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Year 3 > MSK > Flashcards

MSK Flashcards

1
Q

Articular cartilage (Hyaline cartilage)

of Synovial Joints

A

Change in collagen orientation from superficial to deep

Superficial/tangential layer:

  • Articular Surface
  • Flattened chondrocytes that produce collagen and glycoproteins (e.g. lubricin)

Transitional layer:

  • Bony Surface
  • Round chondrocytes that produce proteoglycans such as aggrecan

> 75% water (water = incompressible)

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2
Q

Glycoproteins

Proteoglycans

A

(e.g. lubricin): proteins to which oligosaccharide chains are attached, i.e. > protein than carb

(e.g. aggrecan): proteins that are heavily glycosylated
(= a protein core to which one or more GAGs attach),
i.e. > carb than protein

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3
Q

Glycosaminoglycans or GAGs

A

(e.g. hyaluronic acid):

long unbranched polysaccharides which are highly polar and thus attract water

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4
Q

Articular cartilage thickness

A

average: 2-3 mm
interphalangeal joint: 1 mm
patella: 5-6 mm

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5
Q

Synoviocytes

A

Type A
Look like macrophages
Remove debris
Contribute to synovial fluid production

Type B
Fibroblast like
Main producer of synovial fluid

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6
Q

Synovial fluid

A

Viscous fluid
Hyaluronic acid & lubricin
Fluid component (from blood plasma)

Small volumes (knee joint: ̴0.5 ml )
Rapid turnover (  ̴2 hours)

Nutrition of cartilage
Removal of waste products
Lubrication - less friction - less wear

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7
Q

Lubrication

A

Boundary
- Glycoproteins such as lubricin bind to receptors on articular surfaces to form a thin film

Hydrodynamic
- Surfaces kept apart by liquid pressure. Viscosity changes with load and velocity of movement

Weeping
- Fluid that is present in the cartilage is squeezed out into the synovial cavity to increase fluid volume

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8
Q

Bursae

A

Synovial membrane
Fluid-filled
Reduce friction
Bursitis

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9
Q

Ageing

A 
Viscosity of synovial fluid increases
Slower joint movements
Reduced lubrication
Water content of cartilage decreases
Reduced shock absorption

Less protection of articular surfaces
& increased risk of damage

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10
Q

Osteoarthritis

A

Bone Spar and Narrow Disc

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11
Q

Bone Infection

A

Osteomyelitis

acute
chronic

Specific - TB

non- Specific Common

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12
Q

Joint Infection

A

Septic Arthritis

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13
Q

Acute Osteomyelitis

Organisms

A

Infants <1 year:
Staph aureus, Group B streptococci, E. coli

Children:
Staph aureus, Strep pyogenes, Haemophilus influenzae

Adults: Staph aureus
Mycobacterium tuberculosis
Coagulase negative staphylococci (prostheses)
Pseudomonas aeroginosa (2ry to penetrating foot injuries, IVDAs)

Other: Diabetic foot - mixed infection
Sickle cell disease – Salmonella spp
Mycobacterium marinum (fishermen, filleters)
Candida (debilitating illness, HIV AIDS)

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14
Q

long bones with metaphysis

joints with intra-articular metaphysis

A

distal femur
proximal tibia
proximal humerus

hip
elbow (radial head)

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15
Q

Acute Osteomyelitis

Pathology

A

starts at Metaphysis

Vascular stasis
(venous congestion + arterial thrombosis)

Acute Inflammation – Increased pressure

Suppuration

Release of pressure (medulla, sub-periosteal, into joint)

Necrosis of bone (sequestrum)
New bone formation (involucrum)
Resolution - or Not (Chronic osteomyelitis)

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16
Q

Acute Osteomyelitis

Clinical Features

Infant

Child

A 
May be very ill, Failure to thrive
Possibly drowsy or irritable
Metaphyseal tenderness + swelling
Decrease ROM (Range of motion)
Positional change
Commonest around the knee

Severe pain
Reluctant to move (neighbouring joints held flexed)
Tender fever (swinging pyrexia) + tachycardia
malaise (fatigue, nausea, vomiting)
Toxaemia

17
Q

Acute Osteomyelitis

Clinical Features Adults

A

Primary OM

  • Seen commonly in thoracolumbar spine, Backache
  • history of UTI or urological procedure
  • Elderly, Diabetic, immunocompromised

Secondary OM > common
- Open fracture, surgery (esp. ORIF)

18
Q

Acute Osteomyelitis

Diagnosis

A

History and clinical examination (pulse + temp.)

