This creates balance in the knee that you simply cannot do without!
Start with 3 sets, and work up to 6. Start with a light weight, and progress up.
Your hams are only 60-70% as strong as your quads. Keep that in mind.
Also, remember to do even number of sets between the 2 muscle groups.
For example: if you do 3 sets of leg extensions in the last 15% of extension, and you get self willed, and add 3 sets of normal full range leg extensions, do 6 sets on hamstring curls!
Supplements: Glucoseamine Sulfate (Not Glucoseamine HCL) in the amount of 1200-1500 mg/day. It will make a huge difference in soft tissue/ligament and tendon repair! Prevent injury and arthritis! Make sure you get it from a reputable source!
Always remember to stretch!
You can read more on training and injury prevention on my web sight!