The Journal of Arthroplasty 29 (2014) 1318–1322
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Outcome of Porous Tantalum Acetabular Components for Paprosky Type 3 and 4 Acetabular Defects Eldridge D. Batuyong, MD, Hugh S. Brock, MD, Nikhil Thiruvengadam, BS, William J. Maloney, MD, Stuart B. Goodman, MD, PhD, James I. Huddleston, MD Department of Orthopaedic Surgery, Stanford University Medical Center, Stanford, California
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Article history: Received 16 October 2013 Accepted 4 December 2013 Keywords: porous tantalum acetabulum osseointegration Harris Hip Score radiolucent line revision hip surgery
a b s t r a c t Porous tantalum acetabular implants provide a potential solution for dealing with significant acetabular bone loss. This study reviews 24 acetabular revisions using tantalum implants for Paprosky type 3 and 4 defects. The mean Harris Hip Score improved from 35 ± 19 (range, 4–71) to 88 ± 14 (range, 41–100), p b 0.0001. Postoperative radiographs showed radiolucent lines in 14 hips with a mean width of 1.3 ± 1.0 mm (range, 0.27–4.37 mm). No gaps enlarged and 71% of them disappeared at a mean of 13 ± 10 months (range, 3–29 months). At a mean follow-up of 37 ± 14 months (range, 24–66 months), 22 reconstructions showed radiograpic evidence of osseointegration (92%). The two failures were secondary to septic loosening. When dealing with severe acetabular bone loss, porous tantalum acetabular components show promising shortterm results. © 2014 Elsevier Inc. All rights reserved.
Over 40,000 revision hip arthroplasties are performed each year in the United States and are projected to increase by 137% by the year 2030 [1]. Over 50% of these revisions involve the acetabular component [2]. Broadening indications for primary total hip arthroplasty (THA) along with increasing numbers of acetabular revisions and re-revisions have caused surgeons to encounter cases with increasing surgical complexity. One of the most difficult challenges in hip revision surgery is treating large acetabular defects [3]. Traditional solutions include the use of structural allograft/cage constructs, the long term results of which could be improved [4]. Porous tantalum metal provides an alternative solution with promising preliminary results [1–11]. Osseointegration is important for long-term survival of cementless acetabular components and has led to the development of three dimensional surfaces to permit bone in-growth. Porous tantalum is one such surface that has a porosity of 80%, an average pore size of 550 microns, and an elastic modulus of 185 gigapascals (GPa), giving it a structure similar to trabecular bone [12–14]. These characteristics allowed excellent osseointegration to occur in canine studies [14,15]. Porous tantalum also has a coefficient of friction of 0.88 against cancellous bone, providing it with good initial stability in cases where bone stock is compromised [8]. Not only has porous tantalum been shown to osseointegrate successfully, radiographic studies have
The Conflict of Interest statement associated with this article can be found at http:// dx.doi.org/10.1016/j.arth.2013.12.002. Reprint requests: James I. Huddleston, MD, Department of Orthopaedic Surgery, 450 Broadway Street, MC: 6342, Redwood City, CA 94063. http://dx.doi.org/10.1016/j.arth.2013.12.002 0883-5403/© 2014 Elsevier Inc. All rights reserved.
shown that periacetabular gaps up to 5 mm in size fill in with new bone over time [16,17]. At our institution, porous tantalum components have been used in the majority of complex revision THA cases that have involved suboptimal conditions for bone ingrowth. We report our short-term radiographic and clinical results of porous tantalum components with a minimum of two-year follow-up.
