The Journal of Arthroplasty xxx (2015) xxx–xxx
Contents lists available at ScienceDirect
The Journal of Arthroplasty journal homepage: www.arthroplastyjournal.org
Trends in Total Knee Arthroplasty Implant Utilization Long-Co L. Nguyen, BS a, Mandeep S. Lehil, MD a, Kevin J. Bozic, MD, MBA b,c a b c
School of Medicine, University of California, San Francisco, San Francisco, California Department of Orthopaedic Surgery, University of California, San Francisco, San Francisco, California Philip. R Lee Institute for Health Policy Studies, University of California, San Francisco, San Francisco, California
a r t i c l e
i n f o
Article history: Received 16 September 2014 Accepted 4 December 2014 Available online xxxx Keywords: total knee arthroplasty implants bearing constraint level fixation trends
a b s t r a c t The incidence of total knee arthroplasty (TKA) has increased alongside our knowledge of knee physiology, kinematics, and technology resulting in an evolution of TKA implants. This study examines the trends in TKA implant utilization. Data was extracted from The Orthopedic Research Network to evaluate trends in level of constraint, fixed vs. mobile bearing, fixation, and type of polyethylene in primary TKAs. In 2012, 88% used cemented femoral and tibial implants, and 96% involved patellar resurfacing. 38% of implants were cruciate retaining, 53% posterior stabilized or condylar stabilized, 3% constrained. 91% were fixed-bearing, 7% mobilebearing. 52% of tibial inserts were HXLPE. TKA implant trends demonstrate a preference for cemented femoral and tibial components, patellar resurfacing, fixed-bearing constructs, metal-backed tibial components, patellar resurfacing, and increased usage of HXLPE liners. © 2014 Elsevier Inc. All rights reserved.
Total knee arthroplasty (TKA) has been widely established as a highly successful and cost-effective treatment for advanced degenerative joint disease of the knee in terms of pain relief, increased function, and improvement in quality-of-life dimensions [1–4]. First introduced into clinical practice in the 1970s, TKA has now become one of the most common inpatient surgical procedures performed in the United States [5]. Recent studies on the projected future demand purport that TKA use is expected to exponentially rise in the next 10 years, driven by the aging baby boomer generation, obesity epidemic in the United States, public expectations, and investment in health-care interventions [1]. According to data from the Millennium Research Group [6], the number of TKA procedures in the US grew 2.9% in 2012 to 734,100 procedures. 80% of these procedures were primary TKA, 8% were unicondylar replacements, 10% were revision TKA, and 2% were patello-femoral replacements. Over the past 40 years, the number of implants available on the market has grown considerably and usage has evolved as experience has been gained with different implant materials and designs. However, much of the published outcomes associated with different implants are from small single-surgeon or single-center case series performed by design surgeons. The increased demand for TKA as well as the potential biases of previously published reports requires a better understanding of the implants that are currently utilized during TKA procedures and how they behave in vivo so steps can be taken to improve outcomes.
The Conflict of Interest statement associated with this article can be found at http:// dx.doi.org/10.1016/j.arth.2014.12.009. Reprint requests: Kevin J. Bozic, MD, MBA, University of California, Department of Orthopaedic Surgery, Core Faculty, Philip R. Lee Institute for Health Policy Studies, 500 Parnassus, MU 320W, San Francisco, CA 94143-0728.
The purpose of this study was to analyze trends in implant utilization for TKA in the United States between 2001 and 2012 to ultimately inform clinical decision making. Materials and Methods Data used in this study were obtained from the Orthopedic Research Network (ORN) database, which is collected from hospitals participating in www.implantdata.com [7]. In 2012, the database included 165 hospitals, representing approximately a 3% sample of mainly community hospitals and some academic centers within the United States. The participating hospitals are located in 20 different states widely distributed among different regions of the nation. Though the data used in this study were provided by a group of self-selected hospitals—and thus may not be nationally representative—informal surveys have indicated that the collected data are depictive of national trends [8]. Data are submitted from participating hospitals on a continuous basis and are made available to registered users every three months. The ORN publishes reports on the data received on knee implant utilization annually. For this study, data were collected from the ORN on a quarterly basis after the data were anonymized and cleaned by excluding cases found to be invalid, TKA constructs were calculated, and products were classified using GIC code, material, sizes, and product lines. Data from a total of 273,285 TKA procedures collected from 2001 to 2012 were analyzed to evaluate trends in procedure type, level of constraint (posterior cruciate ligament-substituting, posterior cruciate ligament-retaining systems), fixed vs. mobile bearing, fixation type (cemented versus cementless), type of polyethylene (highly-crosslinked polyethylene, polyethylene, vitamin E infused polyethylene), and patellar resurfacing. The average selling price of these different implants was also obtained. The data
http://dx.doi.org/10.1016/j.arth.2014.12.009 0883-5403/© 2014 Elsevier Inc. All rights reserved.
