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Red Flags - Knee Pain

It is important to differentiate joint pain from bone pain.

Bone pain is a “red flagand is a common feature of leukaemia, metastatic neuroblastoma and primary bone tumours. This may be night pain or constant 'nagging' pain.  These malignancies may present with a swollen joint(s) and can mimic arthritis.

Osteoid osteomas (the most common benign bone tumour) are usually located in the femoral neck (so can cause referred pain to the knee) and typically cause night pain that can be relieved by NSAIDs.

Primary malignant bone tumours - are more common at the distal femur or proximal tibia, so often present with knee pain, sometimes with effusion.  Radiographs of the knee should include the femur and the tibia. 

Persistent swelling and pain in the absence of trauma warrants investigation as this may indicate arthritis.

Referral is needed urgently if there are red flags and should not wait for results of investigations. 

The radiograph below shows periosteal elevation and soft tissue calcification in a malignant tumour of the proximal tibia (arrow). 

The radiograph below shows a benign non-ossifying fibroma in the distal left femur (arrow) and highlights the importance of radiograph requests including femur and tibia for knee pain.

The MRI below shows the same non-ossifying fibroma in the distal left femur (arrow)