Soreness in the kneecap every time you have your period may be related to rheumatic diseases, cold knees and arthritis, and should be taken seriously. 1. Rheumatic diseases: When rheumatic diseases affect the knee joints, knee pain may also occur during menstruation, accompanied by knee stiffness. 2. Cold knees: Knee pain during menstruation may also be caused by cold knees, mainly because women’s own immune system will be reduced during this period, when the body is cold, it will have a certain impact on the knees. 3. arthritis: every time you menstruate kneecap pain may also be related to the body itself arthritis or osteoporosis reasons, it is recommended to pay attention to timely. There may also be other reasons for the soreness of the kneecap every time you have your period, so it is recommended that you go to the hospital in time, complete the examination to clarify the cause of the disease and then give targeted treatment or treatment.