Trabecular Metal Used for Major Bone Loss in Acetabular Hip Revision

The Journal of Arthroplasty Vol. 26 No. 8 2011

Trabecular Metal Used for Major Bone Loss in Acetabular Hip Revision Jonah Hebert Davies, MD, G. Yves Laflamme, MD, FRCSC, Josee Delisle, RN, BScN, MSc, and Julio Fernandes, MD, MSc, PhD, MBA

Abstract: The purpose of this study was to evaluate the outcome of trabecular metal (TM) acetabular components used in revision hip arthroplasty with major bone deficiency. We retrospectively reviewed the records of 46 patients undergoing revision hip arthroplasty with severe acetabular bone loss. Clinical outcomes were assessed using Harris Hip Score, Western Ontario and McMaster Universities, and Short-Form 12. Mean follow-up was 50 months. All patients had Paprosky type IIc or III acetabular bone deficiency. Major complications included 1 infection, 2 dislocations, and 1 arterial bleeding. Average Harris Hip Score was 78.2. Short-Form 12 scores were within population-based age-matched averages. Western Ontario and McMaster Universities scores were mainly in the 2 lowest disability categories. Porous tantalum shows promising results in revision arthroplasty with severe acetabular bone loss. Keywords: trabecular metal, revision, arthroplasty, acetabulum. © 2011 Elsevier Inc. All rights reserved.

Treating large segmental acetabular defects and achieving stable implant fixation are among the most difficult challenges in hip revision arthroplasty. Reconstruction with structural acetabular allografts protected by a cage is the traditional solution for large segmental defects, yet it does not provide biological fixation and often ends in failure [1]. Data are accumulating in support of porous tantalum (PT) as an alternative [1-3]. The inherent properties of trabecular metal (TM) implants allow for many potential benefits in revision arthroplasty. Recent studies have reported results with TM components showing low short-term failure rates [4-8]. The largest cohort reported by Van Kleunen et al [7] included 97 acetabular revisions with Paprosky type 2 (64%) and type 3 (36%). There were no aseptic failures at a minimum of 2 years of follow-up. Kim et al [9] reviewed 46 acetabular revisions with types 2 and 3 bone defects, with only 1 failure at a mean follow-up of 40 months. In 2009, a retrospective comparative study showed similar results for tantalum and titanium cups in acetabular revision with minor bone defect (Paprosky From the Division of Orthopaedic Surgery, University of Montreal, Hôpital du Sacré-Coeur, Montreal, Quebec, Canada. Submitted September 9, 2010; accepted February 10, 2011. The Conflict of Interest statement associated with this article can be found at doi:10.1016/j.arth.2011.02.022. Reprint requests: Jonah Hebert Davies, MD, University of Montreal, Division of Orthopaedic Surgery, Hôpital du Sacré-Coeur, 5400 Gouin Ouest, Local C-2095, Montreal, Quebec, Canada, H4J 1C5. © 2011 Elsevier Inc. All rights reserved. 0883-5403/2608-0022$36.00/0 doi:10.1016/j.arth.2011.02.022

types 1, 2a, and 2b). In hips with major bone deficiency (Paprosky types 2c and 3), 12% of tantalum cups and 24% of titanium cups developed failure. Furthermore, 80% of cups that failed did so in less than 6 months [8]. The purpose of this study was to evaluate the outcome of TM acetabular components used in revision total hip arthroplasty with major bone deficiency. It was our belief that using TM components would yield equivalent or superior results to standard treatment even in cases of severe bone loss.

Materials and Methods We retrospectively reviewed the clinical records and radiographs of 46 patients undergoing revision hip arthroplasty with major bone deficiency, defined as Paprosky type 2c and Paprosky type 3, using TM implants (Fig. 1A-C). All surgeries were performed by the same surgeon. Before the study, we obtained institutional review board approval. We excluded minor bone defect classified as Paprosky Types 1 and 2a-b. Patients were seen at 1, 3, 6, and 12 months postoperatively and then yearly. Minimum follow-up was 2 years. A radiographic evaluation of the patient's hip was performed on preoperative and postoperative radiographs (based on anteroposterior and shoot-through lateral views) as well as on most recent follow-up radiographs. Two independent reviewers recorded results on predefined radiographic evaluation forms. Preoperative anteroposterior radiographs were graded according to the acetabular defect classification of

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Fig. 1. (A) Paprosky type 2c acetabular defect. (B) Type 3a; the “up and out” defect. (C) Type 3b; the “up and in” defect.

