Specific Recommendations

Specific recommendations for the diagnosis and initial treatment of patients presenting with an acute or recent onset swelling of the knee are as follows:

Recognition: A patient who presents with acute knee swelling should be thoroughly examined to confirm swelling.
Referral: When septic arthritis is suspected, or there is a history of trauma or onset of swelling within 12 hours, the patient should be immediately referred to a physician with expertise in musculoskeletal diseases. Although bone tumors affecting the knee are rare, patients in whom this diagnosis is suspected should be referred to an orthopaedic surgeon within 1 week. Rheumatology referral within 6 weeks is recommended for patients in whom inflammatory arthritis is suspected.
History: A conventional medical history is needed, including previous and concurrent diseases and medication use. In addition, the history should include specific information concerning traumatic vs nontraumatic causes of knee swelling, speed of onset, pain characteristics, first or recurrent episodes, the presence of systemic symptoms such as fever, involvement of other joints and/or back, and a recent history of infection.
Physical examination: In a patient presenting with an acute or recent onset of knee swelling, physical examination should first focus on the affected knee. However, the unaffected knee and other joints should also be evaluated. When indicated because of systemic complaints or other markers of a generalized condition, a general physical examination should also be performed. Knee examination should determine the location and characteristics of the swelling (intraarticular vs extraarticular), presence of effusion, stability, generalized or local tenderness, temperature and appearance of the overlying skin, range of motion, and muscular and neurovascular evaluation.
Laboratory tests: For patients with an episode of trauma leading to an acute swollen knee, laboratory testing is not needed for diagnosis. Normal acute phase reactants and normal white blood cell count may help rule out inflammatory diseases, especially septic arthritis, in patients with an acute swollen knee of nontraumatic origin. Other laboratory tests may be indicated depending on presentation.
Joint fluid aspiration: Patients suspected of having septic, crystal, or inflammatory arthritis should undergo joint fluid aspiration. Joint fluid should be examined macroscopically and microscopically for leukocytes, crystals, and bacteria by Gram staining and culture. When significant traumatic effusion is present but radiographic results are negative for fracture, hemarthros can be aspirated. When a tumor is suspected, however, joint fluid aspiration should not be performed.
Imaging: Patients presenting with an acute swollen knee should have a plain radiographic examination of the affected knee in 2 planes. Ideally, this should be a weight-bearing anterior-posterior view. Additional radiographic studies may be helpful in specific cases.
Ultrasound: When diagnosis is unclear from history and clinical examination, ultrasound may help detect joint effusion and synovial hypertrophy. When indicated, ultrasound, magnetic resonance imaging (MRI), and other imaging procedures may help diagnose intraarticular and extraarticular structural abnormalities.
Diagnostic procedures: Diagnostic arthroscopy is recommended in patients presenting with acute swelling of the knee only in exceptional cases, such as when a biopsy is needed.
Diagnosis: The evaluation described above should lead to an appropriate diagnosis, which should be the basis for therapeutic management.
Initial management: General measures to relieve knee pain and swelling should be tailored to the individual patient. These may include advice for partial or nonweight bearing, splints, cold packs, and prescription of simple analgesics and nonsteroidal anti-inflammatory drugs if not contraindicated. However, antibiotics should not be started before cultures are obtained from appropriate diagnostic sampling. Similarly, intraarticular steroids should not be administered unless an appropriate diagnosis has been reached and contraindications have been ruled out.

Landewé RB et al, EULAR/EFORT recommendations for the diagnosis and initial management of patients with acute or recent onset swelling of the knee. Ann Rheum Dis. 2010;69:12-19