Materials and Methods Between 2005 and 2010, 96 acetabular revisions using tantalum components were performed at our institution. A retrospective review of these cases showed 36 hips in 36 patients had acetabula with Paprosky type 3 or 4 defects [18]. Twenty-six hips were classified with Paprosky type 3a defects, 8 hips were classified with Paprosky type 3b defects, and two hips as Paprosky type 4 defects. We excluded minor bone defects classified as Paprosky types 1 and 2, as well as patients with less than 2 years follow-up. Approval for this study was obtained from our institutional review board. Twenty-four hips classified as Paprosky type 3 or 4 with a minimum of two years follow-up or with failure requiring further surgery are included in this study. Of the included hips, 19 were classified as Paprosky type 3a, 3 as Paprosky type 3b, and 2 as Paprosky type 4. All operations were performed by one of the three senior authors (S.G., J.H., or W.M.) through either a posterolateral or anterolateral approach. Acetabula were reamed line-to-line and elliptical sockets were inserted using press-fit technique and secured with screws. Impaction grafting using allograft bone chips and demineralized bone
E.D. Batuyong et al. / The Journal of Arthroplasty 29 (2014) 1318–1322
matrix was used at the discretion of the surgeon. Augments and cages were used when the surgeon felt that there was insufficient host bone to securely support the cup in the presence of physiologic loads. Plates were used in the setting of associated transverse acetabulum fractures. Patients were seen in the clinic at 6 weeks, 3 months, 6 months, one year, two years, and 5 years subsequent to their operation. An anteroposterior pelvic radiograph and cross table lateral radiograph of the hip were taken and a questionnaire inquiring into the patient’s level of pain and function was filled out at selected visits. Patients who had not returned for their 2 year exam were invited by phone for a follow-up consultation or asked to send in a questionnaire and have local radiographs taken and sent via mail. Clinical examination was performed by the surgeon and independently by a single, experienced physical therapist. A Harris Hip Score (HHS) was calculated at each clinic visit [19,20]. Radiographs were analyzed by two orthopedic arthroplasty fellows who were not involved in the surgical procedures. Acetabular defects were classified according to the Paprosky system based on the preoperative anteroposterior (AP) pelvis radiograph [18]. The presence of a pelvic discontinuity was recorded at the time of surgery. Analysis of radiolucent lines was carried out for each patient using postoperative AP pelvis radiographs and measured within each of the three DeLee and Charnley zones modified by Gruen (Fig. 1) [16,21]. Radiolucent lines were considered to be present if they occupied at least 50% of the zone and measured at the widest distance between the edge of the prosthesis and the bone. Measurements were multiplied by a conversion factor (0.87) based on the magnification of our computerized radiographs. Gap sizes were compared between the initial postoperative radiographs and subsequent postoperative radiographs taken at each follow-up visit. Failure of cup osseointegration was defined as the presence of a continuous, circumferential radiolucent lines present at the component-bone interface at the most recent radiograph or evidence of gross migration on serial radiographs. Intraoperative and postoperative complications were recorded based on chart review. Complications were defined as any adverse medical or surgical event that required treatment and/or prolonged hospitalization. Survivorship of the cup was calculated based on the number of acetabular components that had to be revised. Osseointegration rate
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was determined using the number of cups that failed to osseointegrate. Statistical analysis of HHS was carried out using the paired t-test.
Results A total of 36 revision THAs classified as having a Paprosky type 3 or 4 defects were performed using porous tantalum acetabular implants between 2005 and 2010. Of these revision cases, 24 hips had a minimum of two years of follow-up or needed revision and are reported in this study. Of the 12 patients that did not have a minimum of 2 years of follow-up, 6 patients had 12 month postoperative radiographs which showed radiographic evidence of osseointegration of the acetabular component. The other 6 were lost to follow-up. There were no deaths. The average age of the included patients was 67 ± 16 years (range, 16–85 years) and the average follow-up was 37 ± 14 months (range, 24–66 months). Sixty-three percent of the patients were female. The most common diagnosis for revision was aseptic loosening (75%, Table 1). Nineteen patients had Paprosky type 3a defects, 3 patients had Paprosky type 3b defects, and 2 patients has Paprosky type 4 defects. The average number of preceeding surgeries for the revision THAs was 2 ± 1 (range, 1–7). Tantalum acetabular modular augments were used in five cases and a cup/cage construct in one case to address concerns regarding immediate stability. Two cases had associated transverse acetabular fractures (pelvic discontinuity) requiring plate fixation. The mean HHS improved from 35 ± 19 (range, 4–71) to 88 ± 14 (range 41–100) (P b 0.0001) with 83% of patients in the “excellent” or “good” categories. Of the remaining 4 patients that had a “fair” or “poor” outcome, 2 patients experienced persistent abductor dysfunction with associated pain, 1 patient developed instability and a chronic infection treated with resection arthroplasty, and 1 patient had a persistent infection requiring a two-stage revision. Allograft was used for bony deficiences in 23 of 24 cases. Of the bone-grafted cases, 15 cases utilized corticocancellous allograft mixed with demineralized bone matrix, 6 cases used corticocancellous allograft alone, 1 case used structural femoral head allograft as well as corticocancellous allograft mixed with dimineralized bone matrix and 1 case used structural femoral head allograft alone.
Fig. 1. Radiolucent gap in Zone 2 at 1.5 months postop (A) and 15 months postop (B). Corticocancellous allograft bone chips with demineralized bone matrix was used in this case.
