Locked knee (unable to fully extend)
Possible displaced meniscal tear or loose body. Urgent MRI and orthopaedic referral.
Rapid swelling within 2 hours of injury
Haemarthrosis. Likely ACL tear, fracture, or patellar dislocation. X-ray, MRI.
Hot, swollen knee with fever
Exclude septic arthritis. URGENT aspiration, blood tests, IV antibiotics.