The elbow is a complex joint formed by the articulation of three bones – the humerus, radius, and ulna. The elbow joint helps in bending or straightening of the arm to 180 degrees and lifting or moving objects.
The bones of the elbow are supported by:
- Ligaments and tendons
- Blood vessels
Bones and Joints of the Elbow
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 bone of the forearm located on the inner surface of the joint. It 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 articulation between the ulna and radius helps the forearm to rotate.
The elbow consists of three joints, namely:
- The humeroulnar joint is formed between the humerus and ulna and allows flexion and extension of the arm.
- The humeroradial joint is formed between the radius and humerus and allows movements like flexion, extension, supination, and pronation.
- The radioulnar 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 with synovial fluid, which further enables the smooth movement of the bones.
Muscles of the Elbow Joint
There are several muscles extending across the elbow joint that help 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 towards the body
- Brachioradialis: Forearm muscle that flexes, straightens and pulls the arm at the elbow
- Pronator teres: Muscle that extends from the humeral head, across the elbow, and towards the ulna, and helps to turn the palm facing backward
- Extensor carpi radialis brevis: Forearm muscle that helps in movement of the hand
- Extensor digitorum: Forearm muscle that helps in movement of the fingers
Ligaments and Tendons of the Elbow
The elbow joint is supported by ligaments and tendons, which provide stability to 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:
- Medial or ulnar collateral ligament: Comprised of triangular bands of tissue on the inner side of the elbow joint
- Lateral or radial collateral ligament: A thin band of tissue on the outer side of the elbow joint
- Annular ligament: Group of fibers that surround the radial head, and hold the ulna and radius tightly in place during movement of the arm
Together, the medial and lateral ligaments are the main source of stability and hold the humerus and ulna tightly in place during movement of the arm.
The ligaments around a joint combine to form a 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 fibers that connect muscle to bone. The various tendons that 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
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 sensory signals such as touch, pain, and temperature back to the brain.
Any injury or damage to these nerves causes pain, weakness or joint instability.
Blood Vessels Supplying the Elbow
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.
Although the elbows are not weight-bearing joints, they are considered to be most important for the functioning of the upper limbs. Hence, even minor trauma or disease affecting the elbow may cause pain and limit the movements of the upper limbs. Arthritis is one of the common disease conditions affecting the elbow joint.
The biceps muscle, located in the front of the upper arm allows you to bend the elbow and rotate the arm. Biceps tendons attach the biceps muscle to the bones in the shoulder and in the elbow. The biceps tendon that attaches the muscle at the elbow is known as the distal biceps tendon.
Inflammation of the olecranon bursa leads to a condition called olecranon bursitis. The causes of elbow bursitis may include trauma or a hard blow on the elbow, excessive leaning on the elbow, infection by puncture wounds or insect bites, or conditions such as gout and rheumatoid arthritis. People in certain occupations such as plumbing or air conditioning, which involve a lot of crawling on the elbows, are highly prone to this condition.
Elbow impingement is a medical condition characterized by compression and injury of soft tissue structures, such as cartilage, at the back of the elbow or within the elbow joint. It is a condition caused by repetitive forced extensions and overuse of the elbow. It can either occur in isolation or as valgus extension overload syndrome - also known as pitcher’s elbow - commonly noted in athletes in overhead-throwing sports like baseball, football, volleyball, and tennis. It can also result from gymnastics and aggressive weight-lifting.
Damage to any of the structures that make up the elbow joint can cause elbow pain. An elbow dislocation occurs when the bones that make up the joint are forced out of alignment as when you fall onto an outstretched hand. They can also occur from any traumatic injury such as motor vehicle accidents. When the elbow is dislocated you may experience severe pain, swelling, and lack of ability to bend your arm. Sometimes, you cannot feel your hand or may have no pulse in your wrist because arteries and nerves that run along your elbow may be injured.
Little league elbow, also called medial apophysitis, is an overuse condition that occurs when there is overstress or injury to the inside portion of the elbow. It is commonly seen in children involved in sports activities that require repetitive throwing such as baseball.
Radial tunnel syndrome is a painful condition caused by pressure on the radial nerve of the forearm. The entrapment or compression occurs frequently in the proximal forearm in the radial tunnel; a narrow space formed by muscles, bone, and tendon near the elbow joint.
The triceps or triceps brachii is a crucial muscle of the upper arm (humerus). It runs along the upper arm bone between the shoulder and elbow. The triceps tendons connect the triceps muscles to the shoulder blade and elbow in your arm. Tendons are strong bands of tissue that attach muscle to bone. A triceps injury is damage to the tendon that attaches the triceps muscle at the back of your upper arm to the shoulder blade and elbow bone.
An athlete uses an overhand throw to achieve greater speed and distance. Repeated throwing in sports such as baseball and basketball can place a lot of stress on the joints of the arm, and lead to weakening and ultimately, injury to the structures in the elbow.
Ulnar nerve neuritis, also known as ulnar nerve entrapment or cubital tunnel syndrome, is a condition in which the ulnar nerve becomes irritated and inflamed due to constant pressure on it, leading to various symptoms. The nerve can become compressed at several places along its length, such as at the collarbone or wrist; but the most common area of compression is an area of the elbow called the cubital tunnel.
Viscosupplementation is a minimally invasive procedure that involves the injection of a hyaluronic acid preparation into the elbow joint to treat arthritis. Hyaluronic acid is a naturally occurring substance which is present in the joint fluid that acts as a shock absorber and enhances lubrication.