Press fit fixation of cementless cups: how much stability do we need indeed?

Using screws for a better primary and secondary fixation has been discussed in the literature of the recent years, although the principle of press fit has been explained as the principle of a push-button. The authors wanted to compare their own results in patients using X-rays from the postoperative course to decide if it is really safer to use screws or not.

Two hundred and twenty one consecutive, not selected patients were treated with total hip arthroplasty using a cementless cup type Duraloc. They were followed up over a time of 5 years for radiological changes of the bony acetabulum around the cup ("acetabular zones" according to De Lee and Charnley). One hundred and ten cups were additionally fixed with one to three screws at the upper part in region C1, 101 cups were implanted without the use of screws.

Periprosthetic changes visible on the radiographs (immediate postoperative gaps, subsequent sclerosis and radiolucent lines) were assessed according to the time of their appearance. A gap in zone C2 was seen more often immediately after operation within the group without screws (17.8% vs. 7.3%) and disappeared within the following 25 months. Within the group with screws significantly more often a gap was found in zone C1 and C3 compared to the group without screws (7.3% vs. 1.9%). In the group with screws a sclerosis of the bone in zone C1 developed in 32.7% mostly within the first 5 months. It was followed by a radiolucent line in zone C3 in 28.2% mainly within 5-25 months postoperatively and in zone C1 in 20.9% within 16 months. Significantly less seldom were these phenomena seen at the cups without screw fixation. There was no correlation between lateral or medial positioning and deviations from the ideal inclination to the bony changes around the cups. No signs of loosening occurred in either group.

Less radiological changes around the cup if no screws were used and no disadvantages within this group led to the conclusion that an additional screw fixation in principle is not necessary in press-fit cups.