Paprosky et al (Fig. 1A-C). Postoperative radiographic evaluation was based on the 3 acetabular zones of DeLee-Charnley [10]. Cups were considered radiographic failures if any of the following criteria were identified: migration of the cup of more than 5 mm in either horizontal or vertical directions [11], radiolucent lines of 2 mm or more in all DeLee-Charnley zones, breakage of screws, or variation of cup angle greater than 5°. The number of lucent lines (2 mm or more) was counted around the cups. Clinical outcomes were assessed at latest follow-up using 3 validated quality-of-life scores. Patients responded to Harris Hip Score (HHS) [3], Western Ontario and McMaster Universities(WOMAC) [12], and Short-Form 12 (SF-12) [13] questionnaires during the last postoperative visit in clinic. Surgical Technique All patients were operated on using a standard posterolateral approach, which was occasionally extended with a greater trochanter osteotomy to expose the femur. The degree of acetabular bone loss was confirmed after removal of the previous acetabular component. When pelvic dissociation was identified, the posterior column was rigidly fixed with a 3.5-mm pelvis reconstruction plate (Synthes, West Chester, PA). Progressive reaming was performed to obtain the best possible press-fit between the anterior and posterior walls. Trial components were used to evaluate the defect's size and the need for additional support. In these cases, either an augment or buttress plate was added for increased stability (Fig. 2). In 2 cases, the bone stock was deemed insufficient to achieve stability; and a cup cage construct was used. Trial augments were inserted to find

the best fit with optimal host bone contact. Definitive augments or buttress plates were then secured with a minimum of 2 screws. Cancellous bone allograft was packed within the augments and the remaining bone defects. The nonmodular TM shell was used in all cases and stabilized with 6.5-mm screws (Zimmer titanium acetabular screws; Zimmer, Warsaw, IN). The TM acetabular revision shells are available in sizes from 48 to 80 mm in 2-mm increments. Polyethylene liners with an inner diameter of 28 mm are available for all cup sizes: 32 mm for cups starting at 54 mm, 36 mm for cups larger then 58 mm and 40 mm for cups 62 mm and larger. In our series, cups between 58 and 70 mm were used. If the location of the screw holes within the shell were insufficient, we drilled custom screw holes using a

Fig. 2. Clockwise from left: buttress plate, oblong augment, button augment, square buttress, and cup cage.

Trabecular Metal Used for Major Bone Loss  Davies et al

high-speed burr, allowing optimal positioning of the additional screws. Finally, we cemented a posterior lipped cross-linked polyethylene cup into the shell using Simplex cement with tobramycin (Stryker, Mahwah, NJ) as well as augments and buttress plates, according to manufacturer's recommendations. Head sizes were between 32 and 36 mm, except in 1 case where a monoblock stem with 22-mm head was not revised. All patients were allowed toe-touch weight bearing for 6 weeks postoperatively. A standard limited range of motion protocol was used to protect from dislocation.

Results From 2002 to 2007, 46 patients (46 hips) underwent revision hip arthroplasty using TM implants for major acetabular bone loss (see Table 1 for patients' characteristics and clinical details). There were 22 men (48%) and 24 women (52%). Average age was 66.7 years (range, 39-85), and mean follow-up was 50 months (range, 2876). Three patients were lost to follow-up because of unrelated death. The indications for acetabular component were acetabular loosening in 27 patients (59%), osteolysis in 9 hips (20%), and infection in 4 patients (9%). The acetabular component alone was revised in 23 patients; the femoral component was revised in combination for the other 23 patients. A TM augment was used in 15 cases (33%) (Figs. 3 and 4), with 2 patients requiring a cup cage construct. Pelvic bone loss

Table 1. Patient Characteristics and Demographics Sex, n (%) Male Female Average age at revision surgery (y), range (SD) Lost to follow-up Comorbidities None 1 2 3 or more Previous revisions, n 0 1 2 3 Reason for revision Osteolysis Aseptic loosening Infection Other Paprosky classification, n (%) IIc IIIa IIIb Pelvic discontinuity Femur revised, n (%) Augment used, n (%) Average follow-up (mo), n (SD) Range

22 (48%) 24 (52%) 66.7 (39-85) 4 9.1% 29.5% 27.3% 34.1% 13 26 4 3 9 (20%) 27 (59%) 4 (8%) 6 (13%) 22% 44% 25% 9% 23 (50%) 14 (30%) 50 (14.1) 28-84

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Table 2. Functional Outcome Scores Functional Score WOMAC Pain Stiffness Daily activities SF-12 Mental component Physical component HHS

Average

Standard Deviation

Range

3.6 1.4 15

4.5 1.4 13.5

0-22 0-4 0-48

55 42.2 78.2

9.8 9.1 13.8

32-69.6 27-62 26-96

was distributed as follows according to Paprosky classification: 10 type IIc (22%), 21 type IIIa (46%), 11 type IIIb (24%), and 4 (9%) pelvic discontinuities. Major complications included 1 infection that required a 2-stage revision. Dislocation occurred in 2 patients treated with closed reduction, and significant heterotopic ossification (Brooker grade 3 [14]) was seen in 3 cases. One patient with an intrapelvic cup sustained arterial bleeding necessitating endovascular repair. Patients with a cup cage construct were at increased risk for dislocation (P b .05) There were no cases of aseptic loosening. No polyethylene liner dislodgments or liner fractures were seen. Nonprogressing periacetabular radiolucencies were present in 5 patients (11%) on the latest radiographs, with no patients having complete radiolucency. Interobserver reliability was considered excellent with a κ value of 0.879. Quality-of-life scores were available for 37 patients. This excluded 3 patients who died and 6 who were lost to follow-up. Complete breakdown of results can be seen in Table 2. Average HHS was 78.2 (range, 26-96), with 58% of patients in the “excellent or good” categories. Average SF-12 scores were 55 (32-70) for the mental component and 42.3 (27-62) for the physical component. Both these scores were within populationbased age-matched averages [15]. The WOMAC scores for pain, stiffness, and activities were 3.6, 1.4, and 24.9, respectively. Most patients were in the 2 lowest disability categories (91% and 81%, respectively). A higher number of revision (second or third) correlated with a lower functional score (WOMAC, HHS; P b .05) (Figs. 3 and 4).

