high-performance total knee...

79Bulletin of the Hospital for Joint Diseases 2013;71(1):79-88

Ilalov K, Cohn RM, Slover J. High-performance total knee replacement. Bull Hosp Jt Dis. 2013;71(1):79-88.

Abstract

The concept of a high-performance total knee replacement has gained prominence because of continued technological improvements by implant manufacturers and the changing expectations of an increasingly younger, more active patient population. Improvements in surgical technique, instrumen-tation, implant design, biomaterials, and implant fixation have occurred in recent years. The literature is inconclu-sive whether novel approaches can lead to improvements in patient satisfaction rates, address objectively measured parameters, and improve implant survival rates, while doing so in a cost-efficient manner.

Knee replacement has been shown to be cost effec-tive in improving health-related quality of life.1-4 The concept of a high-performance total knee

replacement has gained prominence because of continued technological improvements by implant manufacturers and the changing expectations of an increasingly younger, more active patient population. Mont and coworkers described that the features of a high performance joint replacement are four-fold: 1. the joint must “feel” normal, 2. it may al-low participation in activities, such as high impact sports, 3. it should allow participation in certain activities, such as squatting, kneeling, and allow for deep knee flexion, and 4. it must be durable for many years.5 Changing demographics and perceived success of the total knee replacement—im-proved functional status, pain relief, and low perioperative morbidity and mortality—have expanded demand among

all population segments and increased patient expectations for their postoperative function.6,7 Simultaneously, patient expectations and activity have increased with the improved success of the operation. The unintended effect of the in-creased popularity and the broadening indications may affect the excellent long-term survivorship, which has reached almost 90% at 20 years with conventional implants.8-11

Despite the popularity of TKA, the outcomes remain to be clearly defined.12-16 In some studies, up to a third of subjects failed to match improvements in functional outcome scores with increases in subjectively measured parameters.8,17,18 Although management of patient expectations with regard to postoperative limitations, the length and the difficulty of the recovery period play a major part in shaping patients’ perception of a successful outcome. The role of the physi-cian in addressing the less conventional criteria for success may be underestimated.14,16,19,20 Purely subjective outcome scores have been proposed, but validation of those assess-ment scales remains to be seen.21 The purpose of this paper is to review recent advances in surgical technique and implant design in an attempt to improve the subjective and objective outcomes of total knee replacement.

Surgical ApproachAdvances in the total knee surgical technique, postopera-tive rehabilitation protocols, and implant design have been proposed to aid patient recovery from surgery as well as im-prove long-term performance and implant durability. Some of the recently introduced improvements have focused on utilization of minimally invasive surgical approaches (MIS), careful handling of the soft tissues, employing smaller sur-gical instrumentation, and the use of computer navigation. The distinguishing features of the MIS total knee techniques include a smaller incision, working “through a mobile win-dow,” avoidance of patella eversion, and lack of anterior tibiofemoral joint dislocation.22,23 Some investigators have

High-Performance Total Knee Replacement

Kirill Ilalov, M.D., Randy M. Cohn, M.D., and James Slover, M.D.

Kirill Ilalov, M.D., Randy M. Cohn, M.D., and James Slover, M.D., are in the Department of Orthopaedic Surgery, NYU Hospital for Joint Diseases, New York, New York.Correspondence: James Slover, M.D., Department of Orthopaedic Surgery, NYU Hospital for Joint Diseases, 301 East 17th Street, Suite 1402, New York, NY 10003; [email protected].

Bulletin of the Hospital for Joint Diseases 2013;71(1):79-8880

described incisions as small as 6 cm. The proponents of minimally invasive surgery cite faster recovery time, re-duced pain, blood loss, and improved cosmesis as the main advantages of a smaller incision. However, there is a lack of clinical evidence demonstrating these benefits in clinical practice. Advantages that may exist are confined to the early postoperative period, and no long-term improvements in functional outcome scores with any specific technique have been clearly defined.24

Despite this lack of demonstrable improvement, attempts at creating a more functional total knee through a more minimally invasive approach have continued. The use of minimally invasive techniques is safe and effective in expe-rienced hands and may have benefits in the early recovery period. However, these approaches may increase the risk of complications for some patients. Soft tissue balancing and component positioning in obese patients or those with a significant soft-tissue or bony pathology is more challeng-ing.25-28 In addition, wound complications are more likely to develop in patients who are obese, smoke, or have medical comorbidities such as diabetes or vascular insufficiency. Finally, the learning curve may present a challenge, and the use of MIS techniques has been shown to be an independent risk factor for early failure.29

Quadriceps muscle strength exhibits a marked decline after a total knee arthroplasty, and the recovery of postop-erative knee function is closely correlated to the recovery of quadriceps muscle strength.30 Consequently, approaches designed to minimize quadriceps disruption have prolifer-ated (Fig. 1). In contrast with the standard parapatellar ap-proach, the mid-vastus, sub-vastus, and the vastus medialis oblique (VMO) snip approaches attempt to preserve the attachment of the VMO while allowing adequate joint ex-posure. Some investigators have shown that quad-sparing approaches decrease the postoperative pain and lead to

an earlier return of quadriceps function and the range of motion.31-34 Maintaining the attachment of the VMO may also improve patellar tracking and decrease the need for a lateral release.35 However, many other studies have been less enthusiastic about the vastus sparing approaches and have demonstrated the transient nature of any functional improvement or results equivocal to the standard parapatellar approach at the expense of decreased surgical exposure.36-41 A decreased exposure during a limited approach may lead to increased intraoperative blood loss and surgical errors. 42 Little evidence exists to support one quad-sparing approach over another, and currently, the choice depends on the sur-geon’s familiarity and personal preference.43-45

Instrumentation and TechniqueSince its introduction in the 1970s, total knee arthroplasty instrumentation has become physically smaller, more ac-curate, and easier to use.46 It has given more flexibility to the extension and flexion gap balancing and optimizing of the patellar tracking. Early evidence from knee simulator studies and finite element analysis models suggested that a malalignment of greater than 3° resulted in abnormally high forces on the tibial component, and several technologi-cal advancements designed to decrease outliers have been developed. Computer navigation was introduced with the goal of achieving an even more accurate implant position and helping with ligament balancing. With its potential to avoid the use of intramedullary instrumentation, computer navigation may have a secondary benefit of decreasing the rates of pulmonary emboli and minimizing intraoperative blood loss.47,48 The challenges facing computer assisted surgery include the added surgical time, with its potential to increase the infection rate, the increased cost and complexity, which may make any improvements less cost-effective, and the learning curve.49 Recent Norwegian registry data showed

Figure 1 Approaches for total knee arthroplasty. A, The standard median parapatellar approach provides excellent exposure for total knee arthroplasty but requires detachment of the vastus medialis from its patellar insertion. B, The midvastus and C, subvastus approaches are considered quad-sparing techniques, minimizing disruption of the quadriceps.

