Human Joints Explained

Human joints form where two bones come together. In fact, all of your bones, except the hyoid bone in the neck, form a joint. The joints hold the bones together and allow for the movement of your skeleton.

This article discusses the different types of joints, how they move, and the conditions that can affect them.

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Categories of Joints

Joints are commonly categorized according to whether they allow motion. These categories of movement are:

  • Synarthroses: The joints are fixed and don't allow any movement. The bones in these joints are separated by a layer of connective tissue. Examples include suture joints, which hold plate-like bones together in the skull.
  • Amphiarthroses: These joints allow for slight movement. These can be found in the joints between vertebrae or the ribs connected to your sternum or breastbone.
  • Diarthroses: These joints are freely moving. Most of your joints are diarthroses. They are also called synovial joints because they contain synovial fluid in the joint cavity for lubrication.

Recap

Synarthrosis is a type of joint that's fixed and doesn't allow movement. Amphiarthroses allow some movement, and diarthroses are freely moving.

Types of Movable Joints

Diarthoses (synovial joints) allow the most movement and are the most common joints in mammals. The six different types of these joints are:

  • Ball and socket joint: Allows for a wide range of rotation and movement. The rounded head of one bone fits into the depression of another bone. It permits movements that go forward, backward, sideways, and rotating. The shoulder and hip are ball and socket joints.
  • Condyloid joint: Allows joystick-like movement but no rotation. There are condyloid joints in the jaw and fingers. They allow two planes of movement, such as bending your fingers and spreading your fingers apart.
  • Gliding joint: Lets bones glide past each other. The motion is usually small and tightly held by ligaments. There are gliding joints in your feet, wrists, and spine.
  • Hinge joint: Allows for movement much like that of a door hinge with a back-and-forth movement. Muscles, ligaments, and other tissue help to stabilize the bones. Your knee and part of your elbow have hinge joints.
  • Pivot joint: Lets bones spin and twist around other bones. The bone moves within a ring formed by the second bone and a ligament. There are pivot joints in the neck and the radius part of the elbow.
  • Saddle joint: Allows for back and forth and side to side motion but limited rotation. The two bones fit together like a rider sitting on a saddle. There is a saddle joint at the base of the thumb. This allows the thumb to move away from your palm along two planes.

Recap

Synovial joints are your most common joints. There are six different types, including ball and socket joints (shoulder and hip) and hinge joints (knee and elbow).

How Arthritis Affects Your Joints

When you have arthritis, you have swelling and inflammation in your joints. There are more than 100 different kinds of arthritis that affect your joints and the tissues around them.

Some of the most common types of arthritis are osteoarthritis, rheumatoid arthritis, and gout.

Osteoarthritis

Osteoarthritis is the most common joint disorder with 32 million people affected. When you have osteoarthritis, the protective cartilage that cushions the ends of the bones wears down. If all of the cartilage wears away, the bones will rub against each other.

Although osteoarthritis can affect any joint, it is most common in the hands, lower back, neck, knees, hips, and feet. It particularly affects joints that bear weight regularly.

Rheumatoid Arthritis

Rheumatoid arthritis, by contrast, is an autoimmune disease and an inflammatory type of arthritis. The immune system goes awry and attacks the body's own tissues. It can develop at any age.

Rheumatoid arthritis can also affect any joint in your body. It typically involves your wrists, knuckles, and the middle joints of your fingers.

Gout

Gout is another form of inflammatory arthritis. It occurs when uric acid builds up and forms needle-like crystals in your joints.

Gout usually attacks joints in your big toes, heels, ankles, fingers, wrists, and elbows.

Recap

Osteoarthritis, rheumatoid arthritis, and gout are common types of arthritis that affect the joints. Osteoarthritis is caused by the cartilage in the joint wearing away. Rheumatoid arthritis and gout are forms of inflammatory arthritis, where the body's immune system causes damage to the joints.

Improving Your Joint Health

There are a number of ways to keep your joints healthy. Here are some tips to protect your joints and reduce strain:

  • Stay active: Physical activity can help to increase flexibility and range of motion. Try low-impact exercises that are easier on your knees, like swimming, cycling, or walking.
  • Manage your weight: You can reduce stress on your knees by staying at a healthy weight. One study found that for women, an 11-pound weight loss reduced the risk of knee osteoarthritis by 50%.
  • Eat well. Eating nutritious foods may help you protect your joints or help ease arthritis symptoms. A 2015 study found that patients with osteoarthritis had less pain two weeks after starting a plant-based diet.

Some studies have shown that omega-3 fatty acids may be beneficial for patients with rheumatoid arthritis. Fish and fish oil supplements are rich in omega-3 fatty acids, which produce modest benefits and may reduce inflammation.

Summary

Your joints hold your bones together and allow you to move. Some joints are fixed, some allow slight movement, and others are freely moving. You can help protect your joints from conditions like arthritis by staying active, managing your weight, and eating a nutritious diet.

A Word From Verywell

If you have a joint condition like arthritis, you may be experiencing pain and stiffness that make it hard to stay active. Ask your doctor about ways to help manage your pain and other symptoms. They can help you find ways to do daily activities and increase your quality of life.

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