High migration rate of two types of threaded acetabular cups

Survivorship analysis was performed on 479 Link V-type threaded cups and on 110 modified V-type Bad Bramstedt cups (a modification of the Link V-type cup since 1993 with a smaller primary coil) to evaluate the effect of the modifications.

Indication for hip arthroplasty with a Link V-type cup was an inflammatory arthritis in 310 patients, osteoarthritis in 138 patients and dysplastic hip joints in 31 patients. The average follow-up was 8.6+/-3.2 (range 3.0-15.2) years. The 110 modified V-type Bad Bramstedt cups had a mean follow-up period of 4.5+/-0.7 (range 3.0-5.9) years, including 49 with inflammatory arthritis, 49 with osteoarthritis and 12 with dysplastic hip joints. To evaluate the migration rate and radiolucent lines, radiographical examination according to the method of Nunn et al. and Delee and Charnley was performed on 264 Link V-type cups with a mean follow-up period of 8.2+/-2.7 years and 59 modified V-type Bad Bramstedt cups with a mean follow-up period of 4.6+/-0.7 years. Relevant parameters influencing cup migration were analysed.

The cumulative survival rate of the former Link V-type acetabular cup was 94.5% after 5 years, 88.1% after 10 years and 70.2% after 15 years. The Bad Bramstedt cup showed a 5-year survivorship rate of 97.9%. Migration of more than 3 mm or tilting of the cup greater than 5 degrees was found in 73% of the former type and in 39% of the modified cup. Radiolucent lines greater than 2 mm and detectable in two zones appeared in 6.4% of the former Link V-type and in 1.7% of the Bad Bramstedt cup design. Among the influencing factors analysed, length of follow-up and primary cup positioning showed a significant correlation to cup migration.

The modification of the Link V-type cup showed no satisfactory improvement in cup migration. Therefore, both threaded cups were abandoned in favour of cementless press-fit cups.