A CB


a slightly increased revision rate at 2 years when computer navigation was used with one type of total knee implant.50 In recent analyses of the computer navigated and con-ventional total knee arthroplasty, both techniques led to a statistically similar mechanical alignment, although com-puter navigation decreased the rate of significant deviation beyond 3° in the coronal plane.51,52 However, navigation also increased the duration of surgery and showed no difference with respect to functional outcomes or complication rates. In an 8-year follow-up of 421 total knees, Ritter noted no significant increase in failures in the knees implanted in valgus but noted that the knees in the varus group had an increased rate of revisions and radiographic loosening.53 A recent study by Parratte and colleagues has cast doubt on the deleterious effect of alignment outside of the 3° of normal.54 Over a 15 year period, they noted no difference in survival rates between the total knees implanted within 3° of neutral and the knees that were more than 3° in either varus or valgus. The use of custom cutting blocks, based on preoperative MRI or CT scans, was introduced with the goal of increasing the accuracy of bone cuts as well as, potentially, decreas-ing the surgical time. The technology aims to optimize bony resection while helping with ligamentous balancing thus leading to closer restoration of patient’s anatomy. Early reports of this technology showed conflicting results regarding operating room efficiency and the potential for restoring the knee mechanical axis, which could be impor-tant in determining the long-term implant survivorship.55,56 Although the technology has generated some interest among patients and orthopaedic surgeons, further clinical outcome and cost-effectiveness outcome research is needed prior to more wide-spread acceptance of the technology.57,58

ImplantsThe second major area of focus for achieving a high perfor-mance total knee has been implant design. The most frequent reasons for total knee revisions remain infection, instability, polyethylene wear, and component loosening.59 Although infection and instability are patient and surgeon centric is-sues, implant design and polyethylene wear characteristics can have an important impact on the longevity of the total knee arthroplasty. New manufacturing and processing meth-ods of polyethylene have been developed with the goal of improving wear characteristics to minimize osteolysis and implant loosening.

MaterialsThe repetitive axial and shear stresses in the total knee lead to the well described wear patterns on the implant surfaces that are difficult to replicate in the laboratory. Joint simulators have been developed that permit rigorous preclinical evalu-ation of artificial joints in a controlled environment. They allow independent assessment of multiple variables, such as implant geometry, kinematics, and materials. Although

good at predicting wear properties of materials, simulators are less accurate in measuring wear that will occur in a total knee arthroplasty, where in-vivo shear and axial loads acting on the complex geometry of the implants is more complex leading to increased wear or even catastrophic forms of failure, such as polyethylene fracture. The manufacturing process of polyethylene is complex and proprietary. Variables that are implicated in determin-ing wear characteristics and mechanical properties of the polyethylene include formation of the polyethylene form from resin, sterilization via radiation, or exposure to certain chemicals, as well as packaging. Formation of free radicals during the manufacturing process, in storage, or after im-plantation may lead to oxidation which in turn may lead to accelerated wear and even catastrophic failure.60

Ultra-high molecular weight polyethylene (UHMWPE) has been introduced to increase wear resistance. However, the irradiation during the manufacturing process leads to the creation of free radicals, which predispose UHMWPE to oxidation. Post-processing techniques, such as remelting and annealing, have been introduced to reduce the potential for in-vivo oxidation after implantation but are not always effective.61,62 While the risk of catastrophic failure due to oxidation may be reduced if the UHMWPE is re-melted or annealed prior to implantation, those methods lead to a reduction of mechanical properties, such as yield, ultimate stress and fatigue propagation resistance, which increases fracture risk. The supporting evidence for UHMWPE has come from simulator studies where it has been demonstrated to achieve an up to 80% reduction in wear rates.63,64 Synovial fluid aspirated from the knees implanted with UHMWPE showed a decreased number of particles compared to the joints implanted with conventional polyethylenes.65 The few available retrieval studies demonstrated early preservation of machine marks on the surface of the poly, perhaps sug-gestive that any surface changes post-implantation were not a result of material removal.66,67 Although highly-cross-linked polyethylene appears to be safe with no evidence for increased early catastrophic failure, more long term studies are needed to support its clinical efficacy.66,68,69

Vitamin E infused polyethylene has been introduced as an alternative technique to reduce oxidation and improve polyethylene performance. Vitamin E is an anti-oxidant and reacts with oxygen and oxidized lipids, stabilizing them against further oxidative degradation reactions. In wear simulator studies, vitamin E infused polyethylene demonstrated an improvement in mechanical properties with resisted delamination and bending fatigue while pro-viding appropriately high wear resistance.70,71 Presence of vitamin-E has also been shown to decrease the aging process due to oxidation. Given its effect of reducing cross-linking efficiency during the irradiation process, by applying dif-ferent concentrations of vitamin E to the surface and the core, some investigators have shown the ability to create


