I had knee replacement surgery 5months ago. how long does it take for the leg to straighten out. i go physical therapy and all plus i do workout at home. but my leg is still not straighten out?

It should be straighten out by this time, 5 months post op with physical therapy and home exercise. You need to see your orthopedist for a reevaluation.

Knee motion after knee replacement is critical in the initial weeks after surgery. Months later, it will be difficult to make improvements. If the scar sets in, stretching may not be enough. Review with your surgeon to see if there are interventions that can be taken now, or see if there is a problem which is limiting your progress. Sometimes, revision surgery is necessary.