Abstract
Background: The principal cause of late failure of the cemented acetabular component is aseptic loosening. The acetabulum is a horse shoe of cortico-cancellous bone surrounding a cortical fovea. The cancellous bone becomes denser and less porous peripherally, limiting cement penetration. A radiolucent line in the DeLee and Charnley zone 1 of the acetabulum increases the risk of loosening of the acetabular component by 38.8 times. We propose that the use of 0.5cm keyholes in zone 1 decreases the incidence of zone 1 radiolucency.
Materials and Methods: Two contemporous cohorts of 100 patients were analysed for the incidence of zone 1 radiolucency on the first post operative film. In one cohort, zone 1 keyholes were used and in the other they were not. The films were analysed independently by two blinded investigators. The incidence, length and thickness of any radiolucency were recorded.
Results: The cohort of patients in which zone 1 keyholes were used demonstrated a 9% incidence of any zone 1 radiolucency, 8% were of 1mm width or greater and 2% involved 50% or more of the zone. In the cohort of patients in which zone 1 keyholes were not used the incidence of zone 1 radiolucency was 40% with 29% demonstrating a width of 1mm or greater and 12% affecting 50% or more of the zone.
Conclusions: The use of peripheral keyholes aids penetration of cement into the denser peripheral acetabular bone as demonstrated by decreased rates of post operative zone 1 radiolucency. This decrease in the incidence of early radiolucency should result in lower rates of subsequent loosening of the acetabular component.
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