Safety First
1. Deadlift / squat plz wear a weightlifting belt for support. Never go without one.
2. Focus on form, form and form. Weight is secondary.

As to prevent muscle wastage, take glutamine on a daily basis. But do check with doctor on this first.

just to add when you don;t train, your muscle will start to deteriorate away. Glutamine helps to slow down the muscle breakdown. However for injury healing thats another different story.

For joints health, typically go for chondrotine and glucosamine supplements.