Hot Swollen Joints

The presentation of one or more hot swollen joints raises a number of diagnostic possibilities, but septic arthritis should always be suspected. This is the most important diagnosis to exclude, as if left untreated the sequelae include permanent joint damage in up to a third of patients, impairment of function and death in up to 11% of patients.¹ The latter especially occurs in the elderly and very young.

• The annual incidence of septic arthritis in the UK is 2 to 10 per 100,000 people.²
• The incidence is higher in patients with prosthetic joints and in rheumatoid arthritis.
• Gout presents far more commonly affecting 1% of the UK population and in men has an incidence of 1-3 per 1000.^3,4

Risk factors

The following have been identified as risk factors for septic arthritis:⁵

• Diabetes
• Old age
• Malignancy
• Rheumatoid arthritis
• Prosthetic joint
• Recent intra-articular steroid injection
• Alcoholism
• Intravenous drug use

Symptoms

Typically a patient with septic arthritis will present with a single hot and extremely painful joint and a reluctance to move and put weight on that joint.
This scenario can occur with other pathologies and diagnosis may be particularly difficult in patients with pre-existing inflammatory arthritis. Consider septic arthritis in any patient with inflammatory arthritis who presents with a joint flare, particularly if one joint has flared more often than others.

It is important to ascertain the following:

• Was the onset of joint swelling sudden or gradual? Septic arthritis and crystal induced arthropathies tend to present acutely as opposed to rheumatoid arthritis or osteoarthritis which have a more insidious onset. Sudden onset swelling or excessive swelling of one joint compared to others in patients with inflammatory arthritis should raise the possibility of septic arthritis.
• How many joints are involved? Gout and septic arthritis generally present as a monoarthritis (although more than one joint can be involved) whereas reactive arthritis and rheumatoid arthritis tend to affect several joints.
• Which joints are affected?
  • Although any joint can be affected the most usual sites for septic arthritis are the knee in adults and the hip in children.
  • In gout up to 70% of attacks first occur in the big toe but it can also occur elsewhere in the foot as well as the ankle, knee, wrist elbow and small joints of the hands.⁴ Atypical presentations of gout are more common in patients aged over 60 years.³
• Are there any constitutional symptoms?
  • A patient with septic arthritis may have general malaise and a history of fever and rigors but bear in mind that systemic symptoms occur in less than half of adults with confirmed septic arthritis.⁵ The development of constitutional symptoms may be a helpful pointer to the onset of sepsis in patients with inflammatory arthritis.
  • A history of a gastrointestinal or genitourinary infection raises the possibility of reactive arthritis (Reiters syndrome).
  • Lyme disease, which is associated with a typical rash (erythema migrans) is often accompanied by general symptoms of fever, malaise, arthralgia, myalgia and headache and is worth considering if the patient has had a potential exposure to Deer ticks in an endemic area.
• Is there any history of trauma?
  • Haemarthrosis usually develops rapidly after an episode of trauma and results in a swollen painful joint.
  • Make note of a history of a recent animal or human bite over the affected joint as a puncture wound can be source of septic arthritis.
• Loss of function. Sudden loss of function in patients with inflammatory arthritis can indicate sepsis.

Signs

• Consider the general appearance of the patient and note any pyrexia.
• Inspect the joints for swelling, redness and any deformity.
• Redness is relatively uncommon and if present should raise suspicions of septic arthritis or gout. If sudden redness develops in patients with inflammatory arthritis, sepsis should be excluded.
• Warmth is best elicited using the back of the fingers and suggests the presence of an inflammatory process but beware of a recently removed bandage or application of a hot compress.
• Swelling is an important sign of active current inflammation. It may be due to an effusion in the joint or oedema of surrounding tissues For detail on examining for a knee effusion see knee examination. Swelling over a bursa or tendon indicates inflammation of that structure and bony swelling would be in keeping with osteoarthritis.
• Tenderness should be elicited by gentle palpation over the affected joint. Point tenderness may be the result of inflammation in a periarticular soft tissue and suggests bursitis or muscle injury.
• Passive and active range of movement is usually significantly diminished in septic arthritis.
• Also look out for any associated signs of joint disease such as rheumatoid nodules or gouty tophi.

