• • The inner layer of bone tissue is called Cancellous or Spongy or Trabecular bone. Don’t be fooled by the name, as this area of bone is light but strong and has a honeycomb appearance. This honeycomb structure is organised in such as way to provide strength without adding bone mass, particularly in areas of pressure or stress. This helps to make bones both light and strong.

  • Inside both the compact and spongy bone are cells called Osteocytes. These cells can either deposit or absorb calcium salts into or out of the bone tissue. These cells are also responsible for bone growth and changes in the shape of bones.

• • Finally the cavities of the bones contain bone marrow. There are two types of bone marrow that can be found in most bones.

    • Yellow Marrow. This tissue is found in most bones but mainly fiils the shafts on long bones. It is made up blood vessels, nerve cells and primarily of adipose tissue (fat cells). This type of marrow can be converted into red bone marrow and produce blood cells when needed e.g. in severe blood loss following trauma.

    • Red marrow. This is found in spongy bone, at the ends of long bones, in the ribs, sternum, vertebrae and pelvis. It produces red blood cells, white blood cells (lymphocytes) and platelets.

Bone Growth

After birth many bones are composed entirely of cartilage. This cartilage material is dense and fibrous, it can support weight and it is very flexible. About 7 months before birth bone formation begins by a process called ossification. This is the process where the cartilage cells begin to be replaced by cells that form bone. Bone tissue begins to form as Osteocytes secrete mineral deposits of calcium and phosphorus and lay down near the centre of each bone – the primary centre of ossification. This primary centre is often in the shaft or diaphysis of long bones such as the femur. This gradually begins to replace the original cartilage. As the foetus develops ossification commences in the extremities and the epiphyses form secondary centres of ossification.

Classification of Bones

Bones can be classified into one of four categories depending upon their shape…

Task

With a skeleton/picture of a skeleton in front of you look at the various bones and decide how they might be classified. After you have looked at many bones try and answer the questions below:

Anatomical features of bones

Additional Information for anatomy geeks......as you go through the course or go on placement, particularly if you are involved in orthopaedic practice where surgery or xrays are discussed you may hear some of these terms:

When studying bones more closely you will see various surface features forming lines, hollows, gaps and projections. The names of commonly occurring features of bones and the shapes of surfaces are listed below:

• • Facet

    • Small flattish surface (not always articular)

  • Condyle

    • Knuckle shaped

• Trochlea

  • Grooved like a pulley

• Head

  • Proximal end of many long bones

• Tubercle, Tubersoity & Trochanter

  • Roughly rounded projections

• Process

  • Large projection

• Spine

  • Elongated or pointed projection

• Crest

  • Elongated Elevation

• Line

  • Elongated less pronounced than a crest

• Lip

  • Boundary edge (eg of a crest)

• Epicondyle

  • Projection next to a condyle

• Protruberance, Eminence & Prominence

  • Slight Elevations

• Fossa

  • a Hollow

• Fovea

  • a small hollow

• Sulcus/Groove

  • elongated depression

• Foramen (plural = foramina)

  • canal

• Aperture

  • large hole

• Fissure

  • Elongated hole