Joints

What are joints?

A joint is any place in your body where two bones meet. They’re part of your skeletal system. You might see joints referred to as articulations.

You have hundreds of joints throughout your body, and many ways healthcare providers group them together (classification). Joints are usually classified based on:

• Their function: How they move.
• Their composition: What they’re made of (histologically).

Joints support your body from head to toe. Whether it’s a joint you’re aware of (like your ankle) or some you’ve maybe never heard of (like the joints that hold your skull together), all of your joints help you use your body every day.

What do joints do?

Joints support your body. They help you sit, stand and move.

Some joints provide structural support. Others let you move. Depending on how much a joint moves, it fits into one of three categories:

• Synarthroses: Joints that don’t move at all. These joints provide structural support.
• Amphiarthroses: Joints with limited movement that give you a mix of stability and some motion.
• Diarthroses: These are joints you can move freely in most directions. These joints allow the most movement.

What are joints made of?

Your joints are made of bones and the connective tissues that hold them together, including:

• Cartilage.
• Tendons.
• Ligaments.
• Nerves.

Healthcare providers classify joints into three categories depending on how much connective tissue they contain:

• Fibrous joints.
• Cartilaginous joints.
• Synovial joints.

What are fibrous joints?

Fibrous joints aren’t very flexible. Some of them don’t move at all. Their name reflects what they’re made of — thick connective tissue that’s tightly woven together like fiber. Fibrous joints usually contain a lot of collagen.

There are three types of fibrous joints, including:

• Sutures: The joints that hold the plates of your skull together.
• Gomphoses: Joints that hold your teeth in place in your jaw bones (mandibles).
• Syndesmoses: Joints that hold two closely related bones together in place. A syndesmosis joint keeps your tibia (shin bone) connected to your fibula (calf bone).

What are cartilaginous joints?

Cartilaginous joints are cushioned by a layer of cartilage that joins the bones together. Most cartilaginous joints have some movement, but don’t move far or in many directions.

The joints where your ribs meet your sternum (breastbone) are cartilaginous. The pubic symphysis joint that joins your left and right pelvic bones together is another cartilaginous joint.

What are synovial joints?

Synovial joints have the most freedom to move. They’re made of a cavity in one bone that another bone fits into. Slippery hyaline cartilage covers the ends of bones that make up a synovial joint. A synovial membrane — a fluid-filled sac that lubricates and protects the joint — lines the space between the bones. This extra cushioning helps synovial joints move with as little friction as possible.

There are six types of synovial joints:

• Hinge joints: Joints that open and close in one direction. Your knees and elbows are hinge joints.
• Ball and socket joints: In a ball and socket joint, the rounded end of one bone fits into an indentation in another bone. They can rotate and turn in almost any direction. Your shoulders and hips are ball and socket joints.
• Condyloid joints: Condyloid joints are made of two oval-shaped bones that fit together. They’re similar to ball and socket joints, except they can’t rotate in a full circle (360 degrees). Your wrist and the joints where your toes meet the rest of your foot are condyloid joints.
• Pivot joints: Pivot joints rotate in place without moving out of their original position. A pivot joint in your neck lets your head move from one side to another.
• Planar joints: Planar joints are formed when two mostly flat bones come together. They move by one piece of bone sliding over the other without rotating. The carpal bones that join your wrist to your forearm and the joints between the vertebrae in your spine are planar joints.
• Saddle joints: Saddle joints are formed when two curved bones meet. Picture two U-shaped bones fitting together in the curved space between each other. Saddle joints can move in any direction, but can’t twist or rotate. The joint where your thumb joins your hand is a saddle joint.

What are common conditions that affect joints?

Joints can be affected by anything that damages your bones or connective tissue, including:

• Arthritis.
• Osteoarthritis.
• Bursitis.
• Tendinitis.
• Osteoporosis.

People with autoimmune diseases often experience symptoms in their joints. Some of the most common include:

• Rheumatoid arthritis.
• Psoriatic arthritis.
• Lupus.
• Sjögren’s syndrome.

Your joints can also be damaged by traumas like falls and car accidents. Injuries that affect joints include:

• Sports injuries.
• Bone fractures.
• Dislocations.
• Sprains.

What are common symptoms that affect joints?

Which symptoms you’ll have depends on which condition or injury you’re experiencing. Many joint issues cause symptoms like:

• Pain (especially when moving a joint).
• Inflammation (swelling).
• Discoloration or redness around a joint.
• A feeling of warmth or heat.
• A grinding feeling.
• A popping noise or feeling.

What tests are done to joints?

Which tests you’ll need depends on the symptoms you’re experiencing. Visit a healthcare provider as soon as you notice changes or new pain in one of your joints. Some of the most common tests providers use to diagnose joint issues include:

• X-rays.
• Ultrasounds.
• Joint aspiration.
• CT scans.
• MRIs.

How can I take care of my joints?

The best way to take care of your joints is to maintain good overall health, including:

• Following a diet that’s healthy for you.
• Exercising and moving. Everyone’s body and needs are different. Cycling, strength training, swimming, low impact cardio or water aerobics are all great options. Which type of exercise is best for you depends on your joint health and fitness level. Talk to your provider about which type of physical activity is best for you and your joints.
• Wearing proper protective equipment for any activity, sport or work you’re doing.
• Visiting a healthcare provider for regular checkups and as soon as you notice any changes in your joints.
• Always wearing your seatbelt.

How many joints are in the human body?

Experts often disagree on exactly how many joints are in the human body. Most experts define a joint as any place two bones meet. Others define joints differently, saying joints should only be considered places where two bones meet that move.

Depending on which definition you use, adults have around 350 joints.

A note from Cleveland Clinic

You use your joints every time you do anything, from sitting down after a long day to scrolling through this article on your phone. They’re the nuts and bolts that help your body hold its shape and perform any movement you need it to.

Because they’re so vital to your daily routine, any issue with your joints can be a huge pain (sometimes literally). Visit a healthcare provider if you’re experiencing new pain or other symptoms in your joints.