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Table 1 Patient Characteristics and Demographics. Sex, n (%) Male Female Average age at revision surgery (y), SD, range Lost to follow-up
9 (38%) 15 (62%) 67+/− 16 (16–85) 6/36 and 6/36 with only 12 months of follow-up
Significant comorbidities, n (%) None 1 2 3 or more Primary diagnosis (%) Primary osteoarthritis Rheumatoid arthritis Developmental dysplasia with secondary osteoarthritis Avascular necrosis Post-traumatic arthritis Osteosarcoma Metastatic disease Previous revisions, n 1 2 3 4 or more Reason for revision, n (%) Aseptic loosening Osteolysis Instability Infection Failure of hemiarthroplasty Paprosky classification, n (%) IIIa IIIb without pelvic discontinuity IV with pelvic discontinuity Augment used, n (%) Cage used, n (%) Plate used, n (%) Average follow-up (months, SD, range)
0 9 (38%) 5 (21%) 10 (42%) 58% 17% 8% 4% 4% 4% 4% 6 12 3 3
revision for aseptic loosening of the femoral component at 22 months postoperatively and the other underwent an irrigation and debridement with a head and liner exchange for an acute infection at 1 month. One hip showed radiographic evidence of cup osseointegration at 24 months postoperatively, but developed a chronic infection at 28 months postoperatively requiring a resection arthroplasty (at the time of surgery, the cup was well-fixed). Two cups failed to osseointegrate secondary to sepsis at 3 months and 13 months and were treated with a resection arthroplasty and twostage revision respectively. The two-stage revision resulted in osseointegration of porous tantalum sockets at 12 months postoperatively with no signs or symptoms of recurrent infection. To summarize, all non-infected tantalum cups osseointegrated. Three cups required revision for infection (two of which were loose) resulting in a overall cup survivorship of 88%. There were no revisions for aseptic loosening. We have not commented on the osseointegration rates of the porous tantalum augments due to the difficulty of assessing osseointegration radiographically. Other complications included two cases of sciatic nerve neuropraxia (both of which generally resolved), and 1 case of instability that required conversion of the polyethylene liner to a constrained liner. Discussion
18 (75%) 2 (8%) 2 (8%) 1 (4%) 1(4%) 19 (79%) 3 (13%) 2 (8%) 5 (21%) 1 (4%) 2 (8%) 37 +/− 14 (24–66)
Immediate postoperative radiographs demonstrated radiolucent lines around the socket in 14 hips. There were 5 gaps in zone 1, 9 in zone 2, and 4 in zone 3. The mean gap size was 1.3 ± 1.0 mm (range, 0.3-4.4 mm). No radiolucencies enlarged and 71% of them disappeared at a mean of 13 ± 10 months (range, 3–29 months). In each of the cases where the gaps persisted, corticocancellous allograft bone chips mixed with dimineralized bone matrix was used. The average cup inclination and anteversion angles were 40 ± 7 degrees (range, 30–51 degrees) and 20 ± 13 degrees (range, -4 to 40 degrees), respectively. A total of five hips had to be revised at an average of 13 ± 12 months (range, 1–28 months) postoperatively (see Table 2). Two of the hips did not require removal of the cup and showed evidence of osseointegration of the cup at 24 months; one underwent
Traditional porous-coated hemispherical implants (titanium alloy and cobalt chromium alloy) provide an effective solution in most revision THAs where adequate bone stock is available to support the acetabular component and allow for bone ingrowth [11,22,23]. However, severe acetabular bony deficiency can compromise both the biologic potential and the ability to obtain mechanical stability needed to allow for reliable osseointegration of the acetabular component. Options available to deal with severe bone loss include impaction grafting and cementing a polyethylene component [24], roof or reconstruction cages with structural allograft [25–28], use of jumbo uncemented cups [29], use of oblong components [30], utilizing a high hip center [31], use of a custom triflange prosthesis [32] and resection arthroplasty. The results of each of these options have been mixed. A growing body of evidence now exists reporting favorable short-term results regarding porous tantalum acetabular components in revision cases [9,33,34]. Excellent results have been observed for acetabular revisions using porous tantalum acetabular components. Van Kleunen et al. had no revisions for aseptic failure in 97 cups at a mean of 45 months of follow-up. Harris hip scores improved from 55 to 76 postoperatively [10]. Unger et al. examined 60 revision THAs and found the mean Harris hip scores improved from 74 to 94. Only one cup in a patient with a pelvic discontinuity was revised for aseptic loosening at 18 months [34]. Paprosky et al. performed 23 acetabular revisions with major bone loss using porous tantalum cups and had no mechanical failures at a mean follow-up of 35 months [5]. In a related
Table 2 Cases Requiring Additional Revision Surgery. Paprosky Patient Age Gender Type
Reason for Revision
