Although non-weight bearing, the elbow joint is one of the most complex joints in the body. It is a synovial hinge joint, assembled by the articulation of majorly the proximal ulna and the distal humerus. However, there exist the articulation between the proximal ulna and radius as well as the proximal humerus and radius. These three articulations are mentioned as ulnohumeral, proximal radioulnar, and radiohumeral joints respectively. It comes as no surprise that second to shoulder, the elbow joint is the most commonly involved joint in sports-related injuries because various muscles from the upper and lower arm either attach to or at least cross one element of the elbow joint.
It is the osseous articulation between the trochlea of the humerus and the ulnar olecranon; the olecranon looks like a wrench or a scoop in which trochlear notch inserts around the trochlea of the humerus and acts as the primary point of pivot during extension and flexion of the joint. While the trochlear notch sheath around the humerus is almost 180 degrees, the trochlea of the humerus is wide with a central groove, permitting a tight adaptation of the two structures adding to the stability of the joint. After the ulnohumeral, the remaining major element of stability for the joint comes from the two ligaments- medial collateral ligament (MCL) and lateral collateral ligament (LCL).
MCL (medial collateral ligament) is composed of three smaller ligaments making a triangular shape, namely anterior oblique ligament, posterior oblique ligament, and transverse ligament, also sometimes referred to as Cooper’s ligament. The LCL is also made up of three parts: the lateral radial collateral ligament, the annular ligament, and the lateral ulnar collateral ligament.
Since the elbow is a synovial joint, it has a synovial membrane in addition to a joint capsule which is separated by fat pads. These fat cushions are situated superficial to stress-bearing areas. The areas include the coronoid, radial, and olecranon fossas. Olecranon bursa, a lubricating bursa serves as the lubricating element between the triceps tendon of insertion and the olecranon process of the ulna.
Muscles are also responsible for providing stability, structure, and shape to the elbow. They provide secondary stability in terms of protecting the joint against the valgus and varus forces. Only a few muscles that cross over the joint have an action on the elbow joint movement itself. These are brachialis, biceps brachii, triceps, anconeus, pronator teres, and pronator quadratus. These muscles help in protecting and stabilizing the static ligamentous constraints.
The purpose of the elbow is to extend and flex the arm clutch and holdout for objects. The range of movement can vary from elbow extension (0 degrees) to elbow flexion (150 degrees). The other function is pronation and supination. The range averages around 85 degrees. Most activities are accomplished within the range of 100 degrees of forearm rotation (50 degrees of supination and 50 degrees of pronation). Thus the primary function is in the form of extension and flexion along with the facilitation of hand movement in the form of supination and pronation of the forearm. The anterior oblique ligament, a component of MCL is the most important stabilizer of the joint and acts as a protector against excessive valgus forces. Similarly, all the components of LCL provide protection and strength during varus stresses and posterolateral rotational stability. Hence, serving as the protector against the odd forces.
Nerves crossing elbow joint are predominately responsible for innervations of the hand and forearm. The musculocutaneous nerve is one major nerve accountable for acting on the elbow joint. It innervates both the biceps brachii and brachialis muscles. The radial nerve also crosses laterally over the joint and innervates five muscles- brachialis, anconeus, supinator muscle, brachioradialis, and triceps brachii. The ulnar nerve enters in the cubital tunnel of the elbow and the median nerve traverses anterior to the elbow joint. Both innervate mainly the muscles in the forearm and hand. Also passing the joint is the medial and the lateral antebrachial cutaneous nerve supplying the sensory sensation for the forearm skin.
The brachial artery is the source of feeding all the main arteries into the elbow joint. Deep brachial artery, branch of brachial artery courses posteriorly and gives out few smaller arteries which anastomose with radial artery. The blood flows majorly through the brachial artery distally and divides into ulnar and radial arteries.
The lymphatic structure surrounding the joint are deep and superficial cubital lymph nodes, and the epitrochlear and supratrochlear. The lymph drains into the deep brachial lymph nodes, ultimately draining up in the axillary lymph nodes.
Clinical Relevance and Associated Disorders
The commonly encountered elbow associated disorders are:
Lateral Epicondylitis, or Tennis Elbow Tendinosis
Occurs due to the injury or micro tear to the tendon (extensor carpi radialis brevis). It is mainly seen among racquet players or working in a certain profession that uses similar motion. Pain is a common complaint with difficulty in grasping objects.
Medial epicondylitis, or Golfer’s Elbow
It affects the inner tendons of the elbow. Common among golf and baseball players. Occurs due to repetitive flexion and valgus force to the joint.
Radial Head Subluxation, or Nursemaid’s Elbow
Common pediatric elbow injury, occurring when the arm is outstretched and an abrupt pulling force is applied to the lower arm, causing a displacement of the annular ligament.
Ligament Injury of the Elbow
It can occur due to stretched or torn ligaments as a result of stress or trauma. It can occur in any of the ligaments. There are mainly three mechanisms of elbow injury: posterior translation, posterolateral rotatory, and valgus mechanisms, this valgus stress mechanism has the highest incident and is a common occurring injury.
Olecranon Bursitis, or Student’s Elbow
It is caused due prolonged pressure or trauma to the olecranon bursa, and it can be septic or idiopathic.
It occurs often among athletes, and it is the second most common dislocation after the shoulder. Most severe is the posterior elbow dislocation causing more ligamentous damage.
Osteochondritis Dissecans, or Panner’s Disease
It occurs when a small piece of bone or cartilage becomes dislodged in the joint. Commonly found as a result of sports injury.
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