Please cite this article as: Nguyen L-CL, et al, Trends in Total Knee Arthroplasty Implant Utilization, J Arthroplasty (2014), http://dx.doi.org/ 10.1016/j.arth.2014.12.009
2
L-C.L. Nguyen et al. / The Journal of Arthroplasty xxx (2015) xxx–xxx
100%
100%
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80%
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60%
CO
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40%
Revision
MOB
40%
CR PS
20%
TKA
20%
presented here were obtained from available data in the ORN as of May of 2013. Results The vast majority of primary knee arthroplasty procedures in 2012 were unilateral total knee arthroplasties accounting for 88% of procedures, slightly down from 92% in 2001 (Fig. 1). 4% of primary knee arthroplasty procedures were bilateral, 7% were unicondylar (medial or lateral), and 1% were patello-femoral arthroplasties. In 2012, 96% of all TKA procedures used a patellar implant, which is slightly increased from 93% in 2001. Of the different types of constructs used for TKA, 88% of the procedures in 2012 used cemented femoral and tibial components, increased from 81% in 2001. Hybrid constructs—those with a cementless femur and cemented tibia—accounted for 4% of TKA constructs in 2012, which is down from 14% in 2001. The percentage of cementless femoral and tibial component constructs has remained relatively constant for the past decade, accounting for 5% of primary TKA procedures in 2001 and 4% in 2012 (Fig. 2). Among primary TKA procedures, 38% used a cruciate retaining construct in 2012, down from 50% in 2003 (Fig. 3). 53% used a posterior stabilized or condylar stabilized construct in 2012, up from 31% in 2001. 3% of primary TKA procedures used a constrained construct in 2012, down from 4% in 2011. 91% of primary TKA procedures used a fixed bearing in 2012, up from 81% in 2005, while 7% used a mobile bearing, down from 19% in 2005. 1% of primary TKA procedures used an allpolyethylene tibial implant, down from 2% in 2011. Highly-crosslinked polyethylene (HXLPE) tibial inserts were used in 52% of TKA procedures in 2012, up from 24% in 2001 (Fig. 4). Use of
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Fig. 1. Trends in types of knee arthroplasty from 2001 to 2012 (TKA: total knee arthroplasty).
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Fig. 3. Trends in types of tibial implants from 2001 to 2012 (CR: cruciate retaining, PS: posterior stabilized, MOB: mobile bearing, CO: constrained).
conventional polyethylene tibial inserts declined from 76% in 2001 to 32% in 2012. Vitamin E infused polyethylene accounted for 4% of tibial inserts in 2012, up from 1% in 2009. A recent trend has been the use of custom cutting guides for knee replacement procedures. A CT-scan or an MRI of the knee joint is performed, and this is sent to the manufacturer to create cutting guides that are then delivered to the hospital prior to the patient's surgery. The use of these cutting guides has increased from 1.3% in 2009 to 6% in 2012. The overall average selling price (ASP) for primary TKA implants was $5104 in 2012, a 4% decrease from 2011 (Fig. 5). This was the second consecutive decline in ASP compared to a previous increase of 1.2% between 2009 and 2010. The sharpest increase in ASP occurred between 2000 and 2005 when the average cost of a TKA implant increased from approximately $3000 to $5200, an increase of 73%. Since that time, the price of TKA implants has stabilized and recently has begun to decrease, albeit minimally. The costs reported include the implants themselves as well as bone cement and accessories, bone graft and substitutes, freight and loaner fees, and charges for instruments and cutting guides. These ancillary supplies make up approximately 6% of the total implant costs reported. There is a significant difference in price for the different types of constructs utilized for TKA. Currently, the most expensive is the hybrid construct, consisting of a cementless femoral and cemented tibial implant, which had an ASP of $6764, a 15% decrease from 2011. Surprisingly, the cementless femoral and tibial construct is less expensive than the hybrid construct, with an ASP of $5908, a 1% decrease from 2011. The unicondylar construct had an ASP of $5017, a 2% decrease from 2011. The least expensive construct is the cemented femoral and tibia combination with an ASP of $5005, a 6% decrease from 2011.
100% 90% 80% 70% 60%
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Fig. 2. Trends in fixation from 2001 to 2012.
Please cite this article as: Nguyen L-CL, et al, Trends in Total Knee Arthroplasty Implant Utilization, J Arthroplasty (2014), http://dx.doi.org/ 10.1016/j.arth.2014.12.009
L-C.L. Nguyen et al. / The Journal of Arthroplasty xxx (2015) xxx–xxx
100% 90% 80% 70% 60% 50% 40% 30% 20% 10% 0%
VE Unknown/ Unspecified PE XP
Fig. 4. Trends in material type for tibial inserts from 2001 to 2012 (VE: vitamin E infused polyethylene, PE: polyethylene, XP: highly-crosslinked polyethylene).
According to data from Deaton Consulting LLC, the knee implant market in the United States grew in 2012, with $4 billion in sales, up 1.2% from 2011. The market has been increasing every year except between 2010 and 2011 when there was a 1.4% decrease in sales. Previously, the market had been experiencing double-digit percentage growth from 2000 to 2005, and single digit percentage growth from 2005 to 2010. Zimmer led the knee implant market in 2012 with 24.6% of the sales, followed by Stryker with 23.1%, DePuy with 20.9%, Biomet with 14.5%, Smith & Nephew with 10.7%, Wright with 1.4%, and all others with 4.8%. Discussion Over the past few decades the number of TKA procedures has markedly increased, inspiring advancements in the design and manufacturing of TKA implants. Implant utilization trends have evolved in an effort to develop implants with more physiologic kinematics and increased reliability and longevity, translating into better patient satisfaction and outcomes. One major trend in the past decade for TKA constructs has been a slow decline in the use of cementless fixation for both the femoral and tibial components. Cemented components have been favored due to theoretically (and paradoxically) providing more stable long-term fixation, as cohort studies have demonstrated that they are associated with lower failure rates and better functional outcomes than cementless implants [3,4,9]. Longitudinal studies have demonstrated that TKA implant longevity depends to a very large extent on the design of the prosthesis [10–12], the restoration of mechanical alignment and softtissue balancing [13,14]. Other factors also influence the outcome such as patient age, body weight and activity level [15]. The use of metal-backed tibial components, either cemented or cementless, has been ubiquitous in TKA since 2001 accounting for 98% of implants used. All-polyethylene tibial components have rarely been utilized since 2001, but still account for approximately 1% of implants used. Studies have demonstrated the all-polyethylene tibial component $6,000 $5,000 $4,000 $3,000 $2,000 $1,000
Fig. 5. Total knee average implant cost from 2001 to 2012.
