Strategies to Improve Total Knee Arthroplasty: A Multidisciplinary Research Conference

This supplement to the Journal of the American Academy of Orthopaedic Surgeons (JAAOS) reports on a recent multidisciplinary research conference, Strategies to Improve Total Knee Arthroplasty, which was held in April, 2016, in Bethesda, MD. Total knee arthroplasty (TKA) is discussed at many scientific and clinical venues, including the Annual Meeting of the American Academy of Orthopaedic Surgeons (AAOS), but no comprehensive review of the state of TKA and strategies for improving outcomes has been held since the last National Institutes of Health Consensus Conference nearly 12 years ago.1 To that end, the Knee Society with the support of the National Institutes of Health, AAOS, the American Association of Hip and Knee Surgeons, the Orthopaedic Research and Education Foundation, and Thomas P. Vail, MD, Immediate Past President of the Knee Society, organized a unique conference focused on approaches to improve TKA outcomes. The agenda items for the conference emerged as part of a strategic plan previously developed through the Knee Society. The conference brought together clinicians, scientists, and other important stakeholders to exchange ideas and develop strategies to improve the outcomes of TKA. The format was one of the presentations by leading experts in each area (their presentations are captured in the articles in this supplement to JAAOS), followed by extensive discussions among all conference participants through which a comprehensive list of research questions was drafted. The aim was to formulate questions directed to determine how well to prevent or manage complications and thus improve outcomes and satisfaction for patients who choose arthroplasty to treat their severe knee arthritis or injury. Background Total knee arthroplasty is among the most common and expensive surgical procedures in the Medicare population,2 and TKA has gained greater acceptance for younger adults as well.3 An aging population, growing rates of obesity, and the increasing use of TKA in younger patients all contribute to an increased demand. Rates of TKA are expected to increase by 67.3% to nearly 3.5 million surgeries annually by 2030.4 Though expensive, TKA is cost-effective5,6 and is ranked among the most cost-effective medical and surgical interventions because of its ability to minimize pain and the associated disability.7 Total knee arthroplasty carries a high survivorship, with more than 90% of prosthetic knees remaining in place up to 10 years and beyond.8,9 Despite excellent long-term survivorship, studies have consistently reported that 15% to 30% of patients with TKA remain unsatisfied with the outcomes of TKA,10–12 and more than 6% suffer from a complication within 90 days of their TKAs. Thus, TKA is not achieving its goal of restoring pain-free function in a substantial portion of patients, and some would argue that implant survivorship data overlook patient dissatisfaction.13 As the aim of our conference was to focus on the strategies to improve TKA, identifying the opportunities for the greatest impact from research was imperative. Several authors recently reported on why knees are currently failing compared to historic data.14–17 Aseptic loosening, prosthetic joint infection, and knee instability are the three most common reasons for combined early and late failure, although infection is the most common reason for early failure. Infection failures continue to occur despite improved compliance with prophylactic antibiotics and other widely adopted means for lowering the risk for infection. Based on this background clinical information and the research strategic plan previously developed by the Knee Society, three key areas were addressed. The first two dealt with common reasons for TKA failure: infection and instability. The third area dealt with the use of patient-reported measures to inform the need for and the timing of TKA, to evaluate TKA outcomes, and to aid in establishing the value of TKA. Periprosthetic Joint Infection Periprosthetic joint infection (PJI) places an overwhelming personal burden on the patient with TKA and an economic burden to society, which threatens the management of this patient population. By 2020, nearly 49,000 PJIs are projected to be associated with TKA, with costs projected to reach $1.6 billion.4 Prevention of a PJI would be the ideal solution, and great strides have indeed been made to reduce the risk. First among these has been the routine use of prophylactic antibiotics that have lowered the risk to approximately 2% of patients with TKA.18 Commensal bacteria on the skin is a common source of PJI, so decolonization techniques of culturing multiple body sites to identify the bacteria followed by the use of 2% chlorhexidine gluconate antiseptic applied to the surgical site and mupirocin ointment to the nasal cavity have effectively prevented infection.19Staphylococcus aureus decolonization protocols have also been proven cost-effective.20 The emergence of resistant bacteria, particularly methicillin-resistant Staphylococcus (S epidermidis and S aureus), is a major challenge to the success of preventing and treating patients with a PJI. Obesity, diabetes, and smoking are additional risk factors for surgical site infection and PJI.21 Bacteria are capable of establishing a biofilm that hinders our ability to successfully eradicate the infection without removing the foreign body or the prosthesis.22 Surgery to remove the prosthesis is generally followed by 6 weeks of intravenous antibiotic therapy and then reimplantation or a second surgery to place a new prosthesis. A better understanding of how biofilms evade immune-mediated clearance in an immune-competent host may lead to novel strategies to treat PJIs. To this end, staphylococcal biofilms both in a mouse orthopaedic implant infection model and in human PJIs have been found to be biased toward an anti-inflammatory state typified by the preferential recruitment of myeloid-derived suppressor cells and alternatively activated macrophages. Both