Anatomy and Physiology: Now with a Self-Repairing Option!
Now with a Self-Repairing Option!
One of the things I have always found amusing about medicine is how far we have come in some areas, and how little things have changed in others. Although we are able to detect the extent of a brain tumor via a completely noninvasive MRI, when it comes to fixing broken bones, most of the time all we are doing is helping the body to do what it does naturally. We can find out the extent of the break with a simple X-ray, but at that point some old-fashioned horse sense takes over. The only thing left is to set the bone in the right position and immobilize it, often in the same type of plaster cast that my parents wore when they were little. The real wonder is what the body does next, completely without the doctor's help!
Them's the Breaks!
There are many different types of fractures, depending on the nature of the accident, as well as the age of the patient (see Figure 5.4)! If you ask around, you'll find that most people broke more bones in childhood than at any other time in their lives. I personally broke my left arm once, and my right arm twice, all before the age of 13, and I've broken nothing else in close to 30 years!
Part of that is simply due to the greater activity of the young, not to mention a little of the carelessness of youth! Luckily, the fractures of childhood are usually the least troublesome. These fractures are given the somewhat poetic name of “greenstick” fractures. This is best understood by a trip into the woods. If you take two sticks, a green one straight from a healthy tree, and a brown one from the ground, and then bend them to the point of breaking, you will see a startling difference.
The brown stick will snap in two, whereas the green one will bend far more, and when it breaks it will not break all the way through. The bones of the young are more pliable, and less likely to break all the way through, merely bending on the other side of the bone opposite the fracture. In terms of our evolutionary past, a young primate in the wild, learning the ropes, or the branches, as it were, did not have access to a veterinarian to set a fracture 30 million years ago. Greenstick fractures and self-healing bones are definitely a good evolutionary combination!
At the opposite end of the spectrum is the frailty of the bones in the elderly. Part of this, especially in women, is due to osteoporosis. When the bone is weakened it no longer can resist stresses that never used to be a problem. Fractures based on medical conditions, including, but not limited to osteoporosis, are called pathologic fractures.
Before looking at the following table of fracture types it is important to mention two other criteria that are used to describe a fracture. Fractures that only break part of the way across the bone are called partial fractures, whereas those that break the bone into two or more pieces are called complete fractures. When a complete fracture occurs, the anatomical alignment of the bone fragments is sometimes retained, and at other times the alignment is disturbed. The disturbed variety is called a displaced fracture, while the other variety is, for lack of a better term, called a nondisplaced fracture.
Lastly, fractures have a way of making sharp edges at the point of the break. If none of the pieces break through the skin, that fracture, regardless of any other complexity, is called a simple or closed fracture. On the more gruesome side, however, are those fractures where a sharp edge of the bone actually pierces the skin; these fractures are known as compound or open fractures.
|Types of Fractures
|Many small fragments exist at the break
|Bone is forcefully twisted apart
|Due to repeated stress wearing down bone
|Break is perpendicular to longitudinal axis
|Break at distal end of the radius
|Break at distal articulation of the fibula
Fibula, Heal Thyself
One interesting thing about bones is their ability to record past injuries through the formation of an external callus. That knowledge is very useful in science and medicine. When wild primates are captured and x-rayed, they routinely are found to have broken bones; so much for the graceful swinging of monkeys! Next time you go to a natural history museum, see if you can find any broken bones in the skeletons (you may be surprised how often you can!). In medicine, a child with a broken arm may be x-rayed more thoroughly to see whether the “fall” was really just another in a long history of child abuse.
Okay, so you've decided, gathering all the courage your four-year-old frame can muster, to ride your tricycle, with no brakes I might add, down your parent's steep driveway. You find yourself going too fast, the tricycle is getting out of control, and you fall over on your side, fracturing your right ulna. Ouch!
Now that the bone is broken, how does it fix itself (see Figure 5.5)? To start off, broken bones bleed! The clot that ultimately forms (after a few hours) and surrounds the bone fragments is called a fracture hematoma. An internal callus of cartilage later forms on the inside of the break, and an external callus of bone and cartilage stabilizes the outside of the bone. During this callus formation, spongy bone starts to form in the middle of the break.
As the trabeculae from each side of the break unite, or knit, and the external callus starts to ossify, the dead bone, the fragments, and the edges of the break are removed by osteoclasts and replaced by the activity of osteoblasts. After the fracture has healed, the bone is left with a widening at the point of the repair called an external callus; although remodeling may cause this to decrease in size over time, it is unlikely to disappear entirely.
Excerpted from The Complete Idiot's Guide to Anatomy and Physiology © 2004 by Michael J. Vieira Lazaroff. All rights reserved including the right of reproduction in whole or in part in any form. Used by arrangement with Alpha Books, a member of Penguin Group (USA) Inc.