Hand & Wrist Anatomy

The anatomy of the wrist, hand and fingers is very complex, because it involves 27 bones and a large number of muscles and ligaments that are used in biomechanical movements. This joint part of the human body is prone to all types of injury, from fractures, tendonitis and even bursitis.

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Parts and anatomy of the hand

Bones and joints

• Scaphoid: 3 of its 6 faces are articular, so it has contact with the radius bones of the forearm, the lunate, the trapezium, the trapezoid, the trapezium and the great bone. It is the bone most likely to fracture.
• Semilunate: Its name derives from the shape of this bone, which is compact, cuboid and spongy. Its facets are related to the radius, large, hooked, scaphoid and pyramidal. Two of these facets are not articular.
• Pyramidal: Like the previous bone, this bone tissue has its name due to its shape. It has 6 facets, 3 of which are articular. It connects with the pisiform, lunate and hooked.
• Pisiform: This bone is located on the outside of the wrist and may form the group with distal location, but it is considered within this sector. It is next to the hook and pyramidal bones. It is a strategic bone because it contains the little finger adductor muscle and the anterior ulnar muscle. Its four facets give rise to the ulnar nerve and the artery of the same name.
• Trapezius: Articulates with the first metacarpal of the thumb. It also connects with the scaphoid and trapezium. It is part of the important trapezometacarpal joint.
• Trapezoid: Articulates with the second metacarpal of the index finger. Of its 6 facets, 4 are articular because it connects with the trapezium, great and scaphoid bones.
• Great: This bone articulates with the second, third and fourth metacarpal bones of the middle or middle finger. Four facets are articular and it is related to the scaphoid, lunate, trapezium and hooked bone.
• Ganchus: It is responsible for the articulation of the fourth and fifth metacarpals of the ring and little fingers. It is related to the large bone, the pisiform, the pyramidal and the lunate.
• Metacarpals: Also called metacarpals, they are five bones and form the palm of the hand. They are counted from the thumb to the little finger. They are responsible for producing the articulation between the palm of the hand and the wrist. They are covered with tendons that restrict the movements of the fingers.
• Proximal phalanx: Corresponds to one for each finger. They are related to each of the metacarpals, forming joints between the metacarpals and the middle phalanges.
• Middle phalange: In this case the number of bones is less than the other phalanges, because the thumb does not have this bone tissue. Its action is to produce movements between the proximal phalanx and the distal phalanx of each finger.
• Distal phalanx: This bone is found one for each finger, forming the last link of the digital bones. This bone may also be referred to as the phalanx or nail phalanx. It articulates with the middle phalanx and in the case of the thumb with the proximal phalanx.
• External sesamoid: A small bone that lies between different joints in the hands, its job is similar to that of a pulley. This means that it reduces the tension on the ligaments and other muscles when certain movements are performed.
• Radio ulnar: This joint allows movement of the ulna and radius of the forearm, which helps the radiocarpal joint.
• Radiocarpal: This body allows movement between the radius and the scaphoid and the radius with the lunate. It is common to find the name of each of these joints called radioscaphoid and radiosemilunar.
• Intercarpal: The movement of the lunate bone, with the piriformis, pisiform, hooked bone and large bone are produced by the action of this joint.
• Carpometacarpal: These joints are found at the junction of the hook bone, the large bone, the trapezium and the trapezium with the metacarpals of the hand. It is possible to distinguish each of these joints by linking the names of the bones they join.
• Carpometacarpal: This is the joint that makes it possible to move the carpal bones with each of the metacarpals of the palm of the hand.
• Metacarpophalangeal: The joint between the metacarpals and the proximal phalanges can move thanks to this joint.
• Proximal interphalangeal: This joint can be found at the junction of the proximal and middle phalanges.
• Distal interphalangeal joint: This joint allows the movement of the middle phalanges with the distal phalanges of the fingers.
• Proximal-distal interphalangeal joint: Unlike the previous articular bodies, this joint is present in each hand, as it is responsible for moving the proximal phalanx with the distal phalanx of the thumb.

