Supposedly, broken glass shards that penetrate the skin and aren’t removed then go on to travel further in, or further out, of your body, because of your muscle movement? Which, and how?
And what if, say, it’s in your eyes? No muscles, only aquea humor and vitreous humor, so are the tiny glass fragments burrowing further in, or being pushed out by your eyes?
Trying to understand if this is actually true, or a medical old wives’ tale.
I’m voting for old wives tale … I’ve had glass shards in my skin before and they just worked out … even better than wood slivers.
Fiberglass will work itself out over the next few days (or at least stop itching). I’ve heard of people that get into car accidents or go through glass windows picking slivers of glass out of their hair/scalp for years, but I’ve never quite understood how that works. Why does it take years.
As far as your eye, my WAG is that once they’re in they stay there. My reasoning for that is only because of the precautions taken for metal/machine shop workers that go for MRIs. The radiologists are always worried about metal slivers in the patient’s eyes being pulled out by the magnet.
Isn’t it kind of hit and miss? There are lots of stories – too many of 'em apocryphal – about people hit with shotgun pellets. Sometimes the pellets pop out where they went in. Sometimes they pop out nearby. Sometimes, the guy will spit one out unexpectedly. And sometimes they just sit in the body, encysted, for the rest of the guy’s life.
Muscle movement could move things around some – but it would be completely variable, depending on location. Some muscles would drive things one direction, and others another.
Really shallow objects will tend to be ejected, because that’s one of the things skin does. But once a sliver of glass gets down into the major muscle fibers, aren’t all bets pretty much even?
I had a cousin who had many gernade fragments in his body from Vietnam. The medics treated his major wounds, shipped him off to a hospital, and left the fragments for later.
For months & years afterwards, he had rather sharp pieces of metal working their way out of his back & side, with a sharp edge coming out thru his skin. His wife would grab them with a needle-nose pliers & pull them out, then disinfect & bandage the wound. He said he didn’t feel them at first – he usually found out about one when he pulled on his shirt and heard it rip from the shrapnel fragment. (He claimed it usually happened when he was putting on a new shirt!)
So metal fragments can indeed stay in the body for quite a while, and then work their way out.
I’m gonna say it’s observational bias.
If somebody has a bunch of shards in them, some will work outwards & surface. Those he/she will notice. Others will stay put. Others will work inwards. Neither of those type will ever move enough to notice or to have consequences.
So folks mistakenly conclude that shards preferentially migrate out. IMO, they don’t.
Ok, let’s say it’s in your eyes. Or, as my immediate family and a host of emergency crew and ophthalmologist surgeons said on or around June 4, 1968: there are shards of glass in Leo Bloom’s left eye.
You say “if they aren’t removed,” so my anecdotal evidence, including some research and empirical evidence since 1968, is not on point, but it seems to me that the one possibility you suggest, “being pushed out,” doesn’t sound right from the get go.
The eye bulb is a sack of liquid. Punching holes in it breaks the bag, and the pressure decreases. In fact, I now have the orthographically special pathology pthisis bulbi, common decades after trauma to the bulb. The image here (non-gross, a cross-section of a CT scan) illustrates the situation nicely: Imgur: The magic of the Internet
Shards of anything are unlikely to be completely symmetrical - they will be marginally more blunt or pointed, jagged or smooth at one end or t’other. Movement will tend to work them in the direction of whichever end penetrates flesh better than the other.
Obstacles such as bone etc notwithstanding of course.
What happens if an embedded shard of glass runs into an old shotgun pellet? I imagine some type of large explosion.
And falling anvils. Do anvils work their way out, or in?
Had glass come out & snag a shirt. Several of my siblings has also. We were an active bunch.
Two strange things:
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Had a lump for in my right palm. Grew to the point of irritation but was not visible from the surface. a Doc appointment was at the end of the day for another thing & I mentioned it. her said he’d take a look if I wanted. Down in the muscle he dug out a blue fibrous chunk of something.
Cool, gonna send to the lab cause this is strand. Report 2 weeks later that is was a a wad of blue fibers, origin unknown. I still wonder… -
Also blue: A chunk of blue glass was smashed and a bit of glass was embedded in my left thigh. ( I always had heard that it would work itself out so I did nada. )
Several years later, something was snagging my jeans. It was a bit of blue glass about 6 inches lower than where the glass had gone in…
Will this glass work itself out of the body?
Sit just right and grunt really hard??? 
I’ve had a small shard of glass in my right wrist for the last 20 years or so (kids, don’t run into glass doors). It hasn’t moved at all as far as I can tell, and I only notice it if I put pressure on the area, a little behind the navicular bone of the hand.
I suppose that it stays put because that area has no muscles and is wrapped in ligaments.
When I was maybe 10 I had a bump come up on my lower back and my Dad kept inspecting and squeezing it. Eventually he extracted a pea-sized object that seemed to be a rock, he tried crushing it with a hammer. We never could figure out how it got inside without me knowing it. 