The publication of our long-term hip replacement follow-up study computer analysis has clearly demonstrated the
association between polyethylene (polyethylene/UHMWPE) wear on the one hand and pain, interface widening
and osteolysis on the other1. From a total of 97 cases, seven had true failure and needed ultimate revision. These
seven cases formed the nucleus of the current study (Group 1). The course of events could then be analysed in
great detail, and compared with the other 90 cases (Groups 2, 3, and 4).
The purpose of this paper was to confirm the role of polyethylene wear (the independent variable) in the limitation
of longevity of the implant; furthermore to identify the cut-off point of wear that is considered acceptable.
At the same time quantification of P, I, O (pain, interface widening and osteolysis) was studied (the dependent
variables). Once again, computer analysis provided us with detailed values that would constitute the cut-off points
These findings then enabled us to categorise the 97 cases into four groups. Of special interest was Group 2:
‘impending failure’. Even though none of the nine cases in Group 2 were revised, this study clearly demonstrated
that they should be classified as failures and managed accordingly.
In this study some other controversial issues were addressed: the degree of wear proved important as opposed
to the tempo, which was not! Equally unimpressive were the patients’ age, activity and body mass, which according
to digital analysis had little effect on implant longevity.