The Journal of Arthroplasty 30 (2015) 249–253
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Treatment of Severe Bone Defects During Revision Total Knee Arthroplasty with Structural Allografts and Porous Metal Cones—A Systematic Review Nicholas A. Beckmann, MD a, Sebastian Mueller, MD b, Matthias Gondan, PhD c, Sebastian Jaeger, PhD d, Tobias Reiner, MD a, Rudi G. Bitsch, MD, PhD a a
Department of Orthopedics, Trauma Surgery and Spinal Cord Injury, Heidelberg University Hospital, Heidelberg, Germany Department of Traumatology, Department of Surgery, University Hospital Basel, Basel, Switzerland c Department of Psychology, University of Copenhagen, Denmark d Laboratory of Biomechanics and Implant Research, Department of Orthopaedics, University of Heidelberg, Heidelberg, Germany b
a r t i c l e
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Article history: Received 25 June 2014 Accepted 11 September 2014 Keywords: allograft porous metal tantalum knee revision arthroplasty AORI knee defects
a b s t r a c t Aseptic loosening and focal osteolysis are the most common reasons for knee arthroplasty failure. The best treatment remains unclear. We reviewed the literature on the treatment of revision knee arthroplasty using bony structural allografts (476 cases) and porous metal cones (223 cases) to determine if a difference in the revision failure rates was discernable. The failure rates were compared using a logistic regression model with adjustment for discrepancies in FU time and number of grafts used (femoral, tibial, or both). In this analysis, the porous implant shows a significantly decreased loosening rate in AORI 2 and 3 defects. The overall failure rate was also substantially lower in the porous metal group than the structural allograft group; little difference in the infection rates was noted. © 2014 The Authors. Published by Elsevier Inc. This is an open access article under the CC BY-NC-ND license. (http://creativecommons.org/licenses/by-nc-nd/3.0/).
Total knee arthroplasty (TKA) is now being recognized as one of the most successful operations in orthopedic surgery for the treatment of degenerative joint disease [1]. In the USA, because of the rapidly aging population and the advent of improved surgical techniques with correspondingly improved results, this procedure is being done with increased frequency. According to Iorio et al. [2] a total of 523,000 TKAs were performed in the USA in 2005, and this number is projected to increase to 3,480,000 in 2030, representing a more than five-fold increase. At the same time the number of revisions, which was 38,500 in 2005 (7.3%), is projected to increase to 268,200 in 2030. The most common indication for knee arthroplasty revision is aseptic loosening in combination with periarticular osteopenia, focal osteolysis and infection [3]. Bony deficiencies are frequently encountered during TKA revision surgery [3] and are classified according to the Anderson Orthopedic Research Institute classification (AORI). Various strategies have been described to manage them [4], which predominantly depend on the size of the bone defect. In addition to the use of long-stemmed prostheses, Disclosure: No external funding was received for carrying out this study. None of the authors have received financial gain directly associated with this work. Some of the authors received grants or institutional support outside the submitted work. The Conflict of Interest statement associated with this article can be found at http:// dx.doi.org/10.1016/j.arth.2014.09.016. Reprint requests: Rudi G. Bitsch, MD, PhD, Heidelberg University Hospital, Department of Orthopedics, Trauma Surgery and Spinal Cord Injury, Schlierbacher Landstraße 200 a, 69118 Heidelberg, Germany.
these strategies often include the use of cement, metal augments, impaction bone grafting with morsellized bone, structural allografting and the use of trabecular metal (TM) cones. For the management of large bone defects (AORI grades 2 and 3) bulk or structural allografts in combination with long-stemmed prostheses have been used for a long time [5]. However, the use of these grafts is associated with a number of disadvantages including late graft resorption, fracture of the graft, nonunion of the graft with the native bone and the risk of disease transmission [6]. The improved osteointegration found with large porous metal augments has resulted in improved outcomes and increased use in hip arthroplasty surgery [7]. Therefore, with the increasing popularity of large porous metal augments, it is likely that the use of structural allografts for revision TKA will diminish in the future [3]. The purpose of this literature review is to determine if the use of TM cones in patients with AORI 2 and 3 defects involving the knee joint improves revision rates compared to the rates with the use of large structural allografts. Material and Methods Search Strategy A search of Medline and Embase was conducted using defined search phrases and via citation tracking. The search included single arm and controlled studies published between January 1980 and
http://dx.doi.org/10.1016/j.arth.2014.09.016 0883-5403/© 2014 The Authors. Published by Elsevier Inc. This is an open access article under the CC BY-NC-ND license. (http://creativecommons.org/licenses/by-nc-nd/3.0/).
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Table 1 Structural (Bulk) Allograft of Knees. F/U Months
Reoperation Due to
First Author
Year
Age Years (Mean)
Total Knees
# Grafts
Mean
(Range)
Aseptic Loosening or Fracture of Allograft
Infection
Non-Allograft Related
Chun [15] Wang [36] Burnett [37] Lyall [38] Bauman [39] Engh [9] Bezwada [40] Backstein [41] Clatworthy [42] Engh [16] Ghazavi [13] Mow [14] Harris [10] Tsahakis [12] Stockley [11] Mnaymeh [20] Wilde [21] TOTAL %
2013 2013 2009 2009 2009 2007 2006 2006 2001 1997 1997 1996 1995 1994 1992 1990 1990
68 69.7 67.3 59 67.9 67 64 73.4 66 70 65.8 63 67 72 69.4 67 62 67.9
27 30 28 15 70 46 11 61 52 30 30 13 14 15 12 10 12 476
38 38 33 15 87 46 11 68 66 33 34 15 14 19 12 10 12 551
107 76 48 65 90 97 42 65 97.2 50 50 47 43 25 50 40 30 70.8
(96–157) (38–136) (24–96) (33–115) (60–178)
0 0 1 1 8 0 0 6 5 0 4 1 0 0 2 2 1 31 6.51%
1 0 1 1 5 2 0 4 4 0 3 0 1 0 3 1 0 26 5.46%
0 0 0 0 3 2 0 3 4 1 0 3 0 0 0 0 0 16 3.36%
(36–48) (12–192) 97.2 (24–120) (24–132) (30–101) (29–63) (12–48) (24–86) (26–69) (25–51)
