Table 1

Recommendations for the diagnosis and initial management of patients presenting with an acute or recent onset swelling of the knee

RecognitionA patient presenting with acute swelling of the knee should undergo thorough clinical examination in order to confirm swelling.
ReferralPatients with a suspicion of septic arthritis or trauma with an onset of swelling within 12 h, should be referred immediately to a doctor experienced in musculoskeletal diseases.Bone tumours are rare but patients with a suspicion of bone tumour should be referred to an orthopaedic surgeon within 1 week. Patients with a suspicion of inflammatory arthritis should be referred to a rheumatologist within 6 weeks.
HistoryIn addition to taking a conventional medical history (including previous and concomitant diseases and medication) specific information should be obtained about traumatic versus non-traumatic causes, the speed of onset, the characteristics of pain, first versus recurrent episodes, the presence of fever, the involvement of other joints and/or back and a recent history of infection.
Physical examinationPhysical examination of a patient presenting with an acute or recent onset swelling of the knee should first focus on the affected knee and should include the unaffected knee as well as an appropriate assessment of the other joints. A general physical examination should be performed on indication.The examination of the knee should include the localisation and characteristics of the swelling (intra-articular versus extra-articular), the detection of effusion, testing stability, general or local tenderness, skin temperature and appearance, the range of motion, and a muscular and neurovascular assessment.
Laboratory testsIn patients presenting with an acute swollen knee of traumatic origin laboratory testing is not helpful in making a diagnosis. In patients presenting with an acute swollen knee of non-traumatic origin, normal acute phase reactants and normal white blood cell count may be helpful in decreasing the probability of inflammatory diseases including especially septic arthritis. Other laboratory tests should be performed on indication.
Joint fluid aspirationIn the diagnostic process of a patient presenting with an acute swollen knee joint fluid aspiration should be performed in patients suspected of having septic, crystal or inflammatory arthritis. Joint fluid should be examined macroscopically and microscopically for leukocytes, crystals and bacteria (Gram staining and culture). In cases of significant traumatic effusion without radiographic evidence of a fracture, aspiration of haemarthros can be performed as well.In case of suspicion of a tumour joint fluid aspiration should not be performed.
ImagingIn patients presenting with an acute swollen knee a plain x ray of the affected joint in two planes (preferably a weight-bearing anterior–posterior view) should be performed. In specific situations additional x rays may be helpful.Ultrasound (US) may be helpful in detecting joint effusion and synovial hypertrophy if clinical examination is doubtful. US, MRI and other imaging modalities may be helpful in detecting intra-articular and extra-articular structural abnormalities and should be performed on indication.
Diagnostic proceduresIn patients presenting with acute swelling of the knee, diagnostic arthroscopy is only recommended in exceptional cases (eg, for a biopsy).
DiagnosisOn the basis of the procedures described thus far it should be attempted to make an appropriate diagnosis, which should be the basis for further therapeutic decisions. Meanwhile, general measures can be useful to relieve symptoms.
Initial managementGeneral measures to relieve pain and swelling in patients presenting with an acute swollen knee should be tailored to the individual patient and may include partial or non-weight bearing advice, splints, cold packs, the prescription of simple analgesics and non-steroidal anti-inflammatory drugs if not contraindicated. Antibiotics should not be started before appropriate diagnostic sampling has been performed. Intra-articular steroids should not be administered unless an appropriate diagnosis has been made and contraindications have been ruled out.