The sternoclavicular joint is the only bony articulation connecting the upper limb to the axial skeleton. How is it classified, and what covers its articular surfaces?

• A Plane synovial joint covered by hyaline cartilage
• B Secondary cartilaginous joint covered by hyaline cartilage
• C Saddle variety of synovial joint covered by fibrocartilage ✓
• D Ball and socket synovial joint covered by fibrocartilage

Explanation

Despite the clavicular end being rounded and the sternal notch concave, the sternoclavicular joint functions as a saddle-type synovial joint, and unusually for a large synovial joint its articular surfaces are covered by fibrocartilage rather than hyaline cartilage, an adaptation to the compressive loads transmitted across it. It contains a complete fibrocartilaginous articular disc that prevents medial displacement of the clavicle. Secondary cartilaginous joints lack a synovial cavity, so option B is wrong by definition.

Reference: Gray's Anatomy for Students, 4th ed.

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