December 2013 that evaluated the failure rate of TKA revisions with TM cones and structural allograft. The medical subject headings were “structural allograft and/or femoral head allograft in the revision of total knee arthroplasties” and “Trabecular Metal augments in revision total knee arthroplasty”. Studies were included if the bone loss at the time of revision was classified as AORI grade 2 or 3 and either large bulk or structural allografts or TM cones were utilized during the revisions. A description of bone loss judged to be severe enough to fall into the AORI grade 2 or 3 was utilized for studies published prior to the widely spread adoption of the AORI classification. In addition, patients had to have clinical and radiographic follow up. Single case reports and review articles were excluded. Data extraction included names of authors, study type, year of publication, type of revision surgery, mean duration of follow up and revision rate. AORI grade 2 defects involve loss of cancellous bone in one (2A) or both (2B) metaphyses and condyles. These defects require restoration of the joint line and are best managed with a revision component that consists of augments and a stem [8]. AORI grade 3 defects consist of larger metaphyseal defects with bone damage to or above the femoral condyles or up to or below the tibial tubercle requiring large structural grafts and long-stemmed revision implants [8]. In the publications on large structural allografts, the prostheses were cemented to the host bone with the exception of one series [9] and frequently the allograft was cemented to the prosthesis as well [10–16]. In the series utilizing TM cones, only Panni et al [17] did not specify if bone cement was used. In all other series utilizing TM cones, bone cement was used between the prosthesis and host bone and between the prosthesis and TM cone. Bone cement was never used between bone graft or the TM cone and the host bone. The radiographic criteria for loosening included the breaking of the screws fixing the allograft to the native bone, a radiographic lucency around the allograft or prosthesis of 2 mm or more, especially if increasing over time, and movement of the allograft or prosthesis on follow up radiographs. Failure rates described in Tables 1 and 2 reflect the cases requiring surgical revision. In general, revision was performed based upon clinical symptoms (i.e., pain) and not the result of the radiological findings described above. Statistics Primary outcome was a binary, patient-level variable, namely success or failure (i.e., aseptic loosening) within the study-specific followup period. Logistic regression was used to estimate the failure odds ratio and its 95% confidence interval (CI) for the two revision techniques using TM cones and large allografts. Heterogeneity of the studies was
accounted for by means of the robust Huber–White sandwich estimator for the covariance matrix and standard errors of the parameter estimates. The analysis was adjusted for different length of the follow-up period by using the logarithm of the study-specific average follow-up time as an offset variable in the model (see Appendix 4 in Ref. [18]). The follow-up time was further adjusted for those cases, which had received grafts to both femoral and tibial defects, since both the femoral and tibial graft could fail. This adjustment assumes a timehomogeneous failure rate in both treatments, which we argue is a conservative adjustment in the present context. Average failure rates, along with their 95% confidence intervals, were determined from the baseline odds of intercept-only logistic regression models. The secondary outcome, namely, infections and overall revision rates, were analyzed in the same way as the primary outcome. Results After excluding duplicates we found a total of 102 articles and abstracts. Twenty-seven of these publications dealt with TM cones in knee revision surgery. Seventeen of these papers were review articles and experimental studies. Ten papers fulfilled the inclusion criteria with the first clinical series appearing in 2006 [19]. The literature search on large structural allografts in knee revision surgery yielded 75 publications. Of these, 17 fulfilled the inclusion criteria with the first clinical series appearing in 1990 [20,21]. The included articles consist entirely of case series describing the use of TM cones and large bulk allografts in patients with severe bone defects found during knee revision surgery: controlled trials or even randomized controlled trials were not available. There were a total of 10 articles published between 2006 and 2013 (Table 2) that reported on the outcome of 254 TM cones in 223 revision TKAs. Thirty-one of the TKAs involved both tibial and femoral implants, in 75 TKAs cones were placed only in femurs and in 117 TKAs only in tibias. We defined failures as those cases that required reoperation. The average age of these patients at the time of revision surgery was 69.5 years and they had a mean follow up of 33.6 months (2.8 years). The loosening rate of the TM cones was 0.9% (all femoral) and the loosening rate of the prosthesis and/or incidence of periprosthetic fracture was also 0.9%. The infection rate necessitating surgical intervention was 2.2%. Bulk allographs (Table 1) have been used for a much longer period of time and therefore longer follow-up periods are available. There were a total of 551 bulk allografts used in 476 revision TKAs described in 17 articles. In 75 of these revision TKAs, bulk allografts were placed in both
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Table 2 Trabecular Metal Cones. F/U Months
Reoperation Due to
First Author
Year
Age Years (Mean)
Knees With Cones
# Cones
Mean
(Range)
Aseptic Loosening of Cone
Infection
Loose Prosthesis/Fracture
Rao [43] Villanueva-Martinez [44] Derome [45] Schmitz [46] Panni [17] Lachiewicz [47] Howard [48] Meneghini [49] Long [50] Radnay [19] TOTAL %
2013 2013 2013 2013 2013 2012 2011 2009 2009 2006
72 73.3 70 72 75 64.6 64 68.1 66.1 – 69.5
26 21 29 38 9 33 24 15 16 12 223
29 29 33 54 9 33 24 15 16 12 254
36 36 33 37 84 40 33 34 31 10.2 33.6
(24–49)
0 0 0 1 0 1 0 n/a n/a 0 2 0.9%
0 1 0 0 0 1 0 0 2 1 5 2.2%
0 0 0 1 0 1 0 0 0 0 2 0.9%
