Mechanisms of Injury Flashcards
How are injuries classified?
Cause-based or tissue-based
What are the cause-based classifications of injuries?
1) Primary
- Direct/extrinsic
- Indirect/intrinsic
- Overuse
2) Secondary (re-injury)
- Short term
- Long term
What is the cause of a primary direct/extrinsic injury?
External causes, such as a collision with another athlete or piece of equipment
What can primary direct/extrinsic injuries result in?
Fractures, joint dislocation, ligament/muscle injury and skin abrasions
What is a primary indirect/intrinsic injury?
An injury caused by the athlete to themselves, e.g. inadequate warm-up
What is a primary overuse injury?
When apposing structures are in constant contact resulting in frictional wear between the structures e.g. bursitis
What are secondary short term and long term injuries?
Short term: Injury following previous mismanagement
Long term: Injury that leads to degenerative problems e.g. osteoarthritis
What are the tissue-based classifications of injuries?
Soft tissue, hard tissue, special tissue/organ
What is classified as soft tissue?
- Skin
- Musculotendon unit/tenoperiosteal
- Muscle compartments
- Joints (ligaments/tendons)
- Intervertebral discs
What is classified as hard tissue?
- Bone
- Cartilage (hyaline, articulate, epiphyseal)
What is classified as special tissue/organs?
- Brain/nerves
- Eyes/nose/sinus/larynx/teeth
- Thoracic/abdominal/pelvic organs
Describe the characteristics of collagen
- Most abundant protein in the body
- Linear, stable, water insoluble
- Cross-linked fibres
- Withstands high longitudinal stress
What are the 6 forms of collagen based on?
Molecular chain structure, location and function
Where is type 1 and 2 collagen located?
Type 1: Synovium, bone, tendon, skin and eyes
Type 2: Cartilage, eyes
What is the relationship between the collagen type number and the fibre diameter?
As the collagen type number increases, the fibre diameter decreases (e.g. type 1 is the largest)
What type of collagen is used for repair injuries?
Type 3
What are the three phases of general pathology repair?
- Acute inflammation response
- Matrix and cellular proliferation
- Remodelling and maturation
When does the acute inflammation response phase occur and how long does it last?
0-72 hours post injury, can last up to 6 days
How is acute inflammation treated?
RICER
What are the steps of the acute inflammation response phase?
1) Damaged tissues release histamines, increases blood flow to the area
2) Histamines cause capillaries to leak, releasing phagocytes and clotting factors into the area
3) Phagocytes engulf the bacteria, dead cells and cellular debris (phagocytosis)
4) Platelets move out of the capillary to seal the wounded area
What is the effect of aspirin on the healing process?
It delays the healing process
What are the steps of phagocytosis?
1) Microbe adheres to phagocyte
2) Phagocyte forms pseudopods
3) Phagocytic vesicle containing antigen fuses with a lysosome (phagolysosome)
4) Microbe in fused vesicle is killed and digested by lysosomal enzymes
5) Indigestible and residual material is removed by exocytosis
What are the functions of inflammation?
- Destroys injurious agents
- Dilutes toxic chemicals
- Cleans up necrotic waste
- Paves the way for repair
What are the steps of the matrix and cellular proliferation phase?
- Proliferation of capillaries and fibroblasts
- Collagen/proteoglycan matrix production
- Formation of granulation tissue
- Capillary network budding
- Fibroblasts produce type 3 collagen
- Contraction of wound
What is the role of fibronectin in the matrix and cellular proliferation phase?
Acts as an anchoring compound
When does the matrix and cellular proliferation phase occur?
72hrs - 6 weeks + post-injury
When does the remodelling and maturation phase occur?
6 weeks - months post-injury
What does the length of the remodelling and maturation phase depend on?
Person’s conditioning, rehabilitation completed and the tissue damaged
What are the steps of the remodelling and maturation phase?
- Contraction continues
- Reorientation of collagen fibrils (becomes much more organised)
- Collagen matures
- Cell numbers decrease
What is the effect of a musculotendinous injury?
Increased stiffness of terminal sarcomeres and membrane infolding is no longer reproduced
How long should a musculoteninous injury be immobilised for and why?
1-5 days. Immobilisation in a shortened position for more than 7 days causes stiffness from intramuscular collagen and loss of sarcomeres
What are the guidelines for mobilisation?
- Don’t mobilise until the repair tissue is sting enough (gradual process)
- Light stretching helps elongate new sarcomeres
- Should involve stretching for 30 minutes daily (passive then active)
Where is microfatigue most common?
