An intriguing observation noted by registry data and clinical studies is an inverse relationship between implant size and revision rate.
The pain and physical function scales of the WOMAC and SF-36, which have previously been shown to have a large degree of responsiveness in primary hip arthroplasty (Nilsdotter et al. 2001), showed large effect sizes after revision arthroplasty.
As the Pinnacle cup had the majority of the smallest head sizes and revision risk changed when the ASR implant was excluded, it appears that component design is an important factor when interpreting revision risk with different femoral head sizes in MoM THA.
Due to the short follow-up and small sample size, this single revision resulted in a revision rate per 100 observed component years of 2.3.
In the case of potential growth, the size of the revision is quite even from 2005 to 2007 (around half a point), and somewhat smaller in 2004.
In the case of sustainable growth rates, the size of the revision is a quarter of point or less for 2004 2007.
However, other authors (Shimmin and Back 2005, Kim et al. 2008) have not reported any association between femoral head size and increased revision rate.
Firstly, the small size of the revision knee subgroup limits the reliability of the data for this subgroup and the conclusions and comparisons which can be drawn from the data.
In this paper we address a specific computational aspect of belief revision: the size of the propositional formula obtained by means of the revision of a formula with a new one.
In Durgin's revision, the size of the influence spheres decreases with density, and occupancy is normalized by dividing it by influence-sphere size.
