylar process was more common on the left humerus (90%) and in male subjects (60%) (both P < 0.01). None of the processes we observed was bilateral.
[25]
Chapter 6: The bones of the upper limb
Humerus. The humerus (figs. 6-3, 6-4, and 6-11, 6-12, 6-13, 6-14, 6-15, 6-16 and 6-17) is the bone of the shoulder and arm. It articulates with the scapula at ...Clavicle · Humerus · Ulna<|control11|><|separator|>
[26]
Anatomy, Shoulder and Upper Limb, Elbow Collateral Ligaments
... radial collateral ligament (RCL), annular ligament, and accessory collateral ligament. ... lateral epicondyle of the humerus. These two ligaments provide ...
[27]
Anatomy Tables - Forearm & Wrist
medial supracondylar ridge, a narrow ridge running proximally from the medial epicondyle of the humerus, the pronator teres m. takes origin from the common ...
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Anatomy, Shoulder and Upper Limb, Glenohumeral Joint - NCBI - NIH
Mar 3, 2025 · The glenohumeral joint is a ball-and-socket joint of the upper limb formed by the dynamic articulation between the scapula's glenoid cavity and ...Introduction · Structure and Function · Blood Supply and Lymphatics · Nerves
[29]
Anatomy, Shoulder and Upper Limb, Shoulder - StatPearls - NCBI
The glenohumeral joint is a highly moveable ball-and-socket synovial joint that is stabilized by the rotator cuff muscles that attach to the joint capsule, as ...
[30]
Anatomy, Shoulder and Upper Limb, Elbow Joint - StatPearls - NCBI
Jul 24, 2023 · The elbow is a synovial hinge joint made up of articulations of mainly the distal humerus and the proximal ulna.
[31]
Elbow Stiffness Imaging: A Practical Diagnostic and Pretherapeutic ...
Nov 17, 2021 · The maximal elbow flexion–extension range is from 0° to 150° with 75° forearm pronation and an 85° supination [1].
[32]
Mechanics of Glenohumeral Arthroplasty
Overstuffing increased the torque required to achieve 60 degrees of elevation in an anterior plane at right angles to the scapula (the plus 90 degree scapular ...
[33]
Scapular Resting Posture and Scapulohumeral Rhythm Adaptations ...
Jun 8, 2023 · The maximum internal rotation torque generates approximately 50 Nm of force, while after ball impact, the shoulder experiences an adduction ...
[34]
The Appendicular Skeleton - OERTX
The distal end of the humerus has two articulation areas, which join the ulna and radius bones of the forearm to form the elbow joint. The more medial of these ...Bones Of The Upper Limb · Humerus · Carpal Bones
[35]
Joints – Anatomy and Physiology - UH Pressbooks
These include the coracohumeral ligament, running from the coracoid process of the scapula to the anterior humerus, and three ligaments, each called a ...
[36]
Dissector Answers - Joints of the Upper & Lower Limbs
Cultural enrichment: Check out these sections from the 1918 version of Gray's Anatomy of the Human Body! Some of the terms are (of course) out-of-date, but ...
[37]
Joints and Ligaments Tables - Medical Gross Anatomy
a synovial hinge joint; the elbow joint is a complex joint consisting of ... a series of synovial plane joints; small ranges of motion are permitted ...
[38]
Anatomy Tables - Bones of the Upper Limb
medial supracondylar ridge, a narrow ridge running proximally from the medial epicondyle of the humerus, the pronator teres m. takes origin from the common ...
[39]
Muscles of the Upper Limb | UAMS Department of Neuroscience
Muscles of the Upper Limb ; anconeus, lateral epicondyle of the humerus, lateral side of the olecranon and the upper one-fourth of the ulna ; biceps brachii ...
[40]
Anatomy, Shoulder and Upper Limb, Muscles - StatPearls - NCBI - NIH
Function: Lateral rotation of arm · Origin: Posterior scapula, inferior to the scapular spine · Insertion: Greater tubercle of humerus, between supraspinatus and ...
[41]
Anatomy, Shoulder and Upper Limb, Shoulder Muscles - NCBI - NIH
The glenohumeral joint is the point of articulation between the humerus, the scapula, and the thoracic cavity, with the latter occurring through the ...Muscles · Surgical Considerations · Clinical Significance
[42]
Anatomy, Shoulder and Upper Limb, Brachial Plexus - NCBI - NIH
Nerve fibers from the anterior division of the brachial plexus are contained in the musculocutaneous, median, and ulnar nerves. These nerves innervate the ...Anatomy, Shoulder And Upper... · Nerves · Clinical Significance
[43]
Anatomy, Shoulder and Upper Limb, Axillary Nerve - StatPearls - NCBI
After exiting the quadrangular space posteriorly, the anterior branch of the axillary nerve wraps around the surgical neck of the humerus, with the posterior ...Introduction · Structure and Function · Blood Supply and Lymphatics · Muscles
[44]
Nerves of the Upper Limb | UAMS Department of Neuroscience
Nerves of the Upper Limb ; axillary n. · posterior cord of the brachial plexus, superior lateral brachial cutaneous nerve ; brachial cutaneous, inferior lateral ...
