I have taught workshops on knee and hip replacements – but it was before we were recording them on film, darn it! There are two types of approaches for hip replacements – posterior and anterior. The posterior approach cuts through a lot of muscle and tendons, and the scar tissue is what provides stability to the joint after healing, which takes at least 6 months. The anterior approach is less invasive, and used to be done solely on younger people and athletes…..but is getting far more common, which is a good thing. The best way to know the difference is to ask where their scar is – either on the glutes between the hip and sitting bone for posterior, or next to the tensor fascia latae on the lateral hip for anterior. Each has different contraindications….but the most important time for contraindications is in the first 6 months to one year post surgery. The easiest way to be safe is ask your students what your doctor or PT said you can NOT do 🙂  The good news is, 1-2 years post surgery the scar tissue is set in and the risks of dislocation are very minimal. The main thing is to work within the parameters of pain for your student, i.e. no ‘uh-oh’ pain – if it feels wrong, come out immediately.