Does a titanium-coated polyethylene press-fit cup give reliable midterm results?

BACKGROUND: Uncemented acetabular components have demonstrated low revision rates and high patient satisfaction but with concerns regarding increased costs compared with monoblock cups. Some newer lower-cost uncemented monoblock options have become available in the last decade, but limited data are available on their performance.

QUESTIONS/PURPOSES: (1) Does an uncemented, titanium-backed all-polyethylene acetabular cup provide reliable fixation? (2) What is the frequency and what are the causes for revision with this cup?

METHODS: Between 2004 and 2008, we elected to use an uncemented, titanium-backed all-polyethylene acetabular cup in older patients with limited physical demands. We performed 615 hip replacements in 550 patients with greater than 5 years of clinical and radiographic followup. When patients who were dead (80 hips in 75 patients), lost to followup (98 hips in 93 patients), or revised (three hips in three patients) were excluded, there were 434 hips in 379 patients for comparison of the postoperative and 5-year radiographs. Two observers not involved in the index surgical procedures (NH, HS) assessed radiographs for signs of migration or loosening. Some degree of early movement sometimes is seen before cup stabilization; however, to be conservative, we defined cups with greater than 3° of change of position (even if they subsequently stabilized) as potentially at risk and report them separately. Revision surgery, time from the index procedure, and the reason for revision were recorded from the New Zealand Joint Registry.

RESULTS: By 5 years there was a median change in inclination of 2° (range, 0°-13°; 95% confidence interval [CI], 2.0-2.4; p < 0.001) and 2° of anteversion (range, 0°-11°; 95% CI, 2.0-2.4; p < 0.001). Although at last followup all cups appeared to have stabilized with no radiolucent lines or medial migration, 22% of the cups (94 of 434) had moved more than 3° and so were deemed to be potentially at risk. There were 11 revision procedures (of 429 hips; 2.5%) of which six were for recurrent dislocation, four for femoral fracture, and one for femoral loosening to give an overall all-cause revision rate for all components of 0.25 per 100 component years (95% CI, 0.13-0.43). No revisions were performed for acetabular loosening.

CONCLUSIONS: The short- to medium-term results of this all-polyethylene monoblock cup demonstrated a low frequency of revision. However, 94 cups were identified as potentially at risk based on movement of > 3° before apparent stabilization. Although those patients seem to be doing well enough now, the current duration of followup may not be sufficient to know that these cups will be durable, because other ongrowth designs have demonstrated a high frequency of late failure after apparent early success.

LEVEL OF EVIDENCE: Level IV, therapeutic study.