[45]
Anatomy, Shoulder and Upper Limb, Radial Nerve - StatPearls - NCBI
Nov 5, 2023 · Radial nerve in the arm Further distally, it passes around the humerus' radial groove together with the profunda brachii (deep brachial) artery ...
[46]
Anatomy, Shoulder and Upper Limb, Nerves - StatPearls - NCBI - NIH
Jul 30, 2023 · The radial nerve gives off the posterior cutaneous nerve of the arm, then descends between the long and lateral heads of the triceps brachii.
[47]
Anatomy, Shoulder and Upper Limb, Musculocutaneous Nerve - NCBI
The musculocutaneous nerve innervates the three muscles of the anterior compartment of the arm: the coracobrachialis, biceps brachii, and brachialis muscles.Introduction · Structure and Function · Muscles · Surgical Considerations
[48]
Anatomy, Shoulder and Upper Limb, Arm Nerves - StatPearls - NCBI
The terminal branches of the brachial plexus include the axillary, musculocutaneous, radial, ulnar, and median nerves. · The axillary nerve originates from the ...
[49]
Anatomy, Shoulder and Upper Limb, Ulnar Nerve - StatPearls - NCBI
The ulnar nerve is one of the 5 terminal branches of the brachial plexus, arising from the medial cord. It supplies motor and sensory innervation to the upper ...
[50]
Template:Upper limb ossification table - UNSW Embryology
The fusion of the epiphyses of the phalanges with the diaphyses takes place in the 18th-20th year. Ossification begins generally in the 13th - 14th years, and ...
[51]
Ossification centers of the pectoral girdle | Radiology Reference Article
Aug 25, 2025 · Ossification centers of the proximal humerus · diaphysis (shaft): 8 weeks in utero · head: 1-6 months · greater tubercle: 1 year · lesser tubercle: ...Missing: timeline | Show results with:timeline
[52]
Proximal humeral anatomy - AO Surgery Reference
Fusion of tuberosities with humeral epiphysis; 7–13 years; Fusion of physis; 14–17 years in females, 16–18 years in males. In a neonatal injury, MRI or ...Missing: timeline | Show results with:timeline
[53]
Ossification centers of the elbow | Radiology Reference Article
Aug 6, 2025 · capitellum: 2-24 months · radial head: 3-6 years · internal (medial) epicondyle: 4-7 years · trochlea: 8-10 years · olecranon 8-10 years · external ( ...Missing: timeline | Show results with:timeline
[54]
STUDY OF SECONDARY OSSIFICATION CENTERS OF THE ... - NIH
The age interval of appearance and fusion were, respectively: capitulum (0 to 1 year; 10 to 15 years), radius head (2 to 6 year; 12 to 16 years), medial ...Missing: timeline | Show results with:timeline
[55]
Management of Pediatric Proximal Humerus Fractures - PMC - NIH
These secondary ossification centers appear in the proximal humeral epiphysis at around 2-4 months, with the greater tuberosity ossification center appearing ...Missing: timeline | Show results with:timeline
[56]
Formation of the Limb Bud - Developmental Biology - NCBI Bookshelf
Limb buds form when mesenchyme cells proliferate, creating a bulge. FGF10 from lateral plate mesoderm cells initiates this process.
[57]
Genetic Regulation of Embryological Limb Development with ...
The “patterning” process controls the genetic signals governing limb development in three axes: proximal-distal, anterior–posterior, and dorsal–ventral. It ...
[58]
Embryology - Basic Science - Orthobullets
Jul 22, 2022 · Limb development forms between 4-8 weeks, with the limb bud forming at 26 days after fertilization. The AER controls proximal to distal growth.
[59]
Embryology of the Upper Extremity - Musculoskeletal Key
Sep 5, 2018 · Two sources of cells migrate from their origins into the limb bud. The cells from the lateral plate mesoderm become bone, cartilage, and tendon.
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The roles of FGFs in the early development of vertebrate limbs
The purpose of this review is to discuss the functions performed by members of the FGF family in one of the best-studied vertebrate developmental systems—limb ...Fgf Ligand And Receptor... · Fgf Function In The... · Fgf Function In Limb Bud...
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Non-syndromic phocomelia: A rare case report signifying prenatal ...
Aug 16, 2024 · Phocomelia affects approximately 0.6 to 4.2 per 100,000 live births globally, with a higher incidence observed in left-sided upper limbs.
