Dislocation following THA: comparison of two acetabular component designs.

One hundred ninety-seven consecutive primary cemented total hip arthroplasties using 22 mm heads were evaluated for the rate of dislocation. All surgery was performed by one surgeon through a posterior approach. A Charnley type femoral component was used in each case. Patients were divided into three groups based on the acetabular component used. Group I had 60 Charnley HPW cups implanted between January 1985 and December 1986; group II had 70 Tibac cups implanted between January 1987 and August 1987; and group III had 67 Charnley HPW cups implanted between September 1987 and February 1988. The groups were similar with regards to age, sex, original diagnosis, and surgical technique. There was a total of 11 dislocations (5.6%), of which 8 (11.4%) occurred in group II (Tibac cup). Furthermore, 6 patients (3%) developed recurrent hip dislocations, 5 (7.1%) of which were from group II. Group II had a statistically significant increase in the dislocation rate (P < .05). The authors conclude that the dislocation rate with the 22 mm Tibac cup is unacceptably high and that the design of the Charnley cup affords greater stability to the artificial hip joint than the hemispherical design of the Tibac cup.