Elbow Anatomy

A bone is a kind of rigid tissue that constitutes a part of the vertebrate skeleton in animals. Bones can protect the various organs in the body, they can produce red and white blood cells, can store minerals, provide structure and these can provide support for the body, and enable mobility. Joints are the regions where two or more bones meet. Most of the joints are mobile, allowing the bones to move. Joints consist of cartilage tissue which is a type of tissue that covers the surface of a bone at a joint. 

There are Three Main Types of Joints:

1. Fibrous Joint: This type of joint is also called synarthrodial and these are immovable. It is held together by a ligament. Examples of these kinds are where the teeth are held to their bony sockets and at both of the radioulnar and tibiofibular joints.

2. Cartilaginous Joint: These joints can occur where the connection in between the articulating bones is made up of cartilage and these are partially movable. An example of these kinds is they are found in between vertebrae in the spine.

3. Synovial Joint: Synovial joints are the most common among the classification of a joint that is found within the human body. They are highly moveable in nature and all have a synovial capsule that is surrounding the entire joint, a synovial membrane that secretes synovial fluid, and the cartilage known as hyaline cartilage which is attached at the ends of the articulating bones. There are about six types of synovial joints which can be classified by the shape of the joint and the movement available. Ball and socket joint, Condyloid joint, Hinge joint, Gliding joint, Pivot joint, and Saddle joint.

Elbow Joint Anatomy

The elbow joint anatomy is classified structurally as a synovial joint. It is also classified as a compound joint structurally, as there are two articulations that are present in the joint. Synovial joints are also called diarthrosis; these are free movable joints. The articular surfaces present in the bones at these joints are separated from each other by a layer of hyaline cartilage. Smooth movements found at these joints is provided by a highly viscous synovial fluid, which acts as a lubricant.

A fibrous capsule can enclose the joint and it is internally lined by a synovial membrane. Synovial joints can be classified further based on their function. The elbow joint is functionally similar to a hinge joint, which allows the movement in only one plane. The elbow is a synovial hinge joint that is located in between the forearm and upper arm. It is formed by the intersection of three bones: 

• The humerus is the upper arm.

• The ulna.

• Radius in the lower arm.

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Elbow Muscles

Like all the other hinge joints, the elbow permits the movement only in one place, namely the flexion and extension of the forearm that is relative to the upper arm. However, the elbow also allows the wrist to rotate by pivoting the radius around the ulna. The muscles of the elbow help to perform the many movements at the elbow joint by giving both great strength and flexibility to the arm. Let us learn more about elbow muscle anatomy.

There are about seven major elbow muscles that can flex, extend, or rotate the forearm. An additional nine muscles are found crossing the elbow to act upon the wrist and joints of the hand. These muscles can be broadly grouped into two, the flexor and extensor groups of the forearm.

1. The flexor group includes the brachialis, biceps brachii, and brachioradialis. These can bend the arm by decreasing the angle present in between the forearm and upper arm. The brachialis is the primary flexor muscle of the elbow and it is found mainly in the upper arm in between the humerus and the ulna. Superficial to the brachialis muscle, the long biceps brachii muscle is found that runs from the anterior portion to the humerus from the scapula to the radius. These biceps mostly function as a flexor muscle at the elbow region, but it is also able to supinate the forearm and can turn the palm of the hand anteriorly. Although biceps are found mostly in the region of the forearm, the brachioradialis is the third flexor muscle of the elbow that runs from the region of the distal end of the humerus to the region of a distal end of the radius.

2. Two muscles are the triceps brachii and anconeus; these act as the extensors of the forearm. The triceps brachii is a long muscle that runs from the posterior region to the humerus from the scapula to the olecranon of the ulna. The anconeus is a much smaller muscle that begins at the region of the distal end of the humerus near the elbow and ends at the region of the olecranon. These two muscles working together can increase the angle between the humerus, the ulna, and radius. The straightening of the arm can be done until the olecranon locks with full extension into the olecranon fossa of the humerus.

