• Today’s objective is to Relate the Structure of the Hand Bones to Their Function
• Let’s take a moment to appreciate all of the fine, complex movements that our hands perform each day.
• The hand and wrist have a total of 27 bones that are arranged to roll, spin and slide which allows the hand to explore and control the environment and objects.
Many of the movements of the hand, such as manipulating objects, griping, and grasping, are all made possible by the opposing movement of the thumb.
• In fact, many scientists believe that the hand's existence promoted brain development by allowing humans to manipulate, interact with, explore, and gain information from the environment.
• The 27 bones of the hand fall into 1 of 3 categories: The carpals which are the short bones of the wrist, the metacarpals which are the long bones of the palm and the phalanges which are the long bones of the fingers or digits.
• The cluster of carpal bones in the wrist make it both strong and flexible. The wrist has a wide range of motion including adduction or radial deviation, abduction or ulnar deviation, flexion – moving the hand anteriorly, and extension - moving the hand posteriorly.
• These movements are made possible by the configuration of the 8 carpal bones that are categorized as short bones because they are roughly as tall as they are wide. These types of bones allow gliding movements to occur between them.
• The 8 carpals are stacked into 2 irregular rows contain 4 bones each.
The proximal row of the carpus or wrist contains the scaphoid, the lunate, triquetrum, and the pisiform.
• The distal row contains the trapezium, the trapezoid, the capitate and the hamate.
• Only 2 carpals, the scaphoid and the lunate, make contact with the radius. If you circumduction the wrist, as shown in the video clip here, you can feel that the motion is more connected to the radius than the ulna, allowing for a lot of freedom of movement.
• Interestingly, the ulna is not considered part of the wrist joint. This is because the ulna only makes intermitted contact with the carpals bones.
• For example, the Triquetrum only makes contact with the ulna during abduction.
• Even though the ulna is technically not considered part of the wrist joint, the ulna does articulate with the radius at the distal radioulnar joint.
• The fact that the ulna does not articulate with the carpals, nut the radius does, while being connected to the ulna via the distal radioulnar jointt, in part, allows for the unique movements of pronation supination of the hands Pronation being when the palms face downwards and supination when the palms face upwards.
I will now briefly discuss each of the carpal bones.
• The scaphoid is the largest carpal of the proximal row. It articulates with the radius and with other carpals in such a way that it helps to link the 2 rows of wrist bones together.
• The scaphoid gets its name from a word meaning boat-shaped, due to its somewhat boat-like structure.
• The lunate is in the middle of the proximal row and articulates with the radius. The lunate contributes significantly to wrist motion, due to its large cartilaginous surface area.
• The lunate gets its name from its crescent shape and is named for the word meaning crescent moon.
• The triquetrum is located on the pinky side of the 1 row of carpals. It adds stability and Gives the wrist a larger surface to bear weight transmitted from the hand
• The triquetrum is named after the Latin word for triangular due to its roughly triangular shape.
• The pisiform is a small sesamoid bone that sits within the flexor carpi ulnaris tendon. This bone is easily palpated on the anteromedial side of the wrist.
• The function of the pisiform bone is to change the direction of the pull of its surrounding tendon.
• The pisiform gets its name from a Latin word meaning pea, due to its small rounded appearance.
• The trapezium articulates with the pollex, thereby stabilizing it and allowing it to move in multiple directions.
• The word trapezium is derived from a Latin term meaning little table.
• The trapezoid articulates with the metacarpal of the index finger, holding it in place.
• As you may have guessed, this bone is named due to its trapezoidal shape.
• The capitate is the largest of the carpals and it articulates with the metacarpal of the middle finger. It forms joints with multiple other carpals and makes a significant contribution to wrist motion.
• The capitate gets its name from a Latin word meaning head or head-shaped.
• The hamate articulates with both the ring finger and the pinky and serves as an attachment for multiple ligaments.
• The Hamate is named after the word meaning hook-like, for its hook-like appearance.
• A great mnemonic to help you remember the carpals in order, is Sally Left The Party To Take Ca
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