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The proximal row of carpal articulations (Fig. 311) comprises the joints. between the navicular, lunate, and triquetral bones. On their adjacent aspects these bones are partly articular and partly non-articular.
Three sets of simple but strong, although short, ligamentous bands bind these three carpal bones together, and form an investment for three sides of their intercarpal joints. These are (1) the ligamenta intercarpea volaria (anterior or volar ligaments), two in number, which consist of transverse fibres passing between the adjacent rough volar surfaces of the bones; (2) the ligamenta intercarpea dorsalia (posterior or dorsal ligaments), also two in number, and composed of similar short transverse fibres passing between the adjacent dorsal surfaces; (3) the ligamenta intercarpea interossea (interosseous ligaments) (Fig. 310), again two in number, and transverse in direction, situated on a level with the proximal articular surfaces, and extending from the volar to the dorsal aspect of the bones while attached to non-articular areas of the opposing surfaces. The radio-carpal joint is entirely shut off from the intercarpal joints, and also from the joint between the two rows of carpal bones, except in rare cases, when an interosseous ligament is wanting.
The distal row of carpal articulations (Fig. 311) includes the joints between the greater multangular, lesser multangular, capitate, and hamate bones. Articular facets occur on the opposing faces of the individual bones.
Associated with this row there are again simple bands of considerable strength, and presenting an arrangement similar to that seen in the proximal row. As in the former case, they invest the intercarpal articulations, except on the proximal aspect, where they communicate with the transverse carpal joint, and on the distal aspect, where they communicate with the carpo-metacarpal joint cavity.
The ligamenta intercarpea volaria (anterior or volar ligaments) are three in number. They extend in a transverse direction between contiguous portions of the rough volar surfaces of the bones. The ligamenta intercarpea dorsalia (posterior or dorsal ligaments), also three in number, are similarly disposed on the dorsal aspect. The ligamenta intercarpea interossea (interosseous ligaments) (Fig. 311) are two or three in number. That which joins the capitate to the os hamatum is the strongest; that between the lesser multangular and the capitate bone is situated towards the dorsal parts of their opposing surfaces; the third, situated between contiguous non-articular surfaces of the greater and lesser multangular bones, is always the feeblest, and is frequently absent.
The transverse carpal articulation (Fig. 311) is situated between the proximal and distal rows of the carpus. The bones of the proximal row present the following characters on their distal aspect. The lateral part of the articular surface is strongly convex, both in the antero-posterior and in the transverse directions, but the medial part of the same surface is concavo-convex, more especially in the transverse direction.
Proximally, the articular surfaces of the distal row of carpal bones present an irregular outline. That part pertaining to the greater and lesser multangular bones is concave in the antero-posterior and transverse directions, and lies at a considerably more distal level than the portion belonging to the capitate and os hamatum, which is, moreover, markedly convex in the antero-posterior and transverse directions, with the exception of the most medial part of the os hamatum, where it is concavoconvex in both of these directions.
This articulation is invested by a complete short articular capsule (Fig. 310) which binds the two rows of the carpus together, and sends prolongations to the investing capsules of the proximal and distal articulations. The ligament, as a whole, is very strong, and individual bands are not readily defined, although certain special bands may be described. The lig. carpi radiatum (radiate carpal ligament (volar ligament)) radiates from the capitate bone to the navicular, triquetral, and pisiform bones. The interval between the capitate and lunate is occupied by oblique fibres, some of which pass from navicular to triquetral, while these are joined by others, prolonged obliquely distally and medially, from the radial end of the anterior radio-carpal ligament. By these different bands the volar aspect of the joint is completely closed.
The ligamenta intercarpea dorsalia (dorsal ligaments) are more feeble than the
volar. They form a thin, loosely arranged stratum, in which the only noteworthy bands are one which joins the navicular to the capitate, and another which joins. the triquetral to the os hamatum.
Lig. Collaterale Carpi Radiale. The radial collateral carpal ligament (O.T. external lateral) (Fig. 310) extends between contiguous rough areas on the lateral aspects of the navicular and greater multangular bone. By its margins it is continuous both with the volar and dorsal ligaments.
