The old adage that children are simply young adults simply does not hold true especially when considering their bones and bony development. Injury patterns, the forces and the result of injuries that occur to the immature skeleton do not minic or parallel those of the adult bones. Therefore it becomes important for the physicians, coaches and medical personnel taking care of the young athlete to be aware of these changes, the ramification of them and the appropriate treatment of them.
Bone initially develops very early in the embryonic stage. The original streaks of bone can be seen as early as six weeks into the embryonic stage. Initially the entire skeleton of a small child is made of soft tissue cartilage or collagen.
Collagen is the most abundant fibrous tissue seen in the body, which makes up scar tissue and many of the basic building blocks of the human skeleton. Within this soft tissue framework that bone cells will actually develop and begin making the bony skeleton that we see in adulthood.
The cartilage/collagen skeleton is much more flexible than the calcium skeleton seen in an adult. These bones are very soft and supple and can be easily bent. This is important so that the child can pass easily through the birth canal without breaking, bending or causing long-term disruption of the bones themselves. Once birth has occurred it becomes important now that these bones gain better structural strength so they can begin to support the young human as the baby begins to grow.
There are two main centers of growth in each of the long bones in our bodies.
First, at the end of the bones is what is called the secondary ossification center. In the ends of the bones groups of cartilage shells get together and differential into bone producing cells. These bone producing cells actually start piling calcium on top of one another so that small centers of ossification or bone is produced. These centers grow from the center of the ends of the bones and form the shape of the joints that articulate with one another. This bone formation begins at the center of the ends of the cartilage bones and grows outwards to make the end of the bones, as we know them in adults.
The second site of bone development occurs at the growth plates. The growth plates are located between the shaft of the long bones and at the end of the long bones where the secondary ossification center occurs. These primary ossification centers or growth plates allow for the growth of bone in length. These primary ossification centers are what allows us to grow in height. It is these primary ossification centers or growth plates that are often times damaged in the young athlete with immature bones.
The bone begins at six weeks from the time of conception and continues until the last growth plate fuses around the age of twenty-one. In addition to the primary ossification center, in which bones grow in length, in a secondary ossification center at the end of the bones that allows the joints to be formed, a third way to have bone growth is through periosteal bone growth. Periosteum is a thick covering around the outside of the bone much like the bark around a tree. This covering around the bone provides for growth around the entire circumference of the bone allowing it to grow in width.
Of the three types of bone growth, the periosteal growth is what contributes the most to the overall size of the bone. Periosteum is a fibrous layer, which is extremely thick at the time of birth and thins out to adulthood into a layer just a couple millimeters in width. Finally, growth plates are often stimulated by traction and generally inhibited by compressions. Great impact or heavy loads across the growth plate can cause damage and further create shortening of the limbs or abnormal angular growth of the bones.
The cartilaginous growth plate represents the weak link in the bone system. Not only is the growth plate weaker than the bone next to it, it is also weaker than the ligaments that hold the joints together above and below it. Ligaments are ropes that hold one bone to another bone and hold the joints in place. Growth plates are weaker than these ligaments.
Sprains occur to a joint when the bone ends move out of position and the ligaments become stretched or torn. Knowing now that these growth plates, up until the age of 12 to 13, are weaker than the ligaments it is nearly impossible for a young person to tear the ligaments themselves. Sprains in young people under the age of 12 to 13 generally don't occur but rather injuries to the growth plates are seen.
Remember the growth plate is the weakest link of the entire system of the extremity. Any injury that occurs will not affect the bone proper,(?) which is made of strong calcium, it will not affect the joint that's held together by ligaments but rather the failure will occur at the level of the growth plate.
The growth plate fails by various mechanisms. Rotation forces, bending forces or compressive forces can all injury the growth plate.
The simplest injury to the growth plate is a fracture, which does not cause the growth plate to move out of position but rather irritates it. These mild fractures are usually treated with 3 weeks of immobilization and heal quite nicely. More significant fractures can cause displacement or movement of the bones on either side of the growth plate out of an acceptable position. Now we not only risk not having the bones lined up nicely but potential for growth plate abnormalities can occur which leads to either bones not growing or growing at an angle that can be unacceptable.
These suspected injuries to extremity should be evaluated as an injury to the growth plate. Medical personnel that deal with young athletes must first examine and observe the injured extremity. Careful palpation of all bony prominence to include the growth plates at either end of the long bone must be done. If any tenderness exist over a growth plate it is assume that an injury has occurred. If there is swelling, deformity or pain to pressure over a growth plate the extremity should be immobilized and the young athlete transported to the nearest health care facility. X-rays will be taken and many times these x-rays will be normal showing a widen appearance of the growth plate itself.
Remember cartilage does not show up on x-rays and therefore direct x-ray observation of abnormality may not occur. Fracture must be treated the same as fracture in an adult with gentle immobilization in either a cast or surgical intervention if indeed the bones have moved out of position.