Sternoclavicular and Acromioclavicular Joints

Sternoclavicular and Acromioclavicular Joints

TERMINOLOGY

Abbreviations

• Sternoclavicular (SC) joint
• Acromioclavicular (AC) joint

GROSS ANATOMY

Sternoclavicular Joint

• Between medial end of clavicle & manubrium

Synovial sellar-type (saddle) joint

Medial end of clavicle = large & bulbous

Much larger than manubrial concavity

< 1/2 of medial clavicle articulates with manubrium

– Stability through capsuloligamentous structures
• Intraarticular disc

Attached to joint capsule anteriorly & posteriorly

Complete or incomplete ± perforations

Thickest posterosuperiorly (3 mm)
• Ligaments of SC joint

Capsular ligaments

– Cover anterosuperior & posterior aspects of SC joint

– Prevent upward displacement of medial clavicle, which may be caused by downward force on shoulder

– Anterior stronger than posterior portion

Interclavicular ligament

– Connects superomedial aspect of clavicle to capsular ligaments & upper manubrium

– Covers anterosuperior & posterior aspects of joint

– Prevents excessive upward motion of clavicle

Costoclavicular ligaments

– Unite inferior surface medial end clavicle to upper surface of 1st rib

– Anterior fibers arise from anteromedial surface of 1st rib & resist upward motion

– Posterior fibers arise lateral to anterior fibers & resist downward motion
• Muscle attachments to medial clavicle & sternum

Pectoralis major from anterior aspect medial 2/3 clavicle (clavicular head)

Sternocleidomastoid from posterior surface medial 1/3 of clavicle (clavicular head)

Sternohyoid & sternothyroid muscles separate great vessels from SC joint

Acromioclavicular Joint

• Synovial joint between lateral end of clavicle & medial end of acromion

Articular surface of clavicle oriented posterolaterally whereas articular surface of acromion oriented anteromedially

– Angle of inclination between opposing articular surfaces varies with clavicle overriding acromion (50%), vertical orientation between acromion & clavicle (25%), clavicle underriding acromion (5%), & mixed pattern (20%)

– Maximum width of normal joint on US = 5 mm if < 35 years & < 4.4 mm if > 35 years

– Maximum thickness of capsule from bony surface = 2.7 mm if < 35 years & < 3.6 mm if > 35 years
• Intraarticular disc

Undergoes rapid degeneration beginning in 2nd decade → marked degeneration of disc by 4th decade

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Apr 9, 2020 | Posted by admin in MUSCULOSKELETAL IMAGING | Comments Off

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