Lig. Collaterale Carpi Ulnare.-The ulnar collateral carpal ligament (O.T. internal lateral) (Fig. 310) is arranged like the former in regard to its margins, and by its ends it is attached to the contiguous rough ulnar surfaces of the triquetral and the os hamatum.
Both of these collateral ligaments are directly continuous with the corresponding collateral ligaments of the radio-carpal joint.
A lig. interosseum (interosseous ligament) (Fig. 311) is occasionally found within the capsule, extending across the joint cavity between the capitate and the navicular.
Articulatio Ossis Pisiformis.-The pisi-triquetral articulation is an arthrodial diarthrosis. The mutual articular surfaces of the two bones are flattened and circular, and permit of only a small amount of gliding movement.
The joint is provided with a thin but complete articular capsule, the fibrous stratum of which is specially strengthened distally by two strong bands, viz., lig. pisohamatum and lig. pisometacarpeum (Fig. 310). Both of these bands extend from the distal and medial aspect of the pisiform to adjoining parts of the hook of the os hamatum and base of the fifth metacarpal bone respectively. To a great extent these ligamentous bands may be regarded as extensions of the insertion of the tendon of the flexor carpi ulnaris muscle, which is attached to the proximal part of the pisiform bone. Looked at as ligaments, however, they are specially strong to prevent the displacement of the pisiform bone during contraction of the muscle inserted into it.
The synovial strata (synovial membranes) (Fig. 311) of the carpal joints are two in number. Of these, one is restricted to the pisi-triquetral articulation, and is correspondingly simple, although occasionally the joint cavity may communicate with that of the radio-carpal joint.
The other synovial stratum is associated with the transverse carpal joint which extends transversely between the two rows of carpal bones, with prolongations into the intervals between the adjoining bones of each row, i.e. the the intercarpal articulations. It is, therefore, an elaborate cavity, which may be still further extended, by the absence of interosseous ligaments, so as to reach the radio-carpal and carpo-metacarpal series of joints. The first condition is rare, but the second is not uncommon, and may result from the absence of the interosseous ligament between the greater and lesser multangular bones, or of that between the lesser multangular and the capitate bone, but it may occur when all the interosseous ligaments are present.
Recessus sacciformis of distal radio-ulnar joint
FIG. 311.-FRONTAL SECTION through the radio-carpal, carpal, carpometacarpal, and intermetacarpal joints, to show joint cavities and interosseous ligaments (diagrammatic).
Intermetacarpal Joints.-The four medial metacarpal bones articulate with each other at their proximal ends or bases, between the opposing surfaces of which joint cavities are found-arthrodial diarthroses. These cavities are continuous with the carpo-metacarpal joint (not yet described), and hence the ligamentous arrangements only enclose three aspects of each joint.
Three strong transverse ligaments (Figs. 310 and 311) bind adjacent volar, dorsal, and interosseous areas of the bases of the metacarpal bones, and hence they are called ligamenta basium (oss. metacarp.) volaria, dorsalia et interossea. synovial stratum is associated with each of these joints, but it may be regarded as a prolongation from the carpo-metacarpal articulation.
Carpo-metacarpal Joints.-The articulation of the metacarpal bone of the thumb with the greater multangular differs in so many respects from the articulation between the other metacarpal bones and the carpus, that it must be considered separately..
(4) The articulatio carpometacarpea pollicis (Figs. 310 and 311) is the joint between the disto-lateral surface of the greater multangular and the proximal surface of the base of the first metacarpal bone. Both of these surfaces are saddleshaped, and they articulate by mutual co-aptation.
The joint cavity is surrounded by an articular capsule, in the fibrous stratum of which we may recognise volar, dorsal, lateral, and medial bands, the last being the strongest and most important.
A synovial stratum lines the fibrous stratum, and the joint cavity is isolated and quite separate from the other carpal and carpo-metacarpal articulations.
At this joint movements occur around at least three axes. Thus, around a more or less transverse axis, flexion and extension take place; in an antero-posterior axis abduction and adduction (movements which have reference to the middle line of the hand) are found; while a certain amount of rotation is possible in the longitudinal axis of the digit. The very characteristic movement of opposition, in which the tip of the thumb may be applied to the tips of all the fingers, results from a combination of flexion, adduction, and rotation, and by combining all the movements possible at the various axes a considerable degree of circumduction may be produced.