an implant that is highly cross-linked on the surface with high wear characteristics while maintaining higher fatigue strength in the deeper layers.72 Therefore, it may be a better future alternative due to decreased oxidation compared with conventional poly with improved mechanical properties compared with highly cross-linked polyethylene. Development of hard-on-hard articulations has remained a challenge in total knee replacement, where high contact stresses that require significant mechanical performance have prevented the use of most available biomaterials. Although the design of early all-metal hinged total knees diminished the unconstrained contact stresses, the high failure rates of those implants pointed toward the need to look for better hard-on-hard couples.73 Therefore, the use of alternative materials has been explored, and the focus has been on the development of low-friction surfaces, such as ceramics. Compared to metal alloys, ceramics have an inherently high resistance to abrasion, better wettability and lubrication. They may also present advantages in patients with metal hypersensitivity. The incidence of metal hyper-sensitivity has been estimated to be present in up to 15% of the general population.74 Newer manufacturing techniques aimed at addressing the problem of brittleness by decreasing the ceramic powder grain size and using combinations of alumina, with its high wear resistance, and zirconia, with its high toughness. Improved ceramic formulations have led to a wide-spread acceptance of all-ceramic total hips, beginning in the 1990s, but experience is limited in TKA. Most experience with ceramic total knees comes from Japan, where it has been used since the early 1980s. The potential benefits of ceramic femoral components have been supported by knee simulator studies. In the study by Tsukamoto and colleagues, ceramic femur on conven-tional polyethylene showed a four-fold decrease in wear compared to conventional couplings.75 Wear of highly-cross-linked polyethylene on a ceramic femur was undetectable, after more than five million cycles. Clinical experience with purely ceramic total knees is sparse. In a study out of Japan, by Koshino and colleagues, 90 all ceramic total knees were followed for 5 years.76 The investigators noted significant improvements in knee society scores while complications included three cases of bony femoral fracture, but no ceramic fractures. Oxinium was introduced as an alternative to all-ceramic total knees. It is prepared by subjecting a metallic zirconium alloy to a thermally driven oxidation process. Although the 5 µm to 10 µm thick layer of oxidized zirconia that is created is not as hard as a true ceramic surface, it is thought to be much harder and more scratch resistant than a conventional cobalt chrome alloy. Lower wear rates have been demonstrated in simulator studies, with an up to eight-fold reduction.77 Ten-year clinical survival rates of the oxinium total knee implants are as high as 96% without complications that could be attributed to the implants, such as wear, osteolysis, aseptic loosening, or component failure.78 However, concerns over

durability of the oxinium layer remain, with several investi-gators reporting damage observed in retrieved femoral head implants, which can lead to accelerated wear.79,80

FixationAlternative component fixation has also been explored to achieve better performance. Multiple fixation methods of cementless tibial trays have been introduced, including pegs, screws, stems, as well as extensive porous coating. Although a number of studies showed promising survival rates at 10 years, longer follow-ups revealed increasing failure rates of cementless tibias and especially metal-backed patellar com-ponents.81,82 Patients experienced failure secondary to screw osteolysis, failure of ingrowth and loosening. In a study by Berger and colleagues, at an 11 year follow-up, 48% of the metal-backed patellar components and 8% of the press-fit tibial trays had to be revised for aseptic loosening.83

The success of cementless total knee techniques needs to be examined against the excellent results achieved with the conventional cemented implants, which have been shown to achieve 20 year survivorship rates of 90% and higher by some investigators.84 Most of the patients in these studies were older and led sedentary lifestyles. Although some stud-ies have supported similar success rates in younger patients, other studies are less enthusiastic.85 A study by Odland and colleagues that looked at younger patients, who underwent a total knee replacement at an average age of 48, showed a 16% rate of aseptic loosening and osteolysis at 10 years.86 In those patients, substituting an implant-cement interface for biologic fixation, with its potential to remodel in response to stress, may provide a longer lasting alternative. Long-term outcome studies with cementless total knee replacements are needed, but the ability of cementless fixa-tion to respond to physiologic stress may be attractive in the younger, active patient. New materials, such as porous tantalum, have shown high in-growth potential in revision scenarios and may be useful in primary cementless total knees. Current designs of porous tantalum for orthopedic implants maintain a high volumetric porosity (70% to 80%), low modulus of elasticity (3 MPa), and high frictional characteristics, making this metal conducive to biologic fixation.87 Hydroxyapatite coatings have been shown to increase the shear strength of these uncemented implants by up to a factor of three, and newer bearing surfaces may minimize the problem of osteolysis. Applications of newer biomaterials and novel implant designs will continue in the future. The greatest challenge will be to demonstrate the clinical superiority of the newer implants over the highly successful and cheaper conventional alternatives.

Implant DesignIn addition to changes in bearing materials, implant geom-etry of total knee implants has continued to evolve in search of a perfect balance between the increased conformity, with its lower contact stresses, and the need to allow the high


degree of freedom present in the normal human knee. For example, mobile-bearing total knee arthroplasty was devel-oped with the goal of achieving a longer-lasting and “more natural” feeling alternative. Knee kinematics may be more closely approximated in the designs that allow indepen-dent flexion and rotation. The native tibiofemoral joint is a modified hinge that allows for some rotation when flexed. Conventional “fixed-bearing” designs rely on the rotation in the tibiofemoral joint by decreasing the degree of constraint between the polyethylene and the femoral component. This may increase point stresses and potentially, lead to increased wear of the bearing surfaces. By allowing independent rota-tion between the tibial tray and the polyethylene, mobile-bearing designs allow more conforming articulations, which simulator studies have shown to decrease point contact stresses throughout the arc of motion.88

As the increased sizing options make modularity a virtual necessity in conventional implants, tibial tray locking mech-anisms remain a complex interface that can generate debris through micromotion of the poly on the metal baseplate. Another advantage of mobile bearing designs is that they eliminate the need for a locking mechanism by introducing a controlled articulation through a much easier-to-manufacture smooth surface between the polyethylene and the tibial tray. Increasing the degrees of freedom from pure rotation, to rotation with anterior-posterior translation, to a completely unconstrained polyethylene insert also has the potential of transferring greater amounts of implant-bone stresses to the soft tissues. Decreased stresses at the implant-bone interface may potentially lead to a longer lasting implant. Despite these theoretical advantages, establishing su-perior efficacy of the mobile-bearing implants has proven to be difficult even in biomechanical studies. In a study by Otto and colleagues, who used a biomechanical simulator as well as a finite element model to study the behavior of mobile bearings under physiologic loads of the gait cycle, the investigators confirmed the high-conformity of the implant.89 However, they also noted the high-frictional forces between the polyethylene and the baseplate, which may explain why some of the mobile-bearings fail to rotate in-vivo. In a wear simulator study by Grupp, mobile-bearing designs showed a significantly decreased wear rates per unit area.90 However, because the unit area was also greatly increased in the highly conforming designs, there was no significant decrease in the overall wear rates. Mobile-bearing designs have many design derivatives. In a recent attempt by the FDA to classify the mobile-bearing designs, 46 different designs were identified, of which five were available in the United States. In addition, less conventional designs, such as meniscal bearing, have been developed. Some investigators have even proposed an op-tion of preserving both the ACL and the PCL, when they are well functioning, to more closely mimic the 4-bar-link biomechanics of the native knee and provide better proprio-ception.91,92

