1. Approach to Acute Monoarthritis of the Knee
Henry Averns
Assistant Professor Rheumatology Division
Queens University

2. Aims of Workshop
To consider the differential diagnosis of acute and chronic knee monoarthritis
I.e. provide a systematic approach to the investigation and differential diagnosis of patients presenting with monoarticular pain.
To briefly review examination of the knee
To discuss indications for aspiration and injection of the knee
To practice knee injection on model knees

3. APPROACH TO MONOARTHRITIS OF THE KNEE
POLYARTHRITIS
Acute or Chronic?
Is it inflammatory?
Extra- articular features?
Systemic or local problem?
ARTICULAR
EXTRA-ARTICULAR

4. History I Age, time profile Features of inflammation Preceding illness
stiffness, redness, pain, swelling, warmth
Preceding illness
GU or GI infection
history of trauma, portal of entry for infection
Associated symptoms
red eye, rash, balanitis

5. History 2 Associated medical complaints Drug history Family history
psoriasis, IBD, Ankylosing spondylitis
bleeding disorders
predisposition to infection
Drug history
immunosuppressants, aspirin, diuretics
Family history
of gout, psoriasis, IBD, AS

8. Differential diagnosis I
Acute monoarthritis
Septic arthritis (staph aureus)
Reactive arthritis
GI infection - campylobacter, salmonella, shigella, yersinia
GU infection - chlamydia
Crystal arthritis
Gout (uric acid)
Pseudogout/chondrocalcinosis/calcium pyrophosphate deposition disease (CPPD)
Haemarthrosis

9. Septic Arthritis Risk factors prosthetic hip or knee joint,
skin infection,
joint surgery,
rheumatoid arthritis,
age greater than 80 years,
diabetes mellitus.
Intravenous drug use and large-vein catheterization are predisposing factors for sepsis in unusual joints (e.g., sternoclavicular joint).

10. Common Errors in Diagnosing Acute Monoarthritis
The problem is in the joint, because the patient complains of "joint pain."
The soft tissues around the joint can be the source of the pain (e.g., prepatellar bursitis of the knee).
Crystal-proven diagnosis of gout or pseudogout rules out infection.
Crystals can be present in a septic joint.
The presence of fever is useful in distinguishing infectious causes from other causes.
Fever may be absent in patients with infectious monoarthritis but can be a presenting feature in acute attacks of gout or pseudogout.
A normal serum uric acid level makes gout a less likely diagnosis.
Serum uric acid levels often are lowered in patients with acute gout (30%). There may be unrelated hyperuricemia in patients with other conditions.
Gram staining and culture of synovial fluid are sufficient to exclude infection.
Culture results may be negative in early infection

11. Examination of the Knee
Demonstration
Module

12. ARTHROCENTESIS / INJECTION
Indications
Diagnostic
Synovial fluid analysis
Therapeutic
Inflammatory arthritis
Gout
Osteoarthritis

13. ARTHROCENTESIS
The things you need;

15. ARTHROCENTESIS Contraindications No touch technique adequate
Infection locally OR elsewhere
Abnormal skin (relative CI)
Warfarin therapy is not a contraindication
No touch technique adequate
Local anaesthesia difficult to achieve…is it worth it? Probably not
Have appropriate tubes ready

17. Fig. 81. 21 An infected RA joint
Fig An infected RA joint. A high degree of clinical suspicion of infection in patients with RA is essential. Pus may be present as in this case.

24. Additional slides for reference

25. Extra-articular features which suggest seronegative spondyloarthritis
nails (pitting, ridging, hyperkeratosis)
enthesitis, dactylitis and tenosynovitis
nodules (elbows/ears)
skin (local infection, psoriasis, keratoderma blenorrhagicum, balanitis)
eyes (conjunctivitis, uveitis)
mouth ulcers

26. Investigations I Haematology - CBC, ESR, clotting
Biochemistry - U&E, LFTs, urate, CRP
Immunology
Microbiology
blood/urine/stool/urethral/sputum cultures
serology

27. Investigations II Synovial fluid Imaging volume/viscosity/cellularity
polarised light microscopy (crystals)
gram stain/culture
Imaging
plain films
loss of joint space, osteophytes, subchondral cysts, osteosclerosis, erosions, chondrocalcinosis
MRI, bone scan

28. Septic Arthritis Staph aureus—most common Strep (splenic dysfunction)
Neisseria gonorrhea (young, sexually active)
Gram negatives (immunocompromised, GI infection)
Mycobacteria (immunocompromised)
Fungus (immunocompromised)
Lyme disease

29. Acute septic arthritis
Prosthetic joint infection
Acute osteomyelitis
Chronic osteomyelitis
Staph aureus
+++
Coag neg staph +
Haemolytic strep ++
Skin anaerobes
Gram negative cocci
H influenzae
Ps aeruginosa
Salmonella
Intestinal anaerobes
Mycobacteria