Iliotibial (IT) Band Syndrome: This condition is a common cause of lateral knee pain, especially in runners or cyclists. The IT band is a ligament that runs down the outside of the thigh from the hip to the knee, and when it becomes inflamed, it can cause pain and tenderness on the outside of the knee.

Lateral Meniscus Tear: A tear in the cartilage of the knee can cause pain on the lateral (outer) side of the knee, especially with twisting or bending movements.
Patellofemoral Pain Syndrome (PFPS): Although more commonly associated with anterior knee pain, PFPS can sometimes cause lateral knee pain due to maltracking of the patella.
Popliteus Tendinitis: Inflammation of the popliteus tendon, which is located at the back of the knee, can cause lateral knee pain, especially with activities that involve twisting or bending.

Osteonecrosis of the Femoral Condyle: A condition where the bone tissue dies due to lack of blood supply, which can cause severe knee pain and must be treated promptly to prevent further damage.
Infection (Septic Arthritis or Osteomyelitis): Infections in the knee joint or bone can cause severe pain, redness, and swelling, and require urgent medical attention.
Tumor (e.g., Osteosarcoma): Although rare, a tumor in the bone or soft tissue around the knee can cause persistent pain and must be ruled out with imaging studies.

Pellegrini-Stieda Syndrome: A rare condition characterized by inflammation of the medial (inner) collateral ligament of the knee, which can cause lateral knee pain due to referred pain.
Ganglion Cyst: A benign lump that can develop near the knee joint, causing pain and stiffness, especially if it compresses nearby nerves or tendons.