Time of Revision (Months) Comments
Outcome
22
Cup stable at time of revision
Cup well ingrown 24 months postop
1
Irrigation and debridement, head and liner exchange Resection arthroplasty, cup well ingrown at time of revision 1) Resection arthroplasty 2)Reimplantation 1) Constrained liner 2) Resection arthroplasty
Cup well ingrown, infection-free 66 months postop Resection arthroplasty
1
55
Female
3b
2
70
Female
3a
Aseptic loosening of femoral component Acute septic failure
3
76
Male
3a
Chronic septic failure
28
4
56
Male
3b
5
68
Female
3a
Persistent chronic septic failure (failed reimplantation) 1) Instability, 2) Chronic septic failure
1) 2) 1) 2)
13 22 2 3
Successful 2-stage revision, cup ingrown 12 months postop Resection arthroplasty
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study, they found no revisions at 2 to 6 years of follow-up in 13 patients with pelvic discontinuities [9]. Gross and colleagues reported a 4% failure rate in 53 revision cups due to mechanical loosening at 2 years average follow-up in patients with 50% or less host bone contact [8]. Fernandez-Fairen et al. reviewed 263 consecutive acetabular revisions using porous tantalum cups with a mean follow-up of 73.6 months and showed all acetabular components to be radiographically stable with no requirement for rerevision for loosening [35]. Kim et al. reported 2–4-year follow-up of 46 acetabular revisions with Paprosky 2 and 3 bone deficiencies and reported only one acetabular shell requiring rerevision [36]. In a recent study of the Finnish Registry, Skyttä showed 98% survival at 3 years in 827 cup revisions [37]. Porous tantalum implants have been used in orthopedic surgery since 1997 and provide excellent initial stability and bone ingrowth [13,38]. It has a honeycomb structure with an average pore size of 550 microns and a porosity of 75–80%, which is similar to trabecular bone [14]. This is much higher than the porosity of either titanium (Ti) mesh (40-50%) or cobalt-chromium (Co-Cr) beads (30-50%), allowing for a higher absolute volume of ingrowth than conventional porous coatings [14]. Porous tantalum also has a higher coefficient of friction (0.88) against cancellous and cortical bone than Ti mesh (0.63) or Co-Cr beads (0.53), offering greater initial stability. This is critical in achieving immediate mechanical stability when bone stock is compromised at the time of implantation [5,7–10,39,40]. In addition, tantalum has a closer elastic modulus (3 GPa) to subchondral bone (1.5 GPa) than Ti (110 Gpa) and Co-Cr (220 GPa) [34]. This minimizes stress shielding adjacent to the cup, optimizing remodeling according to load distribution [41]. Finally, tantalum has only slight release of corrosion byproducts which minimizes the denaturing of proteins in osteoblasts [12]. The osseointegrative properties of porous tantalum have been demonstrated in radiographic studies looking at the elimination of periacetabular gaps over time with monoblock cups. Macheras prospectively studied 156 cups implanted during primary THAs with 8 to 10 years follow-up. The mean Harris hip score improved from 44 to 97. Sixteen percent of hips showed the presence of gaps, which completely disappeared by 10 years [42]. Macheras found similar results in another series of 86 primary THAs showing that all postoperative gaps, including those up to 5 mm, filled by 24 weeks. They had no revisions at a mean followup of 7.3 years [17]. Finally, Gruen studied 414 primary THAs with a minimum of 2 years followup and showed that 84% of gaps had filled in and none had progressed in size. They also had no revisions for aseptic loosening [16]. The present study differs from previously reported studies in that we focused on revision THAs with severe (Paprosky 3 and 4) bony deficienices. Radiographic gaps up to 4 mm in size in were present in 14 hips (58%); none of these enlarged and in 10 hips (71%) the gaps disappeared. We demonstrated an overall cup survivorship of 88% and overall osseointegration rate of 92%. The two tantalum acetabular components that failed to osseointegrate were infected. Our study has several limitations. First, it is a retrospective review of prospectively-gathered data. There also is no control group for comparison. Finally, only 67% of the cases performed had full clinical follow-up at 2 or more years. This raises questions regarding the outcomes of patients who were lost to follow-up. However, 6 of 12 patients with insufficeint follow-up did have 12 month postoperative radiographs which showed radiographic evidence of osseointegration of the acetabular components. This series demonstrates the excellent clinical and radiographic results of porous tantalum acetabular components in complex revision THAs (with/without the use of augments and/or cages). Our findings confirm that tantalum porous cups provide a viable reconstruction option when dealing with Paprosky type 3 and 4 defects in the short term. Further long-term studies are required to determine the longevity of these implants.
