Here's a link to the applicable Aetna Clinical Policy Bulletin:
https://www.aetna.com/cpb/medical/data/600_699/0673.html
For 29881, the policy does specifically exclude M23.200 - M23.269 Derangement of meniscus due to old tear or injury.
The only covered diagnosis codes listed for 29881 are S83.200A - S83.289S Tear of meniscus, current injury.
Aetna does maintain a fairly comprehensive list of their clinical policies on the website. It can be a helpful resource when trying to resolve issues with Aetna. (Not saying that I agree with all of the policies, of course, but at least it is out there as a reference to know what you're up against!)
Hope this helps.