Bed

"However, for my 85yo lady at the moment with AVN of her femoral head, I don't feel mobilisations of her upper Lx spine is going to benefit her too much.... In fact, this poses the question of duty of care. If I did continue to mobilise her spine without referral on to an orthopaedic surgeon, am I putting myself in a possible law suit??? "

Who has made the diagnosis that this woman's pain is from her hip?, her doctor/ surgeon ? or yourself.
medical opinion invarably points the finger at pathology as the driver for pain. sometimes this is correct, sometimes this is not. The only way to be certain is to perform a differential diagnostic routine , sufficiently sensitive and oriented to the very real prospect that spinal referred pain may be occurring . All too often , the staff at hospitals where I have worked , along with geriatric rehab centres etc, will take on a rehab role as if the answers were all provided neatly by pathology, as expained by your example.
Left undealt with are the scores of chronic pain sufferers who , for want of someone to fully and comprehensively explore the referred pain theme, will suffer needlessly. In my own explorations of such cases , it is common to discover that not only did referred pain exist, and was able to be eliminated by CM to the relevant joint(s) , but that with hindsight , it became clear , that pathological 'answers' were either entirely wrong , or incomplete.
To not explore these very real prospects would , in my view , constitute a refusal to act according to the duty of care you mention.