The rotation of the forearm is accomplished by the two muscles that cross the elbow: the pronator teres and the supinator. The pronator teres can cross the elbow at an oblique angle from the medial epicondyle of the humerus to its insertion region on the radius. During the process of contraction, the pronator teres rotate the radius of the elbow and the forearm medially so that the palm can face the posterior angle of the body. The antagonist of the pronator teres is the supinator, it crosses the elbow region obliquely at a right angle to the pronator teres and it connects the lateral epicondyle of the humerus to the radius. Contraction of the supinator helps to rotate the radius and forearm laterally so that the palm faces the anterior part of the body.

Nine more muscles of the forearm can cross the elbow to move the wrist and fingers of the hand. The flexor group includes the flexor carpi ulnaris, flexor carpi radialis, palmaris longus, and flexor digitorum superficialis. These muscles have their origins on the medial epicondyle of the humerus and they run along the anterior forearm to the palm of the hand and fingers. These muscles can contract to flex the fingers as in making a fist and flex the wrist to move the hand closer to the anterior forearm. The extensor group that includes the extensor carpi radialis longus, extensor carpi radialis brevis, and extensor digitorum. These have their origins on the lateral epicondyle region of the humerus and it runs through the posterior forearm to the back of the hand and fingers. Contraction of the extensor muscles helps in the extension of the hand and fingers in order to open a clenched hand and extend the wrist towards the posterior region of the forearm.

Ligaments of Elbow Joint

The collection of ligaments that connects the bones forms the elbow joint to each other by contributing to the stability of the joint. The humeroulnar and the humeroradial joints consist of a ligament that involves the connection of the two bones in the process of articulation: the ulnar collateral and the radial collateral ligaments.

1. The ulnar collateral ligament can extend from the medial epicondyle region of the humerus to the coronoid process of the ulna. It is triangular in shape and is composed of three parts: an anterior band, a posterior band, and an inferior band. 

2. The radial collateral ligament has a low attachment to the lateral epicondyle region of the humerus. The distal fibers can blend with the annular ligament that encloses the head of the radius, as well as with the fibers of the supinator and the extensor carpi radialis brevis muscles.

The annular ligament also reinforces the joints just by holding the radius and ulna of the elbow together at their proximal articulation process. The quadrate ligament is also present at this joint and it maintains constant tension during pronation and supination movements of the forearm.

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Elbow Anatomy - Blood Supply and Innervation

The blood supply to the elbow joint can be derived from a number of periarticular anastomoses that are formed by the collateral and recurrent branches of the profunda brachii, brachial arteries, radial arteries, and ulnar arteries. The brachial artery is present at the proximal to the elbow joint which is the largest artery in the arm, it gives off two branches such as a superior and inferior ulnar collateral artery. The profunda brachii gives off radial collateral and a middle collateral artery. These pass towards the joint contributing to the anastomotic loop supplying the joint. 

Distal to the elbow joint the radial artery is found it gives off the radial recurrent artery, and the ulnar artery gives off the recurrent arteries of the anterior and posterior ulnar region. These arteries are present ascending towards the elbow joint, anastomosing with the branches from the brachial and profunda brachii arteries in the arm. 

Elbow Movements Anatomy

As the elbow joint is a type of hinge joint the movement is in only one plane. The movements at the elbow joint involved the movement of the forearm at the elbow joint. Flexion of the forearm at the elbow joint involves decreasing the angle between the forearm and the arm at the elbow joint. The extension involves increasing the angle between the arm and forearm. 