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Contents lists available at ScienceDirect
The Journal of Arthroplasty journal homepage: www.arthroplastyjournal.org
Outcome of Porous Tantalum Acetabular Components for Paprosky Type 3 and 4 Acetabular Defects Eldridge D. Batuyong, MD, Hugh S. Brock, MD, Nikhil Thiruvengadam, BS, William J. Maloney, MD, Stuart B. Goodman, MD, PhD, James I. Huddleston, MD Department of Orthopaedic Surgery, Stanford University Medical Center, Stanford, California
a r t i c l e
i n f o
Article history: Received 16 October 2013 Accepted 4 December 2013 Keywords: porous tantalum acetabulum osseointegration Harris Hip Score radiolucent line revision hip surgery
a b s t r a c t Porous tantalum acetabular implants provide a potential solution for dealing with significant acetabular bone loss. This study reviews 24 acetabular revisions using tantalum implants for Paprosky type 3 and 4 defects. The mean Harris Hip Score improved from 35 ± 19 (range, 4–71) to 88 ± 14 (range, 41–100), p b 0.0001. Postoperative radiographs showed radiolucent lines in 14 hips with a mean width of 1.3 ± 1.0 mm (range, 0.27–4.37 mm). No gaps enlarged and 71% of them disappeared at a mean of 13 ± 10 months (range, 3–29 months). At a mean follow-up of 37 ± 14 months (range, 24–66 months), 22 reconstructions showed radiograpic evidence of osseointegration (92%). The two failures were secondary to septic loosening. When dealing with severe acetabular bone loss, porous tantalum acetabular components show promising shortterm results. © 2014 Elsevier Inc. All rights reserved.
Over 40,000 revision hip arthroplasties are performed each year in the United States and are projected to increase by 137% by the year 2030 [1]. Over 50% of these revisions involve the acetabular component [2]. Broadening indications for primary total hip arthroplasty (THA) along with increasing numbers of acetabular revisions and re-revisions have caused surgeons to encounter cases with increasing surgical complexity. One of the most difficult challenges in hip revision surgery is treating large acetabular defects [3]. Traditional solutions include the use of structural allograft/cage constructs, the long term results of which could be improved [4]. Porous tantalum metal provides an alternative solution with promising preliminary results [1–11]. Osseointegration is important for long-term survival of cementless acetabular components and has led to the development of three dimensional surfaces to permit bone in-growth. Porous tantalum is one such surface that has a porosity of 80%, an average pore size of 550 microns, and an elastic modulus of 185 gigapascals (GPa), giving it a structure similar to trabecular bone [12–14]. These characteristics allowed excellent osseointegration to occur in canine studies [14,15]. Porous tantalum also has a coefficient of friction of 0.88 against cancellous bone, providing it with good initial stability in cases where bone stock is compromised [8]. Not only has porous tantalum been shown to osseointegrate successfully, radiographic studies have
The Conflict of Interest statement associated with this article can be found at http:// dx.doi.org/10.1016/j.arth.2013.12.002. Reprint requests: James I. Huddleston, MD, Department of Orthopaedic Surgery, 450 Broadway Street, MC: 6342, Redwood City, CA 94063. http://dx.doi.org/10.1016/j.arth.2013.12.002 0883-5403/© 2014 Elsevier Inc. All rights reserved.
shown that periacetabular gaps up to 5 mm in size fill in with new bone over time [16,17]. At our institution, porous tantalum components have been used in the majority of complex revision THA cases that have involved suboptimal conditions for bone ingrowth. We report our short-term radiographic and clinical results of porous tantalum components with a minimum of two-year follow-up.
