The joints of the carpus may be subdivided into - The joints of the first row. The joints of the second row. The medio-carpal, or junction of the two rows with each other.
The Joints of the First Row of Carpal Bones Class. - Diarthrosis. Subdivision. - Arthrodia.
The bones of the first row, the pisiform excepted, are united by two sets of ligaments and two interosseous fibro-cartilages.
The two dorsal intercarpal ligaments extend transversely between the bones, and connect the navicular with the lunate, and the lunate with the triquetral. Their posterior surfaces are in contact with the posterior ligament of the -wrist.
The two volar intercarpal ligaments extend nearly transversely between the bones connecting the navicular with the lunate, and the lunate with the triquetral. They are stronger than the dorsal ligaments, and are placed beneath the anterior ligament of the wrist.
The two interosseous intercarpal ligaments are interposed between the navicular and lunate, and the lunate and triquetral bones, reaching from the dorsal to the volar surfaces and being connected with the dorsal and volar ligaments. They are narrow fibro-cartilages which extend between small portions only of the osseous surfaces. They help to form the convex carpal surface of the radio-carpal joint, and are somewhat wedge-shaped, their bases being toward the wrist, and their thin edges between the adjacent articular surfaces of the bones.
The synovial membrane is a prolongation from that of the medio-carpal joint.
The arterial and nerve-supplies are the same as for the medio-carpal joint.
The Joint of the Pisiform Bone with the Triquetral
This is an arthrodial joint which has a loose fibrous capsule attached to both the pisiform and triquetral bones just beyond the margins of their articular surfaces.
It is lined by a separate synovial membrane. Two strong rounded or flattened bands pass downward from the pisiform, one to the process of the hamate [ligament pisohamatum], and the other [ligament pisometacarpeum] to the bases of the third to fifth metacarpals; these are regarded as prolongations of the tendon of the flexor carpi ulnaris, and the pisiform bone may be looked upon in the light of a sesamoid bone developed in that tendon.
The Joints of the Second Row of Carpal Bones
Class. - Diarthrosis. Subdivision. - Arthrodia.
The four bones of this row are united by three dorsal, three palmar, and three interosseous ligaments.
The three dorsal ligaments extend transversely and connect the greater with the lesser multangular, the lesser multangular with the capitate, and the capitate with the hamate.
The three volar ligaments are stronger than the dorsal, and are deeply placed beneath the mass of flexor tendons; they extend transversely between the bones in a similar manner to the dorsal ligaments.
Three interosseous ligaments connect the bones of the lower row of the carpus together. Two are connected with the capitate, one uniting it with the hamate and the other binding it to the lesser multangular. The third ligament joins the greater and lesser multangular.
The synovial membrane is a prolongation of that lining the medio-carpal joint.
Vessels and nerves
The arterial and nerve -supplies are the same as for the medio-carpal joint.
The Medio-carpal Joint, or the Union op the Two Rows of the Carpus with each other
(I) Class. - Diarthrosis. Subdivision. - Arthrodia.
(II) Class.- - Diarthrosis. Subdivision. - Condylarthrosis.
The inferior surfaces of the bones of the first row are adapted to the superior articular surfaces of the bones of the second row. The line of this articulation is concavo-convex from side to side, and is sometimes described as having the course of a Roman S placed horizontally, a resemblance by no means strained, (i) The lateral part of the first row consists of the navicular alone; it is convex, and bears the greater and lesser multangulars. (ii) Then follows a transversely elongated socket formed by the medial part of the navicular, the lunate, and triquetral, into which are received - (a) the head of the capitate, which articulates with the navicular and lunate; (b) the upper and lateral angle of the hamate, which articulates with the navicular; and (c) the upper convex portion of the medial surface of the hamate, which articulates with the lateral and concave portion of the inferior surface of the triquetral, (iii) The medial part of the inferior surface of the triquetral bone is convex, and turned a little backward to fit into the lower portion of the medial surface of the hamate, which is a little concave and turned forward to receive it. The central part, which forms a socket for the capitate and hamate, has somewhat the character of a condyloid joint, the capitate and hamate being the condyle, to fit into the cavity formed by the navicular, lunate, and triquetral; the other portions are typically arthrodial. The ligaments are: - (1) radiate or anterior medio-carpal; (2) posterior medio-carpal; (3) transverse dorsal.
