Thanks for the support. I'm not sure if I'm to have one just yet, although my doctor did mention the procedure. I'll know exactly what is wrong tomorrow morning when he sees the xrays.
If so, I'll need two, as I am very bowlegged. Consequently the medial compartment ( the inside of the knee ) bears most of my weight (6'2", 235 lbs). The cartilege appears to be worn on the inside only. If this keeps up, I'll be unable to ski at all, and perhaps not walk by retirement. Retirement is 20 years down the road and my goal is to retire by a mountain to teach 4 year olds to go "whoo hoo!".
A tibial osteotomy for my condition is to cut into the inside of the tibia and graft a piece of bone from my hip, thus straightening the leg. The weight will now bear down evenly on both sides of the knee -- on the medial and lateral compartments. This should slow the wear. And I won't need canting shims!
235 is a lot of weight, but it's not all fat -- 220 is my goal weight. That should give me about 15% bodyfat, which is healthy for this age...