Depending on the severity of the meniscus tear, it might not show up on an x-ray, but will show with an MRI.
If the tear is very severe, physical therapy probably won't help much...if at all.
It MIGHT be possible to repair the meniscus...depending on a variety of factors including the severity of the tear and the person's age...and the general health of the knee and the rest of the meniscus.
http://www.arthroscopy.com/sp05026.htm
A meniscectomy is a fairly quick procedure, not terribly painful after the first day or two, and is the fastest "repair" possible. Physical therapy following the "repair" will almost always be ordered by the ortho and will help greatly in regaining mobility.
My knee was fucked up. Demolished ACL, several serious tears in the meniscus. One was so bad that when I walked, it'd "catch" inside the knee and lock it up. Sometimes I'd have to "work" the knee for several minutes to get it to unlock. Now, I'm almost "bone on bone" in a couple of spots, but it's still better than it was. Unfortunately, the gawd-damned thing hurts all the time, and due to the severity of the injury and my age, arthritis has set in...and that just adds to the overall pain level and level of disability.
Actually, meniscus damage
typically doesn't show on x-ray (unless you have the paired cartilage degeneration), but orthos always go that route to check for osteoarthritis, autoimmune conditions, bone cancer, and bone damage. It is rare that physical therapy doesn't help to a certain degree with meniscus damage. If there is a space occupying lesion within the knee, then PT will definitely be limited. However, even severe meniscus tears can benefit from PT due to improving ROM (with joint mobilization, stretching, soft tissue work, PNF techniques), strength, coordination, biomechanics, modifying tension and reloading, etc.
I'm not saying that PT is going to be the answer necessarily, but it is very frequently the first step that orthos suggest considering it has proven efficacy in research, it's conservative, and it's what insurance companies want prior to surgery.
A true meniscectomy is rare nowadays and there's reasons for that. Removing the cartilage is detrimental to long term function. Typically, with the arthroscopic surgeries, the orthos will approach things in several ways. If it's in the red zone of the meniscus where there is some direct blood flow (the periphery of the menisci), they will debride the area to induce bleeding. This bleeding stimulates fibrocartilage formation, which although it isn't as good as the previous hyaline cartilage, it functions better than bone on bone.
Most of the time, they will clean things up, which also isn't considered a meniscectomy - just typically referred to as a knee arthroscopy. This includes removing any debris, shaving off frayed pieces, and smoothing out the surface. That's pretty effective.
However, as I said, PT can sometimes eliminate pain and restore normal function for the individual without surgery. We have joint mobilizations that have shown to promote cartilage regeneration (fibrocartilage), improve joint lubrication, and reduce or eliminate pain. If PT does not fix the issue, then orthos still prefer it before surgery because the patient has a quicker recovery time, due to better coordination, movement patterns, muscle mass, ROM, etc.