Osteomyelitis

OSTEOMYELITIS

Stem:  A pt. who had leg operation with an implant for 3 years, got infected.

Q. How will you classify Osteomyelitis?
          Duration & pathological feature:
           
1. Acute
           2. Chronic

Cierny–Mader classification:
  Anatomic type:
          Type I
.  Medullary
          Type II. Superficial
          Type III. Localized
          Type IV. Diffuse
 Physiological Class
   Host Type:
           A   
Normal -Good immune system & delivery.
           B   
Compromised-Compromised locally (BL) or systemically (BS).
           C   
Treatment is worse than disease-Requires suppressive or no treatment; Minimal disability; Not a surgical candidate

Q. What are the Mode of Infection?

  • Haematogenous (Endogenous):
    • From blood borne infection like sepsis
    • Immature immune system (paediatrics group)
    • Immunocompromised (Pt. on dialysis, elderly pt., post-transplant pt.)
    • IVDA
  • Exogenous:
    • Penetrating trauma: Open Fracture
    • Peri-apical Periodontitis


Q. What is Pus?
         
Thick, yellowish fluid formed as a response to acute infection composed of dead/dying neutrophil, tissue debris & microorganisms.
Q. What is the Pathogenesis of pus formation?
         
Microbial invasion → Fluid exudation, Vascular congestion → PMN infiltration → Pus formation


Q. What is the Fate of Abscess?

  1. Resolution
  2. Rupture
  3. Spread of infection → Sepsis
  4. Chronic abscess formation


Q. Why pus may burst through?

  • Due to increased intraosseous pressure secondary to increased osmolarity due to tissue-breakdown.
  • Due to formation of a large rounded cloacal opening in the involucrum.


Q. Type of Protein deposition in Chronic Osteomyelitis?
         
Amyloid AA.

Q. D/D of swollen knee?

  • OA (overuse syndrome),
  • Septic Arthritis,
  • Reactive arthritis,
  • Gout or Pseudo-gout,
  • Haemarthrosis,
  • Trauma,
  • Tumour.

Type of Crystal in Gouty arthritis:

CharacteristicGoutPseudogout
Crystal depositionMonosodium urate(MSU)Calcium pyrophosphate
Crystal shapeNeedle-shapedRhomboid shaped
BirefringentNegativePositive
Most common site1st MTP jointKnee
RadiographyRat-bite” erosionWhite lines of chondrocalcinosis
1st line treatmentNSAIDsNSAIDs
Type of Crystal in Gouty Arthritis

Q. Common organisms?

  • Gram +ve:
    • Staph. Aureus (M/C)
    • Coagulase-negative staphylococci- Staph. Epidermidis (prosthetics/ implants),
    • Streptococcus,
  • Gram -ve:
    • Enterobacters-
      • E. coli (extremes of ages)
      • Salmonella (Sickle cell ds)
      • Klebsiella,
    • Nisseria,
    • Pseudomonas,
    • Hemophilus
  • Anaerobes
  • Fungal (immunocompromised pt.)
  • Mycobacterium &
  • Mixed.

Q. Pathogenesis of OM?

  • 1. Inflammation & suppuration:
    Microbial invasion
    → trigger acute inflammation
    1. Vascular congestion
    1. Fluid exudation
    1. PMN leukocyte infiltration

Increased intraosseous pressure
→intense pain & obstruction of blood flow

  • 2. Suppuration (2nd day): pus in the medulla spread along the Volkman’s canal; elevation of periosteum→sub-periosteal abscess→ spread of pus along shaft;(spread of pus- back into bone, into the joint or into the soft tissues)
  • 3. Necrosis (Sequestration): (at 1 week):
    increased intraosseous pressure, vascular stasis, infective thrombosis, periosteal stripping; all together comprise the blood supply of bone→ bone death→ Sequestrum formation.
  • 4. New bone (Involucrum) formation (10 days- 2 week): New bone formation from deep layer of stripped periosteum→ thickens to form involucrum (encloses infected tissue & sequestrum).
  • 5. Resolution:
    Infection controlled, intraosseous pressure released→ healing of bone,
  • Chronic Osteomyelitis:
    Persistence of Infection→ pus discharge through perforation of involucrum→ track by sinus formation to skin surface: established as Chronic OM.

Q: Why the fixing plate/implant should be removed?
  As It has become a septic focus due to formation of biofilm over it.


Q: Why SCC developed in the sinus?
 
 Due to chronic irritation.
Q. Single bedside test to do for swollen knee?
 
Aspiration of the knee.

Q. What tests should be done on the aspirate?
Culture & sensitivity
-Cytology
-Chemical/Biochemistry analysis.

 
Q. Type of crystals in Gouty arthritis?
MSU (monosodium urate crystal).

Q. In chronic osteomyelitis, what is the sequence of events by which the draining sinus can develop SCC?
Chronic irritation→ Hyperplasia→ Dysplasia→ Carcinoma.


Q. What is sequestrum?
 A piece of dead bone that has become separated during the process of necrosis from normal or sound bone. It is a complication (sequela) of osteomyelitis.


Q. What is Involcrum?
A reactive woven or lamellar bone depositions forming a shell of living tissue around a sequestrum.

Q. Treatment of OM?

  • Antibiotic therapy: After taking Blood cultures, high-dose intravenous antibiotics, active against Staphylococcus aureus, Streptococci & Gram-negative rods such as Escherichia coli are
    given.
    Cephalosporins, co-amoxiclav or a combination of Flucloxacillin & Gentamicin may be used.
  • Supportive treatment: for pain & dehydration.
  • Splintage of the limb.
  • Surgical drainage: if there is no response to antibiotics for 2 days.

Also see Chronic Osteomyelitis