When does injury occur?
When the loads placed on the musculoskeletal system exceed the mechanical limits of the structures within the musculoskeletal system
How can we understand the loads placed on the musculoskeletal system during injury inciting events?
Understanding biomechanics of movement patterns
How can we understand the mechanical limits of the strucutres of the musculoskeletal system?
Understanding anatomy and the physiology of musculoskeletal tissues
What tissues make up the musculoskeletal system?
- Bone
- Cartilage
- Muscles and Tendons
- Ligaments
What mechanical functions do bones perform?
- Structural
- Protective
What physiological functions do bones perform?
- Calcium ion regulation
- Blood cell production in bone marrow
What proportion of bone is organic vs inorganic?
35% Organic, 65% Inorganic
What is the organic component of bone?
- Cells (osteoblasts, lining cells, osteocytes, osteoclasts)
- Matrix (mostly type 1 collagen)
What does the matrix inside bone provide?
Gives the bone flexibility
What is the inorganic component of bone?
Minerals (hydroxyapatite)
What quality does the mineral content of bone provide?
Makes the bone strong
What is hydroxyapatite?
Complex salt made of calcium and phosphate
What is the ‘diaphysis’ of a bone?
The Shaft
What are the epypheses of bone?
The ends
What are the two types of bone?
Compact/Cortical Bone
Concellous/Spongy/Trabecular Bone
What is Cortical or Compact bone?
The external surface of bone
What percentage of a bone’s mass is cortical/compact?
80%
What is cancellous/spongy/trabecular bone?
- Lattice of fine bone plates
- epiphyses of long bones, vertebral bodies and flat bones
- Intercommunicating spaces in mesh filled with bone marrow
What purpose does cancellous/trabecular bone serve?
Reduces skeletal mass without compromising strength
What is the process of longitudinal bone growth?
- Endochondral Ossification
- First at primary center of ossification
- Second at secondary centre of ossification at the epiphyses
When does longitudinal bone growth cease?
18 yrs
What is the process of circumferential bone growth?
- Diameter increases throughout lifespan
- Rapid prior to adulthood then very slow
What is the process of bone repair after failure?
- Clot forms over failure
- Cartilage fills the gap which is then ossified to form new woven bone (callous)
- Callous remodels over time to be as strong as before the break
What is Bone remodelling?
The process by which bone mass is maintained/increased/decreased
What cells are involved in bone resorption?
Osteoclasts
What cells are involved in bone formation?
Osteoblasts
What is bone atrophy?
Loss of bone mass and mineral content and predominance of osteoclast activity due to physical inactivity
What is bone hypertrophy?
Increase in bone mass and mineral content due to predominance of osteoblast activity due to increase in physical activity
Why does bone fracture occur?
Excessive Forces
Weak Bones
Cumulative damage due to repetitive loading
Define ‘stress’ on a structure like bone, ligament, tendon, etc.
Force/Cross sectional area
What can excessive stress be caused by?
- Large external force like a fall, tackle or landing
- Innapropriate bone dimensions
What are the different diagnostic imaging modalities?
- Radiography
- CT
- Nuclear Medicine
- Ultrasound
- MRI
What are the pros of using radiography?
- Very good 2D resolution
- Simple and affordable
- High reproducibility
- Very good bone info
- Can image blood vessels
- Low dose of radiation
What are the pros and cons of using CT scans?
Very high resolution of bone and some soft tissue
Fast (20s for whole body)
BUT
-moderately expensive
-Radiation dose similar to 200 chest x-rays
What is osteoporosis?
Disease of weak bones due to reduced trabecular bone/mineral density
Why is osteoporosis more common in post-menopausal women?
Reduction in oestogen levels disrupts bone remodelling
When do stress fractures occur?
When the remodelling process cannot keep up with the damage
What are the pros and cons of using nuclear medicine?
- High sensitivity BUT low spatial resolution
- Identifies areas of high remodelling BUT high radiation dose
- Available in most hospitals BUT moderately expensive
What situations might make stress fractures the most likely to occur?
- Change in training type
- Sudden increase in training intensity
- Change in equipment or surface
What is the role of articular cartilage?
- Transfers forces between articulating bones
- Distributes forces in joints
- Allows relative movement between articular surfaces with minimal friction
What is the composition and properties of articular cartilage?
- 5-10% Cells
- 90-95% Intercellular Matrix
- Avascular (blood supply)
- Aneural (no nerves)
What is the composition of the intercellular matrix of articular cartilage?
- 65-80% Water
- 20-35% Structural Macromolecules (Type II Collagen, Proteoglycans)
What qualities does the presence of collagen provide in articular cartilage?
-Tensile stiffness and strength, but little resistance to compression or shear
What qualities does the presence of proteoglycans provide in articular cartilage?
- Visco-elastic properties
- Highly negative electro-static charge
- Attracted to water
- So high compressive strength
What are the physical properties of articular cartilage?
- High parallel tensile strength due to collagen
- High compressive stiffness (more in centre than outer surfaces) due to proteoglycans
What is repair capability of cartilage?
-Avascular so mechanical loading is necessary to keep cartilage healthy through influc of nutrients and efflux of waste. Remodelling response is very limited. Cannot repair to full strength following damage even if minor.
What are menisci?
-Articular cartilage in the knee that act as spacers, stabilisers and shock absorbers between the femur and the tibia
What are the pros and cons of MRI?
Pros: -3D images of all structures -GReater contrast of different soft tissues than CT scan -No ionizing radiation Cons: -Lengthy -Expensive -Can kill patients with certain contraindications
What is a ligament?
- A structure that attaches bone to bone
- Primary purpose is to stabilise the joint and restrict movement
What is a tendon?
- A structure that attaches muscles to bone
- Transfers force from muscle to skeleton to create movement
- Stores and returns elastic energy
What are ligaments/tendons made of?
- Cells: Fibroblasts
- Water (66% wet weight)
- Collagen (70-80% dry weight)
- Proteoglycans
- Elastin
What is the strength of tendons/ligaments dependent on?
- Arrangement of collagen fibres
- Cross Sectional Area
What is the formula for structural strain?
-Change in length/initial length
Where are some common areas of ligament injury?
- ACL
- MCL
- ATFL
- CFL
How does ligament healing occur?
- Inflammation
- type 3 collagen laid down in non-orderly pattern. More stiff and weak than type 2.
- Scar tissue slowly remodels to become normal
What architectural parameters make muscles different from eachother?
- Size (Mass or Anatomical CSA)
- Physiological Cross Sectional Area
- Fibre Type
- Tendon length
What variables affect Physiological cross sectional area?
- Fibre length
- Pennation angle
What does the ratio of muscle fibre length to tendon length depend upon?
- Depends on function of muscle and location in the body.
- Long fibres, short tendons create large active ROM at joints closer to the body
- Shorter fibres and longer tendons at joints further from the body to reduce extremity weight, and also better elastic recoil
What is the formula for elastic energy storage in terms of linear deformation of a spring/tendon?
1/2 Force * Linear Deformation
What is a case where tendon/ligament injury will not heal on its own?
If both ends of the structure are not apposed (full rupture or avulsion fracture)
What are the pros and cons of using ultrasound to image an injury?
Pros: -Cheap and available -Very low risk Cons: -High skill level required -Difficult to get 'general picture' of the area
When does muscle failure occur?
When sarcomeres are lengthened too much
Where does tearing typically occur in the muscle?
-At the muscle fascicle: aponeurosis junction