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Lesser tubercle
Lesser tubercle
Lesser tubercle
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The lesser tubercle of the humerus, although smaller, is more prominent than the greater tubercle: it is situated in front, and is directed medially and anteriorly.

The projection of the lesser tubercle is anterior from the junction that is found between the anatomical neck and the shaft of the humerus and easily identified due to the intertubercular sulcus (Bicipital groove).

Lesser Tubercle of right humerus
Lesser tubercle of right humerus
Insertion of subscapularis muscle
Insertion of subscapularis muscle

Above and in front it presents an impression for the insertion of the tendon of the subscapularis.

Additional images

[edit]
  • The left shoulder and acromioclavicular joints, and the proper ligaments of the scapula.
    The left shoulder and acromioclavicular joints, and the proper ligaments of the scapula.
  • Human arm bones diagram
    Human arm bones diagram

References

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Lesser tubercle

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from Grokipedia
The lesser tubercle, also known as the lesser tuberosity, is a small bony prominence located on the anterior surface of the proximal end of the , the of the upper arm. It lies just inferior to the humeral head and anterior to the anatomical neck, forming the medial border of the intertubercular sulcus () that separates it from the larger laterally. Structurally, the lesser tubercle is a smooth, palpable elevation that ossifies separately during the first six years of life before fusing with the humeral shaft by adolescence. It provides primary insertion points for key shoulder muscles, including the subscapularis, which originates from the subscapular fossa of the scapula and enables internal rotation of the humerus as part of the rotator cuff. The teres major muscle also inserts here, contributing to adduction and further internal rotation of the arm. Additionally, the transverse humeral ligament attaches to its lateral aspect, helping to stabilize the long head of the biceps brachii tendon within the intertubercular sulcus. In terms of function, the lesser tubercle plays a critical role in shoulder joint stability and mobility by anchoring rotator cuff muscles that maintain humeral head alignment during arm movements. Clinically, it is relevant in proximal humerus fractures, rotator cuff tears, or avulsion injuries, where damage can lead to impaired internal rotation, shoulder instability, or require surgical repair such as reattachment or fixation. Such conditions are common in trauma or degenerative shoulder disorders, often assessed via imaging like X-rays or MRI to evaluate tubercle integrity.

Anatomy

Location and relations

The lesser tubercle is a small bony prominence located on the proximal anterior aspect of the , positioned inferior to the humeral head and medial to the . It projects anteriorly from the junction between the anatomical neck and the shaft of the , forming a distinct eminence that is palpable on the anterior . This structure lies immediately distal to the anatomical neck, which separates the humeral head from the tubercles, and proximal to the surgical neck, where the bone narrows toward the shaft. The lesser tubercle forms the medial boundary of the (also known as the ), a deep groove that separates it from the laterally. In relation to the , it is situated anterior to the glenoid cavity during glenohumeral articulation. It is also adjacent to the insertion of the subscapularis on its anterior surface. Developmentally, the lesser tubercle forms through as part of the proximal humeral , with its typically appearing between 3 and 5 years of age and fusing with the humeral shaft by .

Structure and attachments

The lesser tubercle is a smaller projection compared to the , positioned more medially on the proximal , with a prominent anterior orientation that lacks a distinct posterior surface. Its anterior aspect features a smooth surface adapted for muscular insertion, while the insertion zone exhibits a roughened texture to facilitate fiber anchorage. This tubercle forms a palpable ridge on the anterior , identifiable just lateral to the during with the arm in neutral or internal rotation. The primary soft tissue attachment to the lesser tubercle is the of the , which inserts onto its anteromedial aspect, constituting a critical component of the mechanism. This insertion site reinforces the anterior stability of the glenohumeral joint through the 's broad, fan-like distribution across the tuberosity. Secondary attachments include the tendon of the , which inserts onto the crest of the lesser tubercle. The transverse humeral ligament spans between the lesser and greater tubercles superior to the intertubercular groove, helping to retain the long head of the biceps tendon within the groove. Additionally, fibers from the anterior glenohumeral contribute minor attachments to the lesser tubercle, blending with the subscapularis tendon to enhance capsular integrity.

Function

Role in shoulder mechanics

The lesser tubercle serves as a critical attachment site for the subscapularis , enabling it to function as a fulcrum that facilitates internal (medial) of the through mechanical leverage. This bony prominence allows the subscapularis to generate by pulling on the anterior , particularly when the is positioned in adduction or neutral , thereby rotating the humeral head medially relative to the glenoid. As detailed in prior anatomical descriptions, the 's insertion on the lesser tubercle optimizes this lever for efficient force transmission during rotational movements. In the broader context of glenohumeral joint stability, the lesser tubercle contributes to resisting anterior dislocation by anchoring the subscapularis within the mechanism, which collectively compresses the humeral head against the . This dynamic stabilization is essential during activities involving anterior shear forces, where the subscapularis' pull via the tubercle counters translational instability and maintains joint congruence. Biomechanical studies emphasize that disruption to this attachment can compromise the anterior effect, highlighting the tubercle's integral role in preventing . During arm adduction and internal rotation, the lesser tubercle anchors the compressive forces exerted by the subscapularis, which depress the humeral head inferiorly against the glenoid to counteract superior migration. This depressive action is particularly vital in load-bearing positions, where the tubercle serves as a stable base for vectoring muscle forces that balance the deltoid's superior pull and preserve joint centering. The lesser tubercle's positioning further aids in maintaining humeral head centering during overhead activities, such as elevation or throwing motions, by facilitating the subscapularis' contribution to overall balance and congruence under dynamic loads. This ensures smooth arthrokinematics by distributing forces that prevent eccentric loading on the glenoid.

