Elbow Anatomy

The elbow and forearm form a functional unit whose primary role is to accurately position the hand in space.


The elbow is considered the most important single joint of the upper limb, covering 130 degrees of the functional space used in daily activities.

Functional space is defined as the space directly in front of a persons body, below eye level and above the belly button. Because the elbow joint covers the entire functional space by virtue of its arc of motion, there has never been a satisfactory position to fuse an elbow joint if it were ever destroyed by injury or disease.

The elbow consists of three main layers:

  • Bones
  • Ligaments
  • Muscles

Elbow & Forearm Elbow Joint Front View & Side View

The bones are the first layer of the elbow and forearm.

Three bones unite to form the elbow joint:

  • Lower end of the humerus (arm bone)
  • Proximal end of the radius (forearm bone)
  • Proximal end of the ulna (forearm bone)

These three bones allow: 

  • The elbow to bend (flex) and straighten (extend) in a hinged type motion
  • The forearm to rotate the hand in a palm up (supination) and palm down position (pronation).

The joint surfaces of the elbow are covered by hyaline cartilage forming a cushioned layer allowing for smooth gliding and painless elbow motion.

Elbow & Forearm Ligament LayerElbow Joint Ligament Layer


Lateral Elbow Ligament View Medial Elbow Ligament View

The second layer in the elbow and forearm is the capsular ligament layer made up of collagen tissue. These ligaments provide passive stability to the elbow joint keeping the humerus, radius and ulna together, allowing them to function as a unit.

The collagen tissue forming the elbow joint capsule is normally very thin except on the inside (medial) and outside (lateral) sides of the elbow where thickenings in the collagen substance form the ligaments of the elbow.


Foerarm Flexor CompartmentForearm Flexor & Mobile Wad Compartments


Elbow Flexor Muscles Elbow Extensor Muscles

The third layer of the elbow and forearm is the muscle layer. It is formed by the various muscle groups passing through the elbow and forearm.

These muscles either originate or end in the elbow and forearm. In the back of the arm this is the triceps muscle. In the back of the arm this is the brachialis and biceps muscles.

The forearm muscles crossing the elbow joint are divided into three compartments:

  1. Extensor compartment
  2. Flexor compartment
  3. The mobile wad of Henry compartment.

Each compartment contains several muscles working to move the elbow, forearm, wrist and hand in specific directions.

The median, ulnar, and radial nerves pass through the elbow and forearm within the muscle layers and innervate the muscles within these compartments as well as the muscles of the hand.