femurs and tibias; in 195 TKAs, they were placed only in the tibia and in 132 only in the femur. In 74 TKAs the location of the bulk allograft was not specified. The mean follow-up period was 70.8 months (5.9 years). The average age of these patients at the time of revision surgery was 67.9 years. In these patients the failure rate of the allograft requiring reoperation from either loosening or fracture of the graft was 6.5%; the reoperation due to loosening of the prosthesis was 3.4 % and due to infection was 5.5%. The differences in follow-up times also result in differences in incidents (failures), requiring a logistic metaregression to compensate for the difference using offset variables. In the 10 TM and 17 allograft articles, 805 grafts (TM cones and bulk allografts) were evaluated. Thirtythree aseptic graft loosenings were noted: 2 occurred in the TM and 31 in the allograft group, corresponding to a yearly failure rate of 0.3% (CI 0.1 to 0.7%) and 1.0% (CI 0.6 to 1.6%) in the two materials. Assuming time-homogeneous failure rates, metaregression reveals an odds ratio for aseptic loosening of 0.263 (CI 0.085 to 0.816, P = 0.021) in favor of TM (see Fig. 1 Forest plot). Of the 805 grafts evaluated, 31 became infected: there were 5 in the TM group and 26 in the allograft group (yearly failure rate: TM, 0.7%, CI 0.2 to 1.8%; allograft, 0.8%, CI 0.6 to 1.2%). Correspondingly, metaregression analysis did not reveal a substantial difference between the TM and allograft collectives. The odds ratio for infection using an assumed time-homogeneous failure rate was 0.804, slightly in favor of TM, but far from statistically significant (CI 0.273 to 2.364, P = 0.692). When evaluating the overall revision rate of both collectives, again, no significant difference was found. A total of 82 of 805 grafts were surgically revised, with an odds ratio of 0.473 (CI 0.212 to 1.055, P = 0.067) and yearly re-revision rates of 1.2% (CI 0.6 to 2.5%) for TM and 2.6% (CI 1.7 to 2.8%) for allografts, respectively. Although the overall rerevision rate is not statistically significant, a tendency toward a decreased rate from all causes is noted for TM cones. Discussion TM components are believed to have increased biocompatibility [22] and enhanced bone ingrowth and fixation [23]. In a previous publication on revision total hip arthroplasty comparing TM augments with revision rings, we showed a significantly decreased loosening rate of TM components [7]. We therefore conducted a metaregression analysis of the available literature on revision TKA with TM components or structural allografts utilizing the criteria outlined above, and compared the rate of failure due to lack of fixation of the TM graft and bulk allograft to the host bone as well as the infection and overall revision rates. Bone allografts are frequently required in orthopedic surgery. They are usually procured sterile from organ donors and stored at − 80 °C. Consequently, these grafts have limited biological activity [24]. Although morsellized cancellous allografts have been shown to slowly remodel into viable bone [24] and have been shown to be highly
(13–73) (32–48) (24–68)
successful for smaller defects, larger structural allografts are frequently required for large defects in knee revision surgery, where they need to provide structural support [25]. Ideally, the allograft should be attached to the host bone by the stem of the prosthesis alone [26,27], but additional fixation with plate and screws may be necessary. In dog experiments, Stevenson et al. [28] found that bony union is dependent on the type of graft and the immune response of the host. They found only very limited revascularization and remodeling and a very unpredictable incorporation process. Parks et al. [29] examined human bone allografts histologically; these had been retrieved during revision surgery or at autopsy 41 months (range 20–62 months) postoperatively. They found that some new bone was laid down only on the periphery of the structural allograft and that these large allografts showed no remodeling and no revascularization when they were examined. Published complications include resorption of the graft [30], a fracture rate of 16% [31] and a late infection rate of 11.7% [32]. The incidence of nonunion of large frozen allografts with the host bone was 11% [33] although this did not appear to affect the chance of retention of the graft. Since large allografts have significant disadvantages, porous metal implants have been introduced by several orthopedic supply companies. The advantage of these newer materials is thought to be the increased porosity, the low modulus of elasticity and high coefficient of friction [22]. These materials allow for enhanced and accelerated bone ingrowth [34] when compared to older implants with roughened surfaces. In experimental studies, Bobyn et al. [23] found 13% filling in of the tantalum pores with bone after 2–3 weeks and 63–80% bony filling in of the tantalum pores after 16–52 weeks. The highly porous characteristics of these new porous metal compounds are claimed to further increase rapid and early osteointegration [22,34] and should therefore diminish the loosening rate and improve clinical results and long term outcomes. If failures occur, they tend to happen early on in the postoperative period according to Jafari et al. [35]; in their group of 79 patients who had undergone total hip revision surgery with TM augments, 4 out of 5 failures occurred in the first 6 months postoperatively. However, the advantages of these porous implants are negated if they are cemented to viable bone. Because of the increased osteointegration of these materials, their removal in case of revision surgery for any reason can be difficult. In our literature search we compared the overall results of TM cones in knee revision surgery with those results using large allografts (Tables 1 and 2) by using a metaregression analysis. When using TM cones we have seen a statistically significant odds ratio for aseptic loosening of only about ¼ of that seen with structural or bulk allograft. This leaves much room for speculation as to the reason; however, the biological response to the foreign graft is the most likely reason for the discrepancy. As mentioned, osteointegration of a porous metal graft improves secondary stability, whereby bony resorption and restructuring of the allograft can result in graft failure.
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Study
Events Total
Proportion
95%−CI
TM Rao (2013) Villanueva−Martinez (2013) Derone (2013) Schmitz (2013) Lachiewicz (2012) Panni (2012) Howard (2011) Menegini (2009) Long (2009) Radnay (2006)
0 0 0 1 1 0 0 0 0 0
87 87 91 166 110 63 66 42 41 10
0.000 0.000 0.000 0.006 0.009 0.000 0.000 0.000 0.000 0.000
[0.000; 0.042] [0.000; 0.042] [0.000; 0.040] [0.000; 0.033] [0.000; 0.050] [0.000; 0.057] [0.000; 0.054] [0.000; 0.084] [0.000; 0.086] [0.000; 0.308]
Allo Chun (2013) Wang (2013) Burnett (2009) Lyall (2009) Bauman (2009) Engh (2007) Bezwada (2006) Backstein (2006) Clatworthy (2001) Engh (1997) Ghazawi (1997) Mow (1996) Harris (1995) Tsahikis (1994) Stockley (1992) Mnaymeh (1990) Wilde (1990)
0 0 1 1 8 0 0 6 5 0 4 1 0 0 2 2 1
339 241 132 81 652 372 38 368 534 138 142 59 50 40 50 33 30
0.000 0.000 0.008 0.012 0.012 0.000 0.000 0.016 0.009 0.000 0.028 0.017 0.000 0.000 0.040 0.061 0.033
[0.000; 0.011] [0.000; 0.015] [0.000; 0.041] [0.000; 0.067] [0.005; 0.024] [0.000; 0.010] [0.000; 0.093] [0.006; 0.035] [0.003; 0.022] [0.000; 0.026] [0.008; 0.071] [0.000; 0.091] [0.000; 0.071] [0.000; 0.088] [0.005; 0.137] [0.007; 0.202] [0.001; 0.172]
0
0.05 0.1 0.15 0.2 0.25 0.3
Fig. 1. Forest plot displaying study-specific failure rates per person and year for the two materials.
