Hi, I have had two partial meniscectomies on my right lateral meniscus because of meniscal tears, most recently in Feb this year for a degenerative tear. I am 38 and my meniscus first tore when I was in my early 20s. I was also pretty shocked by this as I didn't think I had put that much extra strain on them. To be honest, I think my menisci and knee cartilage is just not too good (my mum has always had problems with her knees too). I was treated on the NHS and received next to no information about what had been done or what kind of state my joint was in following the op other than being told I had developed 'some osteoarthritis'. Like you, I want answers to the same sorts of questions and have recently written to my consultant asking a whole series of them. If I get a reply and there is anything that might be of interest to you, I will pass it on.
But in answer to your question about the benefits of building up the muscles - this is VERY important. I am now seeing a physiotherapist because post-op I've developed grinding and locking in my knee (which is still puffy), which she thinks is because of the muscle loss to both quads and hams. Muscles working optimally support the joint and hold everything in balance and alignment. It is essential to get the muscles working as well as possible. This will support the knee and help reduce the likelihood of further tears, but there is always the possibility that once the meniscus is degenerating you will get more problems. I was very careful with my knees for 15 years before the second tear (no high impact activities, no sudden twisting movements, etc). It's not possible to grow back the meniscus naturally- once it's gone it's gone. However, there are newer techniques of meniscal transplantation and replacement (I have asked the consultant about these in my letter). Degeneration of the menisci is specific to your knees, this is a different kind of cartilage to the hyaline cartilage on the articulating surfaces of the bones. Your knees take the greatest strain of all the joints, which is why they are more prone to wear and tear, but I don't know why some people's menisci are more prone to degenerate earlier than others' - I wish I did!! It may have developed because of alignment problems (I am apparently slightly knock-kneed, which may have been a factor in my problem).
Anyway, hope this helps to some degree. I definitely recommend getting some physiotherapy to build up the muscles.