Approaching An `acutely Swollen Joint`

An Acutely Swollen Joint

When facing an acute monoarthritis, the first question to ask is if this is a case of possible septic arthritis. We need to establish the clinical features of the presenting complaint such as its onset, site, timeframe, precipitating factors e.g. previous surgery or trauma, relieving or aggravating factors as well as the patients ability to bear weight and their level of pain.

We should also establish the presence of any systemic symptoms such as fever, rigors or lethargy. Clarify if there is the involvement of more than one joint and search for clues indicating enteropathic, reactive or psoriatic arthritis. Previous episodes of a similar presentation might indicate an acute exacerbation of a chronic issue, therefore it`s vital to identify the past medical history of the patient and any current medications/drug allergies

An A to E approach is the general way to assess a systemically unwell person before examination of the affected joints. Upon assessment of specific joints note any redness, swelling, skin changes and scars and always compare to the contralateral joint. Assess for evidence of focal tenderness and joint effusions as well as range of motion as part of the holistic knee examination.

Investigations include routine bloods (FBC, CRP etc) as well as ESR and serum urate. Imaging includes a plain film radiograph. Joint aspiration is an important diagnostic tool and it is important to inspect the joint fluid for opacity, colour and the presence of frank pus. The aspirate can be sent for white cell count and MCS as well as light microscopy for crystals.

Differentials include: septic arthritis, haemarthrosis, crystal arthropathy e.g. gout or rheumatological causes. Other causes include osteoarthritis, MSK injury or spondyloarthropathies.

Septic arthritis is most commonly causes by S. aureus and joint aspiration is key to diagnosis. Management includes empirical antibiotics and urgent surgical irrigation and washout.

Gout is caused by accumulation of monosodium urate crystals in a joint, caused by an underlying hyperuricaemia, and it classically affects the 1st MTP joint. Joint aspiration and microscopy show needle shaped monosodium urate crystals in the synovial fluid and X-rays show `punched out` lesions in articular bone in severe cases. Acute gout is treated with NSAIDS. Extra-articular features include gouty tophi or uric acid nephropathy, these patients can be prescribed allopurinol as prophylaxis.

Pseudogout is caused by the deposition of calcium pyrophosphate crystals within a joint, it mimics gout but affects proximal joints with the knee and wrist most commonly affected. Risk factors include advanced age, hyperparathyroidism and hypophosphatemia. Joint aspiration and microscopy will show positively birefringent rhomboid-shaped crystals, and is treated with NSAIDS.

The diagnostic criteria for Rheumatoid Arthritis is the EULAR classification, which classifies 4 categories: joint distribution, serology, symptom duration and acute phase reactants.

Spondyloarthropathies are a group of conditions comprising of: psoriatic arthritis, ankylosing spondylitis, reactive arthritis and enteropathic arthropathy. They are seronegative conditions and are associated with HLA-B27.

Haemarthrosis = bleeding into a joint cavity, the most common cause being traumatic injury but can also occur in patients with bleeding disorders e.g. haemophilia or those on anticoagulants. Management involves RICE and analgesia.

R = rest

I = ice

C = compression

E = elevation of the joint