A SHORT PRIMER ON KNEE REPLACEMENT I try to take good care of my knees. Most important, they help me walk, climb and carry heavy objects.  And when I’m jogging I work to keep my knees bent and land in a mid-foot strike.  Plus, I stop running whenever I feel a pain in my knee.  But I have friends that injured a knee when they were younger and then as older adults developed osteoarthritis in that knee.  Eventually they decided to have a total knee replacement.  For them it was life-changing, both relieving pain and restoring movement. I recently read...