Metacarpus

The metacarpus isintermediate part ofhand skeleton thatlocated betweenfingers distally andcarpus which formsconnection toforearm. It consistsfive cylindrical bones whichnumbered fromradial toulnar side (ossa metacarpalia I-V); each consists ofbodytwo extremities.

Tablecontents

1 Common Characteristics ofMetacarpal Bones 2 Characteristics ofIndividual Metacarpal Bones 3 Articulations

Common Characteristics ofMetacarpal Bones

The body (corpus; shaft)prismoidform,curved, so asbe convex inlongitudinal direction behind, concavefront. It presents three surfaces: medial, lateral,dorsal. The mediallateral surfacesconcave, forattachment ofinterosseus muscles,separated from one another byprominent anterior ridge. The dorsal surface presentsits distal two-thirdssmooth, triangular, flattened area whichcoveredbytendons ofExtensor muscles. This surfacebounded by two lines, which commencesmall tubercles situated on either side ofdigital extremity, and, passing upward, convergemeet some distance abovecenter ofboneformridge which runs alongrest ofdorsal surface tocarpal extremity. This ridge separates two sloping surfaces forattachment ofInterossei dorsales. Totubercles ondigital extremitiesattachedcollateral ligaments ofmetacarpophalangeal joints.

The base or carpal extremity (basis)ofcuboidal form,broader behind thanfront:articulates withcarpus,withadjoining metacarpal bones; its dorsalvolar surfacesrough, forattachmentligaments.

The head or digital extremity (capitulum) presents an oblong surface markedly convex from before backward, less so transversely,flattened from sideside;articulates withproximal phalanx. Itbroader,extends farther upward, onvolar than ondorsal aspect,is longer inantero-posterior than intransverse diameter. On either side ofhead istubercle forattachment ofcollateral ligament ofmetacarpophalangeal joint. The dorsal surface, broadflat, supportstendons ofextensor muscles;volar surfacegrooved inmiddle line forpassage ofFlexor tendons,marked on either side by an articular eminence continuous withterminal articular surface.

Characteristics ofIndividual Metacarpal Bones

The first metacarpal bone (os metacarpale I; metacarpal bone ofthumb) [Fig. 1]shorterstouter thanothers, diverges togreater degree fromcarpus,its volar surfacedirected towardpalm. The bodyflattenedbroad on its dorsal surface,does not presentridge whichfound onother metacarpal bones; its volar surfaceconcave from above downward. On its radial borderinsertedopponens pollicis muscle; its ulnar border gives origin tolateral head offirst Interosseus dorsalis. The base presentsconcavo-convex surface,articulation withgreater multangular;has no facets on its sides, but on its radial side istubercle forinsertion ofAbductor pollicis longus. The headless convex than those ofother metacarpal bones,is broader from sideside than from before backward. On its volar surfacetwo articular eminences,whichlateral islarger, fortwo sesamoid bones intendons offlexor pollicis brevis muscle. image:Gray229.png
Figure 1 : The first metacarpal. (Left.)

The second metacarpal bone (os metacarpale II; metacarpal bone ofindex finger) [Fig. 2] islongest,its baselargest, offour remaining bones. Its baseprolonged upwardmedialward, formingprominent ridge. It presents four articular facets: three onupper surfaceone onulnar side. Offacets onupper surfaceintermediate islargestis concave from sideside, convex from before backwardarticulation withlesser multangular;lateralsmall, flatovalarticulation withgreater multangular;medial, onsummit ofridge,longnarrowarticulation withcapitate. The facet onulnar side articulates withthird metacarpal. The extensor carpi radialis longus muscleinserted ondorsal surface andflexor carpi radialis muscle onvolar surface ofbase.

The third metacarpal bone (os metacarpale III; metacarpal bone ofmiddle finger) [Fig. 3] islittle smaller thansecond. The dorsal aspectits base presents on its radial sidepyramidal eminence,styloid process, which extends upward behindcapitate; immediately distalthis isrough surface forattachment ofextensor carpi radialis brevis muscle. The carpal articular facetconcave behind, flatfront,articulates withcapitate. Onradial side issmooth, concave facetarticulation withsecond metacarpal,onulnar side two small oval facets forfourth metacarpal.

The fourth metacarpal bone (os metacarpale IV; metacarpal bone ofring finger) [Fig. 4]shortersmaller thanthird. The basesmallquadrilateral; its superior surface presents two facets,large one mediallyarticulation withhamate, andsmall one laterally forcapitate. Onradial sidetwo oval facets,articulation withthird metacarpal;onulnar sidesingle concave facet, forfifth metacarpal.

The fifth metacarpal bone (os metacarpale V; metacarpal bone oflittle finger) [Fig. 5] presents on its base one facet on its superior surface, whichconcavo-convexarticulates withhamate,one on its radial side, which articulates withfourth metacarpal. On its ulnar side isprominent tubercle forinsertion oftendon ofextensor carpi ulnaris muscle. The dorsal surface ofbodydivided by an oblique ridge, which extends from nearulnar side ofbase toradial side ofhead. The lateral partthis surface serves forattachment offourth Interosseus dorsalis;medial partsmooth, triangular,covered byExtensor tendons oflittle finger.

image:Gray230.png Figure 2 : The second metacarpal. (Left.)	image:Gray231.png Figure 3 : The third metacarpal. (Left.)
image:Gray232.png Figure 4 : The fourth metacarpal. (Left.)	image:Gray233.png Figure 5 : The fifth metacarpal. (Left.)

Articulations

Besides their phalangeal articulations,metacarpal bones articulate as follows:first withgreater multangular;second withgreater multangular, lesser multangular, capitatethird metacarpal;third withcapitatesecondfourth metacarpals;fourth withcapitate, hamate,thirdfifth metacarpals; andfifth withhamatefourth metacarpal.