What could be the reason for a previously healthy knee becoming painful and red?

Knee pain accompanied by redness may result from non-disease factors, or it could be caused by medical conditions such as trauma or knee arthritis. The specific analysis is as follows:

I. Non-disease factors

When the knee area is exposed to cold stimulation, local soft tissues may spasm, leading to redness and pain. Generally, keeping the knee warm can help alleviate these symptoms.

II. Disease factors

1. Trauma

After the knee suffers external impact, local soft tissue damage may occur, resulting in symptoms such as redness, swelling, and pain. If swelling and redness are severe, it is recommended to apply antibiotic ointments such as erythromycin ointment or mupirocin ointment locally under medical guidance to prevent infection.

2. Knee Arthritis

When aseptic inflammation occurs in the knee joint, inflammatory stimulation can cause local pain and limited movement. If pain is significant, anti-inflammatory and analgesic medications such as diclofenac sodium sustained-release tablets, celecoxib sustained-release capsules, or acetaminophen tablets may be taken under medical supervision.

In addition, conditions such as patellar chondromalacia, gouty arthritis, or rheumatoid arthritis could also be responsible. It is advisable to visit a hospital for appropriate diagnostic tests and, based on the underlying cause, select an appropriate treatment approach.