2․4 Lesser Tubercle

The lesser tubercle is a smaller, rounded projection located on the anterior aspect of the humerus, near the anatomical neck․ It is the attachment point for the subscapularis muscle, a key component of the rotator cuff․ This muscle contributes to internal rotation and stabilization of the shoulder joint․ The lesser tubercle is positioned on the front side of the bone, contrasting with the greater tubercle’s lateral placement․ Its surface is roughened to provide a secure anchorage for the subscapularis tendon, ensuring effective force transmission during movements like arm rotation and scapular stabilization․ This structure is vital for maintaining proper shoulder mechanics and preventing injury․

2․5 Surgical Neck

The surgical neck is a narrowed region of the humerus located just distal to the greater and lesser tubercles․ It is a common site for fractures due to its anatomical location and is clinically significant․ The axillary nerve and the posterior circumflex humeral artery pass near this area, making injuries here potentially complex․ Fractures of the surgical neck can sometimes lead to complications, such as nerve damage or circulatory issues․ Its proximity to major neurovascular structures highlights the importance of precise clinical management in such cases․ This region is also a key area for surgical interventions, hence its name․

Shaft of the Humerus

The shaft, or diaphysis, is the long, cylindrical portion of the humerus between the upper end and the condyles․ It features the deltoid tuberosity, spiral groove, and radial groove, serving as attachments for muscles and pathways for nerves․

3․1 Deltoid Tuberosity

The deltoid tuberosity is a roughened, elongated area on the lateral aspect of the humeral shaft․ Located approximately halfway down the bone, it serves as the insertion point for the deltoid muscle․ This anatomical feature is crucial for shoulder abduction, flexion, and extension․ The tuberosity’s texture provides a secure attachment for the muscle’s tendinous fibers, enhancing mechanical advantage during movement․ Its prominence makes it a key landmark for surgical and anatomical references․ The deltoid tuberosity also lies near the radial nerve and groove, highlighting its importance in both muscle function and nerve protection․

3․2 Spiral Groove

The spiral groove is an oblique depression on the posterior aspect of the humeral shaft․ It begins near the greater tubercle and extends distally toward the elbow․ The radial nerve and deep brachial artery pass through this groove, which provides protection during their course along the bone․ The spiral groove’s location is clinically significant, as it helps in locating the radial nerve during surgical procedures․ It is also a key anatomical landmark for understanding the relationship between the humerus and adjacent neurovascular structures․ This feature is essential for both anatomical studies and clinical applications, particularly in surgeries involving the upper limb․

3․3 Radial Nerve and Groove

The radial nerve courses through the spiral groove on the posterior aspect of the humeral shaft, accompanied by the deep brachial artery․ It originates from the brachial plexus and is responsible for innervating the extensor muscles of the forearm and providing sensory supply to the back of the hand․ The radial groove, located near the greater tubercle, spirals distally and offers protection to the nerve and artery․ This anatomical relationship is critical for maintaining motor and sensory function in the upper limb․ The radial nerve’s proximity to the humerus makes it vulnerable during fractures or surgical procedures, highlighting its clinical significance in orthopedic and neurological assessments․

Lower End of the Humerus

The distal humerus forms the elbow joint, featuring the condyle with capitulum and trochlea for articulation with the radius and ulna, supported by medial and lateral epicondyles․

4․1 Condyle of the Humerus

The condyle of the humerus is a triangular structure at the distal end, forming the elbow joint․ It consists of the capitulum (lateral) and trochlea (medial), which articulate with the radius and ulna, respectively․ The capitulum is a rounded surface for the radius head, while the trochlea is a grooved surface for the ulna․ Together, they enable flexion and extension of the elbow․ The condyle also includes the medial and lateral epicondyles, which serve as attachment points for forearm muscles․ This anatomical design ensures stability and mobility in the elbow joint, making it essential for upper limb function․

4․2 Capitulum and Trochlea

The capitulum and trochlea are key articular surfaces on the distal humerus, facilitating elbow joint movement․ The capitulum, a rounded lateral surface, articulates with the radius head, enabling forearm rotation․ The trochlea, a medial grooved surface, articulates with the ulna, allowing flexion and extension․ Together, they form the humero-ulnar and radio-capitellar joints, essential for elbow stability and mobility․ Their anatomical design ensures precise alignment and smooth motion, making them critical for upper limb function․

