Rachel Klaus, Director of Academic Services, Experience Anatomy
This article is brought to you in partnership with Experience Anatomy, a premier anatomy education provider specializing in training and education with true human specimens.
The elbow joint connects the upper arm to the forearm and is made up of three bones, one in the arm and two in the forearm.
- Humerus (arm bone)
- Radius (thumb-side forearm bone)
- Ulna (pinky side forearm bone)
A joint, or articulation, is where two bones meet. Since three bones adjoin to form the elbow joint, there are three locations of articulation (touching). This means, anatomically speaking, the elbow consists of three different joints.
- Humeroulnar joint: joins the humerus with the ulna
- Humeroradial joint: joins the humerus with the radius
- Radioulnar joint: joins the radius with the ulna
Typically, when we think about the movement our elbow provides, we think about flexion (bending) and extension (straightening). These motions allow us to scratch our nose, reach into a cabinet, pick up heavy weights and set them back down.
The humeroulnar joint is to thank for our ability to bend and straighten the elbow. Because it only allows motion in two directions, the humeroulnar nerve is classified as a hinge joint.
The humeroradial and radioulnar joints in the elbow facilitate our ability to rotate our forearm.
Pronation is the rotation of the arm to face the hand down, as if to lay it palm-down on a table. Supination is the rotation of the arm to face the hand up, as if to accept a small item into your hand.
Both the humeroradial and radioulnar joints are classified as pivot joints because they facilitate rotation around a single axis. Watch for the uniaxial rotation (pronation & supination) of the radius in the video below.
Surrounding each articulation (touchpoint) between the bones are ligaments – connective tissue composed of strong collagen fibers.
Ligaments primarily function to connect bones to other bones and provide support to that connection. Some ligaments look like thick string while others look like narrow or wide bands.
In the elbow, we see four main ligaments.
- Ulnar (medial) collateral ligament: connects the ulna to the humerus on the inside of the elbow
- Radial (lateral) collateral ligament: connects the radius to the humerus on the outside of the elbow
- Annular ligament: forms a ring around the head of the radius anchoring it against the ulna
- Quadrate ligament: connects the radius to the ulna along their shafts
Common Elbow Ligament Injuries
Nursemaid’s Elbow, or radial head dislocation
This injury affects the annular ligament. It is commonly seen in children and is associated with high-force trauma to the arm.
However, don’t be alarmed. Simply swinging your child by the arms, as many parents do, is enough force to pop the radius out of the annular ligament that holds it in place. Radial head dislocation can also occur after a fracture of the radius.
Tommy John Injury, or ulnar collateral ligament tear
This injury is most common in individuals who participate in throwing sports, as the act of throwing a ball puts strain directly on the ulnar collateral ligament. Injury may occur as an acute tear or repetitive injuries may gradually stretch and weaken the ulnar collateral ligament over time.
Radial Collateral Ligament Tear
This injury occurs most commonly from falling on an outstretched hand, placing force on the lateral side of the elbow. The ligament can sprain or tear depending on the severity of the fall.
ELBOW TENDONS & MUSCLES
The muscles surrounding the elbow joints not only facilitate flexion/extension and pronation/supination. Several muscles that act on the wrist and hand joints attach to the humerus at the elbow joint. These muscles live in the forearm and are broadly grouped as either extensor or flexor, meaning they either extend or flex the wrist and hand.
There are a total of nine muscles that form the flexor and extensor groups of the forearm. Because these forearm muscles attach to an elbow joint, it is quite common for people to have elbow pain due to overuse or strain of their forearm muscles.
Most colloquially called Tennis Elbow or Golfer's Elbow, there are actually a number of specific conditions that can cause pain at an elbow joint. It is important to understand their distinctions to properly implement a treatment plan.
We can use human anatomy language to break down these conditions word by word.
- -epicondyl refers to a bony prominence called an epicondyle. The epicondyle in the elbow is where the forearm’s flexor and extensor muscle groups attach. -itis means inflammation. So, epicondylitis refers to inflammation around the bony prominence called the epicondyle.
- -tendin refers to a tendon, which attaches muscle to bone. -itis means inflammation. So, tendinitis means inflammation of a tendon.
- -paratenon refers to the areolar tissue filling the space between a tendon and its sheath, effectively covering and protecting the tendon. -itis means inflammation. So, paratenonitis means inflammation of superficial tendon structures.
- -tendon refers to a tendon, which attaches muscle to bone. -osis refers to an abnormal or diseased condition. In this case, we could say that intratendinous degeneration has started to occur.
As you can see, the elbow is a surprisingly complex part of the body where numerous bones, ligaments, tendons and muscles converge. If you’re experiencing elbow pain or immobility, schedule an appointment online with one of our specialists today. There’s more happening below the surface than you might expect.
Rachel Klaus has been building the academic programming offered by Experience Anatomy since 2019 by integrating her experience and knowledge of various anatomical resources to provide unique educational experiences.
Rachel received her MS in human anatomy from the University of Colorado School of Medicine where she had the opportunity to work on the Susan Potter Visible Human Project to help develop virtual anatomy resources. In her free time, she likes to recreate outdoors and continue to grow her plant collection.