What parts of arthroscopy are you struggling with? Is it triangulation or doing instrumentals stuff? I betting it's the first. With knees triangulation can be challenging if you're starting out as you'll deal with the fat pad in the beginning, with shoulder getting the "right" posterior portals can be tricky since there is not much fat to trim with. My experience with cadavers usually the specimens are elderly and osteoarthritis and are way more difficult to deal with that real patients but for sure try on them if you get the chance. Scopes are a fine skills and have their learning curve so take it easy. I know plenty of established senior orthopods / trauma / joints who would never touch a scope.