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Infraglenoid tubercle

The infraglenoid tubercle is a small, roughened bony prominence located on the lateral surface of the scapula, immediately inferior to the glenoid cavity, which forms the socket of the shoulder joint.^[1]^[2] This tubercle serves primarily as the origin point for the long head of the triceps brachii muscle, a key extensor of the elbow and stabilizer of the shoulder.^[3]^[4] Structurally, the infraglenoid tubercle extends slightly superiorly toward the glenoid labrum and blends with the glenohumeral joint capsule, contributing to the overall stability of the shoulder girdle.^[4] Its rough texture facilitates a secure muscular attachment, allowing the long head of the triceps to originate from this site and converge with the muscle's lateral and medial heads before inserting on the olecranon process of the ulna.^[2]^[3] Through this attachment, the tubercle plays a role in elbow extension, as well as arm adduction and extension at the shoulder joint.^[3]^[5] Clinically, injuries or pathologies affecting the infraglenoid tubercle, such as avulsion fractures, can impair triceps function and shoulder stability, often requiring imaging like MRI for diagnosis and potential surgical intervention if associated with axillary nerve damage.^[3] The tubercle's position near the glenohumeral joint also makes it relevant in conditions like rotator cuff tears or scapular fractures, where altered biomechanics may indirectly impact its attached musculature.^[5]

Anatomy

Location and structure

The infraglenoid tubercle is a small, roughened bony projection situated on the lateral border of the scapula, immediately inferior to the glenoid cavity.^[1]^[6] This tubercle forms part of the scapular neck and appears as a triangular-shaped roughening designed to facilitate tendon attachment.^[7] Its surface texture is notably coarse, providing a stable anchorage point.^[8] Embryologically, the infraglenoid tubercle develops as part of the scapula, which originates from the somatopleuric layer of the lateral plate mesoderm for its glenoid-proximal regions, with contributions from somitic mesoderm to the blade.^[9] The scapular anlage first appears around Carnegie stage 18 (approximately weeks 6-7 of gestation), with endochondral ossification commencing in the glenoid area by week 11.^[10]^[11] Anatomical variations in the infraglenoid tubercle include differences in prominence and overall scapular size across sexes and populations, with males typically exhibiting larger and more pronounced features due to greater upper limb muscle mass requirements.^[12]^[13] These dimorphisms are consistent with broader sexual differences in scapular morphology observed in various ethnic groups.^[14]

Relations to adjacent structures

The infraglenoid tubercle is positioned immediately inferior to the glenoid cavity on the lateral border of the scapula, serving as a key landmark in the shoulder region's bony architecture.^[2] This proximity to the glenoid cavity, which articulates with the humeral head, places the tubercle in close relation to the glenohumeral joint's articular surfaces, with its superior extension blending into the joint capsule.^[2]^[4] Laterally, it aligns with the axillary border of the scapula, the thickest margin that extends superolaterally toward the axilla, facilitating structural continuity along this edge.^[15] In terms of soft tissue adjacencies, the infraglenoid tubercle exhibits lateral and inferior proximity to the origin of the teres major muscle, which arises from the lower portion of the lateral border and the inferior angle of the scapula's posterior surface.^[10] Vascular relations include posterior adjacency to the circumflex scapular artery, a branch of the subscapular artery that courses around the lateral border as part of the scapular anastomosis, supplying the surrounding posterior shoulder structures.^[15] The axillary nerve passes laterally in relation to the tubercle, traveling through the quadrangular space inferiorly to innervate nearby muscles like the teres minor and deltoid.^[16] Ligamentously, the infraglenoid tubercle maintains an indirect connection to the glenohumeral ligaments through its position adjacent to the inferior glenoid rim, where these ligaments—superior, middle, and inferior—attach to reinforce the joint capsule.^[17] In comparative anatomy, the infraglenoid tubercle mirrors the superglenoid tubercle in form and role as a paired bony prominence flanking the glenoid cavity, with the former positioned inferiorly and the latter superiorly to provide symmetric attachment points on opposite aspects of the glenoid.^[2]

Function

Muscle origins

The infraglenoid tubercle primarily serves as the origin for the long head of the triceps brachii muscle, with its tendon fibers attaching directly to the roughened surface of this bony prominence at the inferior margin of the glenoid fossa.^[4]^[3] This attachment provides a stable proximal anchorage for the muscle, enabling its extension across the shoulder joint. The tendon of the long head originates inferiorly from the tubercle, blends with the adjacent glenohumeral joint capsule, and passes through the shoulder joint to descend along the posterior aspect of the humerus.^[4]^[18] It then converges with the lateral and medial heads of the triceps brachii proximal to the elbow, forming a common tendon that inserts onto the olecranon process of the ulna.^[3]^[19] Anatomical variations in this region are uncommon but may include additional slips or fusions of the long head with adjacent structures, such as the teres major muscle, or the presence of a fourth head originating from nearby sites like the shoulder capsule.^[3]^[20] Histologically, the attachment site features dense fibrous connective tissue at the enthesis, where Sharpey's fibers—bundles of type I collagen—perforate the cortical bone to integrate the tendon securely with the underlying osseous structure.^[21]^[22]

