Migration pattern of cementless press fit cups in the presence of stabilizing screws in total hip arthroplasty

Abstract

The aim of this study was to evaluate the initial acetabular implant stability and late acetabular implant migration in press fit cups combined with screw fixation of the acetabular component in order to answer the question whether screws are necessary for the fixation of the acetabular component in cementless primary total hip arthroplasty. One hundred and seven hips were available for follow-up after primary THA using a cementless, porous-coated acetabular component. A total of 631 standardized radiographs were analyzed digitally by the "single-film-x-ray-analysis" method (EBRA). One hundred and one (94.4 %) acetabular components did not show significant migration of more than 1 mm. Six (5.6%) implants showed migration of more than 1 mm. Statistical analysis did not reveal preoperative patterns that would identify predictors for future migration. Our findings suggest that the use of screw fixation for cementless porous-coated acetabular components for primary THA does not prevent cup migration.

Figure 1

Example of EBRA analysis of an a.p. pelvic film with determination of cup and head position. The numbers indicate the order in which the tangent lines to the bony reference points were drawn.

Figure 2

Examples of three different migration patterns: x-ray examples and underneath the year; in the corresponding SlMULGRAF diagrams, one square equals one squared millimetre. Each cup-symbol represents one measurement in a different a.p. pelvic film. a: migration diagram of a patient with 1.5 mm of cup migration cranially, beginning one year after implantation. Restabilisation was achieved in the further follow up of .36 months. b: migration diagram of a patient without significant migration of < 1 mm cranially or horizontally. Follow-up was 3.5 years. c: migration diagram of a an implant with aseptic cup loosening. Note the progressively migrating implant during 21 months of follow-up. The patient underwent revision surgery and replacement of the loosened implant.

Figure 3

a: x-migration: horizontal migration of the study population. One box represents one implant. 105 implants (98.1%) show no significant horizontal migration in contrast to two implants (1.9%, black boxes for implants no 61 and 94) with significant horizontal migration. b: y-migration: vertical migration of the study population. One box represents one implant. 102 implants (95.3%) show no significant vertical migration in contrast to 5 implants (4.7%, black boxes for implants no 16, 27, 38, 61 and 94). c: inclination: cup inclination of the study population. One box represents one implant. 104 implants (97.2%) show no significant change of inclination (> 1.7°) in contrast to .3 implants (2.8%, black boxes for implants no 41, 94 and 61).d: anteversion: cup anteversion of the study population. One box represents one implant. 106 implants (99.1%) show no significant change of anteversion (> 1.7°0) in contrast to 1 implant (0.9%, black box for implant no 94).