ULNA
• The medial bone of the forearm, homologous with the fibula of the lower limb.
• Has upper end, shaft, and lower end.
🔗Upper end is hook-like, with concavity directed forwards.
🔗Lateral border of the shaft is sharp & crest-like.
🔗Styloid process lies posteromedial to the rounded head of ulna at its lower end.
➡ UPPER END:
• Contains the Olecranon process, Coronoid process, Trochlear notch, and Radial notch.
🌀 OLECRANON PROCESS
• Projects upwards from the shaft.
• Anterior surface forms the upper part of the trochlear notch.
• Posterior surface is subcutaneous, separated from the skin by a bursa.
• Superior surface has a roughened area posteriorly.
🌀 CORONOID PROCESS
• Projects forwards from the shaft just below the olecranon.
• Superior surface forms the lower part of the trochlear notch.
• Anterior surface is triangular & rough, leading to the ulnar tuberosity.
• Lateral surface has the radial notch (for the head of the radius) and supinator crest.
🌀 TROCHLEAR NOTCH
• Articulates with the trochlea of the humerus to form the elbow joint.
🌀RADIAL NOTCH
• Articulates with the head of the radius, forming the superior radioulnar joint.
➡ SHAFT:
Has 3 surfaces & 3 borders.
🔹BORDERS:
➖(a) Interosseous (lateral) border
– sharpest in the middle two-fourths.
➖(b) Anterior border
– thick, rounded, and terminates at the medial side of the styloid process.
➖(c) Posterior border
– subcutaneous & terminates at the base of the styloid process.
🔹SURFACES:
📍 Anterior surface
– between the anterior & interosseous borders, contains the nutrient foramen (supplied by the anterior interosseous artery).
📍 Medial surface
– between the anterior & posterior borders.
📍 Posterior surface
– divided into upper & lower parts by an oblique line.
➡LOWER END:
⚙Made up of the head and styloid process.
⚙ Head articulates with the ulnar notch of the radius to form the inferior radioulnar joint.
⚙ Separated from the wrist joint by the articular disc.
⚙ Ulnar artery & ulnar nerve lie on the anterior aspect of the ulna’s head.
⚙Styloid process projects downwards from the posteromedial side of the lower end.