4․3 Medial Epicondyle

The medial epicondyle is a prominent bony projection located on the distal end of the humerus, medially to the trochlea․ It serves as the origination point for the flexor muscles of the forearm, including the flexor carpi radialis, flexor carpi ulnaris, and palmaris longus․ This epicondyle is larger than the lateral epicondyle and provides a broad, rough surface for muscle attachment, enhancing the stability and strength of the elbow joint․ Its anatomical position allows for efficient transmission of forces during wrist and finger flexion, making it a critical structure for upper limb functionality and movement․

4․4 Lateral Epicondyle

The lateral epicondyle is a bony prominence located on the distal end of the humerus, lateral to the capitulum․ It serves as the attachment site for the extensor muscles of the forearm, such as the extensor carpi radialis brevis and extensor digitorum․ This epicondyle is smaller than the medial epicondyle and has a smooth surface for muscle attachment․ Its anatomical position facilitates wrist and finger extension, making it essential for movements like gripping and lifting․ The lateral epicondyle also plays a role in stabilizing the elbow joint during flexion and extension, contributing to overall upper limb functionality and dexterity․

Functional Anatomy

The humerus enables a wide range of upper limb movements by articulating with the scapula and forearm bones, while its surface features provide attachment points for muscles and nerves․

5․1 Articulation with Other Bones

The humerus articulates with the scapula at the shoulder joint and with the radius and ulna at the elbow joint․ Proximally, the humeral head fits into the glenoid cavity, forming a synovial joint that allows for a wide range of shoulder movements․ Distally, the capitulum and trochlea of the humerus articulate with the radius and ulna, respectively, forming the hinge-type elbow joint․ This dual articulation enables flexion, extension, and supination of the forearm․ The olecranon process of the ulna fits into the olecranon fossa of the humerus during elbow extension, while the coronoid process fits into the coronoid fossa during flexion, ensuring stability and efficient movement․

5․2 Muscle Attachments and Movements

The humerus serves as an attachment point for numerous muscles, enabling diverse movements of the upper limb․ Proximally, muscles like the deltoid, supraspinatus, and infraspinatus attach to the greater tubercle, facilitating shoulder abduction, flexion, and external rotation․ The subscapularis attaches to the lesser tubercle, aiding internal rotation․ Distally, the triceps brachii and brachialis muscles attach to the shaft and lower end, enabling elbow extension and flexion․ The radial nerve and ulnar nerve course along the shaft, innervating muscles responsible for wrist and finger movements․ This extensive musculotendinous network allows for precise control of arm and forearm movements, from overhead reaching to fine motor tasks․

Clinical Relevance

The humerus is prone to fractures, particularly at the proximal end, often due to falls or trauma․ Proper treatment is essential to restore arm function and mobility․

6․1 Common Fractures and Injuries

The humerus is susceptible to various fractures, particularly at the proximal and distal ends․ Proximal humerus fractures are common, often resulting from falls or direct trauma․ These fractures can involve the head, neck, or tubercles and may require surgical intervention if displaced․ Distal humerus fractures typically occur near the elbow and can affect the condyles or epicondyles․ Radial nerve injuries are a significant concern in mid-shaft fractures due to the nerve’s proximity to the bone․ Proper diagnosis and treatment are critical to restore function and prevent long-term complications, such as limited mobility or nerve damage․ Timely intervention ensures optimal recovery and return to normal activities․

6․2 Treatment Options

Treatment for humeral fractures depends on the severity and location․ Non-displaced fractures may be managed with immobilization using splints or braces․ For displaced fractures, surgical intervention such as open reduction and internal fixation (ORIF) or arthroplasty may be necessary․ Proximal humerus fractures often involve plate fixation, while shaft fractures might require intramedullary nails․ Distal fractures near the elbow may necessitate screws or plates to restore joint alignment․ Rehabilitation is crucial to regain strength and mobility․ Early physical therapy can prevent stiffness and promote recovery․ In severe cases, bone grafts or shoulder replacement surgery may be required to ensure proper healing and functional restoration․