Infections: Causative Agents - Orthopedics

Infections are an essential topic for the NEET PG exam since it is the major cause of morbidity and mortality in patients and understanding their pathogenesis, diagnosis, and management is crucial for a medical practitioner.

Questions on infections are common in the NEET PG exam and are used to assess the candidate's knowledge of medical microbiology and infectious diseases.

Also, infections are a topic of relevance to multiple specialties such as medicine, surgery, pediatrics, obstetrics and gynecology, and dermatology.

Overall, infections are an integral part of medical education and are an important topic for NEET PG. So, in this blog we have covered the topic in brief.

CAUSATIVE AGENTS

MC – Staphylococcus aureus – involves metaphysis

Exceptions 

• Sickle cell anaemia – Salmonella – Diaphyseal
• IV drug abuser – Pseudomonas
• Foot puncture wound – Pseudomonas
• Open injuries – Staphylococcus
• Human bites – Eikenella
• Animal bites – Pasteurella

Important Information Salmonella can cause multifocal osteomyelitis and involve different areas of the body in sickle cell anaemia patients

MC LOCATIONS – OSTEOMYELITIS

• Lower end of femur
• For Adults – Spine (vertebral body)
• For Joint – Knee (most common)

DEFORMITIES AT HIP

Important Information  Positions that a joint can attain in lower limbs - Faber - Position where hip has more capacity Fadir - Opposite of it

FABER – Flexion, Abduction, External rotation

Causes

• Synovitis (idiopathic, transient, tubercular)
• Infection - Septic arthritis - misnomer, pus in the joint (pyogenic)
• Iliotibial band contracture (polio)
• Anterior dislocation

FADIR - Flexion, Abduction, Internal rotation

Causes

• Posterior dislocation
• Arthritis

Important Information Dislocation of Hip - Posterior dislocation > Anterior dislocation

TOM SMITH ARTHRITIS – HYPERMOBILE HIP

• Joint is totally destroyed
• Initially movements are absent
• Later, head/capital epiphysis of femur is destroyed → Hypermobility and Instability of joint
• Usually movements are absent in infection of limb or joint 
• Tom Smith Arthritis is an exception 

BRODIE'S ABSCESS

• Subacute osteomyelitis > Chronic osteomyelitis
• Upper end femur 
• Sclerotic margin (means good immunity - so not seen in HIV +ve)

CHRONIC OSTEOMYELITIS

• Sequestrum – dead bone (cause of sinus)
• Involucrum – reactive bone (surrounding sequestrum)
• Cloacae – sinuses through involucrum
• Complications – Amyloidosis, malignancy
• MRI – RIM sign

• Paprika sign - While removing the dead bone, there is presence of bleeding from the live bone underneath the dead bone known as paprika sign   

• The instruments Shown here are Bone Nibbler, Bone cutter.

VACUUM ASSISTED CLOSURE/NEGATIVE PRESSURE WOUND THERAPY

• Vacuum dressing: enhances healing of wound by removal of fluid collecting within it
• Suction pressure: -75 to -125 mmHg
• Continuous or intermittent
• Gives good granulation tissue
• C/I: Malignancy, untreated osteomyelitis, necrotic eschar

SAPHO SYNDROME (MULTIFOCAL OSTEOMYELITIS) 

• Autoimmune disease 
• It has ankylosing spondylitis 
• HLA B27 +ve

Clinical Features

• S - Synovitis
• A- Acne
• P - Pustulosis
• H - Hyperostosis (Thickened bone)
• O- Osteitis (Inflamed bone)
• Mnemonic: SAPHO

Important Information MC organism for multifocal OM SAPHO > Sickle cell anaemia (Salmonella)

Treatment

• NSAIDs/Steroids/DMARDs (Disease – modifying antirheumatic drugs)

INFECTIONS OF THE FINGERS

Paronychia

• Infection of nail bed
• MC infection of hand

Felon

• Infection of pulp space of finger

PURULENT TENOSYNOVITIS: KANAVEL SIGN

4 Cardinal Signs of Kanavel

• Pain on extension (stretch)
• Fusiform swelling 
• Flexion of finger
• Tenderness along tendon sheath → Most specific (Percussion tenderness)

Important Information Infection of the thumb can involve the little finger because of connecting bursa.Index, middle & ring fingers have separate sheaths.Therefore, infection of the little finger can involve thumb but not index finger.

MYCETOMA

Eumycetoma	Actinomycetoma
Fungal cause	Bacterial cause
Multiple draining sinus over foot	Multiple draining sinus over mandible

• Above waist - Bacterial cause
• Below waist - Fungal cause
• MRI
• Dot in circle sign

Painless conditions

• Mycetoma
• Charcot's joint

PRACTICE QUESTIONS

Q True/False in view of septic arthritis?

1. Widening of joint space is there
2. Staph aureus is the most common organism in young children & neonates
3. I/D done after culture & aspirate & antibiotics for 24 hrs
4. Kocher’s criteria is used to differentiate from transient synovitis
5. Position of hip is FADIR

Ans - F, T, F, T, F

KOCHER’S CRITERIA

• Patient is not able to bear weight
• ESR ≥40 mm/hr
• Fever > 38.5°C
• WBC > 12,000 cells/µl

Important Information From 3% for one positive to more than 90% for four positive is the sensitivity of Kocher’s criteria

Important Information  In case of any bone in the body king of orthopedics is Staphylococcus aureus

Previous Year Question

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