This is interesting question.

There is a drive from the companies to create more revenue as for the last few years there is a control of the components' prices. So the invention of the patient specific jigs surfaced. If we need to do so we need to go ahead and have either a CT scan (for the majority of the companies) or an MRI (one or two of them).

The moral question is then, do we need to irradiate the patients for the sake of the companies by doing a CT scan or stay with the MRI which is a more expensive investigation?

The next question to answer is the ability of the surgeon to perform the cuts accurately with any of the jigs. Are we so specific to the exact millimetre or the cuts are approximately to the millimetre?

This "approximation" is based on the soft tissue position, the quality of the bone and the stability of any of the used jigs. 

So if we are "approximately" correct do we need to spend more money so to follow the "fashion" that the companies are driving us to.

Anybody can be asked about the presented literature that is potentially supporting the use of such jigs. In such case we need to ask, do we have an independent audit of the presented results? Are the surgeons who support them independent from the companies?

So in my humble opinion we need to understand the principles, the art and the technique of the procedure. I do not think that anybody of us will ask one of the prominent knee surgeons as Ranawat if he would like to use personalised jigs. We really need to know how to do a total knee replacement and do not follow the companies and their fashion. 

Hope that my answer will appear

Thanks George for your views. You would agree, that the consequences of intramedullary violation, malaligned TKA can be hazardous to our patients. Hence, Technologies like CAS, PSI etc have emerged to address these problems. I agree that still the jury is out about their overall superioirity over conventional technique. But surely, PSI in a newer Technology with an affordable cost, small Learning Curve and without any capital investment

I would not disagree with you on the IM violation but I would prefer the companies to agree on MRI investigation only, develop the software for this and cover all the expenses of the MRIs themselves in a private setting without violating the NHS budget.