Flexion: Most of the muscles producing flexion movement are found in the anterior compartment of the arm. There are two muscles in this compartment that helps to produce flexion movement at the elbow joint:

1. Biceps Brachii Originates as Two Heads: The tendon of the long head originates from the region of the supraglenoid tubercle of the scapula. It can pass through the joint of the capsule of the shoulder joint and through the bicipital groove found on the anterior surface of the humerus. The short head of this biceps brachii muscle can originate from the coracoid process of the scapula. These forms of the head can join together in order to form the biceps brachii muscle belly. The muscle inserts onto the radial tuberosity distal through a single tendon to the elbow joint. There is a continuation in the forearm that is related to this tendon as a flattened connective tissue sheath which is known as the bicipital aponeurosis. This aponeurosis blends with the deep fascia in the anterior forearm. 

2. Brachialis can originate from the distal half of the anterior surface region of the humerus, as well as from the intermuscular septa on either side of the region of the anterior compartment. It is generally located deep in the biceps brachii muscle. It forms a singular tendon that inserts onto the tuberosity of the ulna. Both the biceps brachii and brachialis muscles are innervated by the Musculocutaneous nerve.

While the biceps brachii and the brachialis muscles are the main muscles for the flexors of the elbow joint, in the flexion of the forearm the brachioradialis muscle is also involved at this joint. Above the lateral epicondyle, the brachioradialis originates from the lateral aspect of the distal humerus. It further inserts onto the lateral aspect of the distal radius. Although this muscle is primarily present in the forearm, it crosses the elbow joint therefore it acts on the elbow joint. It is innervated by the radial nerve. 

Mnemonic: There are three B's to bend the elbow:

1. Biceps

2. Brachialis

3. Brachioradialis

Extension: Extension of the forearm at the region of the elbow joint involves the increase of the angle at the elbow in order to bring the forearm back to the anatomical position from a flexed position. There is one muscle that is involved in the extension is the triceps brachii muscle. It is the only muscle present in the posterior compartment of the arm.

Triceps Brachii can originate as three heads. The long head of this brachii originates from the infra-glenoid tubercle region of the scapula. The lateral head region originates from the lateral aspect of the humerus above the radial groove. Whereas the medial head of brachii can originate from the medial aspect of the humerus below the level of the radial groove. These three heads converge on a single tendon that can insert onto the olecranon of the ulna. It is supplied by the radial nerve, which passes down through the arm in the radial groove between the lateral and medial heads of the muscle.

While the flexion and extensions are the only movements that can occur at the region of the elbow joint itself. The movement is also afforded at the region of the proximal radioulnar joint, it also contributes to the elbow joint. Movements that are found at this joint are called pronation and supination. These two movements are the rotational movements that can occur at the distal end of the radius. When the radius moves over the distal end of the ulna by rotating the radius that is present in the pivot joint is formed by the circular head of the radius, the radial groove of the ulna, and the annular ligament.

Elbow Anatomy Tendons

Tendons are the soft tissues that help to connect the muscles to bones in order to provide support. There are certain tendons present in the elbow that attach the muscle to the bone. The important tendons of the elbow are the biceps tendon, which is attached to the biceps muscle on the front of your arm, and the triceps tendon, which attaches the triceps muscles that are found on the back of your arm.

1. Biceps Tendon: This tendon attaches the biceps muscle present on the frontier side of the arm to the radius allowing supination that is the rotation of the elbow.

2. Triceps Tendon: This tendon is found attaching to the triceps muscle on the back of the arm to the ulna bone by allowing the elbow to straighten it.

3. Lateral Epicondyle: This bony prominence is located just above the elbow region on the outer side is where the forearm muscles that can straighten the fingers and wrist come together in only one tendon to attach to the humerus.

4. Medial Epicondyle: This bony prominence is located just above the elbow region on the inside. It is where the muscles that allow bending the fingers and wrist come together in one tendon to attach to the humerus.

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Conclusion

In the elbow bone anatomy, we learnt about how the elbow is formed, the muscles that are involved in the movement of the elbow, the blood supply, the tendons and the ligaments that are attached to the elbow. The elbow is a complex joint that is formed by the articulation of three bones like the humerus, radius, and ulna. The elbow joint helps in bending or straightening the arm to about 180 degrees and it assists in lifting or moving the objects.