Very sudden excruciating pain on outer aspect radiating to under knee cap.unable to bear weight.no recent injury..hx.of surgery on knee?

Disk herniation: There are a few things that may cause your symptoms that may not be related to your knees, like a disk herniation in your low back. You should get a musculoskeletal / neurological evaluation by your healthcare provider. Good luck.

Lateral Knee Pain: Lateral knee pain can be from several sources including referred from your back or hip. If originating from your knee the friction from the iliotibial band, injured meniscus, osteoartritis, and patellofemoral pain can be the cause. With you past history of multiple surgeries most likely cause is osteoartritis with a loose body. Would follow up with your orthopedic surgeon. Wish you the best.