Anatomy of a healthy knee joint

Key components of a joint: bones, cartilage, ligaments, tendons, and fluid

A human joint is any place in the human body where two bones connect. This junction allows for movement, but is prone to breakdown and pain. This nine-minute video explains normal joint anatomy and function, with particular attention to the different types of motion each joint facilitates.

Real surgical footage reveals what arthritis looks like up close

Arthritis is a painful condition of human joints that often results from the loss or breakdown of the soft cartilage padding that naturally exists between bones. This video shows footage from an actual knee surgery that beautifully demonstrates the difference between normal cartilage and the degenerative cartilage seen in osteoarthritis.

Diagnosis and treatment of hip and knee osteoarthritis

Osteoarthritis is the most common type of arthritis, resulting from age-related degeneration of the soft cartilage lining between bones. As this layer breaks down, the normal smooth motion between bones is lost and the joint becomes painful.

Breaking down the knee's anatomy

The human knee is a remarkably complex structure carrying the full weight of the body throughout a person’s life while allowing a number of complex twists, flexes, and extensions. It's also one of the body's biggest weaknesses—the location of chronic pain and replacement surgeries for millions of Americans.

Kangaroos evolved exceptionally thick knee cartilage to absorb shock

There is significant conflict in the medical field regarding chronic arthritis. Some advocate for keeping the joint as active as possible while others argue progressive overuse leads to worsening arthritis. To settle the score, scientists have looked outside the human population, discovering kangaroos rarely suffer from arthritis in their knees.

Visualizing a joint under attack from rheumatoid arthritis

A particularly difficult arthritis subtype is rheumatoid arthritis, a painful condition provoking a vicious cycle of joint inflammation, destruction, and dysfunction. It begins with a misfiring of the patient’s own immune system—for unknown reasons, it identifies joint and cartilage cells as foreign, initiating an attack to eliminate the supposed "invaders."

Arthritis explained, with Dr. Nick Golinvaux

Arthritis, a condition affecting millions globally, is more than just joint pain—it’s a breakdown of cartilage that cushions bones, leading to stiffness, swelling, and discomfort. While often associated with aging, arthritis can affect people of all ages, especially after injuries. Though there’s no cure yet, treatments range from medication and physical therapy to surgical interventions like joint replacements.

Arthritis is an umbrella term for various conditions that cause joint pain

Arthritis isn’t one single disease, but rather a range of conditions that all lead back to the same outcome—joint pain. This American Academy of Orthopaedic Surgeons primer is a go-to resource for understanding what arthritis is, the most common types, and various treatment options depending on the underlying cause.

Limb regeneration research may lead to treatments for arthritis

For scientists pursuing the cure for arthritis, the holy grail of discoveries lies in how to regrow healthy cartilage inside human joints. While this feat has so far resisted our best scientific attempts, there are plenty of other human tissues—such as the liver and fingertips—that will successfully regenerate.

The collapse of gas bubbles in the joint synovial fluid causes 'cracking' knuckles

The human population can be divided into two categories: those who crack their knuckles and those who don't. Do you know the technical term for this phenomenon is "tribonucleation?" What actually happens inside a knuckle when it pops? This visual explainer breaks down finger joint popping in real time.

Adhesion molecules and intercellular junctions allow cells to connect together

While some organic structures are mostly composed of non-cellular components (e.g., collagen and calcium phosphate minerals in bones), tissues and organs composed of connected cells rely on specialized proteins and connections to create watertight seals that protect cells within the interior from environmental molecules.

Visualize the difference between a healthy brain and one with Alzheimer's

The brain has three main parts—the cerebrum, brain stem, and cerebellum—each combining to control the entirety of the body's operations. Alzheimer's progressively deteriorates the circuitry in these structures, resulting in what we see as the symptoms of the disease.

Exploring the link between history, art, and anatomy

Throughout centuries, art has played a vital role in sharing—and furthering—scientific understanding. This largely began in 1543 when physician Andreas Vesalius worked with an artist and engraver to transform learnings from his dissections into...

Bone marrow generates roughly 500 billion new blood cells each day

Some of our bones are stuffed to the brim with a fatty, jam-like substance called marrow. Bone marrow comes in yellow and red, with the latter responsible for producing new blood cells, and has become critical in treating diseases like leukemia.

Bone marrow (soft tissue found inside certain bones) generates roughly 500 billion new blood cells each day

Myokines are molecules that facilitate some of the benefits of exercise

When muscles contract, they release ‘hope molecules’ (myokines) such as IL-6 and irisin. These proteins then travel through the bloodstream to reduce inflammation, improve insulin sensitivity, and even support brain repair. This piece illustrates how movement triggers a systemic healing cascade throughout the human body.

Alzheimer's can lead to brain shrinkage, with an average of around 2% of volume reduction per year

There's no definitive test for inflammation, or a baseline for what's considered normal

Existing tests can pick up proteins that indicate an immune response—in particular C-reactive protein, which the liver produces when the body's stressed—but that won't tell you why there's inflammation nor if it's chronic or acute inflammation. (Some users may experience a paywall.)

What is Archaeology?

If you are up-to-date on your Jurassic Park lore, then you likely already know the answer to this question. But for those of us who didn't delve into the world in dinosaurs, it's easy to assume that professionals who study old stuff likely study the remains of what came before us, right? Find out in this article by the Society for American Archaeology.