The variety of the available mobile-bearing implants has made drawing encompassing conclusions difficult. A number of complications specific to these designs have been reported. In their analysis of meniscal-bearing im-plants, Hartford and colleagues looked at implants of 14 different designs and noted a 4% incidence of polyethylene fracture and 0.8% rate of polyethylene dislocation.93 The risk factors for these complications included a failure to achieve good ligamentous balancing or correct a varus or valgus instability. A recent meta-analysis of 14 studies that compared the mobile-bearing and the conventional implants showed no statistically significant difference with respect to functional knee scores or range of motion.94 In a separate meta-analysis of 19 studies that examined the survivorship of mobile-bearing implants, Carothers and colleagues noted a 15 years survival of 96.4% for the rotating-platform designs and 86.5% for meniscal-bearing implants. They also noted a decreased rate of complications after 1995, perhaps sec-ondary to improved understanding of implants and surgical techniques.95 Data from the Australian National Joint Re-placement Registry published in 2009 showed an increased rate of failure with mobile-bearing implants when compared to conventional total knees. Therefore, it is unclear whether the theoretical biomechanical benefits and the potential to reduce wear justify the increased cost of these implants. The expectations of the increasingly younger patient population have placed an increased emphasis not only on the longevity but also on the actual performance of the implants. Recent design directions aimed at achieving mul-tiple goals from the more objective parameters, such as the range of motion and biomechanics, to the purely subjective determinants, such as the “natural feel” of the native knee. High-flexion total knee replacement has been introduced with the goal of restoring an increasingly large range of motion that may be needed for specific functional activi-ties. Whereas the typical arc of motion after a total knee replacement rarely exceeds 115°, some cultural and religious activities may require knee flexion of up to 165°.96,97 Design changes aimed at increasing the range of motion included smaller posterior femoral condyle radii, altered polyethylene geometry to avoid patellar impingement, and to facilitate better roll-back, as well as alterations of the tibial post to delay its contact with the femoral cam at higher degrees of flexion. However, these innovations also introduced new specific problems, such as a potential for accelerated wear when the thinner posterior polyethylene or the patella are exposed to high-contact stresses inherent with deep flexion. Decreased articular conformity of the design and a relative collateral ligament laxity, inherent with increased amounts of flexion, could produce flexion instability. Changes in the femoral design often necessitate increased bone resection from the posterior condyles or the trochlea, which become prob-lematic in smaller femora. In some studies, patients who underwent a high-flex total knee replacement and achieved


a higher degree of flexion, especially with weightbearing in that position, had higher rates of complications with aseptic loosening and the need for revision.98

In a review of literature by Murphy and colleagues, five of the nine studies showed an increased range of motion with high-flexion designs. 99 However, only two of the studies looked at culturally specific activities, and only one found an increase in the ability to squat. Almost half of those patients could not get up without assistance, and all of the patients reported that they did not squat in their daily activities. There were no differences in the reported functional outcome scores at the longest follow-up of 35 months. In a different meta-analysis by Luo, high-flex total knees offered no improvements in the final range of motion or knee society scores.100 Several recent randomized con-trolled studies similarly failed to show any clinical benefit to the high-flexion designs.101,102

Even if increased range of motion is achieved, its poten-tial to affect functional outcomes remains unclear. Miner and colleagues compared a questionnaire-based assessment, the WOMAC score, and the objective measurement of the knee range of motion in their accuracy of predicting the postoperative satisfaction and quality of life improvement. They noted a significant worsening in the WOMAC pain and function scores in patients who achieved less than 95° of flexion. Only the WOMAC scores were predictive of the patient satisfaction and the perceived improvement in the quality of life.103 Although it may be inferred that a restricted motion may have a negative influence on the outcomes, there is little evidence to support that an exceedingly high range of motion provides a tangible benefit in terms of functional outcome scores. Devers examined whether increasingly high flexion improved patient satisfaction, perception, and func-tion after a conventional total knee replacement. Although increased knee flexion had a significant correlation with achievement of expectations, restoration of a more “normal” knee and functional improvement, overall satisfaction after surgery did not increase.104 A possible explanation is that, given a high rate of pain and functional improvement after a total knee replacement in a typical patient, the marginal benefit derived from high-flexion was too small to measure, suggesting the difference is not clinically significant. As a result of these findings, some of the recent advances in total knee arthroplasty have focused on reproducing native knee kinematics to achieve a more normal feel in the knee rather than purely examining flexion. Both the posterior stabilized and cruciate retaining con-ventional total knees fail to recreate the physiologic rollback, as the femur shows paradoxical anterior subluxation in flex-ion. Medial pivot total knee design aims to prevent anterior subluxation by increasing the congruency of the medial compartment, which creates a ball-in-a-socket articulation and allows the lateral side to roll back further in a fashion similar to the native knee joint. Fluoroscopic studies have demonstrated that the medial condyle position stays con-

stant with flexion, while the lateral side rolls back in these designs.105 Patellar tracking and quadriceps function is also optimized by maintaining the quadriceps level arm.106

However, similar to other advancements, the medial pivot design is a relatively new procedure and long-term literature supporting its use is lacking. A few clinical series have demonstrated a near 100% survival of the implants at an average of 5 to 7 years and significant improvements in the functional measurements that were equivalent to the results with the conventional implants.107,108 However, it is unclear whether the more physiologic knee kinematics translates into a clinically important observable benefit. Pritchett looked at 492 patients who underwent a staged bilateral total knee arthroplasty with five different designs, with each patient receiving two different implants. In ad-dition to the conventional implants, the study included the medial pivot, mobile-bearing, and ACL/PCL preserving total knee designs. Patients in the study preferred the ACL/PCL retaining and the medial pivot implants, although no clear reason for their preference was identified. The investigator postulated it could have been related to the differences in proprioception, the subjective sense of stability, or the sagit-tal plane kinematics, but further research is needed.21

ConclusionIntroduction and use of expensive new medical devices and implants has been identified as one of the key factors contributing to the rapidly rising medical costs in the United States. The efforts to contain medical expenses will place an increasing emphasis on examining the cost-effectiveness of every new treatment. A recent study by Gioe and colleagues examined whether the premium implants provided added benefit that would justify an increase in cost sometimes ex-ceeding $1,000.109 In their total knee arthroplasty group, they compared 3,400 conventional total knees to 2,800 premium implants, defined as mobile-bearing, high-flexion, oxidized zirconium, and those using moderately cross-linked poly-ethylenes. There were no differences in the revision rates at the final follow-up of 8 years. Further research is needed to determine if the premium implants provide benefits at longer follow-up or lead to improvements in functional outcomes. Although total knee arthroplasty has proven to be one of the most successful surgical procedures, it is likely that patients will expect even more from their joints in the future. The question remains whether novel approaches can lead to improvements in patient satisfaction rates, address objec-tively measured parameters, and improve implant survival rates while doing so in a cost-efficient manner. Proving a clear benefit to new surgical and rehabilitation techniques and technological advancements will continue to be a chal-lenge, but this evidence should be sought before adoption of changes to this highly successful procedure. Large scale registry data, randomized trials, and cost-effectiveness analyses may assist in this endeavor. Until substantial evi-dence is available, patients and surgeons will continue to


rely on personal experiences and preferences when making decisions regarding surgical technique, rehabilitation pro-tocols, and implant choice.

