parts of the humerus

3 min read 10-03-2025

The humerus, the long bone of your upper arm, is a crucial component of your shoulder and elbow joints. Understanding its anatomy is key to comprehending various upper limb movements and potential injuries. This article will delve into the detailed anatomy of the humerus, exploring its key features and clinical significance.

Proximal Humerus: The Shoulder Connection

The proximal end of the humerus, closest to the shoulder, is characterized by several important structures:

Head of the Humerus: The Ball in the Shoulder Joint

The rounded head of the humerus articulates with the glenoid cavity of the scapula (shoulder blade), forming the glenohumeral joint – your shoulder joint. This ball-and-socket joint allows for a wide range of motion. The articular surface of the head is smooth and covered with articular cartilage to facilitate smooth movement.

Anatomical Neck: A Subtle Boundary

The anatomical neck is a constricted region separating the head from the greater and lesser tubercles. It's a clinically relevant area, as fractures frequently occur here. It’s important to note that the anatomical neck is not a true “neck” in the sense of a narrow constriction but rather a region of anatomical demarcation.

Greater and Lesser Tubercles: Muscle Attachment Points

The greater tubercle and lesser tubercle are bony projections on the lateral and medial sides of the proximal humerus, respectively. Numerous muscles involved in shoulder movement attach to these tubercles. These include the rotator cuff muscles, crucial for shoulder stability and movement.

Intertubercular Sulcus (Bicipital Groove): Housing the Biceps Tendon

The intertubercular sulcus, also known as the bicipital groove, runs between the greater and lesser tubercles. The long head of the biceps brachii tendon runs through this groove, contributing to shoulder flexion and supination.

Surgical Neck: A Fracture Hotspot

The surgical neck lies distal to the tubercles. It's a common site for humeral fractures, particularly in older adults experiencing falls. This is due to its relatively narrow diameter and its position in the trajectory of a fall.

Diaphysis of the Humerus: The Shaft

The diaphysis, or shaft, of the humerus is the long, cylindrical portion of the bone. It's relatively straight and provides structural support for the arm. The diaphysis has several features worth noting:

Deltoid Tuberosity: Deltoid Muscle Attachment

A prominent, roughened area called the deltoid tuberosity is located on the lateral aspect of the diaphysis. This serves as the insertion point for the deltoid muscle, a powerful shoulder abductor.

Radial Groove: Radial Nerve Pathway

The radial groove runs obliquely down the posterior aspect of the humerus. The radial nerve and profunda brachii artery travel within this groove, supplying the posterior compartment of the arm.

Nutrient Foramina: Blood Supply

Numerous small openings called nutrient foramina are scattered throughout the diaphysis. These allow blood vessels to enter and supply nutrients to the bone's internal structures. This is critical for bone health and repair.

Distal Humerus: The Elbow Connection

The distal end of the humerus, closest to the elbow, articulates with the radius and ulna, forming the elbow joint. Key features include:

Capitulum: Articulation with the Radius

The capitulum is a rounded projection on the lateral side of the distal humerus. It articulates with the head of the radius, allowing for forearm rotation.

Trochlea: Articulation with the Ulna

The trochlea is a pulley-shaped structure on the medial side of the distal humerus. It articulates with the trochlear notch of the ulna, forming the primary hinge joint of the elbow.

Medial and Lateral Epicondyles: Muscle Attachments

The medial epicondyle and lateral epicondyle are prominent bony projections on the medial and lateral sides of the distal humerus, respectively. Numerous forearm muscles originate from these epicondyles, playing roles in wrist and finger movements. Golfer's and tennis elbow are often related to injuries in this area.

Coronoid Fossa and Olecranon Fossa: Elbow Joint Stability

The coronoid fossa and olecranon fossa are depressions on the anterior and posterior aspects of the distal humerus. These receive the coronoid process of the ulna during elbow flexion and the olecranon process during elbow extension, respectively, providing stability to the elbow joint.

Clinical Significance

Understanding the anatomy of the humerus is crucial for diagnosing and treating various injuries and conditions. Fractures, dislocations, and strains are common in this bone, particularly at the surgical neck and distal end. Accurate knowledge of its bony landmarks helps in accurate diagnosis via imaging and surgical procedures.

This detailed exploration of the humerus provides a thorough overview of its structure and clinical importance. Remembering the key features of the proximal, diaphysis, and distal regions is essential for anyone studying anatomy, medicine, or related fields.