We hear because soundwaves are converted into electrochemical signals in our ears

This science teacher video systematically walks through the biology of the outer, middle, and inner ear. The explanation starts with the auricle, an external part that funnels sound through the auditory canal, and the tympanic membrane (the ear drum), which vibrates when sounds hit it. Beyond that, as the video details, is the eustachian tube, which is connected to the back of our throats and allows air to pass in and out to equalize ear pressure.

What constitutes a 'healthy' diet?

A natural diet, typically high in plant-based foods and low in processed foods, appears to be the main contributor to a healthy, diverse gut microbiome.

Explore the heart in this interactive 3D model

The heart is the fleshy muscle at the heart (pun intended) of the circulatory system. The heart is segmented into four chambers: two for intake (the right side) and two for output (the left side). Controlled via the autonomic nervous system, also known as the involuntary nervous system, the heart typically beats 60 to 100 times per minute, sending nutrient- and oxygen-rich blood throughout the body.

Friction is the force that resists the sliding of surfaces along one another

Friction always acts to resist movement and is determined by how rough the surfaces are and how hard they are pressed together. In the case of fluids, friction arises from the relative motion between adjacent fluid layers, which act like sliding surfaces.

Sclerosis is the technical term for the lesions or plaques that form without myelin

In the absence of myelin, the body forms scar tissue called sclerosis. That scar tissue hampers nerve's abilities to transmit nerve impulses, essentially acting as a roadblock to speedy communication.

The anatomy of coral polyps, whose mouths consume food and expel waste

The mouth is surrounded by tentacles that help clear away debris and defend the organism, using stinging cells called nematocysts that resemble those of jellyfish. Connective tissue called coenosarc connects individual polyps within colonies and allows them to share nutrients.

Learn how your body is, scientifically, like a firework with its own slow, controlled burn.

What is the blood brain barrier?

Every blood vessel is lined with endothelial cells that act as filters between blood and the rest of the body. In the brain, these cells are tightly packed together to keep a close watch on what substances can access the vital organ. This protective measure poses an obstacle to drugmakers looking to deliver drugs to the well-defended brain for conditions like Alzheimer's. Watch a quick overview here.

Long, happy marriages have these important traits

It may not be rocket science, but a lifetime partnership could still use some study. This quick list of smart traits gets into key traits that typically help a marriage remain happy ever after. Using studies from trained therapists and researchers, the article explains how really knowing each other, accepting bids for attention, seeking resolution to conflict, and more are essential to durable marriages. Read it here.

About 2,000 US babies are born annually without some portion of their limbs, potentially leading to a lifetime of pricey prosthetics.

Tattoos remain visible on your skin thanks to immune cells called macrophages

Listen to an in-depth conversation on the links between Parkinson's disease and herbicide exposure and the challenging pace of scientific investigation.

While the sun's gravity keeps the planets in orbit, their gravity also pulls on the sun, causing it and everything else in the solar system to orbit around a mutual balance point called the barycenter—the true center of the solar system.

The syncytiotrophoblast is the outer layer of the placenta and the largest human cell, spanning an area about twice that of a king-sized bedsheet.

Visualize how CRISPR-Cas9—a type of immune system used by single-celled organisms to attack invasive viruses—targets and makes precise changes to a gene's DNA.

SpongeBob exemplifies Aristotle's philosophy for living well because he understands that happiness doesn't come from external factors like money, recognition, or power.

See how each of the more than two million known species relates to each other—and to common ancestors—in this zoomable tree of life.

Legendary architect Frank Lloyd Wright designed the SC Johnson headquarters in Wisconsin, aiming to make a cathedral-like workplace

The animatronic shark from Steven Spielberg's 'Jaws,' the first modern blockbuster, was a complex underwater apparatus called 'Bruce.'

Corals are themselves not coral reefs—the term refers to the tiny marine invertebrates that build the rigid reef.

Learn how to read a prospectus, the juicy document that any company must file with the SEC before going public.

Poison ivy is in the same family as mangoes, cashews, and pistachios—and they all produce oily urushiol in their raw, unprocessed state—but they are typically prepared in ways to avoid causing human discomfort.

Ebola is a filovirus, meaning it resembles a thread under a microscope, though it sometimes twists and can resemble a bowl of spaghetti.

In 1939, baseball star Lou Gehrig delivered his inspirational 'Luckiest Man' speech after retiring due to the health condition that now bears his name.

The word 'jazz' evolved from 'jasm,' 19th-century American slang for 'energy'

Gerrymandering works through two techniques: cracking opposing voters across districts to dilute their power, and packing them into a few to waste their votes in lopsided majorities.

Take a 3D tour of the Hajj, Islam's annual pilgrimage to Mecca, undertaken by over 1.5 million Muslims.

Scientists can determine Earth's past climate conditions by analyzing air trapped in microscopic bubbles within ice cores—columns of compressed snow layers that build up over hundreds of thousands of years.

Objects can be 3D printed with light by projecting 2D computerized tomography (CT) scans onto rotating cylinders of resin, which solidify upon exposure.

Animal phobias are likely the most common type of phobias, followed by an extreme fear of heights.

Meet the 56 signers of the Declaration of Independence—most of whom didn't put pen to paper until August 2, 1776—and see their original signatures.