[62]
Epidemiology of proximal humerus fractures - PMC - PubMed Central
Jun 22, 2021 · They are the seventh most frequent fractures in adults [2]. Their prevalence varies from 4 to 10% of all fractures, according to several studies ...
[63]
Humeral Shaft Nonunion - Trauma - Orthobullets
Jun 3, 2025 · 5 to 10% with surgical management. Anatomic location. proximal third humeral shaft fractures are felt to have higher rates of nonunion. Risk ...
[64]
Proximal Humerus Fractures - Trauma - Orthobullets
Oct 22, 2025 · Most proximal humerus fractures can be treated nonoperatively including greater tuberosity fracture.
[65]
Humeral Shaft Fractures - Trauma - Orthobullets
Sep 13, 2025 · Humeral shaft fractures are common fractures of the diaphysis of the humerus, which may be associated with radial nerve injury.Missing: structure | Show results with:structure<|separator|>
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Distal Humerus Fractures - Trauma - Orthobullets
Aug 12, 2025 · Distal Humerus Fractures are traumatic injuries to the elbow that comprise of supracondylar fractures, single column fractures, column fractures ...
[67]
Distal Humerus Fractures - StatPearls - NCBI Bookshelf
Heterotopic Ossification: As is the case in most settings of severe trauma, heterotopic ossification can be a postoperative complication. Risk factors that ...Distal Humerus Fractures · Evaluation · Treatment / Management
[68]
Humerus Fracture (Upper Arm Fracture) - Johns Hopkins Medicine
A temporary splint extending from the shoulder to the forearm and holding the elbow bent at 90 degrees can be used for initial management of the fracture.Missing: complications | Show results with:complications
[69]
Humerus Fractures Overview - StatPearls - NCBI Bookshelf
Radial nerve palsy is a feared complication of humerus shaft fractures that can occur during the injury, open reduction, and internal fixation or ...Continuing Education Activity · Introduction · Evaluation · Treatment / Management
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Deltopectoral approach to the proximal humerus
The (anterior) deltopectoral approach can be used for almost any proximal humeral fracture treatment and is often the preferred approach.
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Hemiarthroplasty for proximal humerus fracture—a dying art - Freeman
Primary hemiarthroplasty for proximal humerus fractures has been shown to have mixed results, but it can provide good pain relief and function.Fracture classification · History of shoulder... · Indications for hemiarthroplasty
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Reverse shoulder arthroplasty in recent proximal humerus fractures
Reverse shoulder arthroplasty is now the standard treatment for displaced, three- or four-part, proximal humeral fractures in patients older than 70 years.
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Osteoporosis Guidelines: Screening, Diagnosis, Treatment
Jan 8, 2024 · T-score between −1.0 and −2.5 and a fragility fracture of proximal humerus, pelvis, or distal forearm. T-score between −1.0 and −2.5 and ...
[74]
Osteosarcoma | Radiology Reference Article - Radiopaedia.org
Oct 13, 2025 · Primary osteosarcoma typically occurs in young patients (10-20 years) with 75% taking place before the age of 20 because the growth centers of ...Parosteal osteosarcoma · Osteosarcoma · Conventional osteosarcoma · Distal femur
[75]
Avascular Necrosis and Posttraumatic Arthritis After Proximal ... - NIH
Jan 13, 2023 · The frequency of proximal humerus fractures (PHF) continues to rise, mirroring our aging population. Open reduction and internal fixation (ORIF) ...
[76]
Proximal Humerus Fracture Nonunion and Malunion - Trauma
Jan 20, 2025 · proximal humerus fractures account for 4% to 5% of all fractures. Risk factors for nonunion. fracture characteristics. 2-part (surgical neck) ...
[77]
Risk factors for surgical site infection after closed proximal humerus ...
Nov 27, 2023 · In our study, the mean time from injury to definitive surgery was longer in the infection group (7.9 days) than in the non‐infection group (5.4 ...
[78]
Complication rates and outcomes stratified by treatment modalities ...
Nov 24, 2013 · The overall complication rate was 56%. The most common complications were fracture-displacement, malunion, humeral head necrosis and ...
[79]
Biocomposite-Based Biomimetic Plate for Alternative Fixation ... - NIH
Oct 13, 2025 · For successful healing of proximal humeral fractures, the ideal implant material should degrade gradually, thus transferring mechanical loads ...
[80]
Long-term follow-up of stemless anatomic shoulder arthroplasty with ...
Jul 3, 2025 · Prosthesis survival at 13 years reached 89.9% for all revisions and 90.8% for humeral component revision. Conclusion. Stemless aTSA with a ...Missing: longevity | Show results with:longevity
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Comparative morpho‐functional analysis of the humerus and ulna in ...
Sep 26, 2022 · Our results show that interspecific anatomical differences in the humerus and ulna exist among the three species.
