Medial Meniscus Tear: This is a common injury that can cause pain on the inner side of the knee, especially with twisting or bending movements. The meniscus is a cartilage structure in the knee joint that can tear due to trauma or wear and tear, leading to pain and discomfort.

Medial Collateral Ligament (MCL) Sprain: The MCL is a ligament that connects the femur (thigh bone) to the tibia (shin bone) on the inner side of the knee. A sprain can occur due to a sudden twisting motion or direct blow to the knee, causing pain and instability.
Pes Anserine Bursitis: This condition involves inflammation of the bursa located on the inner side of the knee, where the tendons of the sartorius, gracilis, and semitendinosus muscles attach. It can cause pain and swelling in the area.
Osteoarthritis: Wear and tear of the knee joint can lead to osteoarthritis, which can cause pain on the inner side of the knee, especially with weight-bearing activities.

Deep Vein Thrombosis (DVT): Although less common, DVT can cause pain and swelling in the leg, including the inner side of the knee. It is a potentially life-threatening condition that requires prompt medical attention.
Septic Arthritis: This is a serious infection of the knee joint that can cause severe pain, swelling, and redness. It requires urgent medical attention to prevent long-term damage.
Tumor: Although rare, a tumor in the knee joint or surrounding tissues can cause pain and swelling on the inner side of the knee.

Osteonecrosis: This condition involves the death of bone tissue due to lack of blood supply, which can cause pain on the inner side of the knee.
Slipped Capital Femoral Epiphysis (SCFE): This is a rare condition that occurs in adolescents, where the ball at the top of the femur slips out of place, causing pain and instability in the knee.
Pellegrini-Stieda Syndrome: This is a rare condition that involves inflammation of the medial collateral ligament and surrounding tissues, causing pain and stiffness on the inner side of the knee.