Role in upper limb movement

The infraglenoid tubercle contributes to upper limb movement primarily through its role as the origin point for the long head of the triceps brachii, enabling this muscle head to generate force for elbow extension and assist in shoulder stabilization.^[4] During elbow extension, the long head produces significant torque, particularly when the shoulder is in neutral or low elevation positions, where it generates higher muscle force compared to the lateral and medial heads.^[23] This force contribution supports primary extension at the elbow joint, with biomechanical models indicating the long head's involvement enhances overall triceps efficiency in straightening the arm, especially under resisted conditions.^[24] In addition to elbow extension, the long head's attachment via the infraglenoid tubercle allows secondary actions at the shoulder, including adduction and extension, which help depress the humerus during multi-joint movements.^[25] For instance, in pushing activities like the bench press, the tubercle acts as a stable proximal anchor, facilitating coordinated elbow extension and shoulder stabilization as the long head shows elevated electromyographic (EMG) activity in flat and decline variations compared to incline positions.^[26] EMG studies reveal high activation of the long head during resisted elbow extension when the shoulder is in neutral or low flexion positions (0°-45°), though this shifts toward the medial head at 90° and higher elevations, underscoring the tubercle's role in position-dependent kinematics.^[23]

Clinical significance

Fractures and injuries

Avulsion fractures of the infraglenoid tubercle represent a rare subtype of shoulder injury, comprising a small fraction of all scapular fractures, which themselves account for less than 1% of total skeletal fractures and 3-5% of shoulder girdle injuries.^[27] These avulsions are particularly uncommon but tend to occur more frequently in adolescents due to the relative weakness of open apophyseal growth plates compared to the tensile strength of the attached triceps tendon.^[28] In this demographic, they often arise from sports-related trauma, such as forceful elbow extension against resistance during activities like weightlifting, wrestling, or falls onto an outstretched arm.^[29]^[28] The primary mechanism involves acute tensile failure at the triceps tendon-bone interface, where sudden eccentric contraction of the long head of the triceps pulls the tubercle fragment away from the glenoid.^[30] This can occur in isolation or, more commonly, in association with traumatic anterior shoulder dislocation, where the humeral head impacts the glenoid, exacerbating the avulsive force.^[30] In adults, such injuries are even rarer and typically require high-energy trauma, though isolated cases have been reported in activities like surfing.^[31] Clinically, patients present with acute posterior shoulder pain, localized swelling, and significant weakness in elbow extension due to disruption of the triceps origin, which impairs its role in upper limb extension.^[32] Pathophysiologically, the injury results from the imbalance between muscle pull and bone maturity, leading to bony fragmentation rather than tendon rupture in younger individuals.^[28] Infraglenoid tubercle involvement also occurs in broader scapular body fractures, which constitute approximately 45% of all scapular fractures and frequently affect the lateral border region housing the tubercle.^[27] These body fractures, often from high-energy impacts like motor vehicle accidents or falls, carry an incidence of about 10 per 100,000 population annually, with lateral border disruptions heightening the risk of associated triceps dysfunction.^[33] Risk factors include participation in high-impact sports such as football, gymnastics, and throwing activities, where repetitive or explosive elbow extension predisposes adolescents to avulsion.^[28] In older adults, underlying conditions like reduced bone density may contribute to fracture susceptibility under trauma, though these injuries remain predominantly trauma-driven rather than fragility-based.^[28]

Surgical and diagnostic considerations

Diagnostic imaging plays a crucial role in identifying infraglenoid tubercle avulsions, typically beginning with plain radiography using anteroposterior (AP) and axillary views to detect bony fragments, with a reported sensitivity of approximately 80-86% for glenoid-related fractures.^[34] Computed tomography (CT) is employed for detailed assessment of fracture displacement and fragment size, often utilizing 3D reconstructions to aid in surgical planning, as it provides superior reliability over plain films for evaluating displacement in scapular injuries.^[35] Magnetic resonance imaging (MRI) is indicated for evaluating associated soft tissue involvement, such as triceps tendon tears, offering high sensitivity for detecting tendon pathology and guiding treatment decisions.^[36] Treatment for infraglenoid tubercle avulsions depends on displacement and stability; non-displaced fractures without instability are managed conservatively with immobilization in a sling or brace for 4-6 weeks, followed by gradual rehabilitation to restore range of motion and strength.^[30] For displaced fractures or those with significant tendon retraction, surgical intervention is recommended, involving open reduction and internal fixation (ORIF) with screws for bony fragments or tendon reattachment techniques, achieving success rates exceeding 90% in restoring function when performed acutely.^[37] Postoperative protocols emphasize physical therapy, starting with passive motion and progressing to active elbow extension strengthening exercises over 3-6 months, with full return to activities typically occurring within this timeframe to prevent stiffness.^[38] Prognostic factors include the timeliness of intervention, where early surgical repair for displaced avulsions reduces the risk of chronic triceps weakness and complications to less than 5%, while conservative approaches yield good outcomes in stable cases without long-term instability.^[39]

