Have suspected torn cartlidge in knee. episode of severe leg pain from thigh to foot. is this expected for my condition?

Radiation: Yes, pain can radiate down the leg from the knee. Do you have swelling, pain at night? Was this judged on exam or an injury history?

Usually smaller area: These conditions are very painful and the pain radiates out from the injury. In general the pain is only around the knee, cannot say in your particular case. Obviously if this occurred in the context of falling on the whole area which is now bruised, then that's the cause. A lumbar disk can also involve the area. Often scoliosis, other degenerative condition, occupation hits multiple places.