In heavily repetitive loading areas
What is the cause of spontaneous tendon rupture and who is most at risk?
The degenerative pathology of collagen fibrils, older people
What is the mature composition of ligaments and tendons?
- Large diameter type 1 collagen fibrils, tightly packed
- Small amounts of type 3 collagen
- Elastic fibres
- Proteoglycan gel (fluid matrix)
What are the three regions of a strain curve and what does it represent?
Toe, linear and rupture. Represents the relationship between injury and load deformation
Describe the toe region of the strain curve
Collagen crimp is flattened by 3-4%, but no damage occurs due to elastic properties
Describe the linear region of the strain curve
Partial rupture of cross links, 5-10% strain of initial length
What are the two grades of the linear region of the strain curve?
Grade 1 = 0-50% fibre disruption
Grade 2 = 50-80% fibre disruption
Describe the term ‘fibre disruption’
When the yield point is reached and deformation of fibres continues after the load has been removed (i.e. permanent changes)
Describe the rupture region of the strain curve
10-20% strain of initial length, results in Grade 3 injury (>80% fibre disruption)
What are the indicators of each grade of ligament/tendon injury?
Grade 1: Little bit of pain
Grade 2: Asking for ice/strapping
Grade 3: Past strapping, requiring rest/rehab/surgery
What are the three phases of repair for ligaments and tendons?
- Acute inflammation (0-72 hours)
- Proliferation (4-6 weeks)
- Remodelling and maturation (6 weeks - 12 months)
What occurs during the acute inflammation phase of ligament and tendon repair?
- Injury gap is filled with erythrocytes and leucocytes (swelling)
- Monocytes and macrophages predominate for phagocyctosis
- Fibroblasts commence deposition of type 3 collagen
What occurs during the proliferation phase of ligament and tendon repair?
- Fibroblasts predominate
- Increased H2O content (replacing proteoglycan gel)
- Increased collagen, peaks during weeks 3-6
What is the result of increased scar collagen in ligament and tendon repair?
Increased tensile strength of ligament matrix
What occurs during the remodelling and maturation phase of ligament and tendon repair?
- Decrease in fibroblasts
- H2O returns to normal
- Scar matrix continues to mature slowly
What is intrinsic muscle injury usually attributed to?
Inadequate muscle length/strength and proprioception and muscle fatigue
Where do the majority of muscle injuries occur and why?
Lower limb two-joint muscles, i.e. quads, hamstrings, calves. Due to complex reflexes (co-contraction and co-relaxation)
When does muscle sarcomere disruption at the Z lines occur?
When continually using eccentric exercise
What are muscle contusions?
Common extrinsic injuries that follow the 3 phases of tissue repair
Why is immobilisation of muscle injuries important?
Allows granulation tissue to form with enough tensile strength to survive early muscle contraction
Why is mobilisation of muscle injuries important?
Required for muscle fibres to gain tensile strength and orientate through the reabsorbing connective scar tissue
What are some of the causes of stress fractures?
Overtraining, not enough rehab, overloading, change in environment
What are some of the symptoms of stress fractures?
Point tenderness, swelling, pain, visible deformity
What are avulsion fractures associated with?
Loading tendons/ligaments
What are the two types of acute fractures?
Open: Tissue damage, bone may penetrate through skin
Closed: No displacement of bones (still aligned)
How long should fractures be immobilised in children and adults?
Children: 4-6 weeks
Adults: 6-8 weeks
What are the four steps of bone repair?
1) Hematoma formation (bleeding)
2) Fibrocartilaginous callus formation
3) Bony callus formation
4) Bone remodelling
What are the three types of cartilage injury?
1) Superficial lacerative injury
2) Defect down to subchondral bone
3) Blunt trauma
Describe super lacerative cartilage injuries
- Laceration down to calcified zone (bone level)
- No acute inflammation (due to no blood supply)
- Lesions unchanged over years/further damage
- No osteoarthritis (as not at bone level)
Describe cartilage injuries that reach the subchondral bone
- Inflammatory reaction (blood supply)
- New subchondral bone plate forms
- Defect fills with type 1 & 3 collagen & new type of proteoglycan
- New matrix is not as strong
Describe blunt trauma cartilage injuries
- Trauma below fracture level
- Can cause chondrocyte changes, which alter matrix
- Can lead to chondromalacia (e.g. runners knee)