References

[1]
Infraglenoid tubercle - e-Anatomy - IMAIOS
The infraglenoid tubercle of the scapula is a small bony prominence located at the inferior aspect of the glenoid cavity (glenoid fossa).
[2]
The Scapula - Surfaces - Fractures - Winging - TeachMeAnatomy
### Summary of Infraglenoid Tubercle
[3]
Anatomy, Shoulder and Upper Limb, Triceps Muscle - NCBI - NIH
Long head—The origin of the long head is the infra-glenoid tubercle of the scapula. Because it attaches to the scapula, the long head not only extends the ...<|control11|><|separator|>
[4]
Triceps brachii muscle: Attachments, supply and functions - Kenhub
The long head arises from the infraglenoid tubercle of scapula, which is a rough area at the inferior margin of the glenoid fossa. Its attachment extends ...
[5]
Scapula (Shoulder Blade): What It Is, Anatomy & Function
Feb 7, 2024 · Superglenoid tubercle: Where your biceps muscle attaches. Infraglenoid tubercle: Where your triceps muscle attaches. Posterior (inferior) ...
[6]
Infraglenoid Tubercle | Complete Anatomy - Elsevier
The infraglenoid tubercle (infraglenoid tuberosity) is the rough prominence found along the inferior portion of the head of the scapula.
[7]
Digital Dissector
Infraglenoid Tubercle - triangular-shaped roughening inferior to the glenoid cavity; attachment for the long head of the triceps brachii m. G. Supraglenoid ...
[8]
Anatomy, Thorax, Scapula - StatPearls - NCBI Bookshelf - NIH
Just below the cavity is an impression called the infraglenoid tuberosity where the long head of the triceps brachii originates.
[9]
Dual origin and segmental organisation of the avian scapula
Sep 1, 2000 · (2) The scapular head and neck are of lateral plate mesodermal origin. (3) In contrast, the scapular blade is composed of somitic cells. (4) ...
[10]
Anatomy, Back, Scapula - StatPearls - NCBI Bookshelf - NIH
infraglenoid tubercle of scapula. Insertion: Olecranon process of ulna and fascia of the forearm. Innervation: Radial nerve (C6, C7, C8). Deltoid. Function ...
[11]
(PDF) Shoulder girdle formation and positioning during embryonic ...
Sep 11, 2020 · The scapula is formed by endochondral ossification, and the anlagen is first evident at about Carnegie stage (CS) 18 [19] (Fig. 1.1b). By CS 20, ...
[12]
[PDF] Sex Determination in Egyptian Population from Scapula by ...
Apr 11, 2017 · The results reveal males have larger scapula than females with no statistical significant difference between both sides in either sex. The ...
[13]
Sexual Dimorphism of the Scapula by Morphometric Analysis...
This study was carried out to morphometrically measure the scapula bone that can be used for sex determination among the South Indian population.
[14]
Anthropometric study of the scapula in a contemporary population ...
Jul 10, 2024 · This study aimed to develop a function for sex estimation using scapula parameters and analyze glenohumeral osteoarthritis prevalence, finding ...
[15]
Scapula: Anatomy and clinical notes | Kenhub
Triceps brachii muscle (long head) – its origin is the infraglenoid tubercle found on the lateral border, inferior to the glenoid cavity. It is responsible for ...
[16]
Anatomy Tables - Axilla, Posterior Shoulder, & Arm
(N432, TG2-18A, TG2-18B, Practical), long head: infraglenoid tubercle of scapula ... significance: traversed by the axillary nerve & posterior humeral circumflex ...<|separator|>
[17]
Anatomy, Shoulder and Upper Limb, Glenohumeral Joint - NCBI - NIH
Mar 3, 2025 · The glenoid cavity is a shallow osseous structure deepened by a fibrocartilaginous rim, the glenoid labrum, which spans the vault's osseous ...Missing: infraglenoid | Show results with:infraglenoid
[18]
Triceps brachii muscle - e-Anatomy - IMAIOS
1. Long head. Originating from the infraglenoid tubercle of the scapula, the long head is unique as it crosses the glenohumeral (shoulder) joint. · 2. Lateral ...Musculus Triceps Brachii · Definition · Individual Heads<|separator|>
[19]
Triceps Brachii - Attachments - Actions - TeachMeAnatomy
### Summary of Triceps Brachii Details
[20]
https://anatomicvariations.org/news/2018/6/27/triceps-brachii
[21]
Sharpey's fibers: Location and function | Kenhub
Mar 25, 2024 · Sharpey's fibers, also known as perforating fibers or bone fibers, are bundles of collagen fibers which connect periosteum to bone.
[22]
Where tendons and ligaments meet bone: attachment sites ...
