Revision total hip replacement using the cement-in-cement technique for the acetabular component

The technique of inserting a new femoral component into a well-fixed cement mantle (the cement-in-cement technique) at revision total hip replacement (THR) is well established.^1-5 However, acetabular cement-in-cement revision is less well-recognised, and here we report a series of acetabular revisions using this technique.

Patients and Methods

Between 1988 and 2004, 60 acetabular cement-in-cement revisions were performed in 59 patients (39 women and 20 men) with a mean age at surgery of 74.6 years (39 to 99; sd 11.9). There were 46 revisions (77%) for recurrent dislocation, 12 (20%) at the time of femoral revision (aseptic loosening in eight, stem fracture in two, peri-prosthetic fracture in one and subluxation in one), one for unexplained pain, and one for disarticulation (intra-prosthetic dislocation) of a constrained liner. The cement-in-cement revision was the first revision in 45 procedures (75.0%), the second in 13 (21.7%), the third in one (1.7%) and the fourth in one (1.7%). The mean time from the index surgery to the revision procedure, and therefore the mean time that the acetabular mantle had been in situ at the time of revision, was 6.0 years (0 to 31.5). Osteonics constrained acetabular components were used in 27 hips, Exeter concentric components in 18 and Contemporary flanged components in 15 (all Stryker Howmedica Osteonics, Mahwah, New Jersey). In all, 29 patients died of unrelated causes at a mean of 4.4 years post-operatively (0.1 to 10.0; sd 3.0). One death occurred in the early post-operative period. All others had well-fixed components both clinically and radiologically at the last review before death. The mean follow-up was 8.5 years (5.3 to 12.0; sd 1.8) for the survivors. No patient was lost to follow-up.

Clinical evaluation was recorded pre-operatively and at the latest review using the Charnley⁶ modification of the d’Aubigné-Postel scoring system. Pre-operatively, 18 hips were classified as Charnley category A, 21 as category B and 21 as category C. All hips were evaluated radiologically pre-operatively, immediately post-operatively and at the latest review. The acetabular cement mantle was assessed by a single observer (JC) using the DeLee and Charnley criteria.⁷

Operative technique

For the retention of the acetabular cement mantle it must be well-fixed both radiologically and when assessed intra-operatively⁸ (Fig. 1). The technique used evolved over the 15 years of the study period, and the following is a description of the technique currently used. The worn or mal-orientated acetabular component is first removed without damaging the cement mantle. It is thus not sectioned with osteotomes and removed piecemeal. Except for the rare situation where it has loosened at the cement–prosthesis interface, the acetabular component is removed using standard acetabular reamers as described by Sabboubeh and Al Khatib⁹ (Fig. 2). Consecutively larger reamers are used to ream away the polyethylene implant, similar to reaming the acetabulum in a primary THR. As the polyethylene is softer than bone, it reams away readily. Damp gauze swabs are placed around the acetabulum before reaming to minimise the escape of polyethylene fragments into the soft tissues, and the area is regularly lavaged and suctioned. In order to avoid blunting the reamers, reaming is discontinued when the polyethylene is still 1 mm to 2 mm thick. At this stage the wire marker(s) on the periphery of the implant are usually exposed and can be removed. At this thickness the polyethylene is easily deformed and can usually be levered out from the underlying cement using an elevator or osteotome. The cement mantle should then be carefully inspected to confirm adequate fixation and to check for any damage. If it is loose or there is evidence of lysis behind it, it should be removed in its entirety and an alternative revision technique used.

If the internal diameter of the mantle is adequate, the ridges of cement corresponding to the grooves in the polyethylene can be retained to improve fixation to the new cement. If the diameter of the original component was small it may be necessary to expand the mantle with a power burr to accommodate the new component. If this is done, additional shallow pits can be made in the mantle (Fig. 3) to supplement the bond with the new cement. These pits should not penetrate through to bone unless it is considered that additional key holes into host bone would improve fixation, for example in the presence of a non-progressive lucent line in DeLee and Charnley zone 1.⁷ The advantage of not deepening the pits into bone is that it avoids bleeding and the risk of contamination of blood between the layers of cement. For maximum shear strength a clean, dry interface is essential, and the new cement should be added early (Fig. 4). If a component with a relatively small outer diameter is to be removed, it is not necessary for the new component to be correspondingly 4 mm smaller to ensure an adequate new cement mantle, but instead, a thin mantle of only 1 to 2 mm between the old cement and the new component is acceptable. In such situations any spacers can be removed from the back of the new component to facilitate insertion. Provided the mantle is clean and dry, the new cement will bond to the old cement with a shear strength at the interface similar to that of a solid block of cement.^10-12 The new component is then cemented into the old mantle (Fig. 5), using a different internal diameter or a constrained component if desired.

Statistical analysis

Statistical examination was performed using the Wilcoxon signed-rank test for non-parametric paired data, comparing pre- and post-operative scores for pain, function and range of movement. Analysis was performed using SPSS v.19 for Windows (SPSS Inc., Chicago, Illinois).

