Elbow Anatomy

The elbow is a synovial joint in the upper limb that connects the upper arm bone (humerus) to the two bones of the forearm (radius and ulna). It is a hinge joint that allows for the arm's bending (flexion), straightening (extension), and some rotational movements.

The bones of the elbow are supported by and surrounded by

• Ligaments and tendons
• Muscles
• Nerves
• Blood vessels

Injuries or conditions affecting the elbow joint, such as fractures, dislocations, arthritis, or overuse injuries, can impact its function and may require medical attention for diagnosis and treatment.

Bones & Joints of the Elbow Joint

The elbow joint is formed at the junction of three bones:

• The humerus (upper arm bone) forms the upper portion of the joint. The lower end of the humerus divides into two bony protrusions known as the medial and lateral epicondyles, which can be felt on either side of the elbow joint.
• The ulna is the larger forearm bone located on the joint's inner surface. The curved shape of the ulna articulates with the humerus.
• The radius is the smaller forearm bone situated on the joint's outer surface. The head of the radius is circular and hollow, allowing movement with the humerus. The connection between the ulna and radius helps the forearm to rotate.

The elbow consists of three joints from the articulation of the three bones, namely:

• Humero-ulnar joint is formed between the humerus and ulna and allows arm flexion and extension.
• Humeroradial joint is formed between the radius and humerus, allowing flexion, extension, supination, and pronation.
• Radio-ulnar joint is formed between the ulna and radius bones, allowing the lower arm to rotate.

Articular cartilage lines the articulating regions of the humerus, radius and ulna. Its thin, tough, flexible, and slippery surface acts as a shock absorber and cushion to reduce friction between the bones. The cartilage is lubricated by synovial fluid, which further enables the smooth movement of the bones.

Muscles of the Elbow Joint

Several muscles extend across the elbow joint, which helps in various movements. These include the following:

• Biceps brachii: upper arm muscle enabling flexion of the arm
• Triceps brachii: muscle in the back of the upper arm that extends the arm and fixes the elbow during fine movements
• Brachialis: upper arm muscle beneath the biceps which flexes the elbow
• Brachioradialis: forearm muscle that flexes and pulls the arm at the elbow
• Pronator teres: this muscle extends from the humerus (humeral head) and ulna (ulnar head), across the elbow and towards the radius, and helps to turn the palm downward.
• Extensor carpi radialis brevis: forearm muscle that helps move the wrist backwards.
• Extensor digitorum: forearm muscle that straightens the fingers.

Elbow Joint Ligaments and Tendons

The elbow joint is supported by ligaments, which provide stability, and tendons, which allow muscles to move the joint.

Ligaments are a group of firm tissues that connect bones to other bones. The most important ligaments of the elbow joint are the following:

• Medial or ulnar collateral ligament: composed of triangular tissue bands on the elbow joint's inner side.
• Lateral ulnar collateral ligament: a band of tissue on the outer side of the elbow joint.

Together, the medial and lateral ligaments are the main source of stability and hold the humerus and ulna tightly in place during arm movement.

• Annular ligament: This group of fibres surrounds the radial head and holds the ulna and radius tightly in place during arm movement.

The ligaments around a joint are joined to the joint capsule that contains synovial fluid.

Any injury to these ligaments can lead to instability of the elbow joint.

Tendons are bands of connective tissue fibres that connect muscle to bone. The various tendons which surround the elbow joint include:

• Biceps tendon: attaches the biceps muscle to the radius, allowing the elbow to bend
• Triceps tendon: attaches the triceps muscle to the ulna, allowing the elbow to straighten

Nerves of the Elbow Joint

The elbow joint is innervated by several nerves that provide sensory and motor function to the region. The main nerves associated with the elbow joint include:

• Musculocutaneous Nerve: arises from the brachial plexus and supplies motor innervation to the muscles in the anterior compartment of the arm, including the biceps brachii and brachialis. It also provides sensory innervation to the lateral aspect of the forearm.
• Radial Nerve: A major nerve that runs along the back of the upper limb. It branches off from the posterior cord of the brachial plexus and supplies motor innervation to the extensor muscles of the arm, forearm, and hand. It also provides sensory innervation to the posterior aspect of the arm, forearm, and hand.
• Ulnar Nerve: Also arises from the brachial plexus and provides motor innervation to some of the muscles of the anterior compartment of the forearm, including the flexor carpi ulnaris and the muscles of the hand. It also provides sensory innervation to the little finger and part of the ring finger.
• Median Nerve: Another major nerve originating from the brachial plexus. It supplies motor innervation to several muscles in the forearm involved in flexion and opposition of the thumb. The median nerve also provides sensory innervation to the palmar aspect of the hand, including the thumb, index finger, middle finger, and half of the ring finger.

These nerves play crucial roles in both the motor control and sensation of the elbow joint and surrounding areas. Damage or compression to any of these nerves can result in various symptoms, including muscle weakness, loss of sensation, tingling, or pain.

Blood Vessels of the Elbow Joint

The blood supply to the elbow joint is provided by several arteries and veins that ensure the delivery of oxygen and nutrients while removing waste products. The main blood vessels associated with the elbow joint include:

• Brachial Artery: A major artery of the upper limb that runs along the inner side of the arm. It gives off branches that contribute to the blood supply of the elbow joint. These branches include the deep brachial artery, which supplies the posterior aspect of the elbow joint, and the collateral arteries, which provide additional vascular support.
• Radial Artery: One of the two main arteries of the forearm. It provides collateral blood supply to the joint.
• Ulnar Artery: The other main artery of the forearm, running alongside the ulna bone. It also contributes to the blood supply of the joint.
• Radial Recurrent Artery: A branch of the radial artery that supplies blood to the lateral aspect of the elbow joint.
• Ulnar Recurrent Arteries: Branches of the ulnar artery that supply blood to the medial aspect of the elbow joint.

These arteries divide into smaller branches and form an intricate network of blood vessels around the elbow joint, ensuring a robust blood supply.

Regarding veins, the venous drainage of the elbow joint primarily occurs through the corresponding venous counterparts of the arteries mentioned above. These veins accompany the arteries, and help carry deoxygenated blood away from the joint back to the heart.

Injuries or conditions affecting the blood vessels of the elbow joint, such as vascular trauma or thrombosis, can have serious implications on the blood supply and overall health of the joint.