There was no significant difference in the infection rate between the 2 groups. The odds ratio of 0.804 in favor of TM was not significant (P = 0.692) and the large P-value probably indicates that even a substantially larger collective would not reveal a significant difference between the two groups. Operations in both groups involve implantation of a foreign material, with limited biological potential, which could account for the similarity of the infection rates. Statistical analysis of the overall revision rates does, however, indicate a tendency toward decreased revision rates in the trabecular metal population (odds ratio = 0.473, P = 0.067), or roughly half that seen in the allograft group. The limited population size did not allow for a discernable effect on the conventional statistical significance level. The major drawback of our comparison study is the absence of any randomized controlled trial in the literature, so that all results have to be considered preliminary, stating whether TM might be a promising treatment option or not. An unequivocal recommendation for a specific treatment is not possible on the basis of the current evidence. The results of the present literature review should therefore not be considered as decisive but rather as hypothesis generating regarding future, prospective, randomized controlled studies. Since our analyses are confined to case series, a further problem is the difference in the length of the follow up period of the TM cone group compared to the bulk allograft group. In the statistical comparison we adjusted for these different follow up periods by entering the logarithm of the follow up period as an offset [18]. The offset also accounted for the number of prostheses implanted (femoral, tibial, or both). Such an analysis assumes that the failure rate is constant over time and the same in the two sites (it was not possible to determine separate failure rates for femoral and tibial revisions because not all studies separately reported these numbers). Both assumptions may be incorrect: TM related studies are anticipated to have better long-term outcomes than the average of the yearly failure rate suggests. Both experimental studies [23] and clinical studies [35] show improved early osteointegration with TM components and therefore a decreased loosening rate can be expected later on. If we assume that with TM
components the majority of mechanical complications happen early postoperatively as suggested by Jafari et al. [35], our results clearly favor the use of TM components in knee revision surgery over bulk allografts. In addition, the use and implantation of porous metal is constantly evolving, with some companies providing their own broaching systems to allow for improved press-fit implantation. The increased use of porous metals and the increased familiarity with the technique of its implantation may further improve the outcome of surgical procedures using these materials. Our review of the literature supports the results and conclusions drawn by experimental studies involving large bone allografts [24,28,29] and TM components [22,23,34] showing that the improved biocompatibility and osteointegration of porous implants might result in a substantially lower loosening rate. The limited number of cases did not indicate that the infection rate or overall revision rates varied. These findings are similar to clinical results we found in revision hip arthroplasty [7]. However, for further validation, a longer follow up period in these patients who undergo knee revision surgery with TM components is still required. Because of the observational nature of the included studies, the meta-regression results should not be considered conclusive but rather strongly indicative of improved results with the use of TM cones. References 1. Kurtz S, Ong K, Lau E, et al. Projections of primary and revision hip and knee arthroplasty in the United States from 2005 to 2030. J Bone Joint Surg Am 2007;89–4:780. 2. Iorio R, Robb WJ, Healy WL, et al. Orthopaedic surgeon workforce and volume assessment for total hip and knee replacement in the United States: preparing for an epidemic. J Bone Joint Surg Am 2008;90–7:1598. 3. Haidukewych GJ, Hanssen A, Jones RE. Metaphyseal fixation in revision total knee arthroplasty: indications and techniques. J Am Acad Orthop Surg 2011;19–6:311. 4. Qiu YY, Yan CH, Chiu KY, et al. Review article: treatments for bone loss in revision total knee arthroplasty. J Orthop Surg 2012;20–1:78. 5. Bush JL, Wilson JB, Vail TP. Management of bone loss in revision total knee arthroplasty. Clin Orthop Relat Res 2006;452:186. 6. Dennis DA. The structural allograft composite in revision total knee arthroplasty. J Arthroplasty 2002;17–4(Suppl 1):90.
N.A. Beckmann et al. / The Journal of Arthroplasty 30 (2015) 249–253 7. Beckmann NA, Weiss S, Klotz MC, et al. Loosening after acetabular revision: comparison of trabecular metal and reinforcement rings. A systematic review. J Arthroplast 2014;29–1:229. 8. Engh GA, Ammeen DJ. Classification and preoperative radiographic evaluation: knee. Orthop Clin North Am 1998;29–2:205. 9. Engh GA, Ammeen DJ. Use of structural allograft in revision total knee arthroplasty in knees with severe tibial bone loss. J Bone Joint Surg Am 2007;89–12:2640. 10. Harris AI, Poddar S, Gitelis S, et al. Arthroplasty with a composite of an allograft and a prosthesis for knees with severe deficiency of bone. J Bone Joint Surg Am 1995;77–3:373. 11. Stockley I, McAuley JP, Gross AE. Allograft reconstruction in total knee arthroplasty. J Bone Joint Surg (Br) 1992;74–3:393. 12. Tsahakis PJ, Beaver WB, Brick GW. Technique and results of allograft reconstruction in revision total knee arthroplasty. Clin Orthop Relat Res 1994;303:86. 13. Ghazavi MT, Stockley I, Yee G, et al. Reconstruction of massive bone defects with allograft in revision total knee arthroplasty. J Bone Joint Surg Am 1997;79–1:17. 14. Mow CS, Wiedel JD. Structural allografting in revision total knee arthroplasty. J Arthroplasty 1996;11–3:235. 15. Chun CH, Kim JW, Kim SH, et al. Clinical and radiological results of femoral head structural allograft for severe bone defects in revision TKA—a minimum 8-year follow-up. Knee 2014;21–2:420. 16. Engh GA, Herzwurm PJ, Parks NL. Treatment of major defects of bone with bulk allografts and stemmed components during total knee arthroplasty. J Bone Joint Surg Am 1997;79–7:1030. 17. Panni AS, Vasso M, Cerciello S. Modular augmentation in revision total knee arthroplasty. Knee Surg Sports Traumatol Arthrosc 2013;21–12:2837. 18. Lane PW. Meta-analysis of incidence of rare events. Stat Methods Med Res 2013; 22-2:117. 19. Radnay CS, Scuderi GR. Management of bone loss: augments, cones, offset stems. Clin Orthop Relat Res 2006;446:83. 20. Mnaymneh W, Emerson RH, Borja F, et al. Massive allografts in salvage revisions of failed total knee arthroplasties. Clin Orthop Relat Res 1990;260:144. 21. Wilde AH, Schickendantz MS, Stulberg BN, et al. The incorporation of tibial allografts in total knee arthroplasty. J Bone Joint Surg Am 1990;72–6:815. 22. Levine B. A new era in porous metals: applications in orthopaedics. Adv Eng Mater 2008;10–9:788. 23. Bobyn JD, Stackpool GJ, Hacking SA, et al. Characteristics of bone ingrowth and interface mechanics of a new porous tantalum biomaterial. J Bone Joint Surg Br 1999; 81–5:907. 24. Garbuz DS, Masri BA, Czitrom AA. Biology of allografting. Orthop Clin North Am 1998; 29–2:199. 25. Delloye C, Cornu O, Druez V, et al. Bone allografts: what they can offer and what they cannot. J Bone Joint Surg (Br) 2007;89–5:574. 26. Huten D. Femorotibial bone loss during revision total knee arthroplasty. Orthop Traumatol Surg Res 2013;99–1:S22 [Suppl]. 27. Cuckler JM. Bone loss in total knee arthroplasty: graft augment and options. J Arthroplasty 2004;19–4(Suppl 1):56. 28. Stevenson S, Li XQ, Davy DT, et al. Critical biological determinants of incorporation of non-vascularized cortical bone grafts. Quantification of a complex process and structure. J Bone Joint Surg Am 1997;79–1:1. 29. Parks NL, Engh GA. The Ranawat Award. Histology of nine structural bone grafts used in total knee arthroplasty. Clin Orthop Relat Res 1997;345:17.