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to be comparable to the metal-backed tibial component in terms of adverse outcomes, durability, and clinical outcomes [16–19]. A potential reason for the preferred use of metal-backed tibial components is the modularity which facilitates intra-operative adjustments, as well as the option for modular parts exchange in the setting of periprosthetic joint infection or isolated bearing component wear as a reason for TKA revision. The all-polyethylene implant is significantly less expensive than the metal-backed tibial component and its utilization could help bring down the cost of TKA surgery in the US, especially for older patients who have a lower activity level and are less likely to require revision surgery. Another trend in TKA has been a gradual increase in the use of highly cross-linked polyethylene (HXLPE) liners, which theoretically allow for better wear properties than conventional cross-linked polyethylene liners, although the clinical benefits of HXLPE in TKA in terms of improved clinical outcomes or increased implant longevity have yet to be proven [20,21]. The risks of using highly cross-linked polyethylene compared to conventional polyethylene include fracture of the liner or of a posterior-stabilized tibial post, liner dislodgement or locking mechanism disruption, and possibly increased osteolysis [20,22]. A cautious approach is warranted to the widespread use of highly cross-linked polyethylene in TKA until additional clinical results are available. The recent addition of vitamin E to these liners has the theoretical advantage of absorbing free radicals that are created during the cross-linking process which tend to degrade the polyethylene liner [21]. Further studies will be needed to determine the long-term efficacy of using the vitamin E enhanced HXLPE liners versus HXLPE without Vitamin E. Another trend in TKA implant usage has been the gradual increase in the use of posterior cruciate ligament (PCL) sacrificing (PS) constructs versus PCL-retaining (CR) constructs. The PCL sacrificing constructs can substitute for the PCL with either posterior stabilization or be performed without stabilization. Studies have not clearly demonstrated the superiority of either PS or CR constructs; proponents of PS constructs cite improved range of motion and more reproducible knee kinematics compared to CR constructs [23–25], while proponents of CR constructs cite better proprioception and less bone loss compared with PS constructs [26,27]. The decision to perform a PCL retaining versus PCL sacrificing TKA is multifactorial and surgeon specific. The technique for PCL retention can be technically more challenging because the normal configuration and tension of the PCL need to be reproduced with proper ligament balancing. The PCL sacrificing technique is often felt to be technically easier and may be a contributing reason for its increased popularity among orthopedic surgeons. The polyethylene insert in a TKA can be fixed to the tibial plateau or it can have freedom of rotation and/or translation, the “mobile bearing” construct. The use of mobile bearing TKA constructs was an increasing trend in the early part of the century, but has since declined and remained at about 7% of TKA constructs for the past several years. The “mobile bearing” knee theoretically reproduces more natural knee kinematics compared to the standard fixed-bearing design. However, studies comparing outcomes of fixed and mobile bearing TKA designs have found no difference in survivorship, clinical function (rotation, flexion, and extension), or patient preference [28,29]. Both designs are capable of producing excellent long-term results and clinical outcomes if properly implanted and thus the use of either design is surgeon specific. A recent trend in TKA implant usage has been the increased utilization of custom cutting guides for knee replacement surgeries. This requires the patient to obtain a CT-scan or MRI prior to their surgery so the manufacturer of the implant can create a cutting guide and deliver it to the hospital prior to surgery. Theoretically, these guides could improve the alignment of the joint surfaces and reduce the number of instrument trays and steps during the procedure [30,31]. The major drawback for these custom cutting guides is the added expense of the disposable guides to the procedure and the additional inconvenience and potential risk to the patient for the additional imaging required. As this is a recent trend, there are not enough long-term data for the outcome of TKA done with custom cutting guides to determine whether
Please cite this article as: Nguyen L-CL, et al, Trends in Total Knee Arthroplasty Implant Utilization, J Arthroplasty (2014), http://dx.doi.org/ 10.1016/j.arth.2014.12.009
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the theoretical advantage is actually evident in practice. Further studies will be needed to determine the efficacy of using custom cutting guides. A limitation of our study is that it only included a sample of US hospitals (3%). However, the number of TKA procedures included in the registry used in the study (the Orthopedic Research Network (ORN)) represents roughly 6% of the total number of TKA procedures performed in the US during this time period, which is the largest publicly available US-based implant registry with detailed information about TKA implants over a 10-year period. As further data are collected on TKA implants and more is learned about how they behave in vivo, trends in TKA implant utilization are likely to continue to evolve. Newer materials and different constructs for TKA are sure to continue to develop with the goal of optimizing the longevity and biomechanics of these implants. It will be important