Materials and Methods Between 2005 and 2010, 96 acetabular revisions using tantalum components were performed at our institution. A retrospective review of these cases showed 36 hips in 36 patients had acetabula with Paprosky type 3 or 4 defects [18]. Twenty-six hips were classified with Paprosky type 3a defects, 8 hips were classified with Paprosky type 3b defects, and two hips as Paprosky type 4 defects. We excluded minor bone defects classified as Paprosky types 1 and 2, as well as patients with less than 2 years follow-up. Approval for this study was obtained from our institutional review board. Twenty-four hips classified as Paprosky type 3 or 4 with a minimum of two years follow-up or with failure requiring further surgery are included in this study. Of the included hips, 19 were classified as Paprosky type 3a, 3 as Paprosky type 3b, and 2 as Paprosky type 4. All operations were performed by one of the three senior authors (S.G., J.H., or W.M.) through either a posterolateral or anterolateral approach. Acetabula were reamed line-to-line and elliptical sockets were inserted using press-fit technique and secured with screws. Impaction grafting using allograft bone chips and demineralized bone
E.D. Batuyong et al. / The Journal of Arthroplasty 29 (2014) 1318–1322
matrix was used at the discretion of the surgeon. Augments and cages were used when the surgeon felt that there was insufficient host bone to securely support the cup in the presence of physiologic loads. Plates were used in the setting of associated transverse acetabulum fractures. Patients were seen in the clinic at 6 weeks, 3 months, 6 months, one year, two years, and 5 years subsequent to their operation. An anteroposterior pelvic radiograph and cross table lateral radiograph of the hip were taken and a questionnaire inquiring into the patient’s level of pain and function was filled out at selected visits. Patients who had not returned for their 2 year exam were invited by phone for a follow-up consultation or asked to send in a questionnaire and have local radiographs taken and sent via mail. Clinical examination was performed by the surgeon and independently by a single, experienced physical therapist. A Harris Hip Score (HHS) was calculated at each clinic visit [19,20]. Radiographs were analyzed by two orthopedic arthroplasty fellows who were not involved in the surgical procedures. Acetabular defects were classified according to the Paprosky system based on the preoperative anteroposterior (AP) pelvis radiograph [18]. The presence of a pelvic discontinuity was recorded at the time of surgery. Analysis of radiolucent lines was carried out for each patient using postoperative AP pelvis radiographs and measured within each of the three DeLee and Charnley zones modified by Gruen (Fig. 1) [16,21]. Radiolucent lines were considered to be present if they occupied at least 50% of the zone and measured at the widest distance between the edge of the prosthesis and the bone. Measurements were multiplied by a conversion factor (0.87) based on the magnification of our computerized radiographs. Gap sizes were compared between the initial postoperative radiographs and subsequent postoperative radiographs taken at each follow-up visit. Failure of cup osseointegration was defined as the presence of a continuous, circumferential radiolucent lines present at the component-bone interface at the most recent radiograph or evidence of gross migration on serial radiographs. Intraoperative and postoperative complications were recorded based on chart review. Complications were defined as any adverse medical or surgical event that required treatment and/or prolonged hospitalization. Survivorship of the cup was calculated based on the number of acetabular components that had to be revised. Osseointegration rate
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was determined using the number of cups that failed to osseointegrate. Statistical analysis of HHS was carried out using the paired t-test.
Results A total of 36 revision THAs classified as having a Paprosky type 3 or 4 defects were performed using porous tantalum acetabular implants between 2005 and 2010. Of these revision cases, 24 hips had a minimum of two years of follow-up or needed revision and are reported in this study. Of the 12 patients that did not have a minimum of 2 years of follow-up, 6 patients had 12 month postoperative radiographs which showed radiographic evidence of osseointegration of the acetabular component. The other 6 were lost to follow-up. There were no deaths. The average age of the included patients was 67 ± 16 years (range, 16–85 years) and the average follow-up was 37 ± 14 months (range, 24–66 months). Sixty-three percent of the patients were female. The most common diagnosis for revision was aseptic loosening (75%, Table 1). Nineteen patients had Paprosky type 3a defects, 3 patients had Paprosky type 3b defects, and 2 patients has Paprosky type 4 defects. The average number of preceeding surgeries for the revision THAs was 2 ± 1 (range, 1–7). Tantalum acetabular modular augments were used in five cases and a cup/cage construct in one case to address concerns regarding immediate stability. Two cases had associated transverse acetabular fractures (pelvic discontinuity) requiring plate fixation. The mean HHS improved from 35 ± 19 (range, 4–71) to 88 ± 14 (range 41–100) (P b 0.0001) with 83% of patients in the “excellent” or “good” categories. Of the remaining 4 patients that had a “fair” or “poor” outcome, 2 patients experienced persistent abductor dysfunction with associated pain, 1 patient developed instability and a chronic infection treated with resection arthroplasty, and 1 patient had a persistent infection requiring a two-stage revision. Allograft was used for bony deficiences in 23 of 24 cases. Of the bone-grafted cases, 15 cases utilized corticocancellous allograft mixed with demineralized bone matrix, 6 cases used corticocancellous allograft alone, 1 case used structural femoral head allograft as well as corticocancellous allograft mixed with dimineralized bone matrix and 1 case used structural femoral head allograft alone.
Fig. 1. Radiolucent gap in Zone 2 at 1.5 months postop (A) and 15 months postop (B). Corticocancellous allograft bone chips with demineralized bone matrix was used in this case.