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30. Lombardi AV, Berend KR, Adams JB. Management of bone loss in revision TKA: it's a changing world. Orthopedics 2010;33–9:662. 31. Berrey Jr BH, Lord CF, Gebhardt MC, et al. Fractures of allografts. Frequency, treatment, and end-results. J Bone Joint Surg Am 1990;72–6:825. 32. Lord CF, Gebhardt MC, Tomford WW, et al. Infection in bone allografts. Incidence, nature, and treatment. J Bone Joint Surg Am 1988;70–3:369. 33. Mankin HJ, Doppelt S, Tomford W. Clinical experience with allograft implantation. The first ten years. Clin Orthop Relat Res 1983;174:69. 34. Pulido L, Rachala SR, Cabanela ME. Cementless acetabular revision: past, present, and future. Revision total hip arthroplasty: the acetabular side using cementless implants. Int Orthop 2011;35–2:289. 35. Jafari SM, Bender B, Coyle C, et al. Do tantalum and titanium cups show similar results in revision hip arthroplasty? Clin Orthop Relat Res 2010;468–2:459. 36. Wang JW, Hsu CH, Huang CC, et al. Reconstruction using femoral head allograft in revision total knee replacement: an experience in Asian patients. Bone Joint J 2013;95B-5:643. 37. Burnett RS, Keeney JA, Maloney WJ, et al. Revision total knee arthroplasty for major osteolysis. Iowa Orthop J 2009;29:28. 38. Lyall HS, Sanghrajka A, Scott G. Severe tibial bone loss in revision total knee replacement managed with structural femoral head allograft: a prospective case series from the Royal London Hospital. Knee 2009;16–5:326. 39. Bauman RD, Lewallen DG, Hanssen AD. Limitations of structural allograft in revision total knee arthroplasty. Clin Orthop Relat Res 2009;467–3:818. 40. Bezwada HP, Shah AR, Zambito K, et al. Distal femoral allograft reconstruction for massive osteolytic bone loss in revision total knee arthroplasty. J Arthroplasty 2006;21–2:242. 41. Backstein D, Safir O, Gross A. Management of bone loss: structural grafts in revision total knee arthroplasty. Clin Orthop Relat Res 2006;446:104. 42. Clatworthy MG, Ballance J, Brick GW, et al. The use of structural allograft for uncontained defects in revision total knee arthroplasty. A minimum five-year review. J Bone Joint Surg Am 2001;83-A-3:404. 43. Rao BM, Kamal TT, Vafaye J, et al. Tantalum cones for major osteolysis in revision knee replacement. Bone Joint J 2013;95-B-8:1069. 44. Villanueva-Martinez M, De la Torre-Escudero B, Rojo-Manaute JM, et al. Tantalum cones in revision total knee arthroplasty. A promising short-term result with 29 cones in 21 patients. J Arthroplasty 2013;28–6:988. 45. Derome P, Sternheim A, Backstein D, et al. Treatment of large bone defects with trabecular metal cones in revision total knee arthroplasty: short term clinical and radiographic outcomes. J Arthroplasty 2014;29–1:122. 46. Schmitz HC, Klauser W, Citak M, et al. Three-year follow up utilizing tantal cones in revision total knee arthroplasty. J Arthroplasty 2013;28–9:1556. 47. Lachiewicz PF, Bolognesi MP, Henderson RA, et al. Can tantalum cones provide fixation in complex revision knee arthroplasty? Clin Orthop Relat Res 2012; 470–1:199. 48. Howard JL, Kudera J, Lewallen DG, et al. Early results of the use of tantalum femoral cones for revision total knee arthroplasty. J Bone Joint Surg Am 2011;93–5:478. 49. Meneghini RM, Lewallen DG, Hanssen AD. Use of porous tantalum metaphyseal cones for severe tibial bone loss during revision total knee replacement. Surgical technique. J Bone Joint Surg Am 2009;91(Suppl 2 Pt 1):131. 50. Long WJ, Scuderi GR. Porous tantalum cones for large metaphyseal tibial defects in revision total knee arthroplasty: a minimum 2-year follow-up. J Arthroplasty 2009; 24–7:1086.
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Treatment of Severe Bone Defects During Revision Total Knee Arthroplasty with Structural Allografts and Porous Metal Cones—A Systematic Review Nicholas A. Beckmann, MD a, Sebastian Mueller, MD b, Matthias Gondan, PhD c, Sebastian Jaeger, PhD d, Tobias Reiner, MD a, Rudi G. Bitsch, MD, PhD a a
Department of Orthopedics, Trauma Surgery and Spinal Cord Injury, Heidelberg University Hospital, Heidelberg, Germany Department of Traumatology, Department of Surgery, University Hospital Basel, Basel, Switzerland c Department of Psychology, University of Copenhagen, Denmark d Laboratory of Biomechanics and Implant Research, Department of Orthopaedics, University of Heidelberg, Heidelberg, Germany b
a r t i c l e
i n f o
Article history: Received 25 June 2014 Accepted 11 September 2014 Keywords: allograft porous metal tantalum knee revision arthroplasty AORI knee defects
a b s t r a c t Aseptic loosening and focal osteolysis are the most common reasons for knee arthroplasty failure. The best treatment remains unclear. We reviewed the literature on the treatment of revision knee arthroplasty using bony structural allografts (476 cases) and porous metal cones (223 cases) to determine if a difference in the revision failure rates was discernable. The failure rates were compared using a logistic regression model with adjustment for discrepancies in FU time and number of grafts used (femoral, tibial, or both). In this analysis, the porous implant shows a significantly decreased loosening rate in AORI 2 and 3 defects. The overall failure rate was also substantially lower in the porous metal group than the structural allograft group; little difference in the infection rates was noted. © 2014 The Authors. Published by Elsevier Inc. This is an open access article under the CC BY-NC-ND license. (http://creativecommons.org/licenses/by-nc-nd/3.0/).
