Approach to Acute Monoarthritis of the Knee

Henry AvernsAssistant Professor Rheumatology Division

Queens University

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

MONOARTHRITIS POLYARTHRITIS

ARTICULAR EXTRA-ARTICULAR

APPROACH TO MONOARTHRITIS OF THE KNEE

Acute or Chronic?

Is it inflammatory?

Extra- articular features?

Systemic or local problem?

History I

• Age, time profile• Features of inflammation

– 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

History 2

• Associated medical complaints– psoriasis, IBD, Ankylosing spondylitis– bleeding disorders– predisposition to infection

• Drug history– immunosuppressants, aspirin, diuretics

• Family history– of gout, psoriasis, IBD, AS

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

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).

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

Examination of the Knee

• Demonstration• Module

ARTHROCENTESIS / INJECTION

• Indications– Diagnostic

• Synovial fluid analysis

– Therapeutic• Inflammatory arthritis• Gout• Osteoarthritis

ARTHROCENTESIS

The things you need;

ARTHROCENTESIS

• Contraindications– 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

Additional slides for reference

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

Investigations I

• Haematology - CBC, ESR, clotting• Biochemistry - U&E, LFTs, urate, CRP• Immunology• Microbiology

– blood/urine/stool/urethral/sputum cultures– serology

Investigations II

• Synovial fluid– 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

Septic Arthritis

1. Staph aureus—most common2. Strep (splenic dysfunction)3. Neisseria gonorrhea (young, sexually active)4. Gram negatives (immunocompromised, GI

infection)5. Mycobacteria (immunocompromised)6. Fungus (immunocompromised)7. Lyme disease

Acute septic Acute septic arthritisarthritis

Prosthetic joint Prosthetic joint infectioninfection

Acute Acute osteomyelitisosteomyelitis

Chronic Chronic osteomyelitisosteomyelitis

Staph aureusStaph aureus ++++++ ++++++ ++++++ ++++++

Coag neg staphCoag neg staph ++++++ ++

Haemolytic Haemolytic strepstrep

++++ ++++ ++++

Skin anaerobesSkin anaerobes ++ ++++++ ++ ++

Gram negative Gram negative coccicocci

++ ++

H influenzaeH influenzae ++ ++++ ++ ++

Ps aeruginosaPs aeruginosa ++ ++ ++ ++

SalmonellaSalmonella ++ ++ ++ ++

Intestinal Intestinal anaerobesanaerobes

++ ++

MycobacteriaMycobacteria ++ ++ ++