Disclosure StatementNone of the authors have a financial or proprietary interest in the subject matter or materials discussed, including, but not limited to, employment, consultancies, stock ownership, honoraria, and paid expert testimony.

References1. Rasanen P, Paavolainen P, Sintonen H, et al. Effectiveness of

hip or knee replacement surgery in terms of quality-adjusted life years and costs. Acta Orthop. 2007 Feb;78(1):108-15.

2. Nunez M, Lozano L, Nunez E, et al. Total knee replacement and health-related quality of life: factors influencing long-term outcomes. Arthritis Rheum. 2009 Aug 15;61(8):1062-9.

3. Ethgen O, Bruyere O, Richy F, et al. Health-related quality of life in total hip and total knee arthroplasty. A qualitative and systematic review of the literature. J Bone Joint Surg Am. 2004 May;86-A(5):963-74.

4. NIH Consensus Statement on total knee replacement. NIH Consens State Sci Statements. 2003 Dec 8-10;20(1):1-34.

5. Mont MA, Bonutti PM, Seyler TM, et al. The future of high performance total knee arthroplasty. Semin Arthroplasty. 2006;17(2):80-7.

6. 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 Apr;89(4):780-5.

7. Kurtz SM, Lau E, Ong K, et al. Future young patient de-mand for primary and revision joint replacement: national projections from 2010 to 2030. Clin Orthop Relat Res. 2009 Oct;467(10):2606-12.

8. Ma HM, Lu YC, Ho FY, Huang CH. Long-term results of total condylar knee arthroplasty. J Arthroplasty. 2005 Aug;20(5):580-4.

9. Crowder AR, Duffy GP, Trousdale RT. Long-term results of total knee arthroplasty in young patients with rheumatoid arthritis. J Arthroplasty. 2005 Oct;20(7 Suppl 3):12-6.

10. Gill GS, Joshi AB. Long-term results of cemented, posterior cruciate ligament-retaining total knee arthroplasty in osteo-arthritis. Am J Knee Surg. 2001 Fall;14(4):209-14.

11. Duffy GP, Crowder AR, Trousdale RR, Berry DJ. Cemented total knee arthroplasty using a modern prosthesis in young patients with osteoarthritis. J Arthroplasty. 2007 Sep;22(6 Suppl 2):67-70.

12. Genet F, Schnitzler A, Lapeyre E, et al. Change of impairment, disability and patient satisfaction after total knee arthroplasty in secondary care practice. Ann Readapt Med Phys. 2008 Nov;51(8):671-6, 676-82.

13. Kwon SK, Kang YG, Kim SJ, et al. Correlations between commonly used clinical outcome scales and patient satis-faction after total knee arthroplasty. J Arthroplasty. 2010 Oct;25(7):1125-30.

14. Vissers MM, de Groot IB, Reijman M, et al. Functional ca-pacity and actual daily activity do not contribute to patient satisfaction after total knee arthroplasty. BMC Musculoskelet Disord. 2010 Jun 16;11:121.

15. Bullens PH, van Loon CJ, de Waal Malefijt MC, et al. Pa-

tient satisfaction after total knee arthroplasty: a comparison between subjective and objective outcome assessments. J Arthroplasty. 2001 Sep;16(6):740-7.

16. Merle-Vincent F, Couris CM, Schott AM, et al. Factors pre-dicting patient satisfaction 2 years after total knee arthroplasty for osteoarthritis. Joint Bone Spine. 2011 Jul;78(4):383-6. doi: 10.1016/j.jbspin.2010.11.013. Epub 2010 Dec 31.

17. Bourne RB, Chesworth BM, Davis AM, et al. Patient satisfac-tion after total knee arthroplasty: who is satisfied and who is not? Clin Orthop Relat Res. 2010 Jan;468(1):57-63.

18. Dickstein R, Heffes Y, Shabtai EI, Markowitz E. Total knee arthroplasty in the elderly: patients’ self-appraisal 6 and 12 months postoperatively. Gerontology. 1998;44(4):204-10.

19. Noble PC, Conditt MA, Cook KF, Mathis KB. The John Insall Award: Patient expectations affect satisfaction with total knee arthroplasty. Clin Orthop Relat Res. 2006 Nov;452:35-43.

20. Jorn LP, Johnsson R, Toksvig-Larsen S. Patient satisfaction, function and return to work after knee arthroplasty. Acta Orthop Scand. 1999 Aug;70(4):343-7.

21. Pritchett JW. Patients prefer a bicruciate-retaining or the medial pivot total knee prosthesis. J Arthroplasty. 2011 Feb;26(2):224-8.

22. Bonutti PM, Mont MA, McMahon M, et al. Minimally inva-sive total knee arthroplasty. J Bone Joint Surg Am. 2004;86-A Suppl 2:26-32.

23. Bonutti PM, Mont MA, Kester MA. Minimally invasive total knee arthroplasty: a 10-feature evolutionary approach. Orthop Clin North Am. 2004 Apr;35(2):217-26.

24. Khanna A, Gougoulias N, Longo UG, Maffulli N. Minimally invasive total knee arthroplasty: a systematic review. Orthop Clin North Am. 2009 Oct;40(4):479-89, viii.

25. Schroer WC, Diesfeld PJ, LeMarr A, Reedy ME. Applicabil-ity of the mini-subvastus total knee arthroplasty technique: an analysis of 725 cases with mean 2-year follow-up. J Surg Orthop Adv. 2007 Fall;16(3):131-7.

