The main reasons why the knee may hurt when bending include:
- Injury or trauma, such as torn ligaments, meniscus tears, or fractures, which typically cause sharp pain and swelling.
- Overuse or repetitive stress leading to conditions like patellar tendinitis, iliotibial (IT) band syndrome, or bursitis.
- Arthritis, especially osteoarthritis, causing diffuse pain, swelling, and stiffness.
- Specific tendonitis such as quadriceps or hamstring tendonitis causing pain in certain knee areas.
- Patellofemoral pain syndrome causing dull ache in front of the knee.
- Presence of a Baker's cyst causing tightness and swelling behind the knee.
The exact cause often depends on the location and nature of the pain (sharp vs. dull) and any associated symptoms like swelling, stiffness, or a feeling of instability. In many cases, sudden injury or overuse are common triggers of knee pain when bending. If the pain is severe, persistent, or accompanied by swelling or instability, professional medical evaluation is recommended for accurate diagnosis and treatment.