to continue to monitor these trends to help identify the optimal implant to use for patients requiring TKA in the future. The cost of implants has stabilized since the early part of the 21st century. The hybrid construct designs are more expensive than the more commonly used cemented implants. The decision to use a particular implant is related to a multitude of factors, which include surgeon preference and experience, direct marketing to surgeons and to consumers, relationship between surgeon and device manufacturer, and evidence based data from the literature [32,33]. In the coming years, the economic burden of the increased demand for knee arthroplasty will be huge. Policies should be implemented now to help bring down the cost of this procedure and help decrease the burden to the health care system [34]. In conclusion, TKA implant usage trends favor unilateral primary TKA, cemented fixation, patellar resurfacing, posterior stabilized implants, fixed bearing implants, and HXLPE tibial inserts. The recent trend of vitamin E enhanced HXLPE tibial inserts offers a theoretical advantage of improved wear properties, but further studies will be required to determine their efficacy for long-term use. Similarly, the trend of using custom cutting guides for TKA offers the theoretical benefit of improving the alignment of the joint surfaces, but further studies will be required to determine if the outcomes are significantly different from TKA without the use of cutting guides and whether the outcome justifies the increased cost of the procedure. Multi-stakeholder efforts to control implant costs will be needed in order to preserve access to these potentially life-altering procedures for future patients. Acknowledgments The authors wish to acknowledge Stan Mendenhall, Jan Deaton, and Vanessa Chan, MPH for their assistance in preparing this manuscript. References 1. Santaguida PL, Hawker GA, Hudak PL, et al. Patient characteristics affecting the prognosis of total hip and knee joint arthroplasty: a systematic review. Can J Surg 2008;51(6):428. 2. 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. 3. Dodd CA, Hungerford DS, Krackow KA. Total knee arthroplasty fixation. Comparison of the early results of paired cemented versus uncemented porous coated anatomic knee prostheses. Clin Orthop Relat Res 1990;260:66. 4. Akizuki S, Takizawa T, Horiuchi H. Fixation of a hydroxyapatite-tricalcium phosphatecoated cementless knee prosthesis. Clinical and radiographic evaluation seven years after surgery. J Bone Joint Surg (Br) 2003;85(8):1123. 5. Centers for Disease Control and Prevention. FasStats - Inpatient Surgery. [cited 2013 September 20]; Available from: http://www.cdc.gov/nchs/fastats/inpatient-surgery. htm; 2014. [Accessed September 20 2013].
6. Millenium Research Group. US Markets for Large-Joint Reconstructive Implants 2012 - See more at. http://mrg.net/Products-and-Services/Syndicated-Report.aspx? r=RPUS21LJ12-sthash.JkToX0Js.dpuf; 2012. [[cited 2014 September 20]; Available from: http://mrg.net/Products-and-Services/Syndicated-Report.aspx?r= RPUS21LJ12. Accessed September 20 2014]. 7. Mendenhall S. Hip and knee implant review. Orthop Netw News 2013;24(3):1. 8. Berry DJ, Bozic KJ. Current practice patterns in primary hip and knee arthroplasty among members of the American Association of Hip and Knee Surgeons. J Arthroplasty 2010;25(6 Suppl.):2. 9. Ranawat CS, Meftah M, Windsor EN, et al. Cementless fixation in total knee arthroplasty: down the boulevard of broken dreams—affirms. J Bone Joint Surg (Br) 2012;94(11 Suppl. A):82. 10. Vessely MB, Whaley AL, Harmsen WS, et al. The Chitranjan Ranawat Award: longterm survivorship and failure modes of 1000 cemented condylar total knee arthroplasties. Clin Orthop Relat Res 2006;452:28. 11. Buechel Sr FF. Long-term followup after mobile-bearing total knee replacement. Clin Orthop Relat Res 2002;404:40. 12. Stiehl JB, Hamelynck KJ, Voorhorst PE. International multi-centre survivorship analysis of mobile bearing total knee arthroplasty. Int Orthop 2006;30(3):190. 13. Rasquinha VJ, Ranawat CS, Cervieri CL, et al. The press-fit condylar modular total knee system with a posterior cruciate-substituting design. A concise follow-up of a previous report. J Bone Joint Surg Am 2006;88(5):1006. 14. Font-Rodriguez DE, Scuderi GR, Insall JN. Survivorship of cemented total knee arthroplasty. Clin Orthop Relat Res 1997;345:79. 15. Dahm DL, Barnes SA, Harrington JR, et al. Patient-reported activity level after total knee arthroplasty. J Arthroplasty 2008;23(3):401. 16. Gioe TJ, Maheshwari AV. The all-polyethylene tibial component in primary total knee arthroplasty. J Bone Joint Surg Am 2010;92(2):478. 17. Browne JA, Gall Sims SE, Giuseffi SA, et al. All-polyethylene tibial components in modern total knee arthroplasty. J Am Acad Orthop Surg 2011;19(9):527. 18. Voigt J, Mosier M. Cemented all-polyethylene and metal-backed polyethylene tibial components used for primary total knee arthroplasty: a systematic review of the literature and meta-analysis of randomized controlled trials involving 1798 primary total knee implants. J Bone Joint Surg Am 2011;93(19):1790. 19. Blumenfeld TJ, Scott RD. The role of the cemented all-polyethylene tibial component in total knee replacement: a 30-year patient follow-up and review of the literature. Knee 2010;17(6):412. 20. Fisher J, McEwen HM, Tipper JL, et al. Wear, debris, and biologic activity of crosslinked polyethylene in the knee: benefits and potential concerns. Clin Orthop Relat Res 2004;428:114. 21. Jacofsky DJ. Highly cross-linked polyethylene in total knee arthroplasty: in the affirmative. J Arthroplasty 2008;23(7 Suppl.):28. 22. Lachiewicz PF, Geyer MR. The use of highly cross-linked polyethylene in total knee arthroplasty. J Am Acad Orthop Surg 2011;19(3):143. 