The radiate, anterior or volar medio-carpal is a ligament of considerable strength, consisting mostly of fibers which radiate from the capitate to the navicular, lunate, and triquetral; some few fibers connect the greater and lesser multangular with the navicular, and others pass between the hamate and triquetral. It is covered over and thickened by fibrous tissue derived from the sheaths of the flexor tendons and the fibers of origin of the small muscles of the thumb and little finger.
The posterior or dorsal medio-carpal ligament, consists of fibers passing obliquely from the bones of the first row to those of the second. It is stronger on the ulnar side than on the radial, but is not so strong as the volar ligament.
The transverse dorsal ligament is an additional band, well-marked and often of considerable strength, which passes across the head of the capitate from the navicular to the triquetral bone; besides binding down the head of the capitate, it serves to fix the upper and lateral angle of the hamate in the socket formed by the first row.
The dorsal ligaments, like the volar, are strengthened by a quantity of fibrous tissue belonging to the sheaths of the extensor tendons, and by an extension of some of the fibers of the capsule of the wrist. There are no proper collateral medio-carpal ligaments; they are but prolongations of the collateral ligaments of the wrist.
The synovial membrane of the carpus is common to all the joints of the carpus, and extends to the bases of the four medial metacarpal bones. Thus, besides lining the inter- or medio-carpal joint, it sends two processes upward between the three bones of the first row, and thi'ee downward between the contiguous surfaces of the lesser and greater multangular, the lesser multangular and capitate, and capitate and hamate. From these latter, prolongations extend to the four medial carpo-metacarpal joints and the three intermetacarpal joints.
Vessels and nerves
The arterial supply is derived from - (a) the volar and dorsal carpal rami of the radial and ulnar arteries; (b) the carpal branch of the volar interosseous; (c) the recurrent branches from the deep palmar arch. The terminal twigs of the volar and dorsal interosseous arteries supply the joint on its dorsal aspect.
The nerve -supply comes from the ulnar on the ulnar side, the median on the radial side, and the deep branch of the radial (posterior interosseous) behind.
The relations of this joint are practically the same as those of the radio-carpal joint, except that the flexor carpi ulnaris does not cross the front, the ulnar artery is separated from it by the transverse carpal ligament, and the radial artery passes across its lateral border instead of in front.
The movements of the carpal articulations between bones of the same row are very limited and consist only of slight gliding upon one another; but, slight as they are, they give elasticity to the carpus to break the jars and shocks which result from blows or falls upon the hand.
The movements of one row of bones upon the other at the medio-carpal joint are more extensive, especially in the direction of flexion and extension, so that the hand enjoys a greater range of these movements than is permitted at the wrist-joint alone. At the wrist, extension is more free than flexion; but this is balanced by the greater freedom of flexion than of extension at the medio-carpal joint, and by flexion at the carpo-metacarpal joint, so that on the whole- the range of flexion of the hand is greater than that of extension.
A slight amount of side to side motion accompanied by a limited degree of rotation also takes place; this rotation consists in the head of the capitate and the superior and lateral angle of the hamate bone rotating in the socket formed by the three bones of the upper row, and in a gliding forward and backward of the greater and lesser multangular upon the navicular.
In addition to the ligaments, the undulating outline and the variety of shapes of the apposed facets render this joint very secure.
Bearing in mind the mobility of this medio-carpal joint and of the carpo-metacarpal, we see at once the reason for the radial and ulnar flexors and extensors of the carpus being prolonged down to their insertion into the base of the metacarpus, for they produce the combined effect of motion at each of the three transverse articulations: - (1) at the wrist; (2) at the medio-carpal; (3) at the carpo-metacarpal joints.
Muscles which act upon the mid-carpal joint
The muscles which act upon this joint are the same as those which acts upon the radio-carpal joint, except the flexor carpi ulnaris, which is inserted into the pisiform bone.