| Osteoarthritis | Wear and tear of cartilage due to aging, overuse, obesity, or previous injury | Pain worsened by activity, morning stiffness (<30 minutes), swelling, reduced range of motion, grinding sensation |
| Rheumatoid Arthritis | Autoimmune disease where the immune system attacks the joint lining (synovium) | Prolonged morning stiffness (>1 hour), symmetric joint pain/swelling (often both knees), warmth, fatigue, pain that may improve with movement, flares and remissions |
| Gout | Buildup of uric acid crystals in the joint due to high uric acid levels (hyperuricemia) | Sudden, intense pain (often at night), severe swelling, redness, warmth, extreme tenderness (even light touch hurts), usually affects one knee at a time |
| Meniscus Tear | Twisting injury, degeneration with age, or sports-related trauma | Pain on inner/outer knee, swelling, locking/catching of knee, difficulty straightening leg, popping sensation |
| ACL Tear (Anterior Cruciate Ligament) | Sudden twist, pivot, or direct blow (common in sports) | Popping sound at injury, immediate swelling, instability (“giving way”), severe pain, difficulty bearing weight |
| Patellofemoral Pain Syndrome (Runner’s Knee) | Overuse, muscle imbalance, poor alignment of kneecap | Dull ache around/under kneecap, pain with bending (stairs, squatting), worsening after sitting prolonged |
| Bursitis | Repeated kneeling, overuse, or injury causing inflammation of bursae | Localized swelling, warmth, tenderness, pain with movement or pressure |
| Patellar Tendinitis (Jumper’s Knee) | Repetitive jumping or running stressing the patellar tendon | Pain below kneecap, stiffness, aching worsened by activity |
| Iliotibial (IT) Band Syndrome | Overuse in runners/cyclists; tight IT band rubbing against bone | Pain on outer knee, worsening with activity like running downhill |
