Tricep

Introduction

The triceps brachii is a major muscle located in the posterior compartment of the upper arm. It plays a key role in extending the elbow and stabilizing the shoulder joint. Understanding its anatomy and function is essential for clinical assessment and management of upper limb injuries.

Anatomy of the Triceps

Location and General Description

The triceps brachii occupies the posterior aspect of the humerus and extends from the shoulder to the elbow. It is a large, fusiform muscle that contributes significantly to the bulk of the posterior arm.

Muscle Heads

• Long head: Originates from the infraglenoid tubercle of the scapula and spans both the shoulder and elbow joints.
• Lateral head: Originates 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 lies deep to the long and lateral heads.

Origin and Insertion

The long head arises from the scapula, while the lateral and medial heads originate from the humerus. All three heads converge to form a single tendon that inserts on the olecranon process of the ulna, allowing powerful elbow extension.

Relations

• Anterior relations: Brachialis muscle and humeral shaft.
• Posterior relations: Skin, fascia, and subcutaneous tissue of the posterior arm.
• Neurovascular relations: The radial nerve runs along the radial groove, closely related to the lateral and medial heads, while the profunda brachii artery accompanies it.

Innervation and Blood Supply

Motor Innervation

The triceps brachii is primarily innervated by the radial nerve, which originates from the posterior cord of the brachial plexus (C6-C8). The radial nerve provides motor fibers to all three heads, enabling coordinated contraction for elbow extension.

Sensory Supply

Sensory fibers from the radial nerve provide proprioceptive feedback from the muscle, contributing to coordinated movement and joint stability.

Arterial Supply

• Profunda brachii artery: The main arterial supply, running alongside the radial nerve in the radial groove.
• Other minor vessels: Branches from the brachial and circumflex humeral arteries supplement the blood supply to the triceps heads.

Venous Drainage

Venous drainage mirrors the arterial supply, with the profunda brachii vein and accompanying tributaries draining blood from the muscle into the brachial vein.

Histology and Muscle Fiber Composition

• Type I (slow-twitch) fibers: These fibers are fatigue-resistant and support sustained, low-intensity activities such as maintaining posture.
• Type II (fast-twitch) fibers: These fibers generate high force and power during rapid or strenuous movements like pushing or throwing.
• Connective tissue components: Endomysium, perimysium, and epimysium provide structural support, transmit force, and contain blood vessels and nerves within the muscle.

Function and Biomechanics

• Elbow extension: The primary function of the triceps brachii is to extend the forearm at the elbow joint, enabling pushing and lifting movements.
• Shoulder extension (long head): The long head crosses the shoulder joint, assisting in extending and adducting the arm at the shoulder.
• Contribution to pushing and weight-bearing movements: The triceps stabilizes the elbow and shoulder during activities such as push-ups, bench press, and weightlifting.
• Synergistic and antagonistic muscle interactions: Works synergistically with the anconeus for elbow extension and is antagonized by the biceps brachii and brachialis during flexion.

Development and Growth

• Embryological origin: The triceps brachii develops from the mesenchymal cells of the paraxial mesoderm, forming myotomes that migrate into the posterior compartment of the arm.
• Growth and maturation patterns: Muscle fiber number is largely determined prenatally, while postnatal growth occurs through hypertrophy. Functional maturation allows the triceps to coordinate complex upper limb movements during childhood and adolescence.

Clinical Significance

Injuries

• Muscle strains and tears: Overstretching or sudden forceful contraction can lead to partial or complete tears of the triceps, causing pain, swelling, and weakness in elbow extension.
• Tendon ruptures: Triceps tendon rupture is rare but can occur due to trauma or chronic degeneration, often requiring surgical repair to restore function.

Overuse Syndromes

Repetitive activities such as weightlifting, throwing, or pushing can lead to overuse injuries, presenting as pain, tenderness, and decreased strength in the posterior arm.

Role in Rehabilitation and Strength Training

The triceps brachii is a focus in rehabilitation programs to restore elbow extension strength after injury. Strengthening exercises like push-ups, dips, and resistance training improve functional capacity and joint stability.

Imaging and Diagnostic Evaluation

• Ultrasound: Provides real-time assessment of tendon integrity, muscle tears, and fluid accumulation in the posterior arm.
• MRI: Offers detailed visualization of muscle fibers, tendon insertions, and surrounding soft tissue, useful for diagnosing partial or complete tears.
• Electromyography: Evaluates neuromuscular function, detecting nerve injuries or denervation affecting triceps function.

Current Research and Advances

• Muscle regeneration and repair techniques: Investigations focus on enhancing healing of triceps tears using growth factors, stem cells, and scaffolds to promote tissue regeneration.
• Role in neuromuscular studies: Research on triceps activation patterns contributes to understanding motor control, coordination, and rehabilitation strategies for upper limb disorders.
• Advances in surgical repair of triceps injuries: Minimally invasive techniques and improved suture methods have enhanced outcomes for tendon ruptures and severe muscle injuries.

References

1. Gray H, Standring S. Gray’s Anatomy: The Anatomical Basis of Clinical Practice. 42nd ed. Elsevier; 2020.
2. Moore KL, Dalley AF, Agur AMR. Clinically Oriented Anatomy. 9th ed. Wolters Kluwer; 2018.
3. Martini FH, Nath JL, Bartholomew EF. Fundamentals of Anatomy & Physiology. 11th ed. Pearson; 2017.
4. Kumar V, Abbas AK, Aster JC. Robbins and Cotran Pathologic Basis of Disease. 10th ed. Elsevier; 2021.
5. Standring S, Ellis H, Healy JC, Johnson D, Williams A. Muscles of the Upper Limb. In: Gray’s Anatomy. 42nd ed. Elsevier; 2020. p. 821-830.
6. Peterson B, et al. Surgical repair of triceps tendon ruptures: techniques and outcomes. J Shoulder Elbow Surg. 2019;28(5):912-920.
7. Chang H, et al. Muscle fiber composition and biomechanics of the triceps brachii. Eur J Appl Physiol. 2017;117(12):2453-2463.
8. Fortier LA, et al. Stem cells and muscle regeneration: applications to upper limb injuries. Clin Orthop Relat Res. 2018;476(7):1475-1485.