26. Schroer WC, Diesfeld PJ, Reedy ME, LeMarr AR. Evaluation of complications associated with six hundred mini-subvastus total knee arthroplasties. J Bone Joint Surg Am. 2007 Oct;89 Suppl 3:76-81.

27. Schroer WC, Diesfeld PJ, Reedy ME, Lemarr AR. Surgical accuracy with the mini-subvastus total knee arthroplasty a computer tomography scan analysis of postoperative implant alignment. J Arthroplasty. 2008 Jun;23(4):543-9.

28. Pagnano MW, Meneghini RM. Minimally invasive total knee arthroplasty with an optimized subvastus approach. J Arthroplasty. 2006 Jun;21(4 Suppl 1):22-6.

29. Barrack RL, Barnes CL, Burnett RS, et al. Minimal incision surgery as a risk factor for early failure of total knee arthro-plasty. J Arthroplasty. 2009 Jun;24(4):489-98.

30. Silva M, Shepherd EF, Jackson WO, et al. Knee strength after total knee arthroplasty. J Arthroplasty. 2003 Aug;18(5):605-11.

31. Karachalios T, Giotikas D, Roidis N, et al. Total knee replace-ment performed with either a mini-midvastus or a standard approach: a prospective randomised clinical and radiological trial. J Bone Joint Surg Br. 2008 May;90(5):584-91.

32. Juosponis R, Tarasevicius S, Smailys A, Kalesinskas RJ. Func-tional and radiological outcome after total knee replacement performed with mini-midvastus or conventional arthrotomy: controlled randomised trial. Int Orthop. 2009 Oct;33(5):1233-


7.33. Roysam GS, Oakley MJ. Subvastus approach for total knee

arthroplasty: a prospective, randomized, and observer-blinded trial. J Arthroplasty. 2001 Jun;16(4):454-7.

34. Sastre S, Sanchez MD, Lozano L, et al. Total knee arthro-plasty: better short-term results after subvastus approach: a randomized, controlled study. Knee Surg Sports Traumatol Arthrosc. 2009 Oct;17(10):1184-8.

35. Matsueda M, Gustilo RB. Subvastus and medial parapatellar approaches in total knee arthroplasty. Clin Orthop Relat Res. 2000 Feb;(371):161-8.

36. Lee DH, Choi J, Nha KW, et al. No difference in early functional outcomes for mini-midvastus and limited medial parapatellar approaches in navigation-assisted total knee arthroplasty: a prospective randomized clinical trial. Knee Surg Sports Traumatol Arthrosc. 2011 Jan;19(1):66-73.

37. Li XG, Tang TS, Qian ZL, et al. Comparison of the mini-midvastus with the mini-medial parapatellar approach in primary TKA. Orthopedics. 2010 Oct;33(10):723.

38. Nestor BJ, Toulson CE, Backus SI, et al. Mini-midvastus vs standard medial parapatellar approach: a prospective, randomized, double-blinded study in patients undergoing bilateral total knee arthroplasty. J Arthroplasty. 2010 Sep;25(6 Suppl):5-11, 11 e1.

39. Pan WM, Li XG, Tang TS, et al. Mini-subvastus versus a standard approach in total knee arthroplasty: a prospective, randomized, controlled study. J Int Med Res. 2010 May-Jun;38(3):890-900.

40. Chang CH, Yang RS, Chen KH, et al. Muscle torque in total knee arthroplasty: comparison of subvastus and midvastus approaches. Knee Surg Sports Traumatol Arthrosc. 2010 Jul;18(7):934-8.

41. Cila E, Guzel V, Ozalay M, et al. Subvastus versus medial parapatellar approach in total knee arthroplasty. Arch Orthop Trauma Surg. 2002 Mar;122(2):65-8.

42. Boerger TO, Aglietti P, Mondanelli N, Sensi L. Mini-subvastus versus medial parapatellar approach in total knee arthroplasty. Clin Orthop Relat Res. 2005 Nov;440:82-7.

43. Aglietti P, Baldini A, Sensi L. Quadriceps-sparing versus mini-subvastus approach in total knee arthroplasty. Clin Orthop Relat Res. 2006 Nov;452:106-11.

44. Berth A, Urbach D, Neumann W, Awiszus F. Strength and voluntary activation of quadriceps femoris muscle in total knee arthroplasty with midvastus and subvastus approaches. J Arthroplasty. 2007 Jan;22(1):83-8.

45. Bonutti PM, Zywiel MG, Ulrich SD, et al. A comparison of subvastus and midvastus approaches in minimally inva-sive total knee arthroplasty. J Bone Joint Surg Am. 2010 Mar;92(3):575-82.

46. Insall J, Ranawat CS, Scott WN, Walker P. Total condylar knee replacment: preliminary report. Clin Orthop Relat Res. 1976 Oct;(120):149-54.

47. Kalairajah Y, Cossey AJ, Verrall GM, et al. Are systemic emboli reduced in computer-assisted knee surgery?: A pro-spective, randomised, clinical trial. J Bone Joint Surg Br. 2006 Feb;88(2):198-202.

48. Kalairajah Y, Simpson D, Cossey AJ, et al. Blood loss after total knee replacement: effects of computer-assisted surgery. J Bone Joint Surg Br. 2005 Nov;87(11):1480-2.

49. Slover JD, Tosteson AN, Bozic KJ, et al. Impact of hospi-

tal volume on the economic value of computer navigation for total knee replacement. J Bone Joint Surg Am. 2008 Jul;90(7):1492-500.

50. Gothesen O, Espehaug B, Havelin L, et al. Short-term outcome of 1,465 computer-navigated primary total knee replacements 2005-2008. Acta Orthop. 2011 May;82(3):293-300.

51. Bauwens K, Matthes G, Wich M, et al. Navigated total knee replacement. A meta-analysis. J Bone Joint Surg Am. 2007 Feb;89(2):261-9.

52. Mason JB, Fehring TK, Estok R, et al. Meta-analysis of align-ment outcomes in computer-assisted total knee arthroplasty surgery. J Arthroplasty. 2007 Dec;22(8):1097-106.

53. Ritter MA, Faris PM, Keating EM, Meding JB. Postoperative alignment of total knee replacement. Its effect on survival. Clin Orthop Relat Res. 1994 Feb;(299):153-6.

