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#anatomy #upperlimbanatomy #metacarpalbones #hand #carpalbones #handanatomy METACARPAL BONES 1 The metacarpal bones are 5 miniature long bones, which are numbered from lateral to the medial side. 2 Each bone has a head placed distally, a shaft and a base at the proximal end. i. The head is round. It has an articular surface which extends more anteroposteriorly than laterally. It extends more on the palmar surface than on the dorsal surface. The heads of the metacarpal bones form the knuckles during flexion. ii. The shaft is concave on the palmar surface. Its dorsal surface bears a flat triangular area in its distal part. iii. The base is irregularly expanded Characteristics of Individual Metacarpal Bones 1st a. It is the shortest and stoutest of all metacarpal bones. b. The base is occupied by a concavoconvex articular surface for the trapezium. c. The dorsal surface of the shaft is uniformly convex. d. The head is less convex and broader from sideto-side than the heads of other metacarpals. The ulnar and radial corners of the palmar surface show impressions for sesamoid bones. e. The first metacarpal bone (lying on a more anterior plane) is rotated medially through 90° relative to the other metacarpals. As a result of this rotation, the movements of the thumb take place at right angles to those of other digits. f. It does not articulate with any other metacarpal bone. 2nd The base is grooved from before backwards. The medial edge of the groove is larger . 3rd The base has a styloid process projecting up from the dorsolateral corner . 4th The base has two small oval facets on its lateral side for the third metacarpal, and on its medial side it has a single elongated facet for the 5th metacarpal. 5th The base has an elongated articular strip on its lateral side for the 4th metacarpal. The medial side of the base is non-articular and bears a tubercle. Side Determination of Metacarpals The proximal, distal, palmar and dorsal aspects of each metacarpal bone can be made out from what has been stated above. The lateral and medial sides can be confirmed by the following criteria. 1st The anterolateral surface is larger than the anteromedial. 2nd i. The medial edge of the groove on the base is deeper than the lateral edge. ii. The medial side of the base bears an articular strip which is constricted in the middle. 3rd i. The styloid process is dorsolateral. ii. The lateral side of the base bears an articular strip which is constricted in the middle. iii. The medial side of the base has two small oval facets for the 4th metacarpal. 4th i. The lateral side of the base has two small oval facets for the 3rd metacarpal. ii. The medial side of the base has an elongated articular strip for the 5th metacarpal. 5th i. The lateral side of the base has an elongated articular strip for the 4th metacarpal. ii. The medial side of the base is non-articular and has a tubercle.