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Table 1 Patient Characteristics and Demographics. Sex, n (%) Male Female Average age at revision surgery (y), SD, range Lost to follow-up
9 (38%) 15 (62%) 67+/− 16 (16–85) 6/36 and 6/36 with only 12 months of follow-up
Significant comorbidities, n (%) None 1 2 3 or more Primary diagnosis (%) Primary osteoarthritis Rheumatoid arthritis Developmental dysplasia with secondary osteoarthritis Avascular necrosis Post-traumatic arthritis Osteosarcoma Metastatic disease Previous revisions, n 1 2 3 4 or more Reason for revision, n (%) Aseptic loosening Osteolysis Instability Infection Failure of hemiarthroplasty Paprosky classification, n (%) IIIa IIIb without pelvic discontinuity IV with pelvic discontinuity Augment used, n (%) Cage used, n (%) Plate used, n (%) Average follow-up (months, SD, range)
0 9 (38%) 5 (21%) 10 (42%) 58% 17% 8% 4% 4% 4% 4% 6 12 3 3
revision for aseptic loosening of the femoral component at 22 months postoperatively and the other underwent an irrigation and debridement with a head and liner exchange for an acute infection at 1 month. One hip showed radiographic evidence of cup osseointegration at 24 months postoperatively, but developed a chronic infection at 28 months postoperatively requiring a resection arthroplasty (at the time of surgery, the cup was well-fixed). Two cups failed to osseointegrate secondary to sepsis at 3 months and 13 months and were treated with a resection arthroplasty and twostage revision respectively. The two-stage revision resulted in osseointegration of porous tantalum sockets at 12 months postoperatively with no signs or symptoms of recurrent infection. To summarize, all non-infected tantalum cups osseointegrated. Three cups required revision for infection (two of which were loose) resulting in a overall cup survivorship of 88%. There were no revisions for aseptic loosening. We have not commented on the osseointegration rates of the porous tantalum augments due to the difficulty of assessing osseointegration radiographically. Other complications included two cases of sciatic nerve neuropraxia (both of which generally resolved), and 1 case of instability that required conversion of the polyethylene liner to a constrained liner. Discussion
18 (75%) 2 (8%) 2 (8%) 1 (4%) 1(4%) 19 (79%) 3 (13%) 2 (8%) 5 (21%) 1 (4%) 2 (8%) 37 +/− 14 (24–66)
Immediate postoperative radiographs demonstrated radiolucent lines around the socket in 14 hips. There were 5 gaps in zone 1, 9 in zone 2, and 4 in zone 3. The mean gap size was 1.3 ± 1.0 mm (range, 0.3-4.4 mm). No radiolucencies enlarged and 71% of them disappeared at a mean of 13 ± 10 months (range, 3–29 months). In each of the cases where the gaps persisted, corticocancellous allograft bone chips mixed with dimineralized bone matrix was used. The average cup inclination and anteversion angles were 40 ± 7 degrees (range, 30–51 degrees) and 20 ± 13 degrees (range, -4 to 40 degrees), respectively. A total of five hips had to be revised at an average of 13 ± 12 months (range, 1–28 months) postoperatively (see Table 2). Two of the hips did not require removal of the cup and showed evidence of osseointegration of the cup at 24 months; one underwent
Traditional porous-coated hemispherical implants (titanium alloy and cobalt chromium alloy) provide an effective solution in most revision THAs where adequate bone stock is available to support the acetabular component and allow for bone ingrowth [11,22,23]. However, severe acetabular bony deficiency can compromise both the biologic potential and the ability to obtain mechanical stability needed to allow for reliable osseointegration of the acetabular component. Options available to deal with severe bone loss include impaction grafting and cementing a polyethylene component [24], roof or reconstruction cages with structural allograft [25–28], use of jumbo uncemented cups [29], use of oblong components [30], utilizing a high hip center [31], use of a custom triflange prosthesis [32] and resection arthroplasty. The results of each of these options have been mixed. A growing body of evidence now exists reporting favorable short-term results regarding porous tantalum acetabular components in revision cases [9,33,34]. Excellent results have been observed for acetabular revisions using porous tantalum acetabular components. Van Kleunen et al. had no revisions for aseptic failure in 97 cups at a mean of 45 months of follow-up. Harris hip scores improved from 55 to 76 postoperatively [10]. Unger et al. examined 60 revision THAs and found the mean Harris hip scores improved from 74 to 94. Only one cup in a patient with a pelvic discontinuity was revised for aseptic loosening at 18 months [34]. Paprosky et al. performed 23 acetabular revisions with major bone loss using porous tantalum cups and had no mechanical failures at a mean follow-up of 35 months [5]. In a related
Table 2 Cases Requiring Additional Revision Surgery. Paprosky Patient Age Gender Type
Reason for Revision
Time of Revision (Months) Comments
