Radiographic Anatomy of Hand

RADIOGRAPHIC ANATOMY OF HAND:



Fig: Hand PA view

Phalanges: Each finger and thumb is called a digit and each digit consists of two or three separate small bones called phalanges. The phalanges are 14 in number; the thumb has 2 (proximal and distal) and 3 each for the remaining four fingers (proximal, middle and distal). Each phalanx consists of three parts: a distal rounded head, a bone (Shaft), and an expanded base, similar to that of the metacarpals.

Inter-phalangeal (IP) joint: Beginning distally with the phalanges, all IP joints are ginglymus or hinge-type joints with movements in two directions only- flexion and extension. This movement is in one plane only, around the transverse axis.

First metacarpal: It is placed laterally. It is the shortest and the strongest metacarpal. It has undergone medial rotation of 90⁰. Therefore, the plane of the four metacarpal bones is at right angle to the plane of first metacarpal bone. It articulates with trapezium to form an important joint known as the carpometacarpal joint.

Second metacarpal: It is the longest amongst the metacarpals. The base is expanded and has a groove which articulates with the trapezoid.

Third metacarpal: It has a styloid process which helps in its identification. Its base articulates with capitate.

Fourth metacarpal: It can be identified by means of a small oval facet on the medial side of the base. There are two separate oval facets on the base of its lateral surface. Proximally, it articulates with hamate by means of quadrilateral facet (quadrilateral base means fourth metacarpal bone).

Fifth metacarpal: It is relatively slender. It is identified by the fact that it has no articular facet on the medial side of its base, where a tubercle can be seen. Proximally, it articulates with hamate.

Sesamoid bone: They differ from normal bone in two respects; absence of periosteum and absence of Haversian canal. They develop in the tendon at the site of friction.

Scaphoid or Navicular: It resembles a boat. It is the largest in the proximal row and has the prominent scaphoid tubercle. Its location and articulation with the forearm make it important radiographically because it is the most frequently carpal bone.

Lunate or Semilunar: It is like a moon. It articulates with the triquetral, capitate, radius and the scaphoid. Medial surface of the lunate is quadrilateral in shape and articulates with the triquetral.

Triquetral: It is the medial most bone of the proximal row and articulats with lunate laterally. It is distinguished by its pyramidal shape and anterior articulation with small pisiform.

Pisiform: It is like a pea, and is the smallest of the carpal bones and is located anterior to the triquetrum. It is supposed to be a sesamoid bone which develops in the tendon of flexor carpi ulnaris muscle.

Trapezium or Greater Multangular: It is four sided bone and is the first bone of the distal row of the carpus. It articulates with trapezoid medially and scaphoid proximally. There is saddle-shaped facet for the base of first metacarpal bone distally.

Trapezoid or Lesser Multangular: It is like a boot (shoe). It articulates with second metacarpal bone, trapezium, capitate and scaphoid bones.

Capitate: It has head, hence named as capitate (caput means head) and the largest bone in the carpus. It articulates primarily with the third metacarpal distally and with the trapezoid, scaphoid, lunate and hamate.

Hamate: It is a wedge-shaped bone on the medial side of the hand; it articulates with the fourth and fifth metacarpal, capitate and triquetral bones; it has a distinctive hooked process, the hook of the hamate, that extends anteriorly.

Wrist Joint: It is a condyloid (ellipsoid) type of synovial joint, and is freely movable or diarthrodial of the synovial classification. Of the two bones of the forearm, only the radius articulates directly with two carpal bones, the scaphoid and lunate. This wrist joint is called the radio-carpal joint.

Radius: It is the long bone of the forearm situated on the lateral side. It is connected to the ulna at the upper, middle and lower sites. Head of radius articulates with the ulna and forms the superior radio-ulnar joint. Head of ulna articulates with the radius at the lower end and forms the inferior radio-ulnar joint. Middle articulation is formed by the inter-osseous membrane, connecting inter-osseous borders of radius and ulna.

Lower end of radius: It is broad and quadrilateral. The lower lateral part presents the styloid process (the sharp pointed bony projection). Tip of radial styloid is lower than the tip of ulnar styloid process. Distal surface of the lower end of the radius articulates with scaphoid and the lunate.

Ulna: It is the long bone of the forearm placed medially. It presents shaft, upper and the lower end. It articulates with the humerus and the radius above and the lower end of the radius below. Articulations with the radius, it forms superior radioulnar, middle radioulnar, and the inferior radioulnar joints.

Lower end of ulna: It presents the head and the styloid process.