(B) The articulationes carpometacarpeæ digitorum are the joints between the bases of the four medial metacarpal bones and the four bones of the distal row of the carpus. They are all arthrodial diarthroses, and the opposed articular surfaces present alternate elevations and depressions which form a series of interlocking joints. The joint cavities between the carpal bones of the distal row, and also the more extensive intermetacarpal joint cavities, open into this articulation.
This series of joints is invested by a common articular capsule which is weakest on its radial side, but is otherwise well defined. Its fibres arrange themselves in small slips, which pass obliquely in different directions, and vary in number for each metacarpal bone. Thus the ligamenta carpometacarpea volaria (volar carpometacarpal ligaments (O.T. oblique palmar)) (Fig. 310) usually consist of one slip for each metacarpal bone, but there may be two slips, and the third metacarpal bone frequently has three, of which one lies obliquely in front of the tendon of the flexor carpi radialis muscle.
The ligamenta carpometacarpea dorsalia (dorsal carpo-metacarpal ligaments (O.T. oblique dorsal)) are similar short bands, of greater strength and clearer definition, by which the index metacarpal is bound to the greater and lesser multangular bones; the middle metacarpal to the capitate, and frequently to the lesser multangular; the ring metacarpal to the capitate and os hamatum, and the metacarpal of the 5th finger to the os hamatum.
Ligamenta interossea (interosseous ligaments), one or sometimes two in number, occur within the capsule. They are usually situated in relation to one or both of the contiguous margins of the bases of the third and fourth metacarpal bones, from which they extend proximally to adjacent margins of the capitate and os hamatum. Occasionally they are sufficiently developed to divide the joint cavity into radial
and ulnar sections.
The synovial stratum (Fig. 311) is usually single and lines the fibrous stratum, but, as already explained, it has prolongations into the intermetacarpal and intercarpal series of joints. In connexion with the intercarpal series, the frequent absence of the interosseous ligament between the greater and lesser multangular bones permits the free communication of this joint cavity with that of the transverse carpal joint.
Metacarpo-phalangeal Joints. In the case of the pollex this joint is constructed on the plan of a ginglymus diarthrosis; the four corresponding joints of the fingers are also diarthroses of a slightly modified ball-and-socket variety. With the exception of the metacarpal bone of the pollex, each metacarpal bone has a somewhat spherical head articulating with a shallow oval cup upon the base of the first phalanx. It is important to note that the articular surface upon the head of each of these metacarpal bones is wider on the volar aspect and narrower on the dorsal Second metaaspect. The articulation in the thumb presents features similar to those of an interphalangeal joint.
Each joint possesses a capsula articularis (Fig. 312) which presents very different degrees of strength in different aspects of the articulation. Thus, on the dorsal aspect, it cannot be demonstrated as an independent structure, but the necessity for dorsal ligaments is to a large extent obviated by the presence of the strong flattened expansions of the extensor tendons.
The epiphyseal lines are extra-capsular.
Ligamenta Collateralia.-The collateral ligaments (O.T. internal and external lateral) (Fig. 312) are strong cord-like bands which pass from the tubercles and adjacent depressions on the sides of the heads of the metacarpal bones to the contiguous non-articular areas on the bases of the proximal phalanges. They are intimately connected on their volar aspects with the volar ligaments.
Ligamenta Accessoria Volaria.-The volar accessory ligaments (O.T. palmar ligaments) consist of thick plates of fibro-cartilage loosely connected to the metacarpal bones, but firmly adherent to the phalanges. They are placed between the collateral ligaments, to both of which they are in each case connected. Each plate is grooved on the volar surface for the long flexor tendons, whilst on its dorsal or joint surface it supports and glides upon the head of the metacarpal bone during flexion and extension of the joint. In the case of the thumb this plate of fibro-cartilage is usually replaced by sesamoid bones, and in the case of the index finger one such sesamoid nodule is frequently found at the radial side of the plate.
