Yes. I've had a ruptured Baker's Cyst in my left knee joint - around 20 years ago. It started with a minor impact from something on the inside of my left knee joint. I thought nothing of it. Within days, the joint became tender and sore when I tried to fully straighten my left leg, or when I tried to bend it more than slightly. Being a coward, I ignored it and just decided it'd put itself right. Oh, boy...was I wrong. I'd erred on the side of giving it NO exercise and nothing but REST...not good!
After denial and medical fears set in, and around 5 weeks later, my leg had badly swollen - full length, ankle to top-thigh. When I sat in an armchair, my leg was so heavy, I couldn't even lift my shoe heel from the floor. The swelling made my left jeans leg almost too tight to bear. The skin on the leg began to "split" because of the swelling. The leg was impossible to bend further (it wasn't straight) and was impossible to straighten, now. The entire leg was now turning black. The pain was like nothing I'd ever experienced, before.
I finally involved the medical profession - something that I hate to do! My GP started being very afraid that I had a blocked blood vessel. I asked him if he had ever seen anybody's leg in such a condition before and he said, yes, but that it was after a person had been hit by a fast moving car, from the side, and thrown into the air, some considerable distance. That moved me quite a lot! By this time, I'd begun to have near-miss blackouts because of the blood loss into the leg.
Eventually, he scared me into going to the hospital to have it looked at. I was in the assessment bay, on a recliner. (1) The leg was X-Rayed...no break. They had to X-Ray through the jeans, because they were too tight to move and I wouldn't let them cut them off me. (2) They ultrasounded it - no sign of any thrombosis, but they'd still never seen anything like it. Students were brought from all over the hospital to see it. I was taken to the photography/imaging room and they took photographs of the front, side and rear of the leg, to go in the British Medical Journal. The eventual diagnosis was that it was caused by a ruptured Baker's Cyst.
During the blood tests, they discovered/calculated that I'd lost more blood into the leg than a man who had already bled to death! I was too exhausted to be afraid at the sound of that. So, they gave me some blood transfusions on that Monday and the following Thursday, and that was pretty much that.
I had zimmer walkers in the house, a toilet seat raiser and a few other things. A physiotherapist came for around 5 visits and helped me a lot. Slowly, the joint and leg just went smaller and smaller and the leg became movable again. The whole recovery (from first sign-onwards) was FIVE months, but the recovery was absolute and my leg went back to totally normal, again. Back then, that was the most scary physical thing that had ever happened to me, in the medical sense, and certainly the most serious - even though it wasn't really serious, in the end.
Baker's Cysts are moody-pieces-of-nastiness - ruptured Baker's Cysts are the leg's own version of the AntiChrist! Your husband should now look forward to full recovery and a return to dignity and movement and I wish him a very speedy recovery, indeed.