FBC + diff WBC (neutrophil leucocytosis)
blood cultures x3 (at peak of temperature – 60% +ve)

ESR, CRP

U&Es – ill, dehydrated

X-ray (normal in the first 10-14 days), MRI
USS, Aspiration

Isotope Bone Scan

  • Technetium-99m labelled diphosphonate
  • Gallium 67 citrate delayed imaging
  • Indium-111 labelled WBC scan

blood cultures in haematogenous osteomyelitis and septic arthritis
bone biopsy
tissue or swabs from up to 5 sites around implant at debridement in prosthetic infections
sinus tract and superficial swab results may be misleading (skin contaminants)

19
Q

Acute Osteomyelitis

Differential Diagnosis

A

acute septic arthritis
acute inflammatory arthritis
trauma (fracture, dislocation, etc.)
transient synovitis (“irritable hip”)

rare: sickle cell crisis, rheumatic fever, haemophilia

20
Q

Acute Osteomyelitis

Differential Diagnosis

Soft tissue infection

A

Cellulitis - (deep) infection of subcutaneous tissues
(Gp A Strep)

Erysipelas - superficial infection with red, raised plaque (Gp A Strep)

Necrotising fasciitis - aggressive fascial infection
(Gp A Strep, Clostridia)

Gas gangrene - grossly contaminated trauma (Clostridium perfringens)

Toxic shock syndrome - secondary wound colonisation (Staph aureus)

21
Q

Acute OM Radiographs

A

early radiographs minimal changes
10-20 days early periosteal changes

medullary changes - lytic areas

late osteonecrosis - sequestrum
late periosteal new bone - involucrum

22
Q

Acute Osteomyelitis

Treatment

A

supportive treatment for pain and dehydration – general care, analgesia
rest & splintage
antibiotics
route (IV/oral switch – 7-10 days?)
duration (4-6 wks – depends on response, ESR)
choice - empirical (Fluclox + BenzylPen) while waiting

23
Q

Antibiotic ‘failure’

A 
drug resistance – e.g. lactamases, MRSA
bacterial persistence - ‘dormant’ bacteria in dead bone
poor host defences - IDDM, alcoholism…
poor drug absorption
drug inactivation by host flora
poor tissue penetration
24
Q

Surgery OM

A

indications
aspiration of pus for diagnosis & culture
abscess drainage (multiple drill-holes, primary closure to avoid sinus)
debridement of dead/infected /contaminated tissue
refractory to non-operative Rx >24..48 hrs
timing, drainage, lavage
infected joint replacements - one stage revision/ two stage revision/ antibiotics only?

CX: septicemia, death
metastatic infection
pathological fracture
septic arthritis
altered bone growth
chronic osteomyelitis
25
Q

Chronic Osteomyelitis

Organism

A

Staph. Aureus,
E. Coli,
Strep. pyogenes,
Proteus

26
Q

Chronic Osteomyelitis

Pathology

A

Cavities
Dead bone (retained sequestra)
involucrum
histological picture is one of chronic inflammation

27
Q

Chronic Osteomyelitis

Complications

A

Chronically discharging sinus + flare-ups
ongoing (metastatic) infection (abscesses)
pathological fracture
growth disturbance + deformities
squamous cell carcinoma (0.07%)

28
Q

Chronic Osteomyelitis

Treatment

A

long-term antibiotics?
local (gentamicin cement/beads, collatamp)
systemic (orally/ IV/ home AB)
eradicate bone infection- surgically (multiple operations)
treat soft tissue problems
deformity correction?
massive reconstruction?
amputation? (how many operations/ years later?)

29
Q

Acute Septic Arthritis

Route of infection

A

metaphyseal septic focus

→ either septic arthritis

→ or osteomyelitis

30
Q

Strep Pyogenes

A 
Common:
Staphylococus aureus
Haemophilus influenzae
Streptococcus  pyogenes
E. coli

Year 3 (7 decks)

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