An important accessory ligament is found in connexion with the four medial metacarpo-phalangeal articulations, viz. :
Volar accessory ligament
Ligamenta Capitulorum (Oss. Metacarpalium) Transversa.-The transverse ligament of the heads of the metacarpal bones (or transverse metacarpal ligament) binds together the distal extremities of the four medial metacarpal bones. The name is applied to three sets of transverse fibres of great strength which are situated in front of the three medial interosseous spaces. These fibres are continuous with the ligamenta accessoria volaria (volar metacarpo-phalangeal ligaments) at their lateral margins.
A stratum synoviale lines the capsula articularis of each joint.
ARTICULATIONES DIGITORUM MANUS.
Interphalangeal Joints. Of these joints there are two for each finger and one for the thumb. They all correspond, in being ginglymus diarthroses in which the trochlear character of their articular surfaces is associated with one axis of movement directed transversely.
In their general arrangement they correspond with each other, and to a large extent with the metacarpo-phalangeal series already described. Each is provided with a definite articular capsule (Fig. 312), of which the volar and cord-like lateral portions are well marked, while on the dorsal aspect the extensor tendons act as the chief support. The volar portions contain fibrous plates of considerable thickness, and are attached to the two collateral ligaments and to the intervening rough surface on the distal phalanges, while their proximal margins are not attached to bone. Each ligament has its lateral margins prolonged proximally to the adjacent sharply defined lateral ridges on the phalangeal shafts.
The collateral ligaments (Fig. 312) are strong, rounded, short bands, continuous with the preceding, and attached to the non-articular sides of adjacent heads and bases of the phalanges.
Each joint possesses a synovial stratum which lines its fibrous stratum, but its arrangement presents no special peculiarity. The epiphyseal lines of the bases of the phalanges are extra-capsular.
MOVEMENTS OF THE CARPAL, INTERMETACARPAL, METACARPO-PHALANGEAL
AND INTERPHALANGEAL JOINTS.
The amount of movement which is possible at individual joints of the intercarpal, intermetacarpal, and carpo-metacarpal series is extremely limited, both on account of the interlocking nature of the articular surfaces and the restraining character of the ligamentous bands. Taken as a whole, however, the movements of the carpus and metacarpus enable the hand to perform many varied and important functions. This is largely due to the greater mobility of those joints on the radial and ulnar borders of the hand, as well as to the general elasticity of the arches formed by the carpus and metacarpus. These conditions particularly favour the movements of opposition and prehension. In the opposite direction, i.e. when pressure is applied from the volar aspect, the metacarpal and carpal arches tend to become flattened, but great elasticity is imparted by the tension of the various ligaments.
The four medial metacarpo-phalangeal joints are ball-and-socket joints, and movements of volar-flexion and extension are freely performed about a transverse axis. In exceptional cases a certain amount of dorsi-flexion is possible. About an antero-posterior axis movements occur which are usually referred to the middle line of the hand, and hence called abduction and adduction, but in consequence of the difference in the width of the articular surface on the dorsal and volar aspects of the heads of the four medial metacarpal bones it is only possible to obtain abduction when the joints are extended, while in the flexed position the joints become locked and abduction is impossible.
The movements of the index finger are less hampered than in the case of the others, but each of them can perform a modified kind of circumduction.
The metacarpo-phalangeal joint of the thumb and all the interphalangeal joints are uniaxial or hinge-joints acting about a transverse axis, which permits of volar-flexion and extension being freely performed, but dorsi-flexion is, as a rule, entirely prevented by the volar and lateral ligaments.
ARTICULATIONES ET LIGAMENTA CINGULI
Articulations and Ligaments of the Pelvis.-Although we may consider the pelvis as a separate part of the skeleton, yet it is essential to remember that the bones which enter into its composition belong to the vertebral column (sacrum, coccyx) and the lower limb (hip bone). Accordingly, the articulations, with their corresponding ligaments, may be arranged as follows:
(a) Those by which the segments of the coccyx are joined together (already described, v. p. 310);
(b) That by which the sacrum articulates with the coccyx (already described, v. p. 309);