Arthritis: Osteoarthritis, rheumatoid arthritis, and other forms of arthritis can cause inflammation, joint degeneration, and pain in the knee joint.

Overuse injuries: Repetitive stress or overuse during activities like running, jumping, or sports can lead to conditions in the knee bones such as patellofemoral pain syndrome, tendinitis (e.g., patellar tendinitis, quadriceps tendinitis), or bursitis.

Traumatic injuries: A traumatic injury like ligament tears (e.g., ACL, MCL, LCL), meniscus tears, or fractures can result in significant knee pain and instability.

Biomechanical issues: Abnormalities in the alignment or function of the knee joint, such as patellofemoral malalignment or gait abnormalities, can contribute to knee pain over time.

Muscle imbalances: Weaknesses or imbalances in the muscles surrounding the knee, such as the quadriceps, hamstring, or calf muscles, can increase strain on the joint and lead to pain.

Obesity: Excess weight places additional stress on the knee joint, increasing the risk of developing osteoarthritis and other knee problems.

Age-related degeneration: As individuals age, the cartilage and other structures within the knee joint can naturally degenerate, leading to pain and decreased mobility.

Referred pain: In some cases, knee pain may originate from other areas, such as the hip or lower back, due to nerve compression or muscle tightness.