Total knee arthroplasty (TKA) is now being recognized as one of the most successful operations in orthopedic surgery for the treatment of degenerative joint disease [1]. In the USA, because of the rapidly aging population and the advent of improved surgical techniques with correspondingly improved results, this procedure is being done with increased frequency. According to Iorio et al. [2] a total of 523,000 TKAs were performed in the USA in 2005, and this number is projected to increase to 3,480,000 in 2030, representing a more than five-fold increase. At the same time the number of revisions, which was 38,500 in 2005 (7.3%), is projected to increase to 268,200 in 2030. The most common indication for knee arthroplasty revision is aseptic loosening in combination with periarticular osteopenia, focal osteolysis and infection [3]. Bony deficiencies are frequently encountered during TKA revision surgery [3] and are classified according to the Anderson Orthopedic Research Institute classification (AORI). Various strategies have been described to manage them [4], which predominantly depend on the size of the bone defect. In addition to the use of long-stemmed prostheses, Disclosure: No external funding was received for carrying out this study. None of the authors have received financial gain directly associated with this work. Some of the authors received grants or institutional support outside the submitted work. The Conflict of Interest statement associated with this article can be found at http:// dx.doi.org/10.1016/j.arth.2014.09.016. Reprint requests: Rudi G. Bitsch, MD, PhD, Heidelberg University Hospital, Department of Orthopedics, Trauma Surgery and Spinal Cord Injury, Schlierbacher Landstraße 200 a, 69118 Heidelberg, Germany.
these strategies often include the use of cement, metal augments, impaction bone grafting with morsellized bone, structural allografting and the use of trabecular metal (TM) cones. For the management of large bone defects (AORI grades 2 and 3) bulk or structural allografts in combination with long-stemmed prostheses have been used for a long time [5]. However, the use of these grafts is associated with a number of disadvantages including late graft resorption, fracture of the graft, nonunion of the graft with the native bone and the risk of disease transmission [6]. The improved osteointegration found with large porous metal augments has resulted in improved outcomes and increased use in hip arthroplasty surgery [7]. Therefore, with the increasing popularity of large porous metal augments, it is likely that the use of structural allografts for revision TKA will diminish in the future [3]. The purpose of this literature review is to determine if the use of TM cones in patients with AORI 2 and 3 defects involving the knee joint improves revision rates compared to the rates with the use of large structural allografts. Material and Methods Search Strategy A search of Medline and Embase was conducted using defined search phrases and via citation tracking. The search included single arm and controlled studies published between January 1980 and
http://dx.doi.org/10.1016/j.arth.2014.09.016 0883-5403/© 2014 The Authors. Published by Elsevier Inc. This is an open access article under the CC BY-NC-ND license. (http://creativecommons.org/licenses/by-nc-nd/3.0/).
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Table 1 Structural (Bulk) Allograft of Knees. F/U Months
Reoperation Due to
First Author
Year
Age Years (Mean)
Total Knees
# Grafts
Mean
(Range)
Aseptic Loosening or Fracture of Allograft
Infection
Non-Allograft Related
Chun [15] Wang [36] Burnett [37] Lyall [38] Bauman [39] Engh [9] Bezwada [40] Backstein [41] Clatworthy [42] Engh [16] Ghazavi [13] Mow [14] Harris [10] Tsahakis [12] Stockley [11] Mnaymeh [20] Wilde [21] TOTAL %
2013 2013 2009 2009 2009 2007 2006 2006 2001 1997 1997 1996 1995 1994 1992 1990 1990
68 69.7 67.3 59 67.9 67 64 73.4 66 70 65.8 63 67 72 69.4 67 62 67.9
27 30 28 15 70 46 11 61 52 30 30 13 14 15 12 10 12 476
38 38 33 15 87 46 11 68 66 33 34 15 14 19 12 10 12 551
107 76 48 65 90 97 42 65 97.2 50 50 47 43 25 50 40 30 70.8
(96–157) (38–136) (24–96) (33–115) (60–178)
0 0 1 1 8 0 0 6 5 0 4 1 0 0 2 2 1 31 6.51%
1 0 1 1 5 2 0 4 4 0 3 0 1 0 3 1 0 26 5.46%
0 0 0 0 3 2 0 3 4 1 0 3 0 0 0 0 0 16 3.36%
(36–48) (12–192) 97.2 (24–120) (24–132) (30–101) (29–63) (12–48) (24–86) (26–69) (25–51)
December 2013 that evaluated the failure rate of TKA revisions with TM cones and structural allograft. The medical subject headings were “structural allograft and/or femoral head allograft in the revision of total knee arthroplasties” and “Trabecular Metal augments in revision total knee arthroplasty”. Studies were included if the bone loss at the time of revision was classified as AORI grade 2 or 3 and either large bulk or structural allografts or TM cones were utilized during the revisions. A description of bone loss judged to be severe enough to fall into the AORI grade 2 or 3 was utilized for studies published prior to the widely spread adoption of the AORI classification. In addition, patients had to have clinical and radiographic follow up. Single case reports and review articles were excluded. Data extraction included names of authors, study type, year of publication, type of revision surgery, mean duration of follow up and revision rate. AORI grade 2 defects involve loss of cancellous bone in one (2A) or both (2B) metaphyses and condyles. These defects require restoration of the joint line and are best managed with a revision component that consists of augments and a stem [8]. AORI grade 3 defects consist of larger metaphyseal defects with bone damage to or above the femoral condyles or up to or below the tibial tubercle requiring large structural grafts and long-stemmed revision implants [8]. In the publications on large structural allografts, the prostheses were cemented to the host bone with the exception of one series [9] and frequently the allograft was cemented to the prosthesis as well [10–16]. In the series utilizing TM cones, only Panni et al [17] did not specify if bone cement was used. In all other series utilizing TM cones, bone cement was used between the prosthesis and host bone and between the prosthesis and TM cone. Bone cement was never used between bone graft or the TM cone and the host bone. The radiographic criteria for loosening included the breaking of the screws fixing the allograft to the native bone, a radiographic lucency around the allograft or prosthesis of 2 mm or more, especially if increasing over time, and movement of the allograft or prosthesis on follow up radiographs. Failure rates described in Tables 1 and 2 reflect the cases requiring surgical revision. In general, revision was performed based upon clinical symptoms (i.e., pain) and not the result of the radiological findings described above. Statistics Primary outcome was a binary, patient-level variable, namely success or failure (i.e., aseptic loosening) within the study-specific followup period. Logistic regression was used to estimate the failure odds ratio and its 95% confidence interval (CI) for the two revision techniques using TM cones and large allografts. Heterogeneity of the studies was
accounted for by means of the robust Huber–White sandwich estimator for the covariance matrix and standard errors of the parameter estimates. The analysis was adjusted for different length of the follow-up period by using the logarithm of the study-specific average follow-up time as an offset variable in the model (see Appendix 4 in Ref. [18]). The follow-up time was further adjusted for those cases, which had received grafts to both femoral and tibial defects, since both the femoral and tibial graft could fail. This adjustment assumes a timehomogeneous failure rate in both treatments, which we argue is a conservative adjustment in the present context. Average failure rates, along with their 95% confidence intervals, were determined from the baseline odds of intercept-only logistic regression models. The secondary outcome, namely, infections and overall revision rates, were analyzed in the same way as the primary outcome. Results After excluding duplicates we found a total of 102 articles and abstracts. Twenty-seven of these publications dealt with TM cones in knee revision surgery. Seventeen of these papers were review articles and experimental studies. Ten papers fulfilled the inclusion criteria with the first clinical series appearing in 2006 [19]. The literature search on large