The triceps brachii, commonly referred to as the triceps, is a large, three-headed muscle located in the posterior compartment of the upper arm.[7] It is the primary muscle responsible for extending the forearm at the elbow joint.
Location
The triceps brachii originates from three distinct heads:
- Long Head: Arises from the infraglenoid tubercle of the scapula.
- Lateral Head: Arises from the posterior surface of the humerus, superior to the radial groove.
- Medial Head: Arises from the posterior surface of the humerus, inferior to the radial groove.
The muscle converges into a single tendon that inserts onto the olecranon process of the ulna. It lies posterior to the humerus and is superficial, making it easily palpable.[5]
Anatomy
The triceps brachii, or triceps, is a large, three-headed muscle in the posterior compartment of the arm. It is responsible for extending the forearm and maintaining upper limb stability.
Origin
The triceps brachii has three heads, each originating from a distinct anatomical site:
- Long Head: Originates from the infraglenoid tubercle of the scapula, just below the glenoid cavity.
- Lateral Head: Arises from the posterior surface of the humerus, superior to the radial groove.
- Medial Head: Originates from the posterior surface of the humerus, inferior to the radial groove and medial to the lateral head.
Insertion
- All three heads converge into a single, thick tendon that inserts onto the olecranon process of the ulna, on its posterior surface.[3]
- The triceps tendon is also connected to the antebrachial fascia via a fibrous expansion.
Structure
- The triceps brachii is a fusiform muscle, with each head contributing to the overall bulk of the posterior upper arm.
- The long head is the largest and spans two joints (shoulder and elbow), while the lateral and medial heads are monoarticular, acting only on the elbow joint.
Innervation
- The triceps brachii is innervated by the radial nerve, which arises from the posterior cord of the brachial plexus.
- The nerve supplies branches to the individual heads:
- Long Head: Proximal branches of the radial nerve.
- Lateral and Medial Heads: Distal branches of the radial nerve.
Blood Supply
The muscle is vascularized by branches of the profunda brachii artery (deep brachial artery), which accompanies the radial nerve in the radial groove of the humerus.
Relations
Proximally:
- The long head lies medial to the lateral head and lateral to the teres major and teres minor.
- It also forms part of the triangular and quadrangular spaces, alongside other muscles and neurovascular structures.[1]
Distally:
The triceps tendon is located posterior to the elbow joint, superficial to the olecranon bursa.
Medially:
The medial head lies deep to the long and lateral heads and is in close proximity to the radial nerve and profunda brachii artery within the radial groove.
Fascial Compartment
The triceps brachii is enclosed within the posterior fascial compartment of the arm, separated from the anterior compartment by the medial and lateral intermuscular septa.
Function
The triceps brachii is the primary muscle responsible for forearm extension and plays a crucial role in upper limb movement and stability.[8] Its three heads allow for versatility and strength in performing various actions. Below is a detailed explanation of its functions:
Primary Functions
Extension of the Forearm at the Elbow Joint
- The triceps brachii is the primary extensor of the elbow joint.
- When the muscle contracts, it pulls on its tendon, which inserts into the olecranon process of the ulna, straightening the forearm from a flexed position.
Stabilization of the Elbow Joint
- The triceps provides dynamic stability to the elbow during activities that involve pushing or bearing weight.
- This stabilization prevents unwanted movement, particularly when the forearm is extended against resistance.
Extension of the Shoulder Joint (Long Head)
- The long head of the triceps crosses the shoulder joint and contributes to shoulder extension by pulling the humerus posteriorly.
- It assists in adduction of the shoulder when the arm is abducted.
Secondary Functions
Stabilization of the Shoulder Joint
The long head stabilizes the shoulder joint by maintaining the position of the humeral head in the glenoid cavity during arm movements.
Coordination with Other Muscles
- The triceps works synergistically with the anconeus muscle to extend the forearm.
- It counterbalances the action of the biceps brachii and brachialis, preventing excessive flexion of the elbow.
Role in Functional Activities
Pushing Movements:
- The triceps is heavily involved in activities that require pushing, such as performing push-ups, bench pressing, or pushing objects like doors.[6]
- The muscle generates the force needed for powerful extension of the arm.
Overhead Movements:
It contributes to stability and strength during activities like throwing, striking, or lifting objects overhead.
- Weight-Bearing Tasks: During tasks like using crutches or performing handstands, the triceps supports the body’s weight by maintaining elbow extension.
- Precision and Control: The triceps provides controlled extension for fine motor tasks, such as writing or reaching for objects, ensuring smooth and accurate arm movements.
Dynamic Muscle Recruitment
- Long Head: Active during shoulder extension, adduction, and elbow extension, especially when the arm is positioned overhead.[4]
- Lateral Head: Primarily recruited for movements requiring significant force, such as heavy lifting.
- Medial Head: Functions continuously during all elbow extension movements, providing endurance and fine control.
Clinical Significance
The triceps brachii muscle holds significant clinical importance due to its role in elbow and shoulder movements and its proximity to key neurovascular structures:
- Triceps Tendon Rupture: A rare but serious injury, often caused by trauma or overuse, resulting in the inability to extend the elbow.[2] Surgical repair is typically required.
- Radial Nerve Injury: The radial nerve runs along the radial groove of the humerus, near the medial and lateral heads of the triceps. Fractures of the humerus or direct trauma can damage the nerve, leading to weakness or paralysis of triceps function and wrist drop.
- Tendinitis: Overuse of the triceps during repetitive or high-stress activities, such as throwing or weightlifting, can lead to inflammation of the tendon, causing pain and limited mobility.
- Elbow Stabilization: Weakness or atrophy of the triceps can compromise elbow stability, particularly during weight-bearing activities like pushing or lifting.
- Surgical Landmark: The triceps serves as a key anatomical landmark during surgical approaches to the posterior humerus or elbow joint.
