The CMC1 joint is a synovial joint between the trapezium bone of the wrist and the metacarpal bone at the base of the thumb. This joint is a so-called saddle joint (articulatio sellaris), unlike the CMC joints of the other four fingers which are ellipsoid joints. This means that the surfaces of the CMC1 joint are both concave and convex. Because of its specific shape, the CMC1 joint allows a wide range of motion of the thumb. Movements possible in this CMC1 joint are: * Flexion * Extension * Abduction * Adduction * Opposition * Reposition * Circumduction This high mobility is due to the little intrinsic osseous stability of the joint. This causes the CMC1 joint to be more unstable compared to the CMC joints of the other fingers. Because of this instability, the joint is more susceptible to be damaged. To remain stable the CMC1 joint has to rely on the surrounding ligaments for support. These ligaments provide the ability to subject high pressure loads, particularly during pinch and grasp manoeuvres. 16 ligaments surrounding the CMC1 joint are identified, which give strength and stability to the joint. Of these ligaments, the deep anterior oblique ligament, also known as the palmar beak ligament, is considered to be the most important stabilizing ligament. Showing the bones of the hand
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