Barely any cartridge in either shoulder. moderate to severe neck & lower-back arthritis. any yoga positions to eschew?

Everyone's different: One should not over-flex, over-extend, nor over-rotate joints that have damage, so it's a good idea to avoid the yoga positions that do those undesired things to the damaged joints. How far to flex, extend, or rotate? The general rule is that one should try not to have pain during the stretch or exercise, and should not have pain afterwards (or the person may have over-done it).

Science of Yoga: Yoga practice is being re-evaluated as to safety and appropriateness for people with health condition histories. Make sure your teacher is trained to consider your particular limitations... And listen to yourself. See the new book, science of yoga -- some positions to avoid with your history are: plough, frog, shoulder stands, inverted asanas, extreme twists... Try "gentle yoga" classes. Namaste.

YES: Use your body as a guide, avoid positions that aggravate pain.