HA-coated implants are widely used in both primary and revision total hip arthroplasty. In primary hip arthroplasty, the use of HA on cups appears to be questionable. Some reports have indicated that the outcome is not affected by the presence of HA coating, whereas others have shown an increased risk of cup revision after the use of HA coating (Havelin et al. 2000
, Reikerås and Gunderson 2002
, Cheung et al. 2005
, Stilling et al. 2009
, Lazarinis et al. 2010
). There is very little literature on revision hip arthroplasty, and it involves very few patients, but some studies investigating the outcome of acetabular revision using uncemented HA-coated components have shown promising results (Nivbrant and Kärrholm 1997
, Dorairajan et al. 2005
, Geerdink et al. 2007
, Palm et al. 2007
). However, to our knowledge there have been no studies comparing identical cups with or without HA coating used in revision arthroplasty. Taken together, our results show no evidence that HA coating of acetabular components used in revision THA improved the performance of the 2 cup designs under investigation.
Risk factors for cup re-revision
Age at revision arthroplasty of less than 60 years increased the risk of cup re-revision for any reason and due to aseptic loosening. That younger patients have an inferior outcome after primary THA is well known. In this group of patients, inferior survival of acetabular HA-coated cups has also been reported (Manley et al. 1998
, Puolakka et al. 1999
, Wangen et al. 2008
, Lazarinis et al. 2010
). Higher demands in young patients and increased wear may explain the higher risk of revision. However, in the SHAR there is no distinction between loosening and osteolysis as causes of revision.
HA coating was a risk factor for isolated liner re-revisions, something that may be explained by “third-body wear” induced by HA particles. This phenomenon has been described as a cause of early failure of HA-coated cups after primary THA (Morscher et al. 1998
Use of the Harris-Galante cup enhanced the risk of cup re-revision due to aseptic loosening and for any reason when compared with the Trilogy cup. The Trilogy cup has shown good long-term results after primary THA (Lazarinis et al. 2010
, SHAR 2010
). In revision cases, Tanzer et al. (1992)
reported good medium-term results after using the Harris-Galante cup in acetabular revision, with only 1% component failure after an average follow-up time of 3.4 years. Long-term results (with 10–14 years of follow-up) for this cup used as a revision component have also been reported to be satisfactory (Templeton et al. 2001
, Hallstrom et al. 2004
). The Trilogy cup is a new version of the Harris-Galante design where problems associated with the locking mechanism that secures the polyethylene liner have been addressed (Röhrl et al. 2006
Other factors affecting outcome after cup revision
The type of stem component and its fixation could influence cup survival and thereby possibly distort our findings. Different types of stems were combined with the cups investigated in our study; either they were left in situ at the time of the index revision surgery or they were exchanged during the same revision procedure (). The type of stem fixation varied, with the majority being cemented stems—giving hybrid revision THA. In order to investigate whether the type of stem fixation affected cup survival when both stem and cup were exchanged at the index revision, we performed a separate analysis including this variable (cemented or uncemented stem fixation) as a covariate. We found that stem fixation was not a statistically significant risk factor for cup re-revision for any reason () or due to aseptic loosening.
Distribution of the 3 most commonly used stems combined with the cup types Trilogy (A) and Harris-Galante (B)
It is conceivable that some stems were thought to be stable at the time of the index operation and left in situ while in truth they were unstable. Furthermore, stems left in situ could influence the results, causing difficulties in correct balancing of the soft tissues, and increase the risk of subsequent taper corrosion or dislocation—with a possible influence on the risk of further revisions. To avoid this potential bias, we investigated 2 groups separately according to the type of index revision procedure, e.g. only cup revisions or combined cup and stem revisions. We found no differences between these groups.
Due to the large number of degrees of freedom when entering each individual stem type into a Cox regression model, such analyses were impossible to perform. We therefore studied the various cup and stem combinations in detail and found that HA-coated cups were not commonly used in combination with stems of inferior performance ().
