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Os longum

German: Röhrenknochen

1 Definition

Os longum (long bone) are bones, which have a consistent medullary cavity and like one expect by the name have a longitudinal shape. Examples of long bones are the femur (thighbone), tibia (shinbone), fibula, humerus (upper arm bone), radius and ulna.

2 Composition

A long bone has two epiphyses at the ends and a diaphysis in between. The area between epiphysis and diaphysis is called metaphysis. The long bone, like almost all bones, is overall covered by the periost. One can distinguish two architectures of the bone in a lng bone:

2.1 Epiphysis

The epiphyses form both ends of the long bones and have cartilaginous joint area. In this area of the bone the compacta is thin but in the substantia spongiosa has a pronounced bone trabecula. The characteristic of the trabecula depends on the stress which influences the bone. The trabecula stabilize the epiphysis greatly by low weight. The older the human the more the trabecula is removed, which is called osteoporosis. Osteoporosis means that there is a higher risk of experiencing a fracture and reduced stability.

2.2 Epiphyseal gap

Between the epiphyses and the diaphysis are the so-called epiphyseal gap. During the growing period it is filled with hyalinous cartilage. This is the spot of longitudinal growth of the bone. In the age of approximately 20 there is no growing anymore and this is when the epiphyseal gaps start to ossify and are than visible as epiphyseal line.

2.3 Diaphysis

The diaphysis is in the middle of the bone and is filled with bone marrow in medullary cavity. The medullary cavities are inside of the diaphysis and replace the rarely developed substantia spongiosa of the diaphysis. That means that there is mainly substantia compacta. Inside the diaphysis are foramina nutricia as well. These are small holes where arteries are passing through and into the bone to supply this bone. The supply of the epiphyses is independent of the supply of the diaphysis because of arteriae epiphysiales.

3 Pathology

A fracture of a long bone is a consequence of excessive mechanical force of the bone what happens for example in activities like skiing, cycling with a mountain bike and so on. The reason is mainly a sudden excessive pressure, that the bone cannot withstand. The fracture can be a single or multiple one and open or closed. In many cases there is immense pain, enormous malposition of the bone and abnormal movements are possible. A special case of fractures is a greenstick fracture in which the periost is not damaged so that the fracture is hardly seen on an x-ray. This fracture happens most often in children until the age of 10.

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Specialties: Anatomy

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