Revision of Failed Total Hip Arthroplasty Acetabular Cups to Porous Tantalum Components

The Journal of Arthroplasty Vol. 25 No. 6 2010

Revision of Failed Total Hip Arthroplasty Acetabular Cups to Porous Tantalum Components A 5-Year Follow-Up Study Mariano Fernández-Fairen, MD, PhD,* Antonio Murcia, MD, PhD,y Agustin Blanco, MD, PhD,z Antonio Meroño, MD,§ Antonio Murcia Jr, MD,§ and Jorge Ballester, MD, PhDO

Abstract: We reviewed 263 consecutive patients with failed acetabular components after total hip arthroplasty that were revised using porous tantalum acetabular components and augments when necessary. The mean follow-up was 73.6 months (range, 60-84 months). The improvement of mean Harris hip score, Western Ontario and McMaster Osteoarthritis Index, and University of California Los Angeles activity scales were statistically significant (P b .001). Subjective assessments showed that 87.3% of patients reported “improvement” and 85.9% were “very or fairly pleased” with the results. At the most recent follow-up, all acetabular components were radiographically stable and none required rerevision for loosening. The acetabular revision was considered successful in 87% of cases. From this study, we conclude that the acetabular component used was reliable in creating a durable composite without failure for a minimum of 5 years. Keywords: total hip arthroplasty, acetabular revision, porous tantalum component. © 2010 Elsevier Inc. All rights reserved.

Most acetabular revision procedures are performed using cementless porous-coated hemispherical acetabular components, with or without adjunctive screw fixation and bone grafting for defect repair when necessary [1-11]. The long-term fixation of the acetabular component depends on obtaining optimum initial mechanical stability (macrofixation) followed by bone ongrowth/ingrowth (microfixation). However, the presence of extensive acetabular bone defects frequently compromises the ability to achieve initial macrofixation and early component stability. Various surgical options have been described to treat these

From the *Instituto de Cirugía Ortopédica y Traumatología de Barcelona, Barcelona, Spain; yServicio de Cirugía Ortopédica y Traumatología. Hospital de Cabueñes, Gijón (Asturias), Spain; zServicio de Cirugía Ortopédica y Traumatología. Complejo Hospitalario General, Yagüe-Divino Valles, Burgos, Spain; §Servicio de Cirugía Ortopédica y Traumatología. Hospital Virgen del Rosell, Cartagena (Murcia), Spain; and OUniversidad Autónoma de Barcelona, Barcelona, Spain. Submitted May 30, 2008; accepted July 21, 2009. No benefits or funds were received in support of the study. Reprint requests: Mariano Fernández-Fairen, MD, PhD, Instituto de Cirugía Ortopédica y, Traumatología de Barcelona, Diputación 321, 08009 Barcelona, Spain. © 2010 Elsevier Inc. All rights reserved. 0883-5403/02506-0005$36.00/0 doi:10.1016/j.arth.2009.07.027

difficult revision arthroplasty cases [12-21]. In those cases involving significant acetabular defects, multiple concurrent issues exist for creating a durable acetabular composite. The uncertainty of achieving true biologic fixation in these revision composites involves simultaneously obtaining optimum component fit while maximizing contact with viable host bone and achieving bone graft incorporation [22]. To address the multivariable nature of revising a failed acetabular component, the use of a porous tantalum system of acetabular components and augments was proposed and used as a solution for such cases [22-27]. Tantalum has excellent mechanical and biologic compatibility with host bone and can be manufactured with a high-friction surface for optimizing the primary stability of the component [28]. The characteristics of the porous structure, in conjunction with the bioactivity of material surface, is shown to induce bone ingrowth with complete osseointegration of the scaffold at 4 to 6 months [29,30]. The short-term clinical results of tantalum components for the revision of failed acetabula in total hip arthroplasty are encouraging [22,24-27]. The primary purpose of this study was to analyze the minimum 5-year clinical and radiographic results obtained in a consecutive series of 263 cases of failed acetabular components in total hip arthroplasties revised

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866 The Journal of Arthroplasty Vol. 25 No. 6 September 2010 by means of the Trabecular Metal (TM) acetabular system (Implex Corporation, Allendale, NJ; Zimmer, Warsaw, Ind). The secondary purpose was to consider these results in relation to the acetabular bone deficiency present at the time of revision.

