What is what?

I often get asked questions like what are tendons, what are ligaments, what do they do? So lets get back to basics.

Part 1: Bone

Bone is the most rigid form of connective tissue, despite this rigidity one undergoes constant metabolism and remodelling . Bone is supplied by blood and composed of collagen, calcium phosphate, water, proteins and cells.

The function of bone is to provide support, enhance leverage, protect structures, store minerals, ad serve as an attachment for ligaments and tendons.

Injuries to bones can be caused by direct trauma (a blow) or indirect trauma (falling on an outstretched hand) resulting in fractures but they can also be overuse injuries such as stress fractures which are the result of repetitive physical loading causing failure.

Part 2: Ligaments

Ligaments are fibrous bands of dense connective tissue that connect bones across joints. Ligaments are comprised primarily of water, with collagen (mainly type 1 and some type 3).  The cellular organisation of ligaments makes it ideal for sustaining tensile load and its structural framework helps provide stiffness, of course the location of the ligament will be dependent on its type and location.

Ligaments contribute to the stability of joint function by preventing excessive motion, acting as guides to direct motion and providing proprioceptive feedback for joint function.

We often clarify ligament injuries:

  • Grade I – Mild
  • Grade II – Moderate
  • Grade III – Complete

Ligaments injuries are rarely caused by overuse and are more likely cause of injury is an acute overstretching traumatic injury.

Part 3: Tendons

Tendons attach muscle to bone. They are made up primarily of type 1 and 3 collagen, the thickness of each tendon varies and is largely determined by muscle from which it originates. Tendons are able to transmit load from muscle to bone and because of that are subject to tensile stresses.

Tendons can be classified as:

  • Gliding tendons e.g. flexor tendons of the hand
  • Vascular tendons e.g. achilles tendon

Tendons meet muscles are the myotendinous junction, this area is vulnerable to tensile failure (injury).

Part 4: Muscles

Did you know? There are approximately 430 skeletal muscles in the body.

Muscles are classified as voluntary or involuntary or structural as skeletal (span joints and attach to bones via tendons), smooth (walls of organs) and cardiac (Heart).

The fucnions of muscles are as follows:

Agonist – contracts to produce the desired movement

Synergist – muscle groups that work together to produce desired movement

Antagonist – Opposes the desired movement, by relaxing and lengthening in a gradual manner to ensure desired motion occurs.

Part 5. Muscle fibre types

I’m you have all heard of fast twitch and slow twitch, well here’s the explanation.

There are 4 types of recognised skeletal muscle fibres:

  • Type I  (Slow twitch, red oxidative)
  • Type IIa (fast twitch, red oxidative)
  • Type IIb (fast twitch, white glycolytic)
  • Type IIc (fast twitch, intermediate)

Slow twitch fibres have more mitochondria (Which have a high capacity for oxygen uptake), making them suitable from long duration activities including the maintenance of posture.

Fast twitch fibres are suited to quick, explosive activities such as sprinting. Fast twitch are separated into those that have high amounts of mitochondria (IIa) and those that are mitochondria poor (IIb), type IIc have features of both red and white fibres and those have fast contraction and good fatigue resistance.

Part 6. Bursa

So many people tell me they have bursitis but what is a bursa?

They are flattened, saclike structures that are lined with a synovial membrane and filled with fluid. The bursa produces small amounts of fluid, which allows for the smooth and almost* frictionless motion between muscles, tendons, bones, ligaments and skin.

Bursitis is inflammation of the bursa and it occurs if the bursa gets irritated because of too much movement or infection. Overuse injuries of bursa are quite common

You may have heard of the following bursitis:

  • Subacromial
  • Iliopsoas
  • Ischial

Bursitis is associated with local tenderness, swelling and pain of specific movements .

Part 7. Cartilage tissue

Bone is usually proceeded by the formation of articular cartilage which is highly organised viscoelastic materal made up of chondrocytes, water and an ExtraCellular Matric (ECM) made up of proteoglycans, lipids, water and dissolved electrolytes. Articular cartilage does not contain blood vessels, lymphatics or nerves.

Cartilage tissues exists in 3 forms

Hyaline – covers the ends of long bones and along with synovial fluid that covers it and provides a smooth articulating surface. Articular cartilage plays a role in permitting frictionless motion to occurs between the surfaces of synovial joints. It also functions to distribute forces over a large contact area and dissipating the force associated with the load.

Elastic – specialised and found in areas such as the outer ear.

Fibrocartilage – Functions as a shock absorber in weight bearing and non weight bearing joints. An example is the menisci of the knee, its large fibre content, reinforced with numerous collagen fibres makes it ideal for bearing stresses in all directions.

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