Includes the following:

• Infection - e.g. Staphyloccoccus aureus
• Septic arthritis
• Neisseria gonorrhoea
• Lyme disease
• Crystal arthropathies - gout and pseudogout
• Reactive arthritis (now considered synonymous with Reiters syndrome)
• Traumatic
• Palindromic rheumatism
• Psoriatic arthropathy

Joint aspiration

• If septic arthritis is suspected the affected joint should be aspirated by an experienced clinician using an aseptic technique. Warfarin therapy is not contraindicated in this procedure.
• The synovial fluid is often turbid and purulent, but the absence of pus does not exclude infection.
• Fluid should be sent for Gram staining and culture and also for examination of crystals to excluded acute gout or pseudogout.¹ The absence of organisms on Gram staining does not exclude infection.
• Synovial fluid white cell count and percentage of polymorphonuclear cells may be helpful in patients with monoarticular inflammation and may indicate the need for the treatment of septic arthritis before Gram staining and culture results are available.¹⁰
• If the patient has classic signs and symptoms of gout, the condition should be treated on clinical grounds. The only joint that can realistically be aspirated in primary care is the knee. If other joints require aspiration, the patient should normally be referred to a specialist.⁴

Laboratory tests

• Full blood count - a raised white cell count would be in keeping with an infective process, but can also occur in the crystal arthropathies. It is not always a reliable sign of septic arthritis, particularly in children.¹¹
• Inflammatory markers - erythrocyte sedimentation rate (ESR) and C reactive protein (CRP) are generally higher in septic arthritis than in gout, but this cannot be relied upon for diagnostic purposes. They are useful markers of response to treatment.
• Electrolytes and liver function - these should be measured, as any end-organ damage may affect antibiotic choice.
• Urate - this is not a specific test as hyperuricaemia frequently occurs in patients without gout. Also uric acid levels can actually fall to within the normal range during an acute attack of gout and so should not be used as diagnostic test in the acute setting. Urate levels can be useful for monitoring medication such as allopurinol in between attacks of gout.
• Rheumatoid factor - this should only be requested if there are strong clinical suspicions of a systemic rheumatic disease. It would be of little value in investigating a single hot swollen joint but may be appropriate in the context of a polyarthritis.
• Antinuclear antibodies (ANA) - similarly these should not be requested routinely for patients presenting with swollen joints but reserved for cases of suspected connective tissue disease. ANA titres tend to be positive in most lupus patients and can also be raised in rheumatoid arthritis.
• Blood cultures - these should be taken in suspected cases of septic arthritis. This would normally be done in secondary care when the patient is referred.

Imaging

• X-rays - a plain film should be done if there is a history of trauma. In septic arthritis the diagnostic value of x-rays is debatable but they may show evidence of pre-existing joint disease. In gout radiographs are often normal in the acute setting apart from soft tissue swelling but subsequently erosive changes and tophi may be seen.
• Ultrasound - this can be helpful in deep joints such as the hip when an effusion and joint capsule thickening may be seen in septic arthritis
• Computerised Tomography (CT) and Magnetic resonance imaging (MRI) - these may be used in secondary care with the former sometimes being employed to assist with difficult joint aspirations.

• The management clearly depends on diagnostic findings, but it is recommended that any patient with suspected septic arthritis (short history of hot, swollen, tender joint(s) with restriction of movement) should be referred as an emergency to an orthopaedic surgeon or rheumatologist for joint aspiration and synovial fluid analysis.¹ Pus should be removed by either arthroscopy or needle aspiration.
• If clinical suspicion is high it is imperative to start treatment, even in the absence of fever. There is no evidence on which to base antibiotic regime, but intravenous therapy is usually given for up to 2 weeks, depending upon response to treatment. Oral therapy is continued for up to 4 weeks thereafter. Antibiotic choice is guided by local policy and knowledge of sensitivities, and there is considerable discussion in the literature about the best antibiotics to use.¹² If there are no risk factors for atypical organisms (e.g. known MRSA carrier, ex -nursing home, intravenous (IV) drug abuse etc) flucloxacillin 2g qds IV is the initial choice. Clindamycin 450-600 mg qds IV if penicillin allergic.
• Suspected infection of a prosthetic joint should always be referred to an orthopaedic surgeon.
• Similarly if there is an acute injury and evidence of haemarthrosis the patient should be referred as there may be significant joint damage.