54. Parratte S, Pagnano MW, Trousdale RT, Berry DJ. Effect of postoperative mechanical axis alignment on the fifteen-year survival of modern, cemented total knee replacements. J Bone Joint Surg Am. 2010 Sep 15;92(12):2143-9.

55. Spencer BA, Mont MA, McGrath MS, et al. Initial experi-ence with custom-fit total knee replacement: intra-operative events and long-leg coronal alignment. Int Orthop. 2009 Dec;33(6):1571-5.

56. Klatt BA, Goyal N, Austin MS, Hozack WJ. Custom-fit total knee arthroplasty (OtisKnee) results in malalignment. J Ar-throplasty. 2008 Jan;23(1):26-9.

57. Mont MA, Johnson AJ, Zywiel MG, Bonutti PM. Surgeon Perceptions Regarding Custom-fit Positioning Technology for Total Knee Arthroplasty. Surg Technol Int. 2010 Oct;20:348-51.

58. Slover J, Rubash H, Malchau H, Bosco J. Cost-Effectiveness Analysis of Custom Total Knee Cutting Blocks. J Arthroplasty. 2 Feb;27(2):180-5. doi: 10.1016/j.arth.2011.04.023. Epub 2011 Jun 14.

59. Mulhall KJ, Ghomrawi HM, Scully S, et al. Current etiologies and modes of failure in total knee arthroplasty revision. Clin Orthop Relat Res. 2006 May;446:45-50.

60. Kurtz SM, Hozack WJ, Purtill JJ, et al. 2006 Otto Aufranc Award Paper: significance of in vivo degradation for polyeth-ylene in total hip arthroplasty. Clin Orthop Relat Res. 2006 Dec;453:47-57.

61. Currier BH, Currier JH, Mayor MB, et al. Evaluation of oxida-tion and fatigue damage of retrieved crossfire polyethylene acetabular cups. J Bone Joint Surg Am. 2007 Sep;89(9):2023-9.

62. Currier BH, Van Citters DW, Currier JH, Collier JP. In vivo oxidation in remelted highly cross-linked retrievals. J Bone Joint Surg Am. 2010 Oct 20;92(14):2409-18.

63. Stoller AP, Johnson TS, Popoola OO, et al. Highly cross-linked polyethylene in posterior-stabilized total knee arthroplasty: in vitro performance evaluation of wear, delamination, and tibial post durability. J Arthroplasty. 2011 Apr;26(3):483-91.

64. Popoola OO, Yao JQ, Johnson TS, Blanchard CR. Wear, delamination, and fatigue resistance of melt-annealed highly cross-linked UHMWPE cruciate-retaining knee inserts under activities of daily living. J Orthop Res. 2010 Sep;28(9):1120-6.

65. Iwakiri K, Minoda Y, Kobayashi A, et al. In vivo comparison of wear particles between highly cross-linked polyethylene and conventional polyethylene in the same design of total


knee arthroplasties. J Biomed Mater Res B Appl Biomater. 2009 Nov;91(2):799-804.

66. Muratoglu OK, Ruberti J, Melotti S, et al. Optical analysis of surface changes on early retrievals of highly cross-linked and conventional polyethylene tibial inserts. J Arthroplasty. 2003 Oct;18(7 Suppl 1):42-7.

67. Knahr K, Pospischill M, Kottig P, et al. Retrieval analyses of highly cross-linked polyethylene acetabular liners four and five years after implantation. J Bone Joint Surg Br. 2007 Aug;89(8):1036-41.

68. Bragdon CR, Kwon YM, Geller JA, et al. Minimum 6-year followup of highly cross-linked polyethylene in THA. Clin Orthop Relat Res. 2007 Dec;465:122-7.

69. Muratoglu OK, Greenbaum ES, Bragdon CR, et al. Surface analysis of early retrieved acetabular polyethylene liners: a comparison of conventional and highly cross-linked polyeth-ylenes. J Arthroplasty. 2004 Jan;19(1):68-77.

70. Micheli BR, Wannomae KK, Lozynsky AJ, et al. Knee Simulator Wear of Vitamin E Stabilized Irradiated Ultra-high Molecular Weight Polyethylene. J Arthroplasty. 2012 Jan;27(1):95-104. doi: 10.1016/j.arth.2011.03.006. Epub 2011 May 8.

71. Oral E, Ghali BW, Rowell SL, et al. A surface cross-linked UHMWPE stabilized by vitamin E with low wear and high fatigue strength. Biomaterials. 2010 Sep;31(27):7051-60.

72. Oral E, Wannomae KK, Rowell SL, Muratoglu OK. Diffusion of vitamin E in ultra-high molecular weight polyethylene. Biomaterials. 2007 Dec;28(35):5225-37.

73. Knutson K, Lindstrand A, Lidgren L. Survival of knee ar-throplasties. A nation-wide multicentre investigation of 8000 cases. J Bone Joint Surg Br. 1986 Nov;68(5):795-803.

74. Hallab N. Metal sensitivity in patients with orthopedic im-plants. J Clin Rheumatol. 2001 Aug;7(4):215-8.

75. Tsukamoto R, Chen S, Asano T, et al. Improved wear perfor-mance with cross-linked UHMWPE and zirconia implants in knee simulation. Acta Orthop. 2006 Jun;77(3):505-11.

76. Koshino T, Okamoto R, Takagi T, et al. Cemented ceramic YMCK total knee arthroplasty in patients with severe rheu-matoid arthritis. J Arthroplasty. 2002 Dec;17(8):1009-15.

77. Ries MD, Salehi A, Widding K, Hunter G. Polyethylene wear performance of oxidized zirconium and cobalt-chromium knee components under abrasive conditions. J Bone Joint Surg Am. 2002;84-A Suppl 2:129-35.

78. Bourne RB, Laskin RS, Guerin JS. Ten-year results of the first 100 Genesis II total knee replacement procedures. Orthope-dics. 2007 Aug;30(8 Suppl):83-5.

79. Evangelista GT, Fulkerson E, Kummer F, Di Cesare PE. Surface damage to an Oxinium femoral head prosthesis after dislocation. J Bone Joint Surg Br. 2007 Apr;89(4):535-7.

80. McCalden RW, Charron KD, Davidson RD, et al. Damage of an Oxinium femoral head and polyethylene liner following ‘routine’ total hip replacement. J Bone Joint Surg Br. 2011 Mar;93(3):409-13.