Materials and Methods Between July 2000 and December 2002, 263 consecutive patients across 5 surgical centers underwent revision of a failed acetabular component in which TM acetabular components were used. Patients presenting with infection, tumors, irradiated pelvis, and patients receiving antitumor drugs were excluded from this series. There were 150 women and 113 men with a mean age of 69.5 years (range, 39-84 years) at the time of revision (Table 1). The mean time from the previous procedure to revision was 8.9 years (range, 4 months to 12 years). The procedure was the first revision of the failed index acetabular component in 198 cases (75.2%). The other 65 patients had had a mean of 2.7 previous surgical procedures (range, 2-5). The indication for acetabular revision was aseptic loosening in 186 cases (70.7%), polyethylene wear with or without osteolysis in the presence of stable components in 62 cases (23.5%), and femoroacetabular instability and/or impingement in 15 cases (5.7%). Of those cases presenting with aseptic loosening, there were 148 in which periacetabular lesions were present. The femoral component was simultaneously revised in 170 cases (64.6%). Clinical and radiographic assessments were performed for each patient before and immediately after the revision procedure and at the follow-up points at 3 months, 6 months, and annually thereafter. At the time of admis-

Table 1. Demographic Data Age (y) Sex Male Female Time from previous surgical procedure (y) Indication for revision Aseptic loosening Polyethylene wear Femoroacetabular instability/impingement Charnley classification A B1 B2 C Paprosky classification Type 1 Type 2 Type 2A Type 2B Type 2C Type 3 Type 3A Type 3B

69.5 (39-84) 113 150 8.9 (0.33-12) 186 (70.7%) 62 (23.5%) 15 (5.7%) 33 (12.5%) 99 (37.6%) 111 (42.2%) 20 (7.6%) 20 (7.6%) 194 (73.7%) 73 (27.7%) 82 (31.1%) 39 (14.8%) 49 (18.7) 40 (15.2%) 9 (3.4%)

sion, the Charnley classification for the assessment of comorbidity was used [31]. Before the impending acetabular revision procedure, 33 patients were identified as Charnley class A (12.5%), 99 as Charnley class B1 (37.6%), 111 have both hips replaced (Charnley class B2, 42.2%), and 20 had multiple joint disease or other disabilities leading to difficulties in walking (Charnley class C, 7.6%). Clinical evaluations were performed at all follow-up intervals using the Harris hip score (HHS) [32]. A score of 90 to 100 was considered as excellent, 80 to 90 as good, 70 to 80 as fair, and below 70 as poor. All patients completed the Western Ontario and McMaster Osteoarthritis Index (WOMAC) questionnaire (Spanish adaptation) as a disease-specific, self-administered health assessment [33]. The raw score was normalized to the 0 to 100 scale, with zero as the worst quality of life and 100 the best [34]. The outcome values for this score were divided into 3-part categorical responses, 0 to 63 poor, 64 to 85 good, and 86 to 100 excellent [35]. Patient activity was graded using the University of California Los Angeles (UCLA) activity scale [36]. Patients were also asked whether they were very pleased, fairly pleased, not very pleased, or very disappointed with the operation, and whether their hip was much improved, slightly improved, unchanged, slightly worse, or much worse than before surgery [37]. Questionnaires were administered by MF-F and AM Jr. Standardized anteroposterior and lateral radiographs were obtained at all follow-up intervals and reviewed by the operating surgeon and 2 independent radiologists (AM and NL) having no knowledge of the clinical outcome and not having taken part in any other stage of this work. Implant and screw position, polyethylene wear, radiolucent lines, gaps, and osteolysis were assessed. Radiolucent lines adjacent to the acetabular component and/or augments were identified as described by DeLee and Charnley [38]. The width of radiolucencies was measured to the nearest millimeter using a transparent ruler. Acetabular index, hip center, and migration of acetabular component were considered after the method proposed by Callaghan et al [39]. The vertical distance from the center of femoral head to the interteardrop line and the horizontal distance to the perpendicular to this line at the teardrop figure were calculated. A normal hip center is reported to be 12 to 14 mm above the interteardrop line and 33 to 43 mm lateral to the acetabular teardrop [40]. A high hip center was arbitrarily defined as having the center of rotation on an anteroposterior radiograph greater than 35 mm proximal to the interteardrop line [41]. A component was described as radiographically unstable if a 1 mm or greater lucent line occurred across all 3 acetabular zones or if any measurable cup migration occurred [27]. Loosening was characterized by a change in the component abduction angle of greater than 10° or in the horizontal or vertical position of greater than 6 mm