23. Jacobs WC, Clement DJ, Wymenga AB. Retention versus sacrifice of the posterior cruciate ligament in total knee replacement for treatment of osteoarthritis and rheumatoid arthritis. Cochrane Database Syst Rev 2005;4:CD004803. 24. Dennis DA, Komistek RD, Mahfouz MR, et al. Multicenter determination of in vivo kinematics after total knee arthroplasty. Clin Orthop Relat Res 2003;416:37. 25. Dennis DA, Komistek RD, Colwell Jr CE, et al. In vivo anteroposterior femorotibial translation of total knee arthroplasty: a multicenter analysis. Clin Orthop Relat Res 1998;356:47. 26. Williams TJ, Thornhill TS. The technique of PCL retention in total knee arthroplasty. In: Bellemans J, Ries M, Victor JK, editors. Total Knee Arthroplasty. Berlin Heidelberg: Springer; 2005. p. 177. 27. Schai PA, Thornhill TS, Scott RD. Total knee arthroplasty with the PFC system. Results at a minimum of ten years and survivorship analysis. J Bone Joint Surg (Br) 1998;80 (5):850. 28. Post ZD, Matar WY, van de Leur T, et al. Mobile-bearing total knee arthroplasty: better than a fixed-bearing? J Arthroplasty 2010;25(6):998. 29. Jacobs W, Anderson P, Limbeek J, et al. Mobile bearing vs fixed bearing prostheses for total knee arthroplasty for post-operative functional status in patients with osteoarthritis and rheumatoid arthritis. Cochrane Database Syst Rev 2004;2:CD003130. 30. Fu Y, Wang M, Liu Y, et al. Alignment outcomes in navigated total knee arthroplasty: a meta-analysis. Knee Surg Sports Traumatol Arthrosc 2012;20(6):1075. 31. Cheng T, Zhao S, Peng X, et al. Does computer-assisted surgery improve postoperative leg alignment and implant positioning following total knee arthroplasty? A metaanalysis of randomized controlled trials? Knee Surg Sports Traumatol Arthrosc 2012;20(7):1307. 32. Hanzlik S, Mahabir RC, Baynosa RC, et al. Levels of evidence in research published in The Journal of Bone and Joint Surgery (American Volume) over the last thirty years. J Bone Joint Surg Am 2009;91(2):425. 33. Obremskey WT, Pappas N, Attallah-Wasif E, et al. Level of evidence in orthopaedic journals. J Bone Joint Surg Am 2005;87(12):2632. 34. Brennan TA, Rothman DJ, Blank L, et al. Health industry practices that create conflicts of interest: a policy proposal for academic medical centers. JAMA 2006; 295(4):429.
Please cite this article as: Nguyen L-CL, et al, Trends in Total Knee Arthroplasty Implant Utilization, J Arthroplasty (2014), http://dx.doi.org/ 10.1016/j.arth.2014.12.009
Contents lists available at ScienceDirect
The Journal of Arthroplasty journal homepage: www.arthroplastyjournal.org
Trends in Total Knee Arthroplasty Implant Utilization Long-Co L. Nguyen, BS a, Mandeep S. Lehil, MD a, Kevin J. Bozic, MD, MBA b,c a b c
School of Medicine, University of California, San Francisco, San Francisco, California Department of Orthopaedic Surgery, University of California, San Francisco, San Francisco, California Philip. R Lee Institute for Health Policy Studies, University of California, San Francisco, San Francisco, California
a r t i c l e
i n f o
Article history: Received 16 September 2014 Accepted 4 December 2014 Available online xxxx Keywords: total knee arthroplasty implants bearing constraint level fixation trends
a b s t r a c t The incidence of total knee arthroplasty (TKA) has increased alongside our knowledge of knee physiology, kinematics, and technology resulting in an evolution of TKA implants. This study examines the trends in TKA implant utilization. Data was extracted from The Orthopedic Research Network to evaluate trends in level of constraint, fixed vs. mobile bearing, fixation, and type of polyethylene in primary TKAs. In 2012, 88% used cemented femoral and tibial implants, and 96% involved patellar resurfacing. 38% of implants were cruciate retaining, 53% posterior stabilized or condylar stabilized, 3% constrained. 91% were fixed-bearing, 7% mobilebearing. 52% of tibial inserts were HXLPE. TKA implant trends demonstrate a preference for cemented femoral and tibial components, patellar resurfacing, fixed-bearing constructs, metal-backed tibial components, patellar resurfacing, and increased usage of HXLPE liners. © 2014 Elsevier Inc. All rights reserved.
Total knee arthroplasty (TKA) has been widely established as a highly successful and cost-effective treatment for advanced degenerative joint disease of the knee in terms of pain relief, increased function, and improvement in quality-of-life dimensions [1–4]. First introduced into clinical practice in the 1970s, TKA has now become one of the most common inpatient surgical procedures performed in the United States [5]. Recent studies on the projected future demand purport that TKA use is expected to exponentially rise in the next 10 years, driven by the aging baby boomer generation, obesity epidemic in the United States, public expectations, and investment in health-care interventions [1]. According to data from the Millennium Research Group [6], the number of TKA procedures in the US grew 2.9% in 2012 to 734,100 procedures. 80% of these procedures were primary TKA, 8% were unicondylar replacements, 10% were revision TKA, and 2% were patello-femoral replacements. Over the past 40 years, the number of implants available on the market has grown considerably and usage has evolved as experience has been gained with different implant materials and designs. However, much of the published outcomes associated with different implants are from small single-surgeon or single-center case series performed by design surgeons. The increased demand for TKA as well as the potential biases of previously published reports requires a better understanding of the implants that are currently utilized during TKA procedures and how they behave in vivo so steps can be taken to improve outcomes.
