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Saddle joints are said to be biaxial, [5] allowing movement in the sagittal and frontal planes. [2] Examples of saddle joints in the human body include the carpometacarpal joint of the thumb, [6] [7] the sternoclavicular joint of the thorax, [8] the incudomalleolar joint of the middle ear, [9] and the calcaneocuboid joint of the heel. [2]
The joint space equals the distance between the involved bones of the joint. A joint space narrowing is a sign of either (or both) osteoarthritis and inflammatory degeneration. [12] The normal joint space is at least 2 mm in the hip (at the superior acetabulum), [13] at least 3 mm in the knee, [14] and 4–5 mm in the shoulder joint. [15]
The inferior surface is oval, concave from side to side, convex from before backward, so as to form a saddle-shaped surface for articulation with the base of the first metacarpal bone. This saddle-shaped articulation is partially responsible for the thumb's opposable motion. The dorsal surface is smooth. The palmar surface is narrow and rough.
It is composed of 270 bones at the time of birth, [2] but later decreases to 206: 80 bones in the axial skeleton and 126 bones in the appendicular skeleton. 172 of 206 bones are part of a pair and the remaining 34 are unpaired. [3] Many small accessory bones, such as sesamoid bones, are not included in this.
The proximal surface is triangular, smooth and convex. [3] The lateral surface is narrow and gives attachment to the radial collateral ligament. The medial surface has two facets, a flattened semi-lunar facet articulating with the lunate bone, and an inferior concave facet, articulating alongside the lunate with the head of the capitate bone. [4]
Development of the joints; Classification of joints; The kind of movement admitted in joints; Articulations of the trunk Articulations of the vertebral column; Articulation of the atlas with the epistropheus or axis; Articulations of the vertebral column with the cranium; Articulation of the mandible; Costovertebral articulations; Sternocostal ...
Joints can also be classified based on their anatomy or on their biomechanical properties. According to the anatomic classification, joints are subdivided into simple and compound, depending on the number of bones involved, and into complex and combination joints: [19] Simple joint: two articulation surfaces (e.g. shoulder joint, hip joint)
The term “flat bone” is something of a misnomer because, although a flat bone is typically thin, it is also often curved. Examples include the cranial (skull) bones, the scapulae (shoulder blades), the sternum (breastbone), and the ribs. Flat bones serve as points of attachment for muscles and often protect internal organs.