Revision of THA Acetabular Cups to Porous Tantalum Components  Fernández-Fairen et al

observed in successive radiographs, after correcting for magnification [25]. Osteolysis was considered present when lucent areas were visible on plain radiographs and measured at least 4 mm2 [27]. Helical computed tomography with metalartifact minimization was made in each patient preoperatively to estimate the location and volume of bone defects [42]. Preoperatively, acetabular bone deficiency was categorized using the classification of Paprosky et al [43]. Twenty cases (7.6%) were graded type 1. Type 2 was seen in 194 cases (73.7%), type 2A in 73 cases (27.7%), type 2B defect in 82 cases (31.1%), and type 2C in 39 cases (14.8%). Forty-nine hips (18.7%) had Paprosky type 3 defects. Forty hips (15.2%) had a type 3A defect, and 9 hips (3.4%) had type 3B defects. A standard posterolateral approach was used for 160 cases (60.8%), and anterolateral approach for the other 103 cases (39.2%). An extended trochanteric osteotomy was performed in 78 (45.8%) of 170 cases where acetabular and femoral components revised. Acetabular reconstruction involved removal of the failed acetabular component, debridement of the acetabular cavity, and careful assessment of the bone quality and bone loss. Progressive reaming was performed to shape the acetabulum to a size capable of engaging the shell into the anterior and posterior columns for component stability. An uncemented press-fitted TM Monoblock Acetabular Cup was used in 78 (29.6%) of 263 cases. The 78 cases using this cup included 18 type 1 acetabular defects and 60 type 2 acetabular defects. A TM Revision Shell allowing screw augmentation and a polyethylene liner cemented inside the cup. Adjunctive screw fixation was used in 136 of 214 cases, including the remaining type 1 and 2 cases and in all 49 patients with type 3 defects. The decision to use adjunctive screw fixation was made intraoperatively while assessing the stability of the trial component. If the fixation was thought to be questionable, the TM Revision component was used with the necessary adjunctive screw fixation. Acetabular component augments were added to reduce the enlarged acetabular defect volume thus restoring the acetabular rim to aid in the support of the revision component. A TM Modular Augment, shaped similar to a partial hemisphere with large windows and rim screw holes, was indicated when less than 50% host acetabular bone was present, when additional support to the tantalum metal component was needed, or when it was necessary to stabilize a pelvic discontinuity [27]. The decision to use augments was made at the time of surgery based on the inability to stabilize the revision component. Once the desired cup position was identified, the augment was positioned and tailored to optimize the filling and fit to the bone defect and to provide primary support for the acetabular component. The augments used were 10 and 20 mm in height and were fixed by screws to the host bone. The location and orientation of

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the augments depended upon the specific bone loss pattern, but the most frequent position was posterosuperior. A combination of TM Revision Cup and porous tantalum modular augments was used in 34 cases (12.9%), 3 type 2B defects (3/82; 3.6%), 22 type 3A defects (22/40; 55%), and in the 9 hips with type 3B defects. Morsellized bone allograft was added to repair bone defects in 126 cases (48%), and structural bone graft was not used. Postoperatively, the patients were instructed to partially weight bear on the operative leg, using an adjunctive walking aid for a minimum of 6 weeks. Fifty-two patients were also asked to use a hip abduction orthosis during this time. Patients were carefully monitored for complications associated with revision. The intimate fit of the cup into the acetabulum, as manifested by radiographic evidence of interface gaps, and stability were assessed in the radiographs obtained at the different periods of follow-up. Periacetabular gaps were defined as areas in which the porous surface of the acetabular component did not achieve direct initial contact with bone. This is to differentiate areas of apparent decreased density from radiolucent lines that appear on subsequent radiographs in areas where no gaps existed previously [44]. Periacetabular gaps were recorded as “present” when they involved 50% or more of the acetabular I, II, or III zone, as categorized by DeLee and Charnley [38], on the early postoperative radiograph [45]. The width of gaps was measured by the methodology of the measurement of lucent lines described above. Radiographic evidence of bone ingrowth and stable fixation was assumed when the implant was in closed contact with bone and lucent lines were absent in 2 of the 3 zones. Fibrous stability was considered present when there was a less than a 1 mm lucent line in 2 of the 3 zones. Evidence of ingrowth and the absence of late migration determined the stability of acetabular component radiographically [27]. Success of revision was defined as an increase in the scores of 20 or more points, a stable cup, with no additional surgery on the acetabulum [46], and the patient “feeling improved” and “pleased” with the operation. Statistical analyses were performed using SPSS statistical software version 16.0 for Windows (SPSS Inc, Chicago, Ill). Statistical tests performed included the t test, paired t test, and Wilcoxon signed ranks test for paired samples, the Mann-Whitney U test to estimate differences between the different groups, and analysis of variance for the appropriate data set. The χ2 test was used to analyze the correlation between the Charnley grade and the clinical scores and between outcomes and Paprosky type of defect. Significance for each statistical test was set at P b .05. The intraobserver reproducibility was performed for each examiner by comparing the results of 2 blinded nonconsecutive assessments of each radiograph. Statistical analysis was performed using nonparametric correlations. κ values between 0.61 and 0.8 were considered “substantial agreement” and