the depletion of myeloid-derived suppressor cells and skewing macrophages toward a proinflammatory state lead to significant reductions in staphylococcal biofilm burdens, suggesting that redirecting the anti-inflammatory biofilm milieu may prove beneficial for the PJI treatment in combination with conventional antibiotic therapy. Success in managing PJI requires collaborative research among basic scientists and clinicians focusing on strategies for prevention, improved diagnosis, and optional treatment of the patient. Key areas include (1) the orthopaedist’s perspective on PJI prevention and diagnosis, (2) strategies to prevent PJI and reduce the risk for readmission of the patient, (3) microbiology and antimicrobial challenges of PJI, (4) the potential use of new diagnostic imaging probes and novel antimicrobial implant coatings, and (5) improving the immune response to biofilm-associated infection. Joint Instability The natural knee joint is exquisitely designed to maintain an appropriate functional position throughout its range of motion. However, after TKA, joint instability is common, leading to patient dissatisfaction by causing pain and limiting patient's activities.23,24 Though they may never be revised, and therefore would be considered a success in a registry tracking survivorship, such patients nonetheless consider themselves as having a failed TKA. The design of the implant components is certainly a principal factor in determining joint stability,25 but the literature does not support one design approach over another. Indeed, technologies such as high flexion and gender-specific designs recently introduced to the market to improve function and clinical outcomes have failed to have a beneficial effect.26,27 The problem of recreating adequate joint stability with TKA is confounded by the complex static constraints provided by the ligaments and joint capsule and by the active contribution of muscle forces. Some investigators believe that muscles bear primary responsibility for controlling stability,28 whereas others believe that the tibiofemoral articulation plays that role.29,30 Indeed, clinical evidence is emerging which suggests that implants with more stable articulations are appreciated by patients.31,32 Considerable kinematics data exist from radiostereometric and fluoroscopic in vivo studies of normal and TKA knees,33–35 and load data have been gathered from instrumented TKAs,36,37 but considerable variation among patients limits the conclusions that can be drawn. Similarly, complex computational models of TKA have been developed,38,39 providing a means for unraveling most important structures controlling in vivo function and hence stability. But again, model validation is hampered by considerable variations in the inputs to models. Addressing joint instability requires integration of kinetics, kinematics, and joint loads with an understanding of how patient anatomy, surgical technique, implant design, and rehabilitation affect knee stability. To initiate discussion and reach consensus on research directions in joint instability, key areas include (1) the multiplanar target for a stable knee, (2) intraoperative measurements and tools that a surgeon can use to assess stability, (3) computational modeling to be used to improve TKA function, and (4) linking postoperative outcome measures of joint stability and function to patient satisfaction. Patient-reported Outcomes Although TKA reduces pain and improves function substantially, not all symptoms improve for most patients with TKA. Historically, studies have consistently reported that 15% to 30% of patients with TKA are dissatisfied with their clinical outcomes.10–12 This is reflected in significant variations in patient-reported outcomes (PROs) associated with both the patient40–42 and other characteristics. These variations underscore the importance of obtaining reliable and valid information from patients in evaluating the impact of TKA. While TKA research routinely uses PROs, clinicians have been slow in integrating PROs into their practices. An important barrier to adoption is that joint-specific instruments are too long for routine use, particularly if they are administered with a generic survey. Joint-specific function can be measured with greater efficiency; however, no crosswalks have been published that allow scores on shorter scales to be directly compared with familiar metrics from their “parent” scales, limiting their usefulness. Despite such barriers, incentives to use PROs in TKA practice have accelerated, driven by commitments of policy makers and payers to quantify the patient's assessment of surgical success.43 The United States has one of the largest registries collecting PRO data (P50 HS018910-04; www.force-tjr.org),44 and a 2014 CMS Technical Expert Panel submitted recommendations on using PROs to evaluate outcomes in performance-based measurement systems including the Patient-Reported Outcomes Measurement Information System (PROMIS) 10-item Global Health measure.45 Thus, with mounting demand and demonstrated feasibility, implementation across US surgeons is likely, so the value of brief, specific knee pain and function measures is a priority for surgeons and policymakers. Key items to be discussed in this area include (1) patient-reported outcomes to measure in patients with TKA, (2) collecting PROs in a busy TKA practice, (3) the role of PROs in quality improvement, and (4) the role of PROs in value-based payments. Conference Proceedings We hope to extend the momentum gained from the conference through the publication of the articles on each of the three topics along with the article at the end of this issue that presents the future direction for research. The development of the material presented in this issue is intended to stimulate individual investigators and multicenter collaborators to pursue impactful studies that will directly improve the satisfaction and outcomes for the hundreds of thousands of Americans who undergo TKA each year. We thank all participants in the conference for their valuable contributions.