Phalanges of the Human Arm

March 15, 2024
David Sunnyside

The humerus has two major articulation areas at its distal end. The proximal area, the trochlea, forms an elbow joint with the ulna. The distal area, called the capitulum, forms an abutment with the radius bone at the wrist. The ulna also has a depression, the olecranon fossa, which receives the large projection of the olecranon bone (the olecranon process) when the arm is fully extended from the body.

The thumb is missing a middle phalanx, and the four remaining middle phallanges (phalanges of the fingers) are shorter and squatter than those of the other digits. The proximal ends have a rounded head with a non-articular surface that serves as an attachment site for the collateral ligaments of the finger.

Each middle phalanx has a base and a head, which resembles a pulley in shape and appearance. The heads articulate with the bases of their adjacent distal phalanges to form the metacarpophalangeal joints of the hand. There are five distal phalanges in each finger, and they have a flattened, wrinkled dorsal surface that provides traction against the underlying skin.

The proximal end of the radius is somewhat similar to the trochlea in the humerus. However, the ulna is different in that it has a C-shaped depression on its superior surface. This area, the ulnar notch, articulates with a concave region on the humerus at the elbow joint. Just above the ulnar notch is the olecranon fossa, a larger depression which receives the olecranon process of the ulna when the arm is fully extended from the body.

David Sunnyside
Co-founder of Urban Splatter • Digital Marketer • Engineer • Meditator
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