Carpometacarpal joints. They are the Articulation points between the carpal and metacarpal bones , the base of the four metacarpals together with the distal row of the carpal bones , form a common metocarpal joint that presents a regular and articular line. The joints are flat synovial joints as a whole, the only exception being the slightly beveled joint surfaces between the hook and the fifth metacarpal.
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- 1 Joint surface
- 2 Joint capsule and synovial membrane
- 3 Ligaments
- 1 Dorsal Carpometacarpal Ligaments
- 2 Palmar carpometacarpal ligaments
- 3 Interosseous ligament
- 4 Blood risk and investment
- 5 Relationships
- 6 Stability
- 7 Movement
- 1 Accessory movements
- 8 Source
The base of the second metacarpal fits into the recess by forming the trapezius on the medial side, the trapezoid distal surface and the anterolateral corner of the large bone, the base of the third metacarpal articulates only with the distal surface of the large bone . The base of the fourth metacarpal bone is articulated mainly by the anterolateral distal surface of the hook, but it also reaches the anteromedial corner of the large bone, and finally the base of the fifth metacarpal rests on the anteromedial portion of the distal surface of the hook.
Joint capsule and synovial membrane
A fibrous capsule surrounds the joint joint and it is possible to identify different capsular scars. The synovial membrane covers the capsule and all non-articular surfaces, and is inserted at the non-articular edges. The joint cavity extends proximally between the bones of the body and usually communicates with the methocarpal joint. Distally, the joint space extends between the four medial metacarpal bones.
The dorsal and palmar carpometacarpal ligaments are actually thickening of the joint capsule.
Dorsal carpometacarpal ligaments
They present a series of fibrous bands that extend from the distal row from the carpal bones to the metacarpal base. Usually, each metacarpal receives two bands. Those that reach the second metacarpal, go from the trapezoid to the trapezoid; Those that reach the third metacarpal go from the trapezius to the large bone, and those that reach the fourth metacarpal go from the large bone to the hook bone. The base of the fifth metacarpal receive only a single band that arises from the hook.
Palmar carpometacarpal ligaments
The assumption of the fibrous bands that make up the palmar carpometacarpal ligaments is similar to the dorsal ligaments, except that the base of the third metacarpal receives three bands that arise from the large, hooked trapezoid bone.
There is usually a short interosseous ligament that runs from the adjacent lower angles of the large hooked spindles to the base of the third or fourth metacarpal or both. Sometimes the ligament divides the joint space into the medial and lateral compartments.
Blood risk and investment
The arterial risk of circulation depends on the dorsal and palmar carpal networks, while the innervation corresponds to the branches of the anterior and posterior interosseous nerves , and to the deep and dorsal branches of the ulnar nerve.
The carpometacarpal joints of the fingers are located deep in the tendons of the superficial and deep flexor muscles of the fingers. The tendon of the carpal radial flexor muscles crosses the joint at the most lateral base of the palmar surface and is inserted at the base of the second metacarpal, while the tendon of the carpi ulnar flexor muscle runs at the most medial level. The muscles of the hypothenar eminence also line the joint medially. On the posterior aspect of the joint are the tendons of the extensor muscles that enter the hand, which, laterally and medially, are: the long and short radial extensors of the carpus, the long extensor of the thumb, the extensor of the index , the extensor digitorum and little finger, and the extensor carpi ulnaris.
The joint is very stable and provides a firm base between the wrist and hand joints .
There is little movement of the carpometacarpal joints of the fingers , the second and third metacarpal are essentially immobile, although some degree of displacement is possible between the fourth metacarpal and the hook. Only the fifth metacarpal shows some movement when sliding over the hook, which is due to the fact that the articular surfaces are beveled. The movement is flexion and grasps when you hold something firmly and when there is opposition between the thumb and the little finger. In addition, a slight rotation occurs during opposition due to the action of the opposing little finger muscle.
A slight degree of anteroposterior slippage can occur between the base of the metacarpal and the adjacent carpal bone , if adequate pressure is applied.