Elbow
Elbow Anatomy
The elbow is a hinged complex joint made up of three bones, the humerus, ulna, and radius. The ends of the bones are covered with cartilage. Cartilage has a rubbery consistency that allows the joints to slide easily against one another and absorb shock. The bones are held together with ligaments that form the joint capsule. The joint capsule is a fluid filled sac that surrounds and lubricates the joint.
The bones of the elbow joint are supported by ligaments, muscles, nerves and blood vessels.
Bones
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 in to four bony protrusions – two on the outside known as the medial and lateral epicondyles which can be felt on either side of the elbow joint. The other two – the capitellum and trochlea form the joint with the upper end of radius and ulna.
- The Ulna is the larger bone of the forearm located on the inner surface of the joint. The curved shape of the ulna articulates with the humerus.
- The Radius is the smaller bone of the forearm situated on the outer surface of the joint. The head of the radius is circular and hollow which allows movement with the humerus. The connection between the ulna and radius helps the forearm to rotate.
The Joint
The elbow consists of three joints because of articulation of the three bones namely:
- Humero-ulnar joint is formed between the humerus and ulna and allows flexion and extension of the arm.
- Humero-radial (radio-capitellar) joint is formed between the radius and humerus, and allows movements like flexion, extension, supination and pronation.
Proximal Radio-ulnar joint is formed between the ulna and radius bones, and allows rotation of the lower arm.
Articular cartilage lines the articulating regions of the humerus, radius and ulna. It is a thin, tough, flexible, and slippery surface that 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.
Ligaments
The joint capsule of the elbow is strengthened by ligaments medially and laterally.Part of the capsule are distinctly thickened and stronger these are the ligaments which provide stability to the joint.
The radial collateral ligament is found on the lateral side of the joint, extending from the lateral epicondyle, and blending with the annular ligament of the radius (a ligament from the proximal radioulnar joint).
The ulnar collateral ligament originates from the medial epicondyle, and attaches to the coronoid process and olecranon of the ulna.
Any injury to these ligaments can lead to instability of the elbow joint.
Muscles around Shoulder
There are three main muscles around the elbow joint. The biceps and brachialis are at the front whilst the triceps is at the back of the elbow.
Tendons of the shoulder
Tendons are strong fibrous tissue which connect the muscle to the to the bone. Around the shoulder two important group of tendons which are the biceps and triceps.
Biceps tendon begins at the shoulder with the two heads and forms into a single muscle belly and then a tendon which attaches to the radial tuberosity (bony prominence on upper radius). This also forms a sheet of tissue in front of the forearm called the lacerates fibrosus. The biceps tendon allows the elbow to bend as well as supinate (rotate – palm facing upwards) The triceps attaches to the tip of the ulna bone – the olecranon and allows the elbow to straighten.
Nerves of the Shoulder
The main nerves of the elbow joint are the ulnar, radial and median nerves. These nerves transfer signals from the brain to the muscles that aid in elbow movements. They also carry the sensory signals like touch, pain, and temperature back to the brain.
Any injury or damage to these nerves causes pain, weakness or joint instability.
Blood Vessels of the Shoulder
Arteries are blood vessels that carry oxygen-pure blood from the heart to the hand. The main artery of the elbow is the brachial artery that travels across the inside of the elbow and divides into two small branches below the elbow to form the ulnar and the radial artery.