As we have elsewhere pointed out, the knee is not one joint but several; the chief of which are: 1, the radio-carpal; 2, the carpal; 3, the carpo-metacarpal. In addition, other small articulations exist on the sides of the bones forming the two rows (fig. 354).
The Radio - carpal articulation is formed by the inferior extremity of the radius or lower arm and the superior surface of the upper row of carpal bones, the two parts being suitably modelled to each other. This joint enjoys and imparts to the knee the greatest range of movement.
The Carpal joint is that between the two rows of small bones, and its action, although considerable, is less extensive than that of the radio-carpal.
The Carpo-metacarpal articulation is formed by the inferior surface of the lower row of bones and the superior extremities of the three metacarpal bones. In the movement of the knee this joint contributes nothing to flexion and extension, but allows a gliding movement favourable to the action of the joints above.
The articulations by which the bones composing each row are united together laterally are small, and only allow of such a measure of gliding movement as will enable the larger articulations to perform their more extensive and important functions. The Ligaments. - The ligaments uniting the bones of the knee are numerous, and comprise lateral ligaments, or those passing from the sides of the lower end of the radius - first to the upper row of bones, then to the lower, and finally to the upper extremity of the metacarpal bones (figs. 354 and 355); inter-osseous ligaments, or those situated between the small bones which they unite; and a capsular ligament.
Fig. 354. - The Carpus or Knee-joint.
1, Radius. 2, Large metacarpal or canon bone. 3, Small metacarpal or splint hone. 4, Pisiform bone. 5, Common external ligament. 6, Radio-carpal ligament. 7, Carpometacarpal ligament. 8, Anterior ligaments uniting the two rows of carpal bones. 9, Anterior ligaments proper to the carpometacarpal articulation.
Fig. 355. - Anterior View of Knee-Joint.
1, Radius. 2, Scaphoid. 3, Lunare. 4, Cuneiform. 5, Os magnum. 6, Unciform. 7, Canon. 8, Transverse connecting ligaments. 9, Oblique connecting ligaments.
The capsular ligament of the knee is, like the joint, of considerable extent. Proceeding from above, where it is attached around the articular margin of the radius, it descends, to be similarly connected with the superior extremity of the large metacarpal bone. Behind, it is very thick, and is attached to all the small bones of the knee, and below it is continuous with the check ligament which joins the tendon of the flexor pedis perforans.