How did you hurt your knees? Curious. I was a mediocre left wing my whole life and my knees hurt on a scale of 10 out of 10 due to bursitis 24/7. Is it true that once you have a knee replacement that the pain is reduced to zero?
It's kind of a multi-part answer. tl;dr warning up front.
First, as to part two about the knee replacement, nope, nowhere near zero assuming you want to do something with it other than walk. I can assure you having had 7 knee surgeries including the replacement, and more on other body parts, no surgery reduces pain to zero or returns movement back to 100%. If you get 90%, pain reduction or movement returned, you had a damn good surgeon or your injury was less significant than mine were.
As to the question about goaltending damaging my knee, there was a huge difference in equipment protection from today, especially leg pads. The catching gloves were kid size mittens compared to the gloves used today.
Leg pads were notoriously stiff, like a new baseball glove. By the time you could break them in to get them softened, it was time to replace them. In addition, there was not much choice as to brand - Cooper dominated and Win-Well chased them. We were encouraged to wear pads sized just above the knees with the top two straps loosely tightened so the pad above the knee did not interfere with flexibility. Therefore, the unprotected knee was exposed in between the top of the pad and the thigh pad in the pants. If the pad was turned or you extended the pad butterfly-like flat to the ice, the knee did not do well slamming onto the ice or actually getting hit by a shot puck.
Today, pads are worn much higher on the leg and are engineered to be highly flexible at the knee. When a goalie does a butterfly today, his knee is protected by a pad so pliant it shrouds his knee and only the pad ever touches the ice. The pads today are also much lighter weight and frankly appear much wider to me.
Back then, there was a strap on knee pad you could use, (kind of like your elbow pads but for the knees), which was worn under the uniform and mitigated this damage a little. I tried it for a while but I found it restricted movement significantly. Before long I only wore it when the knee was so bruised it was excruciating to have it get hit by a puck or bang on the ice.
The primary culprit though was the partial butterfly move itself. My goalie coach taught me a method of defending breakaways which involved skating hard toward the approaching player, stopping when he was 10-15 feet away and begin skating backward as he got closer to the net, keeping as close a distance to the shooter as you could based on his speed and your proximity to net you were backing into. You were not supposed to go down until the forward committed. When he did, the ideal move was to flatten the pad on the side to which he committed, butterfly-like, shoot the pad out and throw up any thing else you had, gloves, stick, mask, whatever. The idea was to defend the most likely height of the shot. Believe it or not, the most likely elevation was zero or along the ice, easily defended by the flattened pad.
So right now, try this move (or at least think about it). You're flashing your leg out to flat along the ice (knee to foot) as quickly as you can often smashing the side of your usually unprotected knee onto the ice in the process. Shit adds up.
Bottom line, repeatedly snapping your leg out to sideways flat into an unnatural angle pulls on the ligaments and cartilage until one or both give out. In my case, I think they gave out fairly early in my short "career." But as I learned when I tried to get in the net and play some ten years post "retirement," you have to be in some kind of shape to play goal at any high level. I had to leave the stick time I was at after less than 45 minutes I was so spent. Point being when you're competing at your peak, the surrounding musculature in the knee area is so strong, it is masking the injury.
Last point about the knee replacement. A couple of years ago I tried to go to a public skating session. I was a pretty good skater for a goalie. I could barely get around the ice one lap. I was happy I didn't fall. I looked like someone skating for the first time. Pretty sobering. Titanium unfortunately has no nerves. When I tried to skate it was like my leg stopped at the knee as if it was a prosthetic which I guess it what it is. Interestingly my right knee is fine. All the injuries were to my left knee.
One more thing, do not watch a YouTube of a knee replacement.