"Knee problem" refers to any difficulty or issue that someone may experience with their knee joint. It could include pain, swelling, stiffness, or limited movement in the knee. Full definition
To this day I still constantly struggle with knee problems but have learned to manage the pain and work my programs around it to suit me. (womenshealthandfitness.com.au)
Many trainees neglect the hamstrings, which could be a reason for knee problems in future. (fitnessandpower.com)
I can't wear high heels any longer because of knee problems but don't want to wear flats all the time. (solesociety.com)