Yes, some tendons/ligaments certainly do have Sharpey's fibres – notably fibrous entheses in regions where there is substantial cortical bone, at the sites ...
[23]
The different role of each head of the triceps brachii muscle in elbow ...
Mar 2, 2018 · The long head contributes to elbow extension more at shoulder elevation and the medial head takes over at 90° and above of shoulder elevation.
[24]
The different role of each head of the triceps brachii muscle in elbow ...
The long head contributes to elbow extension more at shoulder elevation and the medial head takes over at 90° and above of shoulder elevation.
[25]
The shoulder extension function of the triceps brachii - ScienceDirect
The purpose of this study was to investigate the influence of elbow and shoulder joint angles on the shoulder extension function of the TB.
[26]
Effects of Variations of the Bench Press Exercise on the EMG Activity ...
The long head of the triceps brachii was more active during the decline and flat bench presses than the other two conditions, and was also more active with ...
[27]
Effect of shoulder position on triceps brachii heads activity ... - PubMed
The present study aimed to compare the electromyographic signal of triceps brachii long and lateral heads among three different elbow ranges of motion (ROM)
[28]
Elbow Extensor Muscles in Humans and Chimpanzees: Adaptations ...
Oct 30, 2022 · We have found that the triceps brachii of chimpanzees is more prepared for strength and power as an adaptation to locomotion.
[29]
Scapular Fracture - Physiopedia
Scapular fracture is the fracture of scapula which is rare and is often caused by direct trauma from the back or side.Missing: Holman | Show results with:Holman
[30]
Avulsion Fractures - StatPearls - NCBI Bookshelf
Epidemiology · Certain fracture types tend to be more common in adolescents, and tend to be associated with sports-related injuries. · Adults avulsion fractures, ...
[31]
Scapular Avulsion Fracture of a High School Wrestler - jospt
Blunt trauma results in scapular frac- tures in the athletic population as well, as depicted by Cain and Hamil- ton in their article detailing four p r e.
[32]
Infraglenoid tubercle avulsion and greater tuberosity fracture ...
Avulsion fractures of the infraglenoid tubercle are uncommon lesions after an anterior shoulder dislocation and, without signs of instability, can be treated ...
[33]
Distal Triceps Injuries - Radsource
Proximal triceps avulsions are rare; one case of a proximal avulsion of the long head from the infraglenoid tubercle was recently reported in a surfer8.
[34]
Scapula Fracture (Shoulder Blade Fracture) | Johns Hopkins Medicine
What are the symptoms of a scapula fracture? Pain at rest; Pain when moving the arm; Swelling; Severe bruising. What is the treatment for a scapula fracture?Missing: infraglenoid tubercle
[35]
Epidemiology of scapular fractures. Incidence and classification of ...
There were 338 scapular fractures in 322 patients. The annual incidence was 10/10(5) inhabitants, of which 30 percent affected the glenoid cavity.
[36]
Indication for Computed Tomography Scan in Shoulder Instability
Oct 30, 2017 · For detection of glenoid bone loss on plain radiographs, the sensitivity was 86% both with and without the axillary view, and the specificity ...
[37]
A Reliable Radiographic Measurement Technique for Extra-articular ...
Our data suggest three-dimensional CT is more reliable than plain radiography in the assessment of scapula fracture displacement.
[38]
What is the best imaging modality for a suspected torn triceps ...
Jun 24, 2025 · Magnetic Resonance Imaging (MRI) is considered the gold standard for diagnosing triceps tendon injuries, including partial and complete tears 2, ...
[39]
Triceps Rupture - Shoulder & Elbow - Orthobullets
Jan 24, 2025 · Triceps Ruptures are rare injuries to the elbow extensor mechanism that most commonly occurs as a result of a sudden forceful elbow contraction ...
[40]
Triceps tendon avulsion - Physiopedia
Avulsion of the triceps tendon may be caused by a trauma, but can also occur spontaneously or after surgical repair from a previous injury.
[41]
Nonoperatively treated infraglenoid tubercle avulsion - PubMed
Infraglenoid tubercle avulsion fractures are extremely rare injuries. We report a 38-year-old male with glenoid cavity fracture and infraglenoid tubercle ...