The joint between the scaphoid, lunate, and triquetral on the one hand, and the second row of carpal bones on the other, is named the midcarpal joint, and is made up of three distinct portions: in the center the head of the capitate and the superior surface of the hamate articulate with the deep cup-shaped cavity formed by the scaphoid and lunate, and constitute a sort of ball-and-socket joint.
On the radial side the greater and lesser multangulars articulate with the scaphoid, and on the ulnar side the hamate articulates with the triangular, forming gliding joints.
The ligaments are: volar, dorsal, ulnar and radial collateral.
- The Volar Ligaments (ligamenta intercarpea volaria; anterior or palmar ligaments).—The volar ligaments consist of short fibers, which pass, for the most part, from the volar surfaces of the bones of the first row to the front of the capitate.
- The Dorsal Ligaments (ligamenta intercarpea dorsalia; posterior ligaments).—The dorsal ligaments consist of short, irregular bundles passing between the dorsal surfaces of the bones of the first and second rows.
- The Collateral Ligaments (lateral ligaments)-The collateral ligaments are very short; one is placed on the radial, the other on the ulnar side of the carpus; the former, the stronger and more distinct, connects the scaphoid and trapezium, the latter the triangular and hamate; they are continuous with the collateral ligaments of the wrist-joint. In addition to these ligaments, a slender interosseous band sometimes connects the capitate and the navicular.
The chief movements permitted in the mid-carpal joint are flexion
and a slight amount of rotation.
In flexion and extension, which are the movements most freely enjoyed, the greater and lesser multangulars on the radial side and the hamate on the ulnar side glide forward and backward on the navicular and triangular respectively, while the head of the capitate and the superior surface of the hamate rotate in the cup-shaped cavity of the navicular and lunate.
Flexion at this joint is freer than extension.
A very trifling amount of rotation is also permitted, the head of the capitate rotating around a vertical axis drawn through its own center, while at the same time a slight gliding movement takes place in the lateral and medial portions of the joint.