structural allografts in knee revision surgery yielded 75 publications. Of these, 17 fulfilled the inclusion criteria with the first clinical series appearing in 1990 [20,21]. The included articles consist entirely of case series describing the use of TM cones and large bulk allografts in patients with severe bone defects found during knee revision surgery: controlled trials or even randomized controlled trials were not available. There were a total of 10 articles published between 2006 and 2013 (Table 2) that reported on the outcome of 254 TM cones in 223 revision TKAs. Thirty-one of the TKAs involved both tibial and femoral implants, in 75 TKAs cones were placed only in femurs and in 117 TKAs only in tibias. We defined failures as those cases that required reoperation. The average age of these patients at the time of revision surgery was 69.5 years and they had a mean follow up of 33.6 months (2.8 years). The loosening rate of the TM cones was 0.9% (all femoral) and the loosening rate of the prosthesis and/or incidence of periprosthetic fracture was also 0.9%. The infection rate necessitating surgical intervention was 2.2%. Bulk allographs (Table 1) have been used for a much longer period of time and therefore longer follow-up periods are available. There were a total of 551 bulk allografts used in 476 revision TKAs described in 17 articles. In 75 of these revision TKAs, bulk allografts were placed in both
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Table 2 Trabecular Metal Cones. F/U Months
Reoperation Due to
First Author
Year
Age Years (Mean)
Knees With Cones
# Cones
Mean
(Range)
Aseptic Loosening of Cone
Infection
Loose Prosthesis/Fracture
Rao [43] Villanueva-Martinez [44] Derome [45] Schmitz [46] Panni [17] Lachiewicz [47] Howard [48] Meneghini [49] Long [50] Radnay [19] TOTAL %
2013 2013 2013 2013 2013 2012 2011 2009 2009 2006
72 73.3 70 72 75 64.6 64 68.1 66.1 – 69.5
26 21 29 38 9 33 24 15 16 12 223
29 29 33 54 9 33 24 15 16 12 254
36 36 33 37 84 40 33 34 31 10.2 33.6
(24–49)
0 0 0 1 0 1 0 n/a n/a 0 2 0.9%
0 1 0 0 0 1 0 0 2 1 5 2.2%
0 0 0 1 0 1 0 0 0 0 2 0.9%
femurs and tibias; in 195 TKAs, they were placed only in the tibia and in 132 only in the femur. In 74 TKAs the location of the bulk allograft was not specified. The mean follow-up period was 70.8 months (5.9 years). The average age of these patients at the time of revision surgery was 67.9 years. In these patients the failure rate of the allograft requiring reoperation from either loosening or fracture of the graft was 6.5%; the reoperation due to loosening of the prosthesis was 3.4 % and due to infection was 5.5%. The differences in follow-up times also result in differences in incidents (failures), requiring a logistic metaregression to compensate for the difference using offset variables. In the 10 TM and 17 allograft articles, 805 grafts (TM cones and bulk allografts) were evaluated. Thirtythree aseptic graft loosenings were noted: 2 occurred in the TM and 31 in the allograft group, corresponding to a yearly failure rate of 0.3% (CI 0.1 to 0.7%) and 1.0% (CI 0.6 to 1.6%) in the two materials. Assuming time-homogeneous failure rates, metaregression reveals an odds ratio for aseptic loosening of 0.263 (CI 0.085 to 0.816, P = 0.021) in favor of TM (see Fig. 1 Forest plot). Of the 805 grafts evaluated, 31 became infected: there were 5 in the TM group and 26 in the allograft group (yearly failure rate: TM, 0.7%, CI 0.2 to 1.8%; allograft, 0.8%, CI 0.6 to 1.2%). Correspondingly, metaregression analysis did not reveal a substantial difference between the TM and allograft collectives. The odds ratio for infection using an assumed time-homogeneous failure rate was 0.804, slightly in favor of TM, but far from statistically significant (CI 0.273 to 2.364, P = 0.692). When evaluating the overall revision rate of both collectives, again, no significant difference was found. A total of 82 of 805 grafts were surgically revised, with an odds ratio of 0.473 (CI 0.212 to 1.055, P = 0.067) and yearly re-revision rates of 1.2% (CI 0.6 to 2.5%) for TM and 2.6% (CI 1.7 to 2.8%) for allografts, respectively. Although the overall rerevision rate is not statistically significant, a tendency toward a decreased rate from all causes is noted for TM cones. Discussion TM components are believed to have increased biocompatibility [22] and enhanced bone ingrowth and fixation [23]. In a previous publication on revision total hip arthroplasty comparing TM augments with revision rings, we showed a significantly decreased loosening rate of TM components [7]. We therefore conducted a metaregression analysis of the available literature on revision TKA with TM components or structural allografts utilizing the criteria outlined above, and compared the rate of failure due to lack of fixation of the TM graft and bulk allograft to the host bone as well as the infection and overall revision rates. Bone allografts are frequently required in orthopedic surgery. They are usually procured sterile from organ donors and stored at − 80 °C. Consequently, these grafts have limited biological activity [24]. Although morsellized cancellous allografts have been shown to slowly remodel into viable bone [24] and have been shown to be highly
(13–73) (32–48) (24–68)
successful for smaller defects, larger structural allografts are frequently required for large defects in knee revision surgery, where they need to provide structural support [25]. Ideally, the allograft should be attached to the host bone by the stem of the prosthesis alone [26,27], but additional fixation with plate and screws may be necessary. In dog experiments, Stevenson et al. [28] found that bony union is dependent on the type of graft and the immune response of the host. They found only very limited revascularization and remodeling and a very unpredictable incorporation process. Parks et al. [29] examined human bone allografts histologically; these had been retrieved during revision surgery or at autopsy 41 months (range 20–62 months) postoperatively. They found that some new bone was laid down only on the periphery of the structural allograft and that these large allografts showed no remodeling and no revascularization when they were examined. Published complications include resorption of the graft [30], a fracture rate of 16% [31] and a late infection rate of 11.7% [32]. The incidence of nonunion of large frozen allografts with the host bone was 11% [33] although this did not appear to affect the chance of retention of the graft. Since large allografts have significant disadvantages, porous metal implants have been introduced by several orthopedic supply companies. The advantage of these newer materials is thought to be the increased porosity, the low modulus of elasticity and high coefficient of friction [22]. These materials allow for enhanced and accelerated bone ingrowth [34] when compared to older implants with roughened surfaces. In experimental studies, Bobyn et al. [23] found 13% filling in of the tantalum pores with bone after 2–3 weeks and 63–80% bony filling in of the tantalum pores after 16–52 weeks. The highly porous characteristics of these new porous metal compounds are claimed to further increase rapid and early osteointegration [22,34] and should therefore diminish the loosening rate and improve clinical results and long term outcomes. If failures occur, they tend to happen early on in the postoperative period according to Jafari et al. [35]; in their group of 79 patients who had undergone total hip revision surgery with TM augments, 4 out of 5 failures occurred in the first 6 months postoperatively. However, the advantages of these porous implants are negated if they are cemented to viable bone. Because of the increased osteointegration of these materials, their removal in case of revision surgery for any reason can be difficult. In our literature search we compared the overall results of TM cones in knee revision surgery with those results using large allografts (Tables 1 and 2) by using a metaregression analysis. When using TM cones we have seen a statistically significant odds ratio for aseptic loosening of only about ¼ of that seen with structural or bulk allograft. This leaves much room for speculation as to the reason; however, the biological response to the foreign graft is the most likely reason for the discrepancy. As mentioned, osteointegration of a porous metal graft improves secondary stability, whereby bony resorption and restructuring of the allograft can result in graft failure.
