Approach to Acute Monoarthritis of the Knee Henry Averns Assistant 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

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

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

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

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 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

Fig. 81. 21 An infected RA joint Fig. 81.21 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.

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 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

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

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