Understandable. Without knowing the details of your issue, all I can say is that even light lifting with free weights will help develop your secondary/stabilizer muscles. You may or may not be able to make it a mainstay of your exercise program, but light to medium free weight exercise will improve your joint condition over time as well. If you do anything that feels iffy, just be sure to get a spotter. Pretty much anything you do in a gym will make you stronger, except getting injured.
I second this -- if lifting heavy things makes you nervous, try lifting lighter things. There's a lot of small stabilizer muscles in your body that will be really weak if left unused, and lifting any free weight will help build them up.
