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  Anatomy Basics »  Viewing Development of Bones     [Image 4 of 24]  :: Jump To  
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AO Fractures Classification * Classification of fractures: The first step in the therapy of every patient is the accurate diagnosis. The diagnosis is bound to a special classification (for example the international classification of disease or ICD). To bring a clinical example, we will take a closer look on the international classification of fractures, based on the anatomic location and the morphological characteristic (severity) of a fracture. It is also called the AO- classification after the founding swiss group Arbeitsgemeinschaft fur Osteosynthesefragen. 
The AO- coding of fractures is an alpha- numeric system, which describes the location of the fracture with first two numbers, followed by a letter and two numbers, which describe the morphological characteristic of the fracture:

Location: The first number describes the bone (see the next image), for example:
1- Humerus
2- Radius/ Ulna
3- Femur
4- Tibia/ Fibula
5- Vertebral column
6- Pelvis
7- Hand
8- Foot

The second number describes the fracture's location more specific by dividing the long bones into three (or four) segments:
1- The proximal segment of a long bone
2- The diaphyseal segment of a long bone
3- The distal segment of a long bone
4- The malleolar segment of Tibia/ Fibula

Morphology: The letter, which follows the first two numbers, describes the morphological characteristic of a fracture:
The diaphyseal fracture characteristics depend on the amount of fragments and on the possibility to achieve a contact of the major fragments after the reposition.

A- Single fragment/ simple fracture
B- More fragments, but contact of all fragments after reposition is possible to achieve
C- More than three fragments, contact of all fragments after reposition is not possible to achieve.

Basic * Regions and Bones of the BodyThis image presents the basic anatomic regions and bones of the human body. To see more details please look further for more images.

De Humani Corporis Fabrica * Title page from De Humani Corporis Fabrica
For a long period of time, the knowledge of anatomy was a hidden treasure waiting to be explored. The invention of printing in the 15th century made it possible to publish multiple copies of illustrated studies of anatomy, to teach anatomy and to eradicate previous errors. One of the most popular studies of the time was Andreas Vesalius’s De Humani Corporis Fabrica (1543), which marked a revolutionary step forward in anatomy. Vesalius was able to correct most errors in ancient writings and anatomic illustrations by his studies of dissection. De Humani Corporis Fabrica became the founding text of modern anatomy, and inspired many scientists, who compared their results with existing texts, corrected errors, and produced new texts with illustrations. The production of images based on dissection became a central component of scientific anatomy.

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Development of Bones.jpg - nov 23, 2004
Diaphysis * Diaphysis of a Long BoneDiaphysis is the shaft of long bones. It is located between both Metaphyses and consists of compact bone walls and an inner cavity (Cavitas medullaris), filled with the yellow (fatty) bone marrow. The external surface of the Diaphysis is covered by the Periosteum.

Osteology 1 * Frontal section through the head of Femur (thigh- bone)
Photography by Pekny P., ©2003

Two different bone components can be found (macroscopically) in human bones: one is dense in texture (Substantia compacta or compact bone tissue) found in the outer parts of bones (thick wall at the shaft of long bones, thin layer at the ends), the other consists of thin fibers and sheets of bone, (trabeculae) which form a reticular, sponge- like network at the ends of long bones and in vertebrae (Substantia spongiosa, trabecular or cancellous bone tissue).
Substantia compacta (cortical bone) is found primarily in the shafts of long bones and forms the outer shell around Substantia spongiosa (cancellous bone) at the end of the joints. The inner parts of the head are filled with spongy bone tissue.

Osteology 2 * Gross Structure of Long BonesThe gross structure of a long bone can be divided into the following regions:

- Epiphysis with articular (joint) cartilages
- Metaphysis
- Diaphysis
- Epiphyseal (growth) plate (Physis) in actively growing bones
Epiphysis is located at the ends of long bones, between the articular cartilages and the growth plate. It is present at each end of long limb bones. Exceptions are the metacarpal and metatarsal bones, the bones of fingers and toes (Phalanges), the ribs (Costae) and the collarbones (Claviculae), where the Epiphysis is present at only one end. The interior of this region is filled with spongy trabecular bone tissue with only a thin external cover of compact bone. It houses the red (bone) marrow. The external surface is covered by the articular cartilage. The non- articulating parts are covered by a dense connective tissue called the Periosteum.
Diaphysis is the shaft of long bones. It is located between both Metaphyses and consists of compact bone walls and an inner cavity (Cavitas medullaris), filled with the yellow (fatty) bone marrow. The external surface of the Diaphysis is covered by the Periosteum.
The external surface of bones (except the articular cartilages) is surrounded by a thin layer of dense connective tissue and Osteoprogenitor cells (see next chapter), called Periosteum. It is anchored to the bony surface by Sharpey fibers (fibrae) that penetrate into the bone.
The articular cartilage (Cartilago articularis) is located at the joints, where the epiphyseal part of the bone articulates with another bone. The function of the articular cartilage is to provide smooth contact surface in a joint (Facies articularis). Similar to other connective tissues, it consists of cells (Chondrozytes) and an extracellular matrix. In contrast to other tissues, it has no vascularization (vessels) and nutrients have to diffuse from synovial fluid (nutrient rich fluid in the joint capsule).

Osteology 3 * Microscopic view of compact bone tissue with Haversian systems
Image based on a template from the LifeART Collection, Lippincott Williams & Wilkins, ©1989- 2001

Compact bones are organized into strong units called Osteons or Haversian systems. These are lamellar cylinders along the long axis of the bones with an average diameter of 0,05mm. Each Haversian system consists of a central canal (Haversian canal or Canalis centralis Havers), surrounded by concentric thin concentric rings of bony tissue (Lamellae). The lamellae are held together by oblique (Sharpey) and reticular fibers between them. The Lacunae are also situated between the Lamellae. They are occupied by Osteocytes. The small communication canals (through Lamellae) between two Lacunae are called Canaliculi. They connect with the central (Haversian) canals.
The Haversian canal contains one or two blood vessels and thin nerve filaments. It communicates with the bone marrow cavity (Cavitas medullaris) and the Periosteum (outside of bone) through oblique canals (Volkmann canals, which penetrate the lamellar structures.

Parts of the Body 2 * Parts of the Body
The human body consists of the following parts (Partes corporis):

Caput- the head
Collum- the neck
Thorax- the chest
Abdomen- the stomach
Pelvis- the pelvis
Membrum superius- the arm(s)
Membrum inferius- the leg(s)

Image: Development of long bones
Image based on a template from the LifeART Collection, Lippincott Williams & Wilkins, ©1989- 2001
The arrows show the direction of endochondral ossification within a hyaline cartilage model, which provides a template of the shape of the bone to be formed. In the next step, the cartilage is replaced by bone. This type of ossification is found in long and short bones, but not in flat bones (which are formed by the intramembranous ossification in membranes of fibrous connective tissue).
Page last updated on nov 23, 2004