Why Your Knuckles Pop
Science reporter Corey Binns occasionally decorates LiveScience with articles about the human body that are informational as well as amusing. His latest is about cracking knuckles and creaking joints. We have four kinds of joints (pivot, ball-and-socket, sliding and hinge), which he illustrates with diagrams that look like machinery. The pops and creaking noises, he says, come from gas bubbles escaping from fluid that lubricates and cushions the moving parts. But then, that’s a pretty amazing thing. “A protective fluid cushions most of the joints in our bodies,” he says. “Inside a capsule that safeguards bones connected at a joint, synovial fluid keeps the cartilage, tissues, and muscles lubricated and well nourished. Nutrients float inside the fluid, along with gases, such as oxygen, nitrogen and carbon dioxide.” Stretching those joints forces gas bubbles out – that makes the snap, crackle and pop we hear. “Before your knuckle can crack again, the fluid must reabsorb the gas.” Other noises can arise from tendons and ligaments snapping back into place, like rubber bands, when we stretch or get up from a sitting position.
Binns leaves it as a debate whether cracking knuckles is harmful. But if you are doing it too often as a habit related to stress, well, that’s another issue. But creaking or not, joints perform a wide variety of functions. Binns lists several: “A baseball pitcher uses the tremendous range of motion of the ball-and-socket joint in his shoulder to throw fastballs,” he says. “And sliding joints in the backbone make gymnasts’ backs so flexible.” Even shaking your head yes or no demands fluid-lubricated cushioning in the joints.
Every kid finds out that our bodies do funny things. Parents usually get a load of physiological questions: Why do we yawn? What makes our ears pop when we drive down from the mountains? Why do our legs fall asleep? Why do they call it a funny bone when it hurts? Why does my stomach growl? What causes goose bumps? How come milk comes out my nose when Susie makes me laugh at breakfast? These are teachable moments. As simple a thing as cracking a knuckle points to an underlying marvel of design. Something has to manufacture a special lubricating fluid, filled with nutrients, to keep our joints supple and responsive. Without it, imagine the pain and wear that would quickly beset us. Our joints, our hearts, our senses, our brains – our bodies usually outlast every artificial technology. It’s only when things go wrong that we appreciate how many things must work together within tight constraints just to get through an ordinary Monday.
The fact that we are curious about our bodies is a curiosity in itself. Our self-consciousness points to a reality that is more than physical. We sense ourselves inhabiting our bodies, as if our selves are mere tenants. We are surprised by the passage of time. C. S. Lewis pointed out how strange this sensation is. We live in time; why should we be surprised by its flow, any more than a fish should be surprised by the wetness of water? These realizations are signposts to a reality beyond the temporal, for which the soul within us yearns. They cannot be explained by materialism.
The Bible speaks of our bodies as temporary dwellings. Peter wrote of his body as a tent (II Peter 1:13; Paul also in II Corinthians 5:1-7); Paul spoke of possessing treasure (the knowledge of the glory of God through Christ) in jars of clay (II Corinthians 4:7). Viewing our bodies, with all their infirmities, as temporary dwellings can give hope to those who love God and His salvation in Christ. Pity the evolutionist who must view this life as the only shot in a senseless lottery. Paul continued (II Cor. 5:17), “Therefore, if anyone is in Christ, he is a new creation; old things have passed away; behold, all things have become new.” To be “in Christ” is to already have the Spirit of God as a guarantee, he said; the only thing left to claim is our new glorified bodies, after these old knuckles loosen their grip on this world, to crack no more.