Discussion Severe bone loss can compromise both the biologic potential and mechanical stability needed for reliable osteointegration of the acetabular component. Defects with minimal bone deficiency and structural support (types I and IIa-b defects) can be reconstructed with the use of a hemispherical acetabular component with or without the use of nonstructural cancellous bone graft. Excellent long-term results have been reported with this type of treatment [16]. Titanium and tantalum cups showed similar results in hip revision with minor

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Fig. 3. (A) Preoperative radiograph of patient with dislocated fractured cage construct and severe bone stock loss. (B) Postoperative radiograph showing cup and augment construct.

deficiency [8]. These authors concluded that conventional titanium acetabular components perform well in most circumstances and that TM cups may be considered when severe bone loss exists. Several options are available to deal with severe bone loss in acetabular revision THA. The use of a cemented polyethylene component with impaction allografting [17,18], reconstruction rings or cages [17,19-21], structural allografting [21-25], use of an extralarge uncemented cup [26], bilobed cementless acetabular components [27], and implantation of a smaller hemispherical component at a high hip center [28,29] have been reported, with mixed results. The PT acetabular shell is a novel implant introduced recently for revision hip arthroplasty. Unger et al [4] first reported on the use of a monoblock TM cup (Zimmer) in 2005 with a series of 60 patients undergoing revision

Fig. 4. (A) Example of buttress plate used to address acetabular defect. (B) Demonstration of cup cage construct.

THA. Seven cases underwent reoperation including 5 for dislocations, 1 for initial cup movement, and another for aseptic loosening. A frequent issue in revision THA is suboptimal mechanical stability of commonly used acetabular cup implants, which then requires supplemental screw fixation [30]. For complex acetabular revision, the TM revision nonmodular cup offers the most versatile option with the possibility of drilling through the tantalum for optimal screw positioning to add a TM augment or a cage creating a cup cage construct [31]. Because the polyethylene liner is cemented into the shell adjusting for anteversion, the optimal position to maximize host bone contact can be achieved with the TM cup. Cementing also locks in the acetabular screws, increasing stability [32]. Kim et al [9] published a cohort study of revision acetabular arthroplasties with Paprosky types 2 and 3 acetabular bone defects. This study of 46 hips followed for an average of 41 (range, 24-51) months with the PT acetabular shell found radiographic evidence of osseointegration of the acetabular component obtained in all but one surviving hip at a mean follow-up of 30.9 months. Siegmeth et al reported a series of 37 patients at a mean follow-up of 34 months including 19 type III Paprosky defects with significant improvement in quality-of-life scores [6]. Comparison of the results of revision THA is difficult because of the varying complexity of acetabular bone defects. One study specifically reviewed Paprosky type 3a treated with TM cup and augment in 28 patients. At an average of 3.1 years of follow-up, only 1 patient required re-revision for recurrent instability. The patients' modified Postel Merle d'Aubigne score improved from 6.8 preoperatively to 10.6 postoperatively [1]. Another study by the same authors reported on type 3b acetabular defects with pelvic dissociation [33].

Trabecular Metal Used for Major Bone Loss  Davies et al

Thirteen patients (13 hips) were treated with the use of a TM acetabular component with 1 or 2 augments to span the discontinuity and provide internal fixation to the superior and inferior hemipelvis. Only 1 patient demonstrated possible radiographic loosening at an average follow-up of 2.6 years. The other 12 patients maintained radiographically stable hips, and the modified Postel–Merle d'Aubigne score improved from 6.1 preoperatively to 10.3 postoperatively (P b .05). Pelvic bone deficiency remains a complicated problem in hip revision surgeries with traditionally poor outcomes. With the advent of newer technologies, better results have been seen in the last decade. Many authors have reported on the good results of TM implants in such revision cases. We feel that the strength of our study stems from the fact that most (78%) of our patients had severe (type III) bone deficiencies. Although a longer follow-up is needed to confirm these findings, our midterm follow-up of 50 months shows encouraging results in these challenging acetabular reconstructions. This study has several imitations. First, it is retrospective in nature and includes only postoperative functional outcome scores. However, validated outcome scores were used. Second, it reflects the experience of only one surgeon with no comparative cohort. To conduct a trial with a higher level of evidence, a multicenter effort would be needed to achieve adequate power. The major drawback to using new implants is the lack of long-term follow-up. In theory, the higher porosity with improved ingrowth should allow for good long-term stability. However, we await the results of longer-term follow-up.

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