What’s Holding Your Skeleton Together?

“What’s holding my bones together?” sounds like something a curious toddler would ask — and that you just don’t know how to answer. Muscles? Joints? It’s a good question!

Think about it: Every time you take a step, reach for a cup of coffee, or turn your head to look out the window, more than 200 bones are bending and pivoting and bearing weight, all without flying apart. So what, exactly, is keeping them all in place?

There isn’t one specific body part to point to (which you couldn’t do without your hand bones), but rather an intricate network of connective tissues. But two stand out in particular (and allow us to stand to begin with).

The Leading Cast

When it comes to keeping your skeleton together, ligaments and tendons are the most important of your connective tissues. Ligaments are small, fibrous bands that connect bones to other bones. They’re flexible yet tough, kind of like internal bungee cords — strong enough to keep everything stable, but with enough give to allow for movement. 

Ligaments direct your joints (where one bone meets another) to move in the right ways and, hopefully, not to move in the wrong ways. Without them, your knee would buckle sideways, your ankle would roll out of its socket, and your shoulder would slip anytime you reached overhead. 

There are more than 900 ligaments in the human body (compared to 206 bones), and they come in different shapes and sizes. Some look like strings, some like wide bands. Ligaments are mostly made up of woven strands of collagen and elastin proteins. Depending on the types of movements they’re likely to be needed for, some have more collagen for toughness, and others have more elastin for elasticity. 

The other important players keeping your skeleton together are tendons, which connect muscle to bone. These transmit the force of a muscle contraction into actual movement, since your bones can’t move on their own. Together, ligaments and tendons form the connective framework that lets the skeleton function as more than just a pile of bones.

The Supporting Characters

While ligaments and tendons are doing most of the heavy lifting (sometimes quite literally), there are a few other things that help keep your skeleton moving smoothly. Bursas are fluid-filled sacs that help reduce friction in joints. The synovial membrane seals the joint (turning it into what’s known as a “joint capsule”) and secretes a thick fluid that aids in lubrication and provides nutrients to the surrounding cartilage. 

Cartilage is a type of connective tissue that acts as a shock-absorbing buffer at the ends of bones, preventing them from grinding directly against one another. Grinding and friction between bones lead to wear and tear, just as they do in garden shears or bicycle chains. Rather than just holding bones together, these tissues help protect them, especially over time.

When most of us think about joints in our body, we think about the moveable ones: hinge joints (such as your elbows and fingers), pivot joints (the top of your spine), and ball-and-socket joints (shoulders and hips), for example. But some joints barely move at all. Your skull, for example, is made of different pieces, but they’re fused together so tightly that they don’t move, making up a type of stationary joint called sutures.

The next time you turn a doorknob or switch on a light without injuring yourself, remember that there’s a whole intricate system working together to get the job done. Without it, we’d all fall apart.