Muscle and ligament involvement

The , recognized as the anterior-most member of the , originates broadly from the subscapular fossa on the anterior surface of the and converges to insert onto the lesser tubercle of the via a robust . This attachment configuration allows the subscapularis to drive internal rotation of the while also contributing to adduction of the , thereby playing a pivotal role in stabilization during these movements. The originates from the inferior angle and lower lateral border of the and inserts onto the crest of the lesser tubercle and the medial lip of the intertubercular sulcus. It assists in adduction and internal rotation of the arm, synergizing with the subscapularis and latissimus dorsi to extend and stabilize the . The transverse humeral ligament extends across the intertubercular groove, bridging the lesser tubercle medially to the laterally, and functions to retain the long head of the biceps brachii tendon within the groove, preventing its medial during motion. Although anatomical studies have debated its existence as a discrete structure—suggesting it may represent superior fibers of the subscapularis tendon or extensions—the ligament's traditional role in biceps tendon stability remains a key aspect of shoulder anatomy. In synergistic function, the subscapularis integrates with the supraspinatus, infraspinatus, and teres minor muscles of the to dynamically compress the humeral head against the , enhancing joint congruence; the lesser tubercle serves as a critical fixed anchor for subscapularis tension, optimizing this compressive force. The subscapularis receives innervation from the upper and lower (arising from C5-C7 roots of the ), while the regional vascular supply to the lesser tubercle and surrounding structures is provided by the anterior humeral circumflex artery, a branch of the .

Clinical significance

Fractures and injuries

Avulsion fractures represent the primary traumatic injury to the lesser tubercle, commonly resulting from the eccentric contraction of the during forced abduction and external of the , which pulls the attachment site. These injuries may also arise from high-energy mechanisms such as falls on an outstretched , where axial loading on the extended upper extremity contributes to the avulsion through indirect tensile forces on the subscapularis . The subscapularis, as the primary internal rotator of the , plays a central role in these avulsive events by generating the forceful pull that detaches the tubercle fragment. In terms of types, isolated avulsion fractures predominate in adolescents, where the relative weakness of the physeal plate or apophysis compared to the strength predisposes the lesser tubercle to separation during trauma. By contrast, in adults, lesser tubercle fractures are frequently associated with more complex proximal fractures, often as part of two-part or multi-part injuries involving the surgical neck or . The underlying mechanisms encompass both direct high-energy impacts, such as those from vehicular accidents or falls from height, and indirect mechanisms driven by violent subscapularis contraction resisting external rotation. These fractures exhibit a higher incidence in the setting of dislocations, particularly posterior glenohumeral dislocations, where the lesser tubercle may engage the glenoid rim or become interposed, complicating reduction. Diagnosis begins with clinical evaluation revealing acute anterior pain, tenderness over the lesser tubercle, and significant weakness or pain during internal maneuvers, such as the lift-off or belly-press tests. Initial imaging via anteroposterior and axillary lateral X-rays is essential to detect the and assess fragment displacement, with advanced modalities like CT reserved for equivocal cases to evaluate size and involvement of the subscapularis tendon.

Pathologies and imaging

Subscapularis tears often lead to degenerative changes in the lesser tubercle, including the formation of subcortical and cortical erosions or irregularities, which serve as indirect indicators of . These , typically round or oval lesions, arise from chronic stress or partial tears at the tendon's insertion site, with a prevalence of 15–45% even in individuals but strongly correlating with full-thickness subscapularis disruptions. Fatty of the can further contribute to tubercle remodeling, manifesting as bony irregularities or expansion due to altered biomechanical loading and muscle retraction over time. Clinically, these pathologies present with chronic anterior pain exacerbated by adduction and internal rotation, alongside weakness in internal rotation and symptoms of subcoracoid impingement, such as point tenderness in the subcoracoid region. Patients may experience insidious onset of discomfort during daily activities or overhead motions, with higher incidence among overhead athletes due to repetitive strain and in elderly individuals with degeneration, where age-related tendon wear predominates. Magnetic resonance imaging (MRI) is the primary modality for assessing soft tissue involvement, revealing high T2 signal intensity cysts at the lesser tubercle footprint, tendon defects, and fatty infiltration graded via Goutallier classification, with sensitivity ranging from 35–88% for tear detection. Computed tomography (CT) provides superior bony detail for evaluating erosions, cysts, or remodeling, particularly in preoperative planning, while ultrasound enables dynamic evaluation of tendon attachments and impingement, though with lower sensitivity (~40%) for subtle changes. Radiographs can initially identify cysts or irregularities, prompting advanced imaging. The presence of lesser tubercle cysts on MRI or radiographs signifies compromised subscapularis integrity and correlates with higher grades of fatty atrophy, portending poorer outcomes in repairs, including increased retear risk (up to 50% in advanced Goutallier stages). Surgical interventions, such as reattachment, emphasize addressing these changes to restore internal strength, with early detection via improving in degenerative cases.

References

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