The five metacarpal bones make up the palm of the hand. The metacarpals are often referred to by the abbreviation “MC” plus the number of the ray to which they belong. Thus, MC1 is the first metacarpal or the thumb metacarpal. Each metacarpal is a tubular bone, with an expanded base which articulates with one or more carpal bones, and a rounded head which articulates with a manual phalanx. It is much easier to identify and side metacarpals using their bases than their heads.
Siding: MC1 can be sided using the asymmetrical nature of the saddle-shaped base. The lateral portion of the saddle is more elongate and narrower than the medial portion.
Siding: MC2 can be sided because the blunted, proximal-most projection of the base is medial.
Siding: The position of the styloid process on the dorsal and lateral side of the base makes siding relatively straightforward
Siding: The most useful feature for siding MC4 is the pronounced 90° angle formed by the articular surfaces for the hamate and MC5 on the medial side of the base.
Siding: The medial location of the medial tubercle makes siding straightforward.