The elbow, a complex joint connecting the upper arm and forearm, is formally known in anatomy as the cubital region. This area is a meeting point for three different bones, allowing for a diverse range of movements. The anatomical name for the joint itself is the articulatio cubiti, and the associated term “cubital” is frequently used to describe related structures, such as the cubital fossa, or “elbow pit.”
The Bony Framework
The elbow joint is formed by the convergence of three bones: the humerus of the upper arm, and the radius and ulna of the forearm. The distal end of the humerus features two distinct projections that facilitate articulation with the forearm bones. The spool-shaped trochlea engages with the ulna, while the rounded capitulum articulates with the radius.
The ulna features a large, C-shaped depression known as the trochlear notch. This notch is designed to fit snugly around the humerus’s trochlea, forming the primary hinge mechanism of the elbow. The prominent bony tip of the elbow is the olecranon process, a projection of the ulna. This process slides into the olecranon fossa on the back of the humerus when the arm is straightened.
The radius, located on the thumb side of the forearm, meets the humerus with its disc-shaped radial head. This head articulates with the capitulum, allowing for the rotational movements of the forearm. The ulna provides the main stability for bending and straightening the arm.
The Joint Complex and Stabilization
The bony framework results in three distinct articulations encased within a single joint capsule. The humeroulnar joint functions as a uniaxial hinge joint, enabling the primary movements of flexion and extension. The humeroradial joint assists with flexion and extension, and is also involved in the rotational movements of the forearm.
The third articulation is the proximal radioulnar joint, where the head of the radius pivots against the ulna’s radial notch. This pivot joint specifically facilitates the forearm’s rotational actions. Stability for this complex is provided by a network of ligaments that thicken the joint capsule.
The ulnar collateral ligament (UCL), also known as the medial collateral ligament, connects the humerus to the ulna. This ligament prevents the elbow from opening up under valgus stress, or forces applied to the outside of the joint. The radial collateral ligament (RCL) helps stabilize the joint against varus stress. The annular ligament wraps around the head of the radius, securing it against the ulna and allowing for smooth rotation during forearm movement.
Primary Movements and Muscle Groups
The elbow’s movements are categorized into two main functional pairs: bending and straightening, and rotation. Flexion, or bending the elbow, is powered by muscles located on the front of the upper arm and forearm. The biceps brachii is a powerful muscle that not only flexes the elbow but also assists with forearm rotation.
The brachialis muscle, situated beneath the biceps, acts as the strongest pure flexor of the elbow. Extension, or straightening the arm, is performed by the triceps brachii, a large muscle on the back of the upper arm that attaches to the olecranon process of the ulna. Rotational movements of the forearm, known as pronation (turning the palm down) and supination (turning the palm up), occur mainly at the proximal radioulnar joint. These movements are controlled by smaller muscles in the forearm, such as the pronator teres and supinator, which effectively spin the radius around the fixed ulna.
Common Ailments and Injuries
Repetitive use and strain can lead to several well-known conditions affecting the elbow’s tendons and bursae. Lateral epicondylitis, commonly called Tennis Elbow, causes pain on the outside of the elbow. This condition involves the degeneration of the wrist extensor tendons where they attach to the lateral epicondyle of the humerus. It is an overuse injury often resulting from repetitive gripping and wrist extension.
Medial epicondylitis, or Golfer’s Elbow, is characterized by pain on the inner side of the elbow. This condition affects the common flexor tendon, which is the attachment point for the wrist flexor and forearm pronator muscles on the medial epicondyle. Like its lateral counterpart, it is an overuse injury caused by repeated forceful gripping or wrist flexion activities.
A third common issue is Olecranon Bursitis, sometimes nicknamed “student’s elbow.” This condition is the inflammation of the olecranon bursa, a fluid-filled sac situated between the bony olecranon process and the skin. Due to its superficial location, the bursa is susceptible to inflammation from a direct blow or from chronic, repetitive pressure, such as leaning on the elbow for extended periods.