The articulations of the upper extremity are the following:
1. The stemo-costo -clavicular.
2. The scapulo-clavicular union.
3. The shoulder-joint.
4. The elbow-joint.
5. The radio-ulnar union.
6. The radio-carpal or wrist-joint.
7. The carpal joints.
8. The carpo-metacarpal joints.
9. The intermetacarpal joints.
10. The metacarpo-phalangeal joints.
11. The interphalangeal joints.
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The wrist-joint (Class. - Diarthrosis. Subdivision. - Condylarthrosis.) is formed by the union of the radius and articular disc above, articulating -with the navicular, lunate, and triquetral bones below; the ulna being excluded by the intervention of the articular disc. The radius and disc together present a smooth surface, slightly concave both from before backward, and from side to side, whilst the three bones of the carpus present a smooth, convex surface, made uniformly even by the interosseous ligaments which bind them together.
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The shoulder articulation [articulatio humeri] is one of the most perfect and most movable of joints, the large upper end of the humerus playing upon the shallow glenoid cavity. Like the hip, it is a ball-and-socket joint. It is retained in position much less by ligaments than by muscles, and, owing to the looseness of its capsule, as well as to all the other conditions of its construction and position, it is exceedingly liable to be displaced; on the other hand, it is sheltered from violence by the two projecting processes - the acromion and coracoid. The ligaments of the shoulder-joint are:
- Articular capsule
Class. - Diarthrosis. Subdivision. - Enarthrodia.
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The scapula is connected with the clavicle by a synovial joint with its ligaments at the acromio-clavicular articulation; and also by a set of ligaments passing between the coracoid process and the clavicle. So, that we have to consider: the acromio-clavicular articulation, the coraco-clavicular ligaments, the proper scapular ligaments are also best described in this section - viz., the coraco-acromial and transverse.
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The radius is firmly united to the ulna by two joints, and an intermediate fibrous union, viz.:
- The superior radio-ulnar - whereat the head of the radius rotates within the radial notch and annular ligament.
- The union of the shafts - the mid radio-ulnar union.
- The inferior radio-ulnar - whereat the lower end of the radius rolls round the head of the ulna.
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The sterno-costo-clavicular articulation Class. - Diarthrosis. Subdivision. - Condylarthrosis.
At this joint the large medial end of the clavicle is united to the superior angle of the manubrium sterni, the first costal cartilage also assisting to support the clavicle. It is the only joint between the upper extremity and the trunk, and takes part in all the movements of the upper limb. Looking at the bones, one would say that they were in no way adapted to articulate with one another, and yet they assist in constructing a joint of security, strength, and importance. The bones are nowhere in actual contact, being completely separated by an articular disc. The interval between the joints of the two sides varies from one inch to an inch and a half (2.5-4 cm.).
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The elbow-joint [articulatio cubiti] Class. - Diarthrosis. Subdivision. - Ginglymus.is a complete hinge, and, unlike the knee, depends for its security and strength upon the configuration of its bones rather than on the number, strength, or arrangement of its ligaments.