868 The Journal of Arthroplasty Vol. 25 No. 6 September 2010 between 0.81 and 0.99 “almost perfect agreement.” Standard life table was constructed, and the survival rate was calculated by means of Kaplan-Meier method.

Results The overall mean follow-up was 73.6 months (range, 60-84 months), and no patient was lost to follow-up. There were 6 deaths unrelated to the revision procedure (2.3%). However, the clinical and radiologic assessments for all 6 patients were collected within the minimum 5year follow-up period and were subsequently included in this study. The preoperative HHS rating improved from a mean of 43.6 ± 11.4 (range, 23-62) before revision, to a mean of 82.1 ± 10.7 (range, 48-96) at 1 year after revision and of 80.4 ± 9.8 (range, 43-94) at the most recent evaluation. At the most recent follow-up, 62 patients (23.5%) were graded as having an excellent result, according to the HHS, 111 (42.2%) with a good result, 64 (24.3%) with a fair result, and 26 (9.8%) with a poor result. The preoperative WOMAC score was 42.9 ± 15.4 (range, 10-65) with an improvement to 80 ± 19 (range, 50-100) at 1-year follow-up and 78.0 ± 15.8 (range, 47-100) at the last review. At this time, the outcome values after the WOMAC score were rated as excellent in 80 patients (30.4%), good in 129 (49%), and poor in 54 (20.5%). The median UCLA score was 3 (range, 1-4) prerevision, rising to 6 (range, 2-8) at 1-year follow-up and at the time of the last evaluation. The improvement from the preoperative to the postoperative clinical evaluation was statistically significant (P b .001) (Table 2). There was no significant difference between the scores at 1 year postoperatively and at the last review (P N .1). Likewise, there was no correlation between outcomes and Paprosky type defect (R, 1.03; 95% confidence interval, 0.90-1.23; P N .05). The reported Charnley grade correlated markedly with the HHS (P b .001), WOMAC (P b .001), and UCLA score (P b .05). At the final review, 178 patients reported their hip “improved” after the revision (67.6%), 52 patients reported their hip to be “slightly improved” (19.7%), 12 patients reported “no change” (4.5%), 13 patients reported they were “slightly worse” (4.9%), and 8 reported that they were “much worse” than before revision surgery (3%). One hundred thirty patients stated they were “very pleased” with the result of revision (49.4%), 96 patients were “fairly pleased” (36.5%), 14 were “not very pleased” (5.3%), and 23 patients were

“very disappointed” with the results of the revision procedure (8.7%). Radiographic assessment showed a mean abduction socket angle of 45.4° ± 7.6° (range, 36°-55°) after revision. The center of the femoral head was relocated from a mean of 3.4 cm proximal to the interteardrop line (range, 1.8-5.2 cm) on the prerevision radiographs, to a mean of 1.2 cm (range, −1.1 to 2.5 cm) after revision, and from a mean of 1.6 cm (range, −5 to 2.4 cm) lateral from the vertical at the teardrop to a mean of 3.1 cm (range, 0-4.9 cm). There was radiographic evidence of full contact between the acetabular component and the peripheral bone, in 227 cases (86.3%). In 8 cases, a gap from 1 to 4 mm width was observed in zone I immediately postrevision, in 22 cases in zone II, and in 6 cases in zone III. At the final examination, 28 gaps had become completely filled (77.7%), 4 were partially filled (11.1%), and 4 remained unchanged (11.1%). All cases involving the use of bone grafts had radiographic evidence of incorporation with complete filling of all the prerevision defects. There was no