The Conflict of Interest statement associated with this article can be found at http:// dx.doi.org/10.1016/j.arth.2014.12.009. Reprint requests: Kevin J. Bozic, MD, MBA, University of California, Department of Orthopaedic Surgery, Core Faculty, Philip R. Lee Institute for Health Policy Studies, 500 Parnassus, MU 320W, San Francisco, CA 94143-0728.
The purpose of this study was to analyze trends in implant utilization for TKA in the United States between 2001 and 2012 to ultimately inform clinical decision making. Materials and Methods Data used in this study were obtained from the Orthopedic Research Network (ORN) database, which is collected from hospitals participating in www.implantdata.com [7]. In 2012, the database included 165 hospitals, representing approximately a 3% sample of mainly community hospitals and some academic centers within the United States. The participating hospitals are located in 20 different states widely distributed among different regions of the nation. Though the data used in this study were provided by a group of self-selected hospitals—and thus may not be nationally representative—informal surveys have indicated that the collected data are depictive of national trends [8]. Data are submitted from participating hospitals on a continuous basis and are made available to registered users every three months. The ORN publishes reports on the data received on knee implant utilization annually. For this study, data were collected from the ORN on a quarterly basis after the data were anonymized and cleaned by excluding cases found to be invalid, TKA constructs were calculated, and products were classified using GIC code, material, sizes, and product lines. Data from a total of 273,285 TKA procedures collected from 2001 to 2012 were analyzed to evaluate trends in procedure type, level of constraint (posterior cruciate ligament-substituting, posterior cruciate ligament-retaining systems), fixed vs. mobile bearing, fixation type (cemented versus cementless), type of polyethylene (highly-crosslinked polyethylene, polyethylene, vitamin E infused polyethylene), and patellar resurfacing. The average selling price of these different implants was also obtained. The data
http://dx.doi.org/10.1016/j.arth.2014.12.009 0883-5403/© 2014 Elsevier Inc. All rights reserved.
Please cite this article as: Nguyen L-CL, et al, Trends in Total Knee Arthroplasty Implant Utilization, J Arthroplasty (2014), http://dx.doi.org/ 10.1016/j.arth.2014.12.009
2
L-C.L. Nguyen et al. / The Journal of Arthroplasty xxx (2015) xxx–xxx
100%
100%
80%
80%
Patello-Femoral
60%
Unknown
60%
CO
Unicondylar Bilateral
40%
Revision
MOB
40%
CR PS
20%
TKA
20%
presented here were obtained from available data in the ORN as of May of 2013. Results The vast majority of primary knee arthroplasty procedures in 2012 were unilateral total knee arthroplasties accounting for 88% of procedures, slightly down from 92% in 2001 (Fig. 1). 4% of primary knee arthroplasty procedures were bilateral, 7% were unicondylar (medial or lateral), and 1% were patello-femoral arthroplasties. In 2012, 96% of all TKA procedures used a patellar implant, which is slightly increased from 93% in 2001. Of the different types of constructs used for TKA, 88% of the procedures in 2012 used cemented femoral and tibial components, increased from 81% in 2001. Hybrid constructs—those with a cementless femur and cemented tibia—accounted for 4% of TKA constructs in 2012, which is down from 14% in 2001. The percentage of cementless femoral and tibial component constructs has remained relatively constant for the past decade, accounting for 5% of primary TKA procedures in 2001 and 4% in 2012 (Fig. 2). Among primary TKA procedures, 38% used a cruciate retaining construct in 2012, down from 50% in 2003 (Fig. 3). 53% used a posterior stabilized or condylar stabilized construct in 2012, up from 31% in 2001. 3% of primary TKA procedures used a constrained construct in 2012, down from 4% in 2011. 91% of primary TKA procedures used a fixed bearing in 2012, up from 81% in 2005, while 7% used a mobile bearing, down from 19% in 2005. 1% of primary TKA procedures used an allpolyethylene tibial implant, down from 2% in 2011. Highly-crosslinked polyethylene (HXLPE) tibial inserts were used in 52% of TKA procedures in 2012, up from 24% in 2001 (Fig. 4). Use of
2012
2011
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Fig. 1. Trends in types of knee arthroplasty from 2001 to 2012 (TKA: total knee arthroplasty).
