What is it that makes the noise when you crack your knuckles?

Question

Is it the bones or the Cartilage or Trapped air?

Answer 1

it's actually, carbon dioxide, a trapped gas

Answer 2

Joints produce that CRACK when bubbles burst in the fluid surrounding the joint.
Joints are the meeting points of two separate bones, held together and in place by connective tissues and ligaments. All of the joints in our bodies are surrounded by synovial fluid, a thick, clear liquid. When you stretch or bend your finger to pop the knuckle, you are causing the bones of the joint to pull apart. As they do, the connective tissue capsule that surrounds the joint is stretched. By stretching this capsule, you increase its volume. And as we know from chemistry class, with an increase in volume comes a decrease in pressure. So as the pressure of the synovial fluid drops, gases dissolved in the fluid become less soluble, forming bubbles through a process called cavitation. When the joint is stretched far enough, the pressure in the capsule drops so low that these bubbles burst, producing the pop that we associate with knuckle cracking.
It takes about 25-30 minutes for the gas to redissolve into the joint fluid. During this period of time, your knuckles will not crack. Once the gas is redissolved, cavitation is once again possible, and you can start popping your knuckles again.

Answer 3

The "popping" of the knuckles results from forcing joint fluid to
very rapidly pass from one side of the joint to the other, where the
"sides" are partitioned off by the main bones of the joint. Let me
rephrase that: a joint is an area where two or more separate and distinct bones meet. The joint fluid provides a cushioning between the joints so that they don't grate into each other. Cracking your knuckles forces the joint fluid from one part of the joint to another, and the popping sound is just the result of the high pressured rushing of fluid.

Answer 4

Cracking joints
From Wikipedia, the free encyclopedia
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Cracking joints is the practice of manipulating one's joints such that it produces a sharp sound, likened to cracking (also likened to popping, etc). To produce the sounds, many people will bend their fingers or other joints into unusual positions, or manipulate them in ways which are not commonly experienced in everyday use. For example, bending the fingers right back towards the back of the hand, pulling them away from the hand, or compressing a finger knuckle palmarly.

In many early motion pictures and subsequently parodied in animated cartoons, the gesture of cracking knuckles was associated with a "tough guy" image, especially when accompanied by the implicit or explicit threat of violence.

The physical mechanism is unknown, but possibilities that have been suggested include:

cavitation within the joint – small cavities of partial vacuum form in the fluid then rapidly collapse, producing a sharp sound (hypothesis in a medical journal)
the sudden stretching of ligaments (hypothesis by one reader of that journal)
release of gas from the joints being adjusted (this applies to the popping that can occur in any joint such as during chiropractic manipulation)
A single event is not enough to cause damage to the joint, although it is possible that prolonged joint stress due to cracking knuckles may eventually lead to a higher risk of joint damage. The long-term consequences of this practice have not been studied thoroughly, and the scientific evidence is inconclusive. However, the common parental advice "Cracking your knuckles gives you arthritis" may be simply a device to deter children from this practice, which many people find annoying because of the sound it makes. In fact, a study by Castellanos and Axelrod found that arthritis was not a product of knuckle cracking. They evaluated 300 consecutive outpatients at Mount Carmel Mercy Hospital to determine whether habitual knuckle cracking is a risk factor for hand dysfunction. They found no relation with osteoarthritis, but noted that 'knuckle crackers were more likely to have hand swelling and lower grip strength.'

A chiropractic perspective:

"As a joint is being distracted, the capsule invaginates inward and as the stress on the capsule reaches a certain threshold, it suddenly snaps back from the synovial fluid, increasing the volume of the capsule (and decreasing pressure) and causing the audible sound. The sudden increase in the volume causes the tension to drop, allowing the joint to increase in movement. Eventually, the elastic limit of the capsule is reached and the process stops. The time elapsed during all this is shorter than that required for completion of the stretch reflex, so it can occur without muscular resistance. The sudden jerk on the capsule and the other periarticular tissues is theorized to cause firing of the high-threshold mechanoreceptors." [1]
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External links
Mechanisms Involved in Joint Manipulation – from a Chiropractic website
Does Knuckle Cracking Cause Arthiritis? – A study on Knuckle Cracking
Joint Crackers Community – Community of Joint Crackers
Howstuffworks "What makes your knuckles pop?" – Another explanation on why knuckles crack

Answer 5

Trapped Air I think

Answer 6

.In between the knuckle joints are what's referred to as Synovial drugs, that are crammed with Synovial Fluid; they act as buffers that end the joints donning out. interior of this fluid are air bubbles which, if compressed, implode and make that cracking sound you hear once you 'pop' your knuckles.

Answer 7

I punched a Scottish bloke on Saturday and broke two knuckles on his face but they don't crack anymore they just sound squidgy but boy was it worth it lol

Answer 8

trapped air

Answer 9

your old bones my friend