Musculoskeletal

Question 1

Briefly describe the pathophysiology of septic arthritis

Answer 1

caused by pyogenic bacteria.

joints normally sterile, meaning no bacteria grow there.

organisms get to the joint via the bloodstream, from an infection elsewhere, or are introduced directly via trauma.

infection of the synovial lining causes painful, red, and swollen joints.

usually one joint is affected, however, polyarthiritis is common in disseminated infection by specific bacteria.

can produce rapid destruction of joint linings and is likely to lead to permanent destruction and bony ankylosis of the joint(stiffening caused by fusion of the bones).

Question 2

Briefly describe the pathophysiology of osteomyelitis

Answer 2

inflammation/infection of bone.

2 major types are Hematogenous osteomyelitis and Secondary osteomyelitis(more common).

Hematogenous osteomyelitis.

• spread of a causative organism through the blood, localising in one bone and setting a focus of infection
• entry site of organism is often an unnoticed skin infection
• site of the osteomyelitis is usually the metaphysis of a long bone, near but not involving the epiphysis
• children most commonly affected
• if untreated infection spreads and causes necrosis of the bone
• purulent infection may produce draining sinuses, necrotic bone must be removed as antibiotics will be ineffective against bacteria that is sited within the dead bone
• symptoms are pain, with local and systemic signs of inflammation
• advanced cases include recurrence of infection, bone deformity and crippling

Secondary osteomyelitis.

• infection spreads to bone secondarily from an adjacent site of infection or open wound
• common causes:
  
  • infected operative sites
  • soft-tissue infections adjacent to bone
  • gangrene of the toes with ulceration and infection

Question 3

Describe the disease process of crush injuries

Answer 3

crush ‘syndrome’ occurs because of prolonged compressive force that impairs muscle metabolism and circulation, and follows the extrication or release of an entrapped limb/body part.

not only in trauma pt’s, also in the pt who may have been lying on a limb for an extended period(4-6 hrs of compression), eg. pt falls and unable to get up.

after a muscle is compressed for 4-6 hrs, its cells begin to died release their contents into the localised vasculature.

when the force compressing the region is released, blood flow is reestablished and the material from the muscle cells quickly returns to the systemic vasculature.

primary substances of concern are:

• lactic acid
• potassium
• myoglobin

in particular the return of myoglobin will likely result in decreased blood pH, hyperkalaemia and renal dysfunction.

ECG changes related to hyperkalaemia might be seen, such as:

• peaked T waves
• widening QRS complex
• prolongedP-R interval
• arrhythmia

Question 4

Describe the disease process of compartment syndrome

Answer 4

within a limb, groups of muscles are surrounded by an inelastic membrane called the fascia, confining them to an enclosed space, or compartment, that only allows a limited amount of swelling.

when bleeding/swelling occurs in a compartment as the result of a fracture or severe soft-tissue injury, the pressure within it rises.

if the pressure rises too high, it can impair circulation and cause pain, sensory changes, and progressive muscle death.

external factors that lead to compartment syndrome:
- bandages
- splints
- casts
applied too tightly and restricting circulation.

internal factors include:

• bleeding within a compartment because of fracture, dislocation, crush injury, vascular injury, bleeding disorder
• fluid leakage/oedema may occur, secondary to ischaemia, excessive exercise, trauma, burns
• any condition associated with the leakage of proteins and fluid from vessels into the interstitial space