The use of an uncemented cup in primary THA was a risk factor for cup re-revision due to aseptic loosening. To our knowledge, this phenomenon has not been described previously. The reason for this finding is unknown. It might be that uncemented cups were more often surrounded by focal osteolyses and osteoporosis due to stress shielding (Digas et al. 2006
). Loosening of cemented cups is often associated with a generalized widening of the acetabulum bordered by a sclerotic rim, which can be partly used for fixation of an uncemented revision cup. Larger acetabular bone defects and inferior bone quality may thus be possible reasons for inferior fixation of revision cups inserted after removal of failed uncemented implants.
The reason underlying the index cup revision was included as a covariate in the Cox regression model. We found that cups that were revised due to aseptic loosening were not more likely to be re-revised due to aseptic loosening than cups that were originally revised for other reasons. In contrast, when analyzing the endpoint cup re-revision for any reason, cups that were originally revised due to dislocation were more likely to undergo re-revision. The fact that dislocation is a risk factor for re-revision for any reason is probably related to a higher risk of recurrent dislocation after revision surgery. Patients undergoing cup revision due to dislocation have been found to be at higher risk of re-dislocation, possibly because of soft tissue laxity or patient-related factors such as cognitive impairment or neuromuscular disorders, age greater than 80 years, and a propensity to fall (Patel et al. 2007
). It appears that conventional revision cups such as those investigated in our study do not sufficiently address the problem of recurrent dislocation. Constrained or dual-mobility acetabular components should perhaps be considered, at least in some of these cases.
Factors such as medication with steroids, non-steroidal anti-inflammatory drugs, or bisphosphonates that are known to influence bone metabolism are not registered in the SHAR and cannot be analyzed in our study. The same applies to other possible confounding factors such as medical conditions that could have a direct or indirect influence on implant survival, e.g. osteoporosis; neurological, mental, and endocrine disorders; or overweight.
Limitations of the study
One limitation of our study was that only 2 cup types were investigated. However, these designs were the only ones available in the SHAR for studies of the effect of HA coating on cup survival after revision arthroplasty. On the other hand, the comparatively large number of revision operations in each group was a strength of our study. To our knowledge, no studies with comparable numbers of patients have been published.
A further limitation was the lack of detailed information on the extent of the acetabular defects and the amount and type of bone graft used during the index cup revision. Especially in Paprosky type III defects (Paprosky et al. 1994
), the use of large-diameter implants—sometimes in conjunction with bone grafting—is often advocated. Supplementary screws and morselized or structural bone grafts are commonly applied to restore the defects that are present during cup revision surgery. In cases of severe acetabular defects, the outcome after revision arthroplasty has resulted in inferior outcomes compared with revisions of Paprosky type I and II acetabular defects (Issack et al. 2009
, Pulido et al. 2011
). That is also confirmed by our subgroup analysis where re-revision of the metal shell due to aseptic loosening was the endpoint. We found that the use of bone graft at the index cup revision was a risk factor for re-revision of the metal shell, possibly reflecting larger acetabular defects and inferior initial (and even long-term) stability. Even if details about the bone defects and grafting are lacking, we have no reason to believe that these circumstances were unevenly distributed between the 2 groups of implants. Importantly, we found no differences between the 2 groups of revision cups with or without HA coating with respect to the use of bone grafts (). Altogether, we have no reason to believe that the size of the acetabular defects at revision surgery skewed our results.
Other information such as the use of additional screw fixation of the cups or the type of polyethylene liner (XLPE or conventional models) is not registered in the revision database, and was therefore not considered in our analyses.
Our results, derived from registry data on 1,780 acetabular hip revisions, lend no support to the notion that HA coating improves the performance of revision cups. On the contrary, HA coating can increase the risk of liner revision, possibly due to third-body wear. Dislocation as the underlying diagnosis for the index revision and age below 60 years at the index cup revision are patient-related risk factors for subsequent cup re-revision. The type of stem fixation at index cup revision did not affect the risk of cup re-revision whereas other technical factors such as the use of a Harris-Galante cup at the index cup revision and uncemented cup fixation at primary THA increased the risk of subsequent re-revision of the cup. Bone grafting is a risk factor for re-revision of the metal shell due to aseptic loosening, probably reflecting a higher degree of acetabular bone deficiency at the time of index cup revision.