Table 2. Clinical Outcomes Mean HHS Mean WOMAC Median UCLA

Prerevision

Last Follow-Up

P

43.6 ± 11.4 (23-62) 42.9 ± 15.4 (10-65) 3 (1-4)

80.4 ± 9.8 (43-94) 78.0 ± 15.8 (47-100) 6 (2-8)

b.001 b.001 b.001

Fig. 1. Type 2C defect. (A) Prerevision. (B) Seven years postrevision performed with morsellized allograft and revision cup and additional screws.

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evidence of new osteolysis foci. No progressive radiolucent lines or component migration was observed at the most recent follow-up. Therefore, all acetabular components were defined as radiographically stable. The κ coefficient for intraobserver and interobserver reproducibility was 0.92 and 0.85, respectively. Representative radiographs of 2 cases are shown in Figs. 1 and 2. There were 8 cases of hip dislocation (3%), successfully treated with closed reduction and brace with no recurrence of hip instability. One patient had a sciatic palsy that was only partially resolved at the most recent follow-up. There were no cases of deep vein thrombosis, pulmonary embolism, or acetabular/pelvic fractures. There were 2 cases of stable acetabular components presenting with late infection (0.76%) during the first postoperative year, of which both were rerevised. None of the patients was rerevised for loosening. Details of life tables are presented in Table 3. The cumulative prosthesis survival calculated with 95% confidence intervals was 99.2% at 5 years after operation (Fig. 3). A successful revision, following the aforementioned criteria, was achieved in 87% of cases.

Discussion Although acetabular revision is a technically demanding operation, our results show that acetabular composite stability and durability can be achieved when using tantalum acetabular components. The rate of success with tantalum components is also similar to that achieved with the custom-made triflange cup [15] and higher than that reached with conventional or extra large cementless cups supplemented by screws, morsellized or structural allografts, and reconstruction rings or cages [17,18,47]. The clinical results in this series are similar or moderately better than those reported in other series using different methods of revision [1,3,4,6,8,13,14,17,18]. We obtained statistically significant increases in HHS, WOMAC, and UCLA scores postoperatively that remain preserved without significant changes from the first year to the most recent follow-up. Although patients originally presenting with poorer preoperative scores and multiple comorbidities tend to have poor postoperative scores, the overall degree of subjective improvement and satisfaction in our study is similar than that reported by other authors [13,37]. In our study, there was no correlation found between the various degrees of acetabular bony defect and the magnitude of clinical results thus indicating that all postoperative outcomes were statistically equal independent of prerevision Paprosky grade. Conversely, GarcíaCimbrelo [4] reported decreased clinical results in cases

Fig. 2. Type 3A defect. (A) Hip dislocation and loosening of cage. (B) Failure of revised hip using impaction grafting technique. (C) Six years postoperative radiograph of stable revision cup and augment.

870 The Journal of Arthroplasty Vol. 25 No. 6 September 2010 Table 3. Life Table * Interval start time Number entering interval Number withdrawing during interval Number exposed to risk No. of terminal events Proportion terminating Proportion surviving Cumulative proportion surviving at end of interval SE of cumulative proportion surviving at end of interval Probability density SE of probability density 95% confidence interval upper bound 95% confidence interval lower bound

0 263 0 263 2 .01 .99 .99 .01 .008 .005 1.00 .98

1 261 0 261 0 .00 1.00 .99 .01 .000 .000 1.00 .98

2 261 0 261 0 .00 1.00 .99 .01 .000 .000 1.00 .98

3 261 0 261 0 .00 1.00 .99 .01 .000 .000 1.00 .98

4 261 0 261 0 .00 1.00 .99 .01 .000 .000 1.00 .98

* The median survival time is 5.00.