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Fig. 3. Trends in types of tibial implants from 2001 to 2012 (CR: cruciate retaining, PS: posterior stabilized, MOB: mobile bearing, CO: constrained).
conventional polyethylene tibial inserts declined from 76% in 2001 to 32% in 2012. Vitamin E infused polyethylene accounted for 4% of tibial inserts in 2012, up from 1% in 2009. A recent trend has been the use of custom cutting guides for knee replacement procedures. A CT-scan or an MRI of the knee joint is performed, and this is sent to the manufacturer to create cutting guides that are then delivered to the hospital prior to the patient's surgery. The use of these cutting guides has increased from 1.3% in 2009 to 6% in 2012. The overall average selling price (ASP) for primary TKA implants was $5104 in 2012, a 4% decrease from 2011 (Fig. 5). This was the second consecutive decline in ASP compared to a previous increase of 1.2% between 2009 and 2010. The sharpest increase in ASP occurred between 2000 and 2005 when the average cost of a TKA implant increased from approximately $3000 to $5200, an increase of 73%. Since that time, the price of TKA implants has stabilized and recently has begun to decrease, albeit minimally. The costs reported include the implants themselves as well as bone cement and accessories, bone graft and substitutes, freight and loaner fees, and charges for instruments and cutting guides. These ancillary supplies make up approximately 6% of the total implant costs reported. There is a significant difference in price for the different types of constructs utilized for TKA. Currently, the most expensive is the hybrid construct, consisting of a cementless femoral and cemented tibial implant, which had an ASP of $6764, a 15% decrease from 2011. Surprisingly, the cementless femoral and tibial construct is less expensive than the hybrid construct, with an ASP of $5908, a 1% decrease from 2011. The unicondylar construct had an ASP of $5017, a 2% decrease from 2011. The least expensive construct is the cemented femoral and tibia combination with an ASP of $5005, a 6% decrease from 2011.
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Fig. 2. Trends in fixation from 2001 to 2012.
Please cite this article as: Nguyen L-CL, et al, Trends in Total Knee Arthroplasty Implant Utilization, J Arthroplasty (2014), http://dx.doi.org/ 10.1016/j.arth.2014.12.009
L-C.L. Nguyen et al. / The Journal of Arthroplasty xxx (2015) xxx–xxx
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Fig. 4. Trends in material type for tibial inserts from 2001 to 2012 (VE: vitamin E infused polyethylene, PE: polyethylene, XP: highly-crosslinked polyethylene).
According to data from Deaton Consulting LLC, the knee implant market in the United States grew in 2012, with $4 billion in sales, up 1.2% from 2011. The market has been increasing every year except between 2010 and 2011 when there was a 1.4% decrease in sales. Previously, the market had been experiencing double-digit percentage growth from 2000 to 2005, and single digit percentage growth from 2005 to 2010. Zimmer led the knee implant market in 2012 with 24.6% of the sales, followed by Stryker with 23.1%, DePuy with 20.9%, Biomet with 14.5%, Smith & Nephew with 10.7%, Wright with 1.4%, and all others with 4.8%. Discussion Over the past few decades the number of TKA procedures has markedly increased, inspiring advancements in the design and manufacturing of TKA implants. Implant utilization trends have evolved in an effort to develop implants with more physiologic kinematics and increased reliability and longevity, translating into better patient satisfaction and outcomes. One major trend in the past decade for TKA constructs has been a slow decline in the use of cementless fixation for both the femoral and tibial components. Cemented components have been favored due to theoretically (and paradoxically) providing more stable long-term fixation, as cohort studies have demonstrated that they are associated with lower failure rates and better functional outcomes than cementless implants [3,4,9]. Longitudinal studies have demonstrated that TKA implant longevity depends to a very large extent on the design of the prosthesis [10–12], the restoration of mechanical alignment and softtissue balancing [13,14]. Other factors also influence the outcome such as patient age, body weight and activity level [15]. The use of metal-backed tibial components, either cemented or cementless, has been ubiquitous in TKA since 2001 accounting for 98% of implants used. All-polyethylene tibial components have rarely been utilized since 2001, but still account for approximately 1% of implants used. Studies have demonstrated the all-polyethylene tibial component $6,000 $5,000 $4,000 $3,000 $2,000 $1,000
Fig. 5. Total knee average implant cost from 2001 to 2012.
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to be comparable to the metal-backed tibial component in terms of adverse outcomes, durability, and clinical outcomes [16–19]. A potential reason for the preferred use of metal-backed tibial components is the modularity which facilitates intra-operative adjustments, as well as the option for modular parts exchange in the setting of periprosthetic joint infection or isolated bearing component wear as a reason for TKA revision. The all-polyethylene implant is significantly less expensive than the metal-backed tibial component and its utilization could help bring down the cost of TKA surgery in the US, especially for older patients who have a lower activity level and are less likely to require revision surgery. Another trend in TKA has been a gradual increase in the use of highly cross-linked polyethylene (HXLPE) liners, which theoretically allow for better wear properties than conventional cross-linked polyethylene liners, although the clinical benefits of HXLPE in TKA in terms of improved clinical outcomes or increased implant longevity have yet to be proven [20,21]. The risks of using highly cross-linked polyethylene compared to conventional polyethylene include fracture of the liner or of a posterior-stabilized tibial post, liner dislodgement or locking mechanism disruption, and possibly increased osteolysis [20,22]. A cautious approach is warranted to the widespread use of highly cross-linked polyethylene in TKA until additional clinical results are available. The recent addition of vitamin E to these liners has the theoretical advantage of absorbing free radicals that are created during the cross-linking process which tend to degrade the polyethylene liner [21]. Further studies will be needed to determine the long-term efficacy of using the vitamin E enhanced HXLPE liners versus HXLPE without Vitamin E. Another trend in TKA implant usage has been the gradual increase in the use of posterior