12.3
上肢の骨：橈骨
橈骨は、前腕を構成する二本の骨のうち、長い方です。橈骨の近位端は、肱骨の小径頭と尺骨の橈側切痕と関節し、肘関節を形成します。橈骨の遠位端は、尺骨と尺側切痕を介して関節し、遠位橈尺関節を形成します。遠位端では、橈骨は手根の骨（舟状骨と月状骨）にも関節して、橈手根関節を形成します。
橈骨には、釘のような…
橈骨は、尺骨と平行に走り、橈骨ノッチで近位に結合し、尺骨ノッチを介して遠位に結合する外側の前腕骨です。
爪の形をした頭と、放射状茎状突起と呼ばれる尖った突起で終わる曲がりくねったシャフトがあります。
近位端では、頭部は上腕骨頭蓋および尺骨と結合し、肘関節を形成します。ラジアルヘッドを回転させることで、手のひらを上下に回しながら前腕を動かすことができます。腕を曲げる間、頭は上腕骨の橈骨窩に移動します。
橈骨頭のすぐ下には、細い首が腕の上腕二頭筋を固定する粗い橈骨結節まで伸びています。
遠位端では、橈骨茎状突起が手首の骨と結合して、橈骨手根関節または手首関節を形成します。
茎状突起プロセスは、手首の横方向の回転を制限するために、短い長い漸散胴靭帯を介して手首関節の動きを安定させます。
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Q1: Where does the radius articulate with other bones at the elbow?
At the proximal end, the radius articulates with the capitulum of the humerus and the radial notch of the ulna to form the elbow joint. The nail-shaped radial head joins these structures, enabling the forearm to flex and rotate. This articulation allows the radial head to move into the radial fossa of the humerus during arm flexion.
Q2: What is the radial tuberosity and what attaches to it?
The radial tuberosity is a rough, oval-shaped prominence located just below the radial neck. The biceps brachii muscle attaches to this tuberosity, anchoring the bicep muscles of the arm. This attachment site is crucial for arm flexion and supination movements.
Q3: How does the radius connect to the wrist bones?
At the distal end, the radius articulates with the carpal wrist bones, specifically the scaphoid and lunate, forming the radiocarpal joint. The radial styloid process, a pointed projection at the distal end, joins with these wrist bones. Ligaments including the radiolunate ligament stabilize this joint and limit lateral wrist rotation.
Q4: What role does the interosseous membrane play in the forearm?
The interosseous membrane connects the radius to the ulna along the entire length of the shaft, providing structural support and stability between the two forearm bones. It also serves as an attachment site for multiple muscles including the pronator teres, pronator quadratus, and supinator, which facilitate pronation, supination, and other forearm movements.
Q5: How does the radius enable pronation and supination of the forearm?
During pronation, the radial head rotates and crosses over the ulna, causing the palm to face posteriorly. Supination reverses this movement, allowing the palm to face anteriorly. An annular ligament surrounding the radial head stabilizes it to the ulnar notch, enabling smooth rotation while maintaining joint integrity.
Q6: What is the relationship between the radius and ulna at the distal end?
At the distal end, the radius articulates with the ulna via the ulnar notch, forming the distal radioulnar joint. This joint allows the radius to rotate around the ulna during pronation and supination. The connection maintains forearm stability while permitting the rotational movements necessary for hand positioning.
Q7: How do structural changes in the radius occur as part of changes in the appendicular skeleton with age?
The radius, as part of the appendicular skeleton, undergoes structural changes throughout life. Understanding how bones like the radius change with age helps explain age-related changes in forearm strength, mobility, and joint stability. These changes affect pronation, supination, and overall upper limb function in aging individuals.