presenting with more severe grades of acetabular bony defect when using a combination of conventional cementless acetabular components, adjunctive screw fixation, and morsellized or structural allograft for revision. The avoidance of poor clinical results related to classic revision methods in cases with a severe bone deficiency may be a primary reason to support the use of porous tantalum for achieving a stable and durable revision acetabular composite [27]. The radiographic assessment of our consecutive series confirms the positive performance of porous tantalum in acetabular revision and the achievement of a stable and durable component composite. The incidence of radiolucent lines observed with the TM acetabular components is significantly lower than that displayed around the conventional porous-coated components [4,6-8,10,11,45]. The excellent osteoconductive properties of porous tantalum trabecular metal may enable faster, wider, and stronger biologic fixation, even when limited viable host bone is available [23]. For this reason, the TM acetabular components have been

Fig. 3. Cumulative prosthesis survival estimate with 95% confidence intervals.

successfully used in Paprosky type 3 defects, with limited host bone contact [22,24,25,27]. The number of postoperative gaps observed in our cases were less than the incidence reported by other authors using tantalum acetabular components also [26,45,48]. The optimum interface contact between the metallic shell and host bone was easily obtained in all cases. In those cases with radiographic evidence of periacetabular gaps, 28 of 36 cases showed complete gap filling within the early follow-up period. Because no migration of the acetabular component was observed in our series, we hypothesize that new bone filled the gaps as similarly reported by other authors [26,45,48]. Tantalum components show a significantly high frequency of biologic resolution of gaps in comparison with porous-coated titanium components [48]. The bioreactive properties of porous tantalum may promote bone formation even across periacetabular defects up to 5 mm in width [48], whereas the width of the defect must be less than 1 mm to obtain the same end result with porous-coated titanium components. For ingrowth to occur, the component must be initially stable. In Paprosky type 1 and in a substantial number of type 2 acetabular defects, excellent stability can be achieved by the tight press-fit of the “expanded hemisphere” hemielliptical cup. In these cases, the equatorial perimeter of the component was more than 1 mm greater than the hemispheric reamer used in preparing the acetabular cavity. The high friction of the rough outer surface of the shell helps in the stabilization of component inside the prepared acetabulum [26]. If press-fit stability was not initially achieved, the appropriate sized revision component was selected and adjunctive peripheral screw fixation was used. In cases presenting with Paprosky type 3 defects, augments were used to fill the large defect and allow for direct apposition of the tantalum surface to host bone. However, in cases where augments may not provide adequate defect repair and component stability, an acetabular cage and component composite may be used [23,27]. In our series, the use of large structural grafts and/or cages was avoided. In addition, the use of component augments allowed us to minimize the volume

Revision of THA Acetabular Cups to Porous Tantalum Components  Fernández-Fairen et al

of morsellized allograft used for defect repair. In this way, the associated risks of allograft use, including a reported high rate of failure, lack of incorporation, bulk allograft resorption [4,15-17], the technical difficulty, and the subsequent high failure rate of rings or cages [23,47,48], were avoided. A favorable biomechanical environment for the incorporation of morsellized graft and osseointegration of components are advantages of porous tantalum compared with other component surface preparations. Revision success was enhanced by the ability to place the component at the center of hip rotation [22]. Durable stability and bone fixation of the reconstructed acetabulum was obtained in 100% of our cases, with no rerevision performed for loosening, and no differences correlating outcomes with the severity of bony defect, the use of nonmodular or modular constructs, and the addition of morsellized graft or not, as reported in the literature for the TM system [22,27]. The strengths of this study include a large sample size (263 cases), the use of a reproducible surgical protocol, the component and augment sizes available, the minimum length of patient follow-up (5 years), and the follow-up evaluation tools, with 100% of patients returning to successive controls. A perceived limitation of this study may involve the use of multiple surgical centers and surgeons. However, we saw no differences in outcomes across surgeons or centers. Continued follow-up of this cohort will be essential to determine the long-term performance of tantalum in revised acetabular components with tougher definition criteria of migration and loosening—weaknesses of this study. In conclusion, the analysis of this consecutive series of acetabular revisions with the TM acetabular component demonstrates promising midterm results similar to those reported by other authors [22,24-27]. We report reproducible results in obtaining a stable and durable acetabular revision composites without deterioration through minimum of 5 years. The TM acetabular components used in our study allow for a reliable method for the management of failed acetabular components in a large variety of periacetabular bone defects.

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