Thumb CMC (Basilar) Joint Anatomy

The Thumb CMC Joint provides an articulation between:

• First Metacarpal: The primary bone of the thumb connecting to the carpals.
• Trapezium: One of the carpal bones.

Ligaments:

• Anterior Oblique Ligament: Primarily responsible for stabilizing the CMC joint.

Tendons Crossing the Thumb CMC Joint:

• Abductor Pollicis Longus (APL) and Extensor Pollicis Brevis (EPB): Tendons that cross and influence movement at the CMC joint.

Joint Type:

• The thumb carpometacarpal (CMC) joint is a saddle joint with articular surfaces that are convex in one plane and concave in another. This saddle-like joint design allows motion in several planes, including the flexion/extension, abduction/abduction, and pronation/supination (rotational) planes.
• Synovial Joint
  • Synovial joints are specialized structures that allow movement at bony articulations. 
  • Composed of a joint cavity lined by synovium containing bones lined with articular cartilage
  • Structural components contain:
    • Articular cartilage - enables low friction movement
    • Ligament
    • Joint capsule - fibrous tissue surrounding joint cavity
    • Synovium - tissue lining non-cartilaginous portions of joint cavity and is composed of two layers, the intimal lining and the connective tissue sublining
    • Synovial fluid - produced and regulated by the synovium