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[PDF] Animal Anatomy
COMPARATIVE ANATOMY OF THE HUMERUS. Cattle. The humerus of cattle is smoother than that of equines. The musculospiral groove is shallower and the deltoid ...
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Functional anatomy of the gibbon forelimb: adaptations to a ... - NIH
Like monkeys and most apes (Howell & Straus, 1961), gibbons possess a dorso-epitrochlearis muscle that connects the latissimus dorsi to the short head of the ...
[84]
Relationship between humeral geometry and shoulder muscle ... - NIH
Suspensory primates (brachiators) have a relatively thick cortical bone in the proximal humerus ... Functional anatomy of the gibbon forelimb: adaptation ...
[85]
The Gross Anatomical and Histological Features of the Humerus in ...
... gibbons, orangutans, gorillas, chimpanzees, and humans. The ... "The Gross Anatomical and Histological Features of the Humerus in African Green Monkeys ...
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Humerus shape evolved in cetaceans under relaxed selection and ...
Mar 29, 2025 · Evolution of the cetacean humerus showed a strong phylogenetic signal in shape variation. However, humerus shape also evolved towards increasing ...
[87]
Cetaceans Humerus Radiodensity by CT: A Useful Technique ... - NIH
Jul 13, 2022 · In cetaceans, the humerus is a relatively short bone that lacks the medullar cavity. However, its bone compartments, cortical and trabecular, ...
[88]
Functional and phylogenetic interpretation of the forelimb myology of ...
May 1, 2023 · It originates via fleshy fibers from the proximal surface of the cranial facet of the lateral supracondylar crest of the humerus (Figure 4a) and ...
[89]
Bone remodeling in the longest living rodent, the naked mole‐rat - NIH
Certainly, this indicates that the ulna fuse its epiphyses before the humerus and therefore stops growing (elongating) earlier. Contrarily, the humerus ...
[90]
Morphological Diversity of the Humerus of the South American ...
Abstract. Humeral variation associated with digging ability in the subterranean rodent Ctenomys was analyzed through 6 functionally significant indexes.
[91]
The early evolution of the tetrapod humerus - PubMed
A comparative analysis of this fossil and other relevant humeri from the Devonian shows that the role of the limb in propping the body arose first in fish fins ...
[92]
Harvard Scientists Reconstruct the Game-Changing Evolution From ...
Jan 23, 2021 · The evolution of the humerus helped early tetrapods become better walkers, enabling the rise of land ecosystems and diverse life on Earth.
[93]
[PDF] The Early Evolution of the Tetrapod Humerus - Semantic Scholar
A comparative analysis of this fossil and other relevant humeri from the Devonian shows that the role of the limb in propping the body arose first in fish ...Missing: Entelognathus | Show results with:Entelognathus
[94]
Adaptive landscapes unveil the complex evolutionary path from ...
Jun 24, 2025 · The reconstructed ancestral landscape for the Synapsida node heavily optimizes humeral torsion, as well as 'spin' muscle leverage, and this ...Missing: elongation | Show results with:elongation
[95]
From sprawling to parasagittal locomotion in Therapsida
Oct 5, 2022 · Evolution “towards” the origin of mammals. Synapsids show a variety of limb postures and associated changes of the locomotor system. Therapsids ...
[96]
The postcranial anatomy of Brasilodon quadrangularis and the ...
Torsion of the humeral shaft. The torsion (or twisting) of the humerus is regarded as a very important character to determinate sprawling or erect posture in ...
[97]
The morphology and evolutionary history of the glenohumeral joint ...
The glenohumeral joint, the most mobile joint in the body of hominoids, is involved in the locomotion of all extant primates apart from humans.
[98]
Humeral torsion and throwing proficiency in early human evolution
Aug 9, 2025 · A more lateral glenohumeral orientation might indicate a shift away from arboreal activities in favor of other activities such as throwing, tool ...
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Assessment of the Morphological Affinities of A.L. 288–1 (A ...
Feb 4, 2015 · The proximal humerus morphology of A.L. 288–1r (A. afarensis) exhibits mixed characteristics, showing some affinities with the modern humans ( ...
[100]
Homoplasy in the evolution of modern human-like joint proportions ...
May 12, 2021 · Here, we find the limb joint proportions of Australopithecus afarensis, Homo erectus, and Homo naledi to resemble those of modern humans.
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The evolution of flight in bats: a novel hypothesis - Wiley Online Library
Sep 10, 2020 · This reduced cortical thickness of the forelimb bones in bats and birds may contribute more to flight capability than pneumatisation (Swartz et ...Missing: ungulates | Show results with:ungulates
[102]
No evidence for parallel evolution of cursorial limb adaptations ...
Aug 17, 2021 · Our study suggests that the macroevolutionary trend of limb elongation in ungulate-like mammals is not universal and is highly influenced by the evolutionary ...Missing: shortening | Show results with:shortening