81. Buechel FF Sr, Buechel FF Jr, Pappas MJ, D’Alessio J. Twen-ty-year evaluation of meniscal bearing and rotating platform knee replacements. Clin Orthop Relat Res. 2001Jul;(388):41-50.

82. Hofmann AA, Evanich JD, Ferguson RP, Camargo MP. Ten- to 14-year clinical followup of the cementless Natural Knee system. Clin Orthop Relat Res. 2001Jul;(388):85-94.

83. Berger RA, Lyon JH, Jacobs JJ, et al. Problems with cement-less total knee arthroplasty at 11 years followup. Clin Orthop Relat Res. 2001Nov;(392):196-207.

84. Font-Rodriguez DE, Scuderi GR, Insall JN. Survivorship of cemented total knee arthroplasty. Clin Orthop Relat Res. 1997 Dec;(345):79-86.

85. Diduch DR, Insall JN, Scott WN, et al. Total knee replacement in young, active patients. Long-term follow-up and functional outcome. J Bone Joint Surg Am. 1997 Apr;79(4):575-82.

86. Odland AN, Callaghan JJ, Liu SS, Wells CW. Wear and lysis is the problem in modular TKA in the young OA patient at 10 years. Clin Orthop Relat Res. 2011 Jan;469(1):41-7.

87. Levine B, Sporer S, Della Valle CJ, et al. Porous tantalum in reconstructive surgery of the knee: a review. J Knee Surg. 2007 Jul;20(3):185-94.

88. Szivek JA, Anderson PL, Benjamin JB. Average and peak contact stress distribution evaluation of total knee arthroplas-ties. J Arthroplasty. 1996 Dec;11(8):952-63.

89. Otto JK, Callaghan JJ, Brown TD. Mobility and contact me-chanics of a rotating platform total knee replacement. Clin Orthop Relat Res. 2001 Nov;(392):24-37.

90. Grupp TM, Kaddick C, Schwiesau J, et al. Fixed and mobile bearing total knee arthroplasty--influence on wear generation, corresponding wear areas, knee kinematics and particle com-position. Clin Biomech (Bristol, Avon). 2009 Feb;24(2):210-7.

91. Stiehl JB, Komistek RD, Cloutier JM, Dennis DA. The cruciate ligaments in total knee arthroplasty: a kinematic analysis of 2 total knee arthroplasties. J Arthroplasty. 2000 Aug;15(5):545-50.

92. Pritchett JW. Anterior cruciate-retaining total knee arthro-plasty. J Arthroplasty. 1996 Feb;11(2):194-7.

93. Hartford JM, Harned ME, Kaufer H, et al. Primary meniscal-bearing knee replacements: 8- to 15-year followup. Clin Orthop Relat Res. 2007 Dec;465:227-31.

94. Smith H, Jan M, Mahomed NN, et al. Meta-Analysis and Systematic Review of Clinical Outcomes Comparing Mo-bile Bearing and Fixed Bearing Total Knee Arthroplasty. J Arthroplasty. 2011 Dec;26(8):1205-13. doi: 10.1016/j.arth.2010.12.017. Epub 2011 Feb 4.

95. Carothers JT, Kim RH, Dennis DA, Southworth C. Mobile-bearing total knee arthroplasty a meta-analysis. J Arthroplasty. 2011 Jun;26(4):537-42.

96. Mulholland SJ, Wyss UP. Activities of daily living in non-Western cultures: range of motion requirements for hip and knee joint implants. Int J Rehabil Res. 2001 Sep;24(3):191-8.

97. Rowe PJ, Myles CM, Walker C, Nutton R. Knee joint kinemat-ics in gait and other functional activities measured using flex-ible electrogoniometry: how much knee motion is sufficient for normal daily life? Gait Posture. 2000 Oct;12(2):143-55.

98. Han HS, Kang SB, Yoon KS. High incidence of loosening of the femoral component in legacy posterior stabilised-flex total knee replacement. J Bone Joint Surg Br. 2007 Nov;89(11):1457-61.

99. Murphy M, Journeaux S, Russell T. High-flexion total knee arthroplasty: a systematic review. Int Orthop. 2009 Aug;33(4):887-93.

100. Luo SX, Su W, Zhao JM, et al. High-Flexion vs Conven-tional Prostheses Total Knee Arthroplasty: A Meta-analysis. J Arthroplasty. 2011 Sep;26(6):847-54. doi: 10.1016/j.arth.2010.09.008. Epub 2010 Nov 12.


101. Kim YH, Choi Y, Kim JS. Comparison of a standard and a gender-specific posterior cruciate-substituting high-flexion knee prosthesis: a prospective, randomized, short-term outcome study. J Bone Joint Surg Am. 2010 Aug 18;92(10):1911-20.

102. Choi WC, Lee S, Seong SC, et al. Comparison between standard and high-flexion posterior-stabilized rotating-platform mobile-bearing total knee arthroplasties: a ran-domized controlled study. J Bone Joint Surg Am. 2010 Nov 17;92(16):2634-42.

103. Miner AL, Lingard EA, Wright EA, et al. Knee range of mo-tion after total knee arthroplasty: how important is this as an outcome measure? J Arthroplasty. 2003 Apr;18(3):286-94.

104. Devers BN, Conditt MA, Jamieson ML, et al. Does greater knee flexion increase patient function and satisfaction after total knee arthroplasty? J Arthroplasty. 2011 Feb;26(2):178-86.

105. Schmidt R, Komistek RD, Blaha JD, et al. Fluoroscopic analyses of cruciate-retaining and medial pivot knee implants. Clin Orthop Relat Res. 2003 May;(410):139-47.

106. D’Lima DD, Poole C, Chadha H, et al. Quadriceps moment arm and quadriceps forces after total knee arthroplasty. Clin Orthop Relat Res. 2001 Nov;(392):213-20.

107. Karachalios T, Roidis N, Giotikas D, et al. A mid-term clinical outcome study of the Advance Medial Pivot knee arthroplasty. Knee. 2009 Dec;16(6):484-8.

108. Fan CY, Hsieh JT, Hsieh MS, et al. Primitive results after medial-pivot knee arthroplasties: a minimum 5-year follow-up study. J Arthroplasty. 2010 Apr;25(3):492-6.

109. Gioe TJ, Sharma A, Tatman P, Mehle S. Do “premium” joint implants add value?: analysis of high cost joint im-plants in a community registry. Clin Orthop Relat Res. 2011 Jan;469(1):48-54.

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