1. CARPOMETACARPAL JOINT OF THE THUMB
This is a saddle-shaped joint between the first metacarpal bone and the trapezium (greater multangular bone); it enjoys great freedom of movement on account of the configuration of its articular surfaces. The joint is surrounded by a capsular ligament, which is thick but loose, and passes from the circumference of the base of the metacarpal bone to the rough edge bounding the articular surface of the trapezium; it is thickest laterally and dorsally. The synovial membrane which lines the capsular ligament is distinct from that of the other carpometacarpal joints (fig. 542).
Muscles producing the movements:
- Flexion and Opposition- Opponens pollicis, Flexores pollicis longus et brevis.
- Extension.- Extensores pollicis longus et brevis.
- Adduction.- Adductor pollicis.
- Abduction.- Abductores pollicis brevis et longus.
2. JOINTS OF THE SECOND, THIRD, FOURTH AND FIFTH METACARPAL BONES WITH THE CARPUS
The joints between the carpals and the second, third, fourth, and fifth metacarpal bones are plane joints. The bones are united by capsular ligaments, strengthened by dorsal, palmar and interosseous ligaments.
The dorsal ligaments, the strongest and most distinct, connect the carpal and metacarpal bones on their dorsal surfaces. The second metacarpal bone receives two fasciculi, one each from the trapezium and trapezoid (greater and lesser multangular) bones; the third metacarpal receives two, one each from the trapezoid and capitate bones; the fourth two, one each from the capitate and hamate bones; the fifth receives a single fasciculus from the hamate bone, and this is continuous with a similar ligament on the palmar surface, forming an incomplete capsular ligament.
The palmar ligaments have a somewhat similar arrangement, with the exception of those of the third metacarpal bone, which are three in number : a lateral one from the trapezium (greater multangular bone), situated superficially to the sheath of the tendon of the flexor carpi radialis; an intermediate one from the capitate bone; and a medial one from the hamate bone.
The interosseous ligaments consist of short, thick fibers; and are limited to one part of the carpornetacarpal articulation; they connect the contiguous inferior margins of the capitate and hamate bones with the adjacent surfaces of the third and fourth metacarpal bones.
The synovial membrane is a continuation of that of the interearpal joints. Occasionally, the joint between the hamate bone and the fourth and fifth metacarpal bones has a separate synovial membrane.
Movements. The movements permitted in the carpometacarpal articulations of the fingers are limited to slight gliding of the articular surfaces upon each other, the extent of which varies in the different joints. The metacarpal bone of the little finger is the most movable, then that of the ring-finger; the metacarpal bones of the index and middle fingers are almost immovable.
THE INTERMETACARPAL JOINTS
The bases of the second, third, fourth and fifth metacarpal bones articulate with one another by small. surfaces covered with cartilage, and are connected together by dorsal, palmar and interosseous ligaments.
The dorsal and palmar ligaments pass transversely from one bone to another on the dorsal and palmar surfaces. The interosseous ligaments connect the contiguoijs surfaces of the bones, just distal to their collateral articular facets.
The synovial membrane of these joints is continuous with that of the carpometacarpal articulations.
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