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Patellar instability following total knee arthroplasty (TKA) is a rare, yet serious complication, potentially requiring revision surgery or resulting in chronic dysfunction. When encountered, it is paramount to understand the etiologies, diagnostic approaches, treatment options, and outcomes of the selected treatment. The most common cause of patella instability is improper positioning of components, leading to lateral maltracking of the patella. Factors such as internal rotation and/or medialization of femoral or tibial components and lateralization of the patellar button have been identified as factors that contribute to instability. Additionally, a longstanding valgus deformity of the knee may exacerbate patella maltracking. Patients typically present with anterior knee pain, worsened by activities like stair climbing, and may report sensations of giving way. Radiographs and computed tomography scans aid in evaluating component positioning and rotation. Operative intervention is often necessary, with options ranging from soft-tissue realignment to component revision. Lateral retinacular release is a common approach, although it is associated with complications such as osteonecrosis of the patella. Proximal or distal realignment procedures may be required if instability persists. Some recent case reports have also described medial patello-femoral ligament (MPFL) reconstruction as a treatment modality, but more investigation on the topic is still pending. It is important that the treatment strategy address the underlying cause, as failure to do so may result in recurrent instability. The best way to avoid patella instability is to pay attention to all the details of component position and soft-tissue balance during the index procedure., Competing Interests: Michael Mont: 3M: Paid consultant American Association of Hip and Knee Surgeons: Board or committee member CERAS Health: Stock or stock Options Exactech, Inc: Paid consultant Hip Society: Board or committee member Johnson & Johnson: Paid consultant; Research support Journal of Arthroplasty: Editorial or governing board Journal of Knee Surgery: Editorial or governing board Knee Society: Board or committee member Kolon TissueGene: Paid consultant Medicus Works LLC: Publishing royalties, financial or material support Medtronic: Research support MirrorAR: Stock or stock Options National Institutes of Health (NIAMS & NICHD): Research support Next Science: Paid consultant Organogenesis: Research support Orthofix, Inc.: Research support Pacira: Paid consultant Patient-Centered Outcomes Research Institute (PCORI): Research support Peerwell: Stock or stock Options Smith & Nephew: Paid consultant Stryker: IP royalties; Paid consultant; Research support Surgical Techniques International: Editorial or governing board Up-to Date: Publishing royalties, financial or material support USMI: Stock or stock Options Wolters Kluwer Health - Lippincott Williams & Wilkins: Publishing royalties, financial or material support Sumon Nandi: American Association of Hip and Knee Surgeons: Board or committee member American Orthopaedic Association: Board or committee member Arthroplasty: Editorial or governing board Journal of Arthroplasty: Editorial or governing board Journal of Bone and Joint Surgery - American: Editorial or governing board Maryland Orthopaedic Association: Board or committee member Springer: Publishing royalties, financial or material support Giles Scuderi: 3M: Paid consultant; Paid presenter or speaker; Research support Biomet: IP royalties; Paid consultant; Paid presenter or speaker Enhanced Medical Nutrition: Stock or stock Options Force Therapeutics: Stock or stock Options Journal of Arthroplasty: Editorial or governing board Journal of Knee Surgery: Editorial or governing board KCI: Paid consultant Next Science: Research support Operation Walk USA: Board or committee member ROM Tech: Stock or stock Options SpringerElsevierThiemeWorld Scientific: Publishing royalties, financial or material support Zimmer: IP royalties; Paid consultant; Paid presenter or speaker Ronald Delanois: Baltimore City Medical Society.: Board or committee member DePuy Synthes Product, Inc.: Research support Orthofix, Inc.: Research support Smith & Nephew: Research support Stryker: Research support Tissue Gene: Research support, (Thieme. All rights reserved.)

Patellar tendon (PT) rupture following total knee arthroplasty (TKA) is a rare, but devastating complication. These injuries occur most frequently in the acute period following TKA due to trauma to the knee. PT ruptures that disrupt the extensor mechanism create a marked functional deficit, impacting every facet of daily life. In complete ruptures of the PT, repair or reconstruction is typically indicated; however, complication rates following intervention remain high. Operative intervention remains the mainstay of treatment, with only certain specific situations where nonoperative intervention is appropriate. Operative techniques are chosen based on the acuity, location of disruption, and status of the residual soft tissues. Treatment options include repair with or without augmentation or reconstruction. Augmentation does reduce the high risk of complications, bringing rates down from 63 to 25%. Augmentation options include autografts, allografts, synthetic grafts, or synthetic meshes. Despite advancements, outcomes are unpredictable and complications are common, highlighting the need for further research to improve treatment protocols. This article provides an overview of PT ruptures following TKA, the various treatment options, and the recommendations of the M.M., R.D., G.S. for each common type of PT injury encountered., Competing Interests: M.A.M. report royalties from Medicus Works LLC, Stryker and consulting fee from 3M, Exactech, Inc, Johnson & Johnson, Kolon TissueGene, Next Science, Pacira, Smith & Nephew, Stryker, also payment or honoraria from Johnson & Johnson, Medtronic, National Institutes of Health (NIAMS & NICHD), Organogenesis, Orthofix, Inc, Patient-Centered Outcomes Research Institute (PCORI