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Conoid tubercle

The conoid tubercle is a small, rough eminence located on the inferior surface of the lateral third of the clavicle, near its posterior border. It serves as the bony attachment site for the conoid ligament, which is the medial component of the coracoclavicular ligament complex that stabilizes the acromioclavicular (AC) joint.

The conoid tubercle plays a crucial role in maintaining the integrity and alignment of the clavicle and scapula, preventing excessive upward displacement of the clavicle. It can be palpated in thin individuals, lying posteromedial to the trapezoid line on the undersurface of the bone.

Synonyms

  • Tuberculum conoideum

  • Inferior clavicular tubercle

  • Conoid process of clavicle

Location and Structure

  • Position: Inferior surface of the lateral third of the clavicle, near its posterior border.

  • Shape: Small, rough, conical projection directed slightly backward and medially.

  • Associated ridge: Continuous laterally with the trapezoid line, the attachment site of the trapezoid ligament.

  • Surface texture: Rugged and irregular for ligamentous attachment.

  • Osseous context: Marks the transition between the flat lateral and curved medial portions of the clavicle.

Relations

  • Superiorly: Subclavius muscle and deltotrapezial fascia (overlying clavicle).

  • Inferiorly: Conoid ligament (of coracoclavicular complex) extending to the coracoid process of scapula.

  • Anteriorly: Trapezoid line and trapezoid ligament.

  • Posteriorly: Posterior border of the clavicle, near the insertion of trapezius.

  • Medially: Shaft of clavicle and costoclavicular ligament region.

  • Laterally: Acromial end of clavicle and attachment of trapezoid ligament.

Attachments

  • Conoid ligament: The primary attachment. It arises from the base of the coracoid process of the scapula and inserts into the conoid tubercle and adjacent inferior surface of clavicle.

  • The conoid ligament functions as the vertical stabilizer of the coracoclavicular joint complex, preventing upward displacement of the clavicle relative to the scapula.

  • Fascial continuity: Blends anteriorly with fibers of the trapezoid ligament and posteriorly with fascia of the trapezius.

Function

  • Structural support: Provides attachment for the conoid ligament, a key component of the coracoclavicular ligament complex.

  • Joint stabilization: Prevents superior displacement of the clavicle and maintains AC joint alignment.

  • Force transmission: Transfers load between the upper limb and axial skeleton through the clavicle-scapula linkage.

  • Landmark significance: Serves as an important radiological and surgical reference for identifying the coracoclavicular ligament complex.

Clinical Significance

  • Fractures: Fractures of the lateral third of the clavicle may involve or occur medial to the conoid tubercle, affecting coracoclavicular ligament stability.

  • Ligament injury: Disruption of the conoid ligament causes acromioclavicular joint dislocation (Type II–V).

  • Ossification variants: The conoid tubercle may appear prominent or accessory ossification centers may mimic pathology.

  • Osteolysis or stress changes: Seen in repetitive overhead activity or chronic instability.

  • Surgical importance: Landmark for coracoclavicular fixation, reconstruction procedures, and clavicular plating.

MRI Appearance

  • T1-weighted images:

    • Cortex: Low signal (dark)

    • Bone marrow: Bright, due to fatty content in normal adult clavicle

    • Conoid ligament attachment: Appears as a low-signal linear structure extending to coracoid process

    • Pathology: Avulsion or ligament tear shows irregular marrow brightness or cortical disruption

  • T2-weighted images:

    • Cortex: Low signal (dark)

    • Marrow: Bright, slightly less intense than on T1

    • Conoid ligament: Dark band-like structure; partial tear or strain shows focal hyperintense signal

    • Adjacent soft tissue edema: Hyperintense in trauma or inflammation

  • STIR:

    • Normal marrow: Intermediate-to-dark signal

    • Pathologic areas: Bright hyperintensity in marrow edema, avulsion, or ligament injury

    • Excellent for detecting acute trauma or stress reaction at the clavicular insertion

  • Proton Density Fat-Saturated (PD FS):

    • Normal tubercle and marrow: Intermediate-to-dark signal

    • Ligament injury or periosteal reaction: Bright hyperintense changes at the ligament attachment

    • Useful for identifying subtle partial tears, avulsions, or bone bruises

  • T1 Fat-Sat Post-Contrast:

    • Normal bone: Uniform mild enhancement

    • Inflamed or injured region: Focal or diffuse enhancement along conoid ligament insertion

    • Post-traumatic changes: Enhance peripherally with central low-signal fibrous tissue

CT Appearance

Non-Contrast CT:

  • Cortex: High attenuation, sharply defined; conoid tubercle easily recognized on inferior clavicular surface

  • Trabecular bone: Fine homogeneous density

  • Ligament attachment site: May appear as shallow depression or irregular roughened area

  • Pathology: Detects fractures, cortical avulsion, or periosteal new bone formation in chronic strain

  • High-resolution CT: Excellent for surgical planning and evaluation of coracoclavicular alignment

Post-Contrast CT (standard):

  • Bone: No intrinsic enhancement

  • Soft tissues: Conoid ligament and periligamentous regions may show contrast uptake in inflammation or injury

  • Useful for detecting post-surgical changes, chronic instability, or infection around the clavicle base

MRI image

Conoid tubercle coronal cross sectional anatomy 3T MRI AI enhanced radiology image-img-00000-00000

CT image

Conoid tubercle ct coronal image

CT image

Conoid tubercle ct sagittal image