Function related specifications for total knee arthroplasty implant devices

Current specifications for total knee implant devices reflect components' properties separate from each other and often in noncomparable units. We can recognize the tibial base plate thickness, size of femoral component, etc. How does it reflect the functional capabilities of the whole assembly, particularly in relation to wear and survivorship? Such approach does not take into account the fact that the individual components interact with each other, which in turn defines the final evaluation. We suggest a new function related approach to specifications which will help to develop clinically relevant standardization methodology. We propose an Index of Congruence to be added in the future as a required specification for implants of all designs. This universal standardization will help surgeons in preoperative planning and may also serve as a common denominator to enable comparative studies between diverse designs and different manufacturers.