All 60 hips were included in the survival analysis using Kaplan-Meier curves, and 95% confidence intervals (CI) were generated with the endpoints of acetabular revision for aseptic loosening and acetabular revision for failure for any reason, including infection. Survival rates at five years are given when there are 30 cases (half of the original cohort) remaining at risk, extended with no further revisions from 3.7 years with 40 cases at risk.¹³ As no patient was lost to follow-up, the construction of a worst-case curve as recommended by Bland¹⁴ was not warranted.

Results

The clinical outcome is shown in Table I.

Of the 60 revisions, 31 (51.7%) had some evidence of at least a partial radiolucency in any zone at the bone-cement interface on pre-operative radiographs. Of these, incomplete lines in DeLee and Charnley zone 1⁷ were seen in 20 hips, six had a complete line in only one zone, and five had lines extending into more than one zone. No components had lines in all three zones pre-operatively.

At the latest review (with 55 films available) no changes at the cement–bone interface were seen in 34 hips (62%) compared with the immediate post-operative image. Progression of radiolucencies is shown in Table II, with only two hips having more than one zone involved.

There were two further revisions for aseptic loosening at 6.9 and 7.7 years, respectively. The first was of a constrained component inserted to manage recurrent dislocation. As no constrained acetabular component for cemented use was available at the time of revision, a constrained component designed to snap-fit into an uncemented shell was scored on the back and rim to enhance fixation and inserted as a cemented component. This debonded at the cement–prosthesis interface 6.9 years post-operatively. The second was of an Exeter concentric acetabular component also used to manage dislocation, which loosened at both the bone–cement and the prosthesis–cement interface, with associated superolateral peri-acetabular lysis. This was re-revised at 7.7 years. There were four dislocations, all of which underwent a further cement-in-cement acetabular revision. One patient suffered intra-prosthetic disarticulation of a constrained bipolar acetabular component, which had not failed at the prosthesis-cement or the bone-cement interface. This was successfully further revised using the cement-in-cement technique. One deep infection was managed by two-stage revision.

The Kaplan-Meier survival rate with aseptic loosening as the endpoint was 100% at five years (Fig. 6). As both revisions for aseptic loosening occurred beyond six years they do not affect the curve. Extension of the curve beyond five years is not recommended owing to small numbers of patients remaining at risk.^13,14 With an endpoint of acetabular revision for any reason, the survival rate is 92.2% (95% CI 84.8 to 99.6%) at five years.

Discussion

The evidence supporting the use of the cement-in-cement technique has been reviewed by Keeling et al.¹⁵ Three of the four biomechanical studies in this area^10,16,17 and the five main clinical papers^2,5,18-20 have all shown clear evidence to support the technique in the short to medium term, at least on the femoral side. The biomechanical study that did not support the technique recognised the problem of contamination with blood or marrow fat at the new interface.²¹ These problems can be overcome with appropriate operative technique.

If this method is to be used, it is essential that there is a well-fixed acetabular cement mantle both radiologically and on direct intra-operative inspection. If there are any signs that it is unsuitable, an alternative technique should be used. Although less common than the indications for a femoral cement-in-cement revision, it is sometimes necessary to change a well-fixed cemented acetabular component. In our series, the main indications were for a change of the orientation or size of the component, or constraint was required to manage recurrent dislocation (77%), or to change the size or orientation of a well-fixed acetabular component at the time of a femoral revision (20%).

One observation of interest is that of the five hips that subsequently underwent further revision for persistent instability or disarticulation of a constrained component, all were managed using a further cement-in-cement technique. This emphasises the relative modularity of the cemented THR at the prosthesis–cement interface, while allowing maintenance of the cement–bone interface, as is also the case on the femoral side.

Although the improvement in outcome was statistically significant for pain, function and range of movement (Table I), there was only a modest increase in the results for function. It should be noted, however, that most operations (77%) were performed for recurrent dislocation and most patients had relatively good function, and therefore the clinical scores would not be expected to change dramatically.

Of the two aseptic failures, one was at the cement–prosthesis interface in a hip where a component not originally designed for use with cement was used. It is quite possible that the relatively weaker bond at this interface (in contrast to the pre-cut grooves in a standard cemented component) was the main factor leading to this failure. The results at a mean of more than seven years, which compare favourably with those using alternative revision techniques,²² and indeed with many primary series in a similar time frame,^23-26 are encouraging and support the continued use of this technique. Limitations of this study include the fact that, despite being prospective, it was an observational case series with relatively small numbers. It was from a specialist unit with a long history of cemented THRs. It remains to be shown whether these results are reproducible elsewhere.

Figures 2, 3 and 5 are reproduced with kind permission of Exeter Hip Publishing.

The authors wish to acknowledge the contribution of Mr G. Gie who performed many of the original operations and pioneered this technique. They would also like to thank the members of the Exeter Hip Unit, R. Sculpher, S. Wraight, L. Collett and C. Harris, for their assiduous work in keeping track of every patient.

The author or one or more of the authors have received or will receive benefits for personal or professional use from a commercial party related directly or indirectly to the subject of this article. In addition, benefits have been or will be directed to a research fund, foundation, educational institution, or other non- profit organisation with which one or more of the authors are associated.