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Study
Events Total
Proportion
95%−CI
TM Rao (2013) Villanueva−Martinez (2013) Derone (2013) Schmitz (2013) Lachiewicz (2012) Panni (2012) Howard (2011) Menegini (2009) Long (2009) Radnay (2006)
0 0 0 1 1 0 0 0 0 0
87 87 91 166 110 63 66 42 41 10
0.000 0.000 0.000 0.006 0.009 0.000 0.000 0.000 0.000 0.000
[0.000; 0.042] [0.000; 0.042] [0.000; 0.040] [0.000; 0.033] [0.000; 0.050] [0.000; 0.057] [0.000; 0.054] [0.000; 0.084] [0.000; 0.086] [0.000; 0.308]
Allo Chun (2013) Wang (2013) Burnett (2009) Lyall (2009) Bauman (2009) Engh (2007) Bezwada (2006) Backstein (2006) Clatworthy (2001) Engh (1997) Ghazawi (1997) Mow (1996) Harris (1995) Tsahikis (1994) Stockley (1992) Mnaymeh (1990) Wilde (1990)
0 0 1 1 8 0 0 6 5 0 4 1 0 0 2 2 1
339 241 132 81 652 372 38 368 534 138 142 59 50 40 50 33 30
0.000 0.000 0.008 0.012 0.012 0.000 0.000 0.016 0.009 0.000 0.028 0.017 0.000 0.000 0.040 0.061 0.033
[0.000; 0.011] [0.000; 0.015] [0.000; 0.041] [0.000; 0.067] [0.005; 0.024] [0.000; 0.010] [0.000; 0.093] [0.006; 0.035] [0.003; 0.022] [0.000; 0.026] [0.008; 0.071] [0.000; 0.091] [0.000; 0.071] [0.000; 0.088] [0.005; 0.137] [0.007; 0.202] [0.001; 0.172]
0
0.05 0.1 0.15 0.2 0.25 0.3
Fig. 1. Forest plot displaying study-specific failure rates per person and year for the two materials.
There was no significant difference in the infection rate between the 2 groups. The odds ratio of 0.804 in favor of TM was not significant (P = 0.692) and the large P-value probably indicates that even a substantially larger collective would not reveal a significant difference between the two groups. Operations in both groups involve implantation of a foreign material, with limited biological potential, which could account for the similarity of the infection rates. Statistical analysis of the overall revision rates does, however, indicate a tendency toward decreased revision rates in the trabecular metal population (odds ratio = 0.473, P = 0.067), or roughly half that seen in the allograft group. The limited population size did not allow for a discernable effect on the conventional statistical significance level. The major drawback of our comparison study is the absence of any randomized controlled trial in the literature, so that all results have to be considered preliminary, stating whether TM might be a promising treatment option or not. An unequivocal recommendation for a specific treatment is not possible on the basis of the current evidence. The results of the present literature review should therefore not be considered as decisive but rather as hypothesis generating regarding future, prospective, randomized controlled studies. Since our analyses are confined to case series, a further problem is the difference in the length of the follow up period of the TM cone group compared to the bulk allograft group. In the statistical comparison we adjusted for these different follow up periods by entering the logarithm of the follow up period as an offset [18]. The offset also accounted for the number of prostheses implanted (femoral, tibial, or both). Such an analysis assumes that the failure rate is constant over time and the same in the two sites (it was not possible to determine separate failure rates for femoral and tibial revisions because not all studies separately reported these numbers). Both assumptions may be incorrect: TM related studies are anticipated to have better long-term outcomes than the average of the yearly failure rate suggests. Both experimental studies [23] and clinical studies [35] show improved early osteointegration with TM components and therefore a decreased loosening rate can be expected later on. If we assume that with TM
components the majority of mechanical complications happen early postoperatively as suggested by Jafari et al. [35], our results clearly favor the use of TM components in knee revision surgery over bulk allografts. In addition, the use and implantation of porous metal is constantly evolving, with some companies providing their own broaching systems to allow for improved press-fit implantation. The increased use of porous metals and the increased familiarity with the technique of its implantation may further improve the outcome of surgical procedures using these materials. Our review of the literature supports the results and conclusions drawn by experimental studies involving large bone allografts [24,28,29] and TM components [22,23,34] showing that the improved biocompatibility and osteointegration of porous implants might result in a substantially lower loosening rate. The limited number of cases did not indicate that the infection rate or overall revision rates varied. These findings are similar to clinical results we found in revision hip arthroplasty [7]. However, for further validation, a longer follow up period in these patients who undergo knee revision surgery with TM components is still required. Because of the observational nature of the included studies, the meta-regression results should not be considered conclusive but rather strongly indicative of improved results with the use of TM cones. References 1. Kurtz S, Ong K, Lau E, et al. Projections of primary and revision hip and knee arthroplasty in the United States from 2005 to 2030. J Bone Joint Surg Am 2007;89–4:780. 2. Iorio R, Robb WJ, Healy WL, et al. Orthopaedic surgeon workforce and volume assessment for total hip and knee replacement in the United States: preparing for an epidemic. J Bone Joint Surg Am 2008;90–7:1598. 3. Haidukewych GJ, Hanssen A, Jones RE. Metaphyseal fixation in revision total knee arthroplasty: indications and techniques. J Am Acad Orthop Surg 2011;19–6:311. 4. Qiu YY, Yan CH, Chiu KY, et al. Review article: treatments for bone loss in revision total knee arthroplasty. J Orthop Surg 2012;20–1:78. 5. Bush JL, Wilson JB, Vail TP. Management of bone loss in revision total knee arthroplasty. Clin Orthop Relat Res 2006;452:186. 6. Dennis DA. The structural allograft composite in revision total knee arthroplasty. J Arthroplasty 2002;17–4(Suppl 1):90.
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