# No, really, how much force to break a clavicle?

According to the internet, you can break a clavicle by applying just seven pounds of force. I know it’s a pretty common fracture, but seven pounds seems suspiciously low; it’s slightly less than the weight of a gallon of water.

Where on the clavicle, and in what direction, could I apply seven pounds of force in order to break it?

When I was 10, I broke my left clavicle when tackled playing football (without any padding and the last play of the day). My doctor commented it could be broken moving by motioning his outstretched hand in a not-very-fast downward chop.

No this is false. You can rest a twenty pound weight on your collar bone, lift a similar weight, etc without breaking it obviously.

It is true the collar bone is relatively fragile. The reasons for why this might be are a matter of some debate. Biomechanics studies (orthopedists love biomech studies) suggest that over 1500N are required in axial load. Tension, shear, and twisting forces will decrease this in an unpredictable way (the clavicle has a fairly irregular shape) but it’s far more than 7 lbs.

[The clavicular fracture: a biomechanical study of the mechanism of clavicular fracture and modes of the fracture. Harnroongroj T1, Tantikul C, Keatkor S.]

The clavicle is much stronger than that sort of story would lead you to believe. It forms the major part of the upper extremity equivalent of the pelvic girdle, so broadly speaking it is sort of a pelvis. And the pelvis is really strong. Of course, the scapular girdle is not nearly as strong as the pelvis in humans because we don’t walk on our hands, but we’re not that far removed from animals who do.

As a general rule, bone is very strong against compression and very weak in tension (which is the opposite pattern to our connective tissues). So the easiest way to break a clavicle is probably to pull it apart from the ends with some shearing force added.

Which is more like 337 pounds.

OK, so “7 pounds to break a clavicle” is sort of like “a duck’s quack doesn’t echo, and no one knows why”, i.e. it’s an apocryphal bullshit factoid that keeps getting passed around without refutation. Thanks!

At about age 13, I broke mine by dropping a gallon of ice cream on it. I was putting a bucket of ice cream back in the freezer when it slipped out of my hands and the edge hit my clavicle. It wasn’t badly broken, but it was bad enough I had to wear an annoying brace for several weeks while it healed. That gallon of ice cream probably weighs 6-8 pounds and dropped probably less than a foot before striking the bone, so it’s definitely true that it doesn’t take much force, assuming that it’s applied in just the right spot in just the right way.

In the midst of this discussion, I wonder whose clavicle? A five-year-old’s? A 12-year-old’s? A 25-year-old’s? A 95-year-old’s? Seems to me there might be some significant differences.

The clavicle screams “Break me! Break me!”. It has no protection to speak of; there’s just a thin layer of skin between it and the outside world. Additionally, both ends of the bone are fairly immobile. A downward strike to the clavicle is (mostly) transmitted to the spinal column by way of the sternum, scapula, and ribs. The spine is specifically configured to oppose this type of compressive force and provides exactly the kind of resistance needed to make such a strike effective.

I’m not sure how these alleged medical sources tested the clavicle to it’s breaking point. 7 pounds per square inch could, if it’s applied in the most effective manner, break a bone the size of a clavicle. But who’s clavicle? An NFL defensive tackle? Probably not. A 130 lb bookworm? Probably. An average medical cadaver from India? Possibly.

The pointy end of a six pound blacksmith sledge hammer

http://www.ebay.com/itm/Vintage-Six-Pound-Blacksmith-Sledge-Hammer-Marked-6-Has-An-Oval-Logo-On-It-/121904909184?hash=item1c62194b80:g:89gAAOSwzgRWznsL

wouldn’t require much speed to crack a bone. While the bones of a forearm are free to swing away from a 7 psi strike, the clavicle is supported at both ends and held ridged by the chest and spine.

Bruce Lee could break your clavicle just by looking at it. While it is true that his equal does not exist today, adept practioners of OS-do can fracture smaller bones (such as the hyoid) by deftly and firmly depressing a combination of keys on a standard keyboard. I don’t know which keys, exactly, but I’m pretty sure that one of them is CTRL.

Actually, IRL, healthy bones are very strong, but it can be amazing how often bones sustain major stresses without breaking, but fail against relatively minor trauma presented just the wrong way.

What on earth?!? Literally none of what you wrote is true.

The shoulder girdle is absolutely nothing like the pelvis and it works very differently from a functional and anatomic perspective. This is true even in quadrapeds. At best you could say they are both joints. That’s about it.

Bone is a type of connective tissue.

Bone is slightly stronger in compression than tension but the two are quite similar when it comes to ultimate yield strength. The idea that bone is weak in tension is ludicrous. If you pulling a bone apart from the ends (?!?) is easier than applying some lateral stress, you are insane.

By the numbers: tensile strength is 50-150 MPa, compressive strength is 100-230 MPa. Not sure what constitutes “very strong” vs. “very weak” vs. “slightly stronger in compression than tension.”