I have a knee joint replacement that is fully healed but the scar is still tender. It keeps me from kneeling down to get things. Is there any way to overcome this problem? Perhaps some kind of cream to toughen up the scar?

Actually, there is a series of desensitization activities you can perform to help with this problem. A physical or occupational therapist can get you set up with a home program
to do this on your own.

The therapist will show you how to massage the scar using vitamin E oil. Then you will be rubbing different things across and along the scar. At first even soft materials can seem
painful. Firm pressure will help to start. Over time lighter contact is possible. You'll also be able to change from soft to firm to rough materials. Each one will be used with firm pressure gradually applying light pressure.

A clean roller like what you see on a bottle of deodorant will also be used to help desensitize the area. The roller is pressed across and along the scar tissue just like the other materials. You can expect to be given a packet of items to use daily (or more often as your schedule allows). It usually only takes a few days to a few weeks to
desensitize painful scar tissue.