Abstract
Introduction
Cementless acetabular fixation in total hip replacement (THA) is reliable and has been the fixation method of choice in the United States for decades. While revision for failure of osseointegration or early loosening is relatively rare, recurrent dislocation remains a leading cause of early revision. Novel acetabular implants and those offered by smaller companies often lack constrained or dual mobility liners, which may result in revision of well-fixed, well-positioned cups in cases of recurrent dislocation.
The purpose of this study was to compare outcomes of THA with three different acetabular cups with differing fixation surfaces. One hydroxyapatite (HA)-coated cup (Trident, Stryker, Kalamazoo, MI, USA) offered dual mobility or constrained liner options. The other cups were a novel highly porous cup (Restoris PST, Stryker, Kalamazoo, MI, USA), and a Calcium Phosphate (CaP)-coated cup (Trinity, Corin, Cirincester, UK), neither of which offered dual mobility or constrained options at the time of investigation. Endpoints of interest were: clinical and radiographic outcomes including evidence of osseointegration, overall reoperations, reoperations for acetabular fixation failure, and reoperations to address dislocation in which a well-positioned shell was revised due to the lack of dual mobility or constrained options.
Methods
A retrospective review of 370 acetabular cups implanted in 328 patients for THA by a single surgeon between February 2013 and June 2016 was performed. There were 100 Trident cups (Stryker, Kalamazoo, MI, USA), 105 Restoris PST Acetabular Cups (Stryker, Kalamazoo, MI, USA), and 165 Trinity Acetabular Cups (Corin, Cirincester, UK). Patient records were reviewed for post-operative complications, clinical outcomes scores and radiographic signs of acetabular osseointegration at minimum 1-year follow-up.
Results
Despite differences in fixation surface, there was no difference in Harris Hip Scores at minimum 1-year follow-up and all three cohorts had 100% 1-year survivorship free of revision for failure of acetabular fixation. No cup showed signs of acetabular migration or loosening.
Overall reoperation rates were low, ranging from 2.4%-3.8% (p=0.81). Femoral fractures and fixation problems were the most common cause of reoperation, occurring in nearly 2% of cases (n=7), but did not differ between groups. Reoperation for infection occurred in less than 1% of cases (n=3) and did not differ between groups.
Revision for recurrent dislocation occurred in 1% of cases (n=4). All occurred with cups lacking dual mobility or constrained options. In all 4 cases the acetabular component was within the Lewinnek “safe zone” and deemed well positioned. In one revision, a lipped liner and longer head were used given concerns about the risk of acetabular component revision due to poor bone stock. In the remaining revisions, the well-positioned cup was revised to allow for the use of constrained or dual mobility implants.
Conclusion
All acetabular revisions in our cohort were related to instability or infection, while none were related to acetabular fixation. Subsequent to this experience and analysis, we are wary to select any “new and improved” acetabular cup that does not have an option for a constrained or dual mobility liner, even when enabling technology makes us confident of safe-zone placement.
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