Abstract
Since wear and loosening of the ultra high molecular weight polyethylene is the one factor limiting the life of the arthroplasty we set out to identify factors associated with either low wear 0.02 mm/year or less, or high wear 0.2 mm/year or more.
In a group of 1092 patients, 1434 Charnley low-friction arthroplasties 190 (13.2%) showed low wear while 149 (10.4%) showed high wear. We used Chi square test to assess the significance.
The characteristics of the low wear group were: female gender (p=0.042) Rheumatoid arthritis (p= 0.014), Charnley category “C” patients (p=0.03) and varus position of the stem (p=0.003) The use of acetabular cement pressurization (p=0.07) and medialization of the cup (p=0.07) approached significance.
In the high wear group there was a predominance of males (p=0.042) with primary arthritis (p=0.006) as the underlying hip pathology, and the stem in valgus position (p=0.023). Rim position of the cup was approaching significance (p=0.07). There was no statistical significance between the two groups for revision for aseptic stem loosening or stem fracture (p= 0.49). There was a highly significant difference (p< 0.0001) between the two groups for revision for wear and aseptic cup loosening: 5.3% against 40%.
Changes in the cup geometry are sufficient to explain the increasing incidence with depth of cup penetration. There is much to be gained from the use of low wearing ceramic – ultra high molecular weight combination. Tissue reaction to the plastic particles cannot be the cause of stem loosening.
Theses abstracts were prepared by Mr Peter Kay. Correspondence should be address to him at The Hip Centre, Wrightington Hospital, Appley Bridge, Wigan, Lancashire WN6 9EP.