Outcome
22
Cup stable at time of revision
Cup well ingrown 24 months postop
1
Irrigation and debridement, head and liner exchange Resection arthroplasty, cup well ingrown at time of revision 1) Resection arthroplasty 2)Reimplantation 1) Constrained liner 2) Resection arthroplasty
Cup well ingrown, infection-free 66 months postop Resection arthroplasty
1
55
Female
3b
2
70
Female
3a
Aseptic loosening of femoral component Acute septic failure
3
76
Male
3a
Chronic septic failure
28
4
56
Male
3b
5
68
Female
3a
Persistent chronic septic failure (failed reimplantation) 1) Instability, 2) Chronic septic failure
1) 2) 1) 2)
13 22 2 3
Successful 2-stage revision, cup ingrown 12 months postop Resection arthroplasty
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study, they found no revisions at 2 to 6 years of follow-up in 13 patients with pelvic discontinuities [9]. Gross and colleagues reported a 4% failure rate in 53 revision cups due to mechanical loosening at 2 years average follow-up in patients with 50% or less host bone contact [8]. Fernandez-Fairen et al. reviewed 263 consecutive acetabular revisions using porous tantalum cups with a mean follow-up of 73.6 months and showed all acetabular components to be radiographically stable with no requirement for rerevision for loosening [35]. Kim et al. reported 2–4-year follow-up of 46 acetabular revisions with Paprosky 2 and 3 bone deficiencies and reported only one acetabular shell requiring rerevision [36]. In a recent study of the Finnish Registry, Skyttä showed 98% survival at 3 years in 827 cup revisions [37]. Porous tantalum implants have been used in orthopedic surgery since 1997 and provide excellent initial stability and bone ingrowth [13,38]. It has a honeycomb structure with an average pore size of 550 microns and a porosity of 75–80%, which is similar to trabecular bone [14]. This is much higher than the porosity of either titanium (Ti) mesh (40-50%) or cobalt-chromium (Co-Cr) beads (30-50%), allowing for a higher absolute volume of ingrowth than conventional porous coatings [14]. Porous tantalum also has a higher coefficient of friction (0.88) against cancellous and cortical bone than Ti mesh (0.63) or Co-Cr beads (0.53), offering greater initial stability. This is critical in achieving immediate mechanical stability when bone stock is compromised at the time of implantation [5,7–10,39,40]. In addition, tantalum has a closer elastic modulus (3 GPa) to subchondral bone (1.5 GPa) than Ti (110 Gpa) and Co-Cr (220 GPa) [34]. This minimizes stress shielding adjacent to the cup, optimizing remodeling according to load distribution [41]. Finally, tantalum has only slight release of corrosion byproducts which minimizes the denaturing of proteins in osteoblasts [12]. The osseointegrative properties of porous tantalum have been demonstrated in radiographic studies looking at the elimination of periacetabular gaps over time with monoblock cups. Macheras prospectively studied 156 cups implanted during primary THAs with 8 to 10 years follow-up. The mean Harris hip score improved from 44 to 97. Sixteen percent of hips showed the presence of gaps, which completely disappeared by 10 years [42]. Macheras found similar results in another series of 86 primary THAs showing that all postoperative gaps, including those up to 5 mm, filled by 24 weeks. They had no revisions at a mean followup of 7.3 years [17]. Finally, Gruen studied 414 primary THAs with a minimum of 2 years followup and showed that 84% of gaps had filled in and none had progressed in size. They also had no revisions for aseptic loosening [16]. The present study differs from previously reported studies in that we focused on revision THAs with severe (Paprosky 3 and 4) bony deficienices. Radiographic gaps up to 4 mm in size in were present in 14 hips (58%); none of these enlarged and in 10 hips (71%) the gaps disappeared. We demonstrated an overall cup survivorship of 88% and overall osseointegration rate of 92%. The two tantalum acetabular components that failed to osseointegrate were infected. Our study has several limitations. First, it is a retrospective review of prospectively-gathered data. There also is no control group for comparison. Finally, only 67% of the cases performed had full clinical follow-up at 2 or more years. This raises questions regarding the outcomes of patients who were lost to follow-up. However, 6 of 12 patients with insufficeint follow-up did have 12 month postoperative radiographs which showed radiographic evidence of osseointegration of the acetabular components. This series demonstrates the excellent clinical and radiographic results of porous tantalum acetabular components in complex revision THAs (with/without the use of augments and/or cages). Our findings confirm that tantalum porous cups provide a viable reconstruction option when dealing with Paprosky type 3 and 4 defects in the short term. Further long-term studies are required to determine the longevity of these implants.
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