cruciate ligament (PCL) sacrificing (PS) constructs versus PCL-retaining (CR) constructs. The PCL sacrificing constructs can substitute for the PCL with either posterior stabilization or be performed without stabilization. Studies have not clearly demonstrated the superiority of either PS or CR constructs; proponents of PS constructs cite improved range of motion and more reproducible knee kinematics compared to CR constructs [23–25], while proponents of CR constructs cite better proprioception and less bone loss compared with PS constructs [26,27]. The decision to perform a PCL retaining versus PCL sacrificing TKA is multifactorial and surgeon specific. The technique for PCL retention can be technically more challenging because the normal configuration and tension of the PCL need to be reproduced with proper ligament balancing. The PCL sacrificing technique is often felt to be technically easier and may be a contributing reason for its increased popularity among orthopedic surgeons. The polyethylene insert in a TKA can be fixed to the tibial plateau or it can have freedom of rotation and/or translation, the “mobile bearing” construct. The use of mobile bearing TKA constructs was an increasing trend in the early part of the century, but has since declined and remained at about 7% of TKA constructs for the past several years. The “mobile bearing” knee theoretically reproduces more natural knee kinematics compared to the standard fixed-bearing design. However, studies comparing outcomes of fixed and mobile bearing TKA designs have found no difference in survivorship, clinical function (rotation, flexion, and extension), or patient preference [28,29]. Both designs are capable of producing excellent long-term results and clinical outcomes if properly implanted and thus the use of either design is surgeon specific. A recent trend in TKA implant usage has been the increased utilization of custom cutting guides for knee replacement surgeries. This requires the patient to obtain a CT-scan or MRI prior to their surgery so the manufacturer of the implant can create a cutting guide and deliver it to the hospital prior to surgery. Theoretically, these guides could improve the alignment of the joint surfaces and reduce the number of instrument trays and steps during the procedure [30,31]. The major drawback for these custom cutting guides is the added expense of the disposable guides to the procedure and the additional inconvenience and potential risk to the patient for the additional imaging required. As this is a recent trend, there are not enough long-term data for the outcome of TKA done with custom cutting guides to determine whether
Please cite this article as: Nguyen L-CL, et al, Trends in Total Knee Arthroplasty Implant Utilization, J Arthroplasty (2014), http://dx.doi.org/ 10.1016/j.arth.2014.12.009
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the theoretical advantage is actually evident in practice. Further studies will be needed to determine the efficacy of using custom cutting guides. A limitation of our study is that it only included a sample of US hospitals (3%). However, the number of TKA procedures included in the registry used in the study (the Orthopedic Research Network (ORN)) represents roughly 6% of the total number of TKA procedures performed in the US during this time period, which is the largest publicly available US-based implant registry with detailed information about TKA implants over a 10-year period. As further data are collected on TKA implants and more is learned about how they behave in vivo, trends in TKA implant utilization are likely to continue to evolve. Newer materials and different constructs for TKA are sure to continue to develop with the goal of optimizing the longevity and biomechanics of these implants. It will be important to continue to monitor these trends to help identify the optimal implant to use for patients requiring TKA in the future. The cost of implants has stabilized since the early part of the 21st century. The hybrid construct designs are more expensive than the more commonly used cemented implants. The decision to use a particular implant is related to a multitude of factors, which include surgeon preference and experience, direct marketing to surgeons and to consumers, relationship between surgeon and device manufacturer, and evidence based data from the literature [32,33]. In the coming years, the economic burden of the increased demand for knee arthroplasty will be huge. Policies should be implemented now to help bring down the cost of this procedure and help decrease the burden to the health care system [34]. In conclusion, TKA implant usage trends favor unilateral primary TKA, cemented fixation, patellar resurfacing, posterior stabilized implants, fixed bearing implants, and HXLPE tibial inserts. The recent trend of vitamin E enhanced HXLPE tibial inserts offers a theoretical advantage of improved wear properties, but further studies will be required to determine their efficacy for long-term use. Similarly, the trend of using custom cutting guides for TKA offers the theoretical benefit of improving the alignment of the joint surfaces, but further studies will be required to determine if the outcomes are significantly different from TKA without the use of cutting guides and whether the outcome justifies the increased cost of the procedure. Multi-stakeholder efforts to control implant costs will be needed in order to preserve access to these potentially life-altering procedures for future patients. Acknowledgments The authors wish to acknowledge Stan Mendenhall, Jan Deaton, and Vanessa Chan, MPH for their assistance in preparing this manuscript. References 1. Santaguida PL, Hawker GA, Hudak PL, et al. Patient characteristics affecting the prognosis of total hip and knee joint arthroplasty: a systematic review. Can J Surg 2008;51(6):428. 2. 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. 3. Dodd CA, Hungerford DS, Krackow KA. Total knee arthroplasty fixation. Comparison of the early results of paired cemented versus uncemented porous coated anatomic knee prostheses. Clin Orthop Relat Res 1990;260:66. 4. Akizuki S, Takizawa T, Horiuchi H. Fixation of a hydroxyapatite-tricalcium phosphatecoated cementless knee prosthesis. Clinical and radiographic evaluation seven years after surgery. J Bone Joint Surg (Br) 2003;85(8):1123. 5. Centers for Disease Control and Prevention. FasStats - Inpatient Surgery. [cited 2013 September 20]; Available from: http://www.cdc.gov/nchs/fastats/inpatient-surgery. htm; 2014. [Accessed September 20 2013].
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Please cite this article as: Nguyen L-CL, et al, Trends in Total Knee Arthroplasty Implant Utilization, J Arthroplasty (2014), http://dx.doi.org/ 10.1016/j.arth.2014.12.009
