Human Joints Explained

Joints are the connection points between two or more bones. They're made up of bone as well as soft tissues like ligaments, cartilage, and tendons.

All joints help hold your bones together, and most allow you to move in different ways. For example, a ball-and-socket joint, like the one that joins your arm to your shoulder, allows you to move your arm up, down, and around. A hinge joint, like your knee, allows you to move back and forth.

This article discusses the different types of joints and their anatomy. It also discusses how they move and the conditions that can affect them.

How Many Joints Are in the Human Body?

You are are born with about 300 bones. As you grow, some of these bones fuse together. By the time you reach adulthood, you have 206 bones. A human adult body has 360 joints. Some joints are immovable (like the sutures in your skull), and some allow various types of movement.

Some of the main areas that you have joints include:

• Shoulders
• Hips
• Elbows
• Knees
• Wrists
• Ankles
• Fingers
• Toes
• Neck
• Jaw

Anatomy of a Joint

Joints are made up of bone, soft tissues, and fluid. These all play a role in providing structure and protection for the joint.

Components of a joint include:

• Ligaments: Connective tissue that attaches the bones together and protects the joint by limiting its movement
• Tendons: Connective tissue that attaches the muscles to bones
• Cartilage: Tissue that covers the bone surface and reduces friction at the joint
• Bursae: Sacs filled with fluid that provide cushioning between the joint's bones and the parts around it, such as muscles and tendons
• Synovial membrane: Tissue that provides lining to form a joint capsule and secretes fluid to lubricate the joint when moving
• Meniscus: A piece of curved cartilage found in joints like the knees
  

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.
  

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.

Joint Diseases and Conditions

Joint pain or stiffness can have a number of different causes. Sometimes it's due to a health condition, like arthritis or lupus. In other cases, it's caused by injury due to a sudden impact or repetitive stress.

The following are just some of the examples of conditions and injuries that can affect your joints.

Arthritis Conditions

Arthritis is one of the most common conditions to affect the joints. In the United States, more than 58 million people, or 24% of all adults, have arthritis.

With arthritis, there is 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 over 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. The immune system attacks healthy tissues unnecessarily. It is also an inflammatory type of arthritis.

Rheumatoid arthritis can develop at any age and affect any joint in your body. It typically involves the wrists, knuckles, and the middle joints of the 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 the big toes, heels, ankles, fingers, wrists, and elbows.

Non-Arthritis Conditions

In addition to arthritis, joint issues can be caused by other chronic (long-lasting) diseases, sudden injuries, or overuse. Some examples include:

Lupus

Lupus is another autoimmune disease. It can lead to chronic inflammation that includes joint stiffness and pain.

Sjögren's Syndrome

Sjögren's syndrome is an autoimmune disease that affects the glands that make moisture. Its symptoms include dry eyes and dry mouth, but it also causes joint pain.

Bursitis

Bursitis happens when the bursae become irritated and inflamed. It's usually caused by overuse, but it can also happen with a sudden injury or condition like arthritis.

Sprains or Strains

Sprains are stretched or torn ligaments around the joint. Strains are stretched or torn muscles or tendons, which could be from a sudden injury or from overuse.

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: Exercise is the first line treatment for reducing pain and improving function in joints. Physical activity the 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 (~2 BMI points) 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.

Some diseases, conditions, and injuries can affect your joints, causing symptoms like pain and stiffness. 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.