Muscles

• Opponent of the thumb: It arises from the tubercle and tensors of the trapezius and the annular ligament of the carpus. It inserts on the first metacarpal. Its action is to rotate the thumb to touch the palm of the hand and the other fingers.
• Abductor pollicis brevis: It travels from the scaphoid and the annular ligament to the first phalanx of the thumb. Its job is to pull the thumb away from the palm of the hand.
• Flexor pollicis brevis: This muscle arises from the large bone, the flexor retinaculum and the trapezius tubercle. It attaches to the sesamoid and the first phalanx. Its downward movement consists of flexion of the thumb.
• Adductor pollicis: It arises from the first row of the carpals, on the scaphoid. It inserts on the opponent of the thumb reaching the external tubercle of its base. The action of this muscle is to control adduction movements.
• Little finger abductor: It arises from the pisiform bone and inserts on the fifth proximal phalanx of the little finger. Its function is to balance the movements of the little finger.
• Little finger flexor digitorum brevis: This muscle can be found from the hooked process to the ulnar border of the first phalanx of the little finger. Its action is to maintain balance in the flexion of this finger.
• Opponent of the little finger: It arises from the hook bone and inserts into the diaphysis of the fifth metacarpal. Its function is to rotate the little finger when it faces the thumb.
• Lumbrical: It is a set of 4 muscles located in the dorsal part of the hand. They arise from each of the deep flexors of the fingers to flex and extend the first phalanx.
• Palmar interosseous: This is also a set of muscles, but in this case there are three. They originate from the metacarpals to the proximal phalanges of the index, ring and little fingers.
• Dorsal interosseous: This muscle is found in each of the fingers from the metacarpals to the first phalanx. It regulates abductor and flexor movements of the hand.
• Ulnar flexor carpi ulnaris: This is a muscle of the forearm that attaches to the pisiform, hook and fifth metacarpal. Its action is to flex and control wrist movements.
• Flexor superficialis: The action of these muscles is to flex the forearm and fingers. The path of this tissue originates in the coronoid process of the ulna and in the medial epicondyle of the humerus up to the ligament of the middle phalanges.
• Deep flexor: These muscles have their origin in the interosseous ligament, ulna and antebrachial aponeurosis. They insert on the third phalanx of the fingers, except for the thumb.
• Palmar brevis: It is an internal muscle and small in size. It originates in the palmar aponeurosis and inserts into the deep part of the skin layer, called the dermis.
• Palmaris major: It originates in the epitrochlea of the elbow and inserts into the second metacarpal of the hand. Flexion of the wrist is related to the action of this muscle.

Ligaments

• Tissues that join the radius to the carpal and metacarpal bones: radioscaphocapitate, radioscaphosemilunate, triquetral radiolunate, ulnotriquetral, ulnolunate and triquetocapitate. Their function is to give stability to the wrist and to limit some movements.
• Ligaments that hold the metacarpal and carpal bones to the ulna of the forearm: ulnar piriformis and ulnar lunate.
• Dorsal intercarpal: This is responsible for joining the lunate bone to the scaphoid.
• Radiopyramidal: This ligament joins the radius bone with the pyramidal bone to limit and stabilise the wrist.
• Radiosemilunar: The lunate bone is attached to the forearm by this ligament.
• Radioscaphoid: The scaphoid and radius are joined by this tissue.
• Radial collateral: This is a ligament that arises in the elbow area and works with the thumb joint from the radius.
• Ulnar collateral: The thumb also receives the insertion of this ligament which arises from the ulnar bone of the forearm. Its job is to flex and extend the right finger.

Biomechanics of the hand, fingers and wrist

• Flexion: This action occurs when the palm of the hand is brought towards the front of the forearm. This is achieved thanks to the tension produced by the ligaments located in the pyramidal, trapezium and trapezoid bones to move the scaphoid bone. The range of motion can be up to 90°.
• Extension: This is the opposite of flexion. It consists of placing the hand, in its dorsal area, as close as possible to the upper part of the forearm. This movement can be executed with an amplitude of up to 85°. The radius, lunate and scaphoid are the bones that act with the ligaments for this task.
• Abduction: This consists of placing the palm of the hand towards the ground and moving it parallel to the ulna and radius towards the trunk. This is achieved between 15 and 25° of amplitude thanks to the joints that move the carpal bones, the scaphoid and the lunate.
• Adduction: This action tries to position the hand in the same way as in abduction, but turn it to the opposite side. In other words, moving towards the outside of the trunk of the body.
• Abduction: When the fingers of the hand are separated, achieving the maximum opening, this arc is known as abduction.
• Adduction: This involves bringing the four fingers together while keeping the thumb separated from the palm of the hand.
• Extension: If the hand is placed in the position of adoption and the thumb is moved towards the palm, the extension movement is produced.
• Flexion: Moving the five fingers towards the palm allows the flexor muscles of the hand to perform this biomechanical action.
• Palmar: This movement allows the fingerprints of the index finger to touch with that of the thumb.
• Lateral: This biomechanical action places the thumb next to the phalanx of the index finger.
• Interphalangeal thumb flexion: It is possible to move the thumb between the two phalanges so as to form a 90° angle. Extension will be the opposite movement.
• Metacarpophalangeal flexion of each finger: Moving each of the fingers at 90 degrees in relation to the phalanx with the metacarpals causes this movement. Metacarpophalangeal extension is the opposite action to this biomechanical task.
• Proximal and middle interphalangeal flexion of each finger: When each finger is moved between the proximal and middle phalanges it is known as flexion (or extension, in the opposite case) of the fingers.
• Distal interphalangeal flexion: To perform this movement it is necessary to bend the middle and distal phalanges while keeping the proximal phalanx straight in relation to the metacarpals. This movement can be performed on all fingers except the thumb.
• Metacarpophalangeal adduction: This movement consists of moving each of the fingers towards the outside of the hand between the proximal phalanges and the metacarpals. Returning to the initial position is known as metacarpophalangeal abduction.
• Cylindrical grip: This consists of keeping the four fingers curved and the thumb underneath, as is done when grasping a cylindrical object.
• Hook: Unlike the cylindrical grip, the thumb is moved away from its lower position. That is to say, it consists of picking up all the fingers and leaving the thumb raised.
• Tip grip: This movement differs from the palmar grip in that it is not the fingerprints that are touched, but the ends of the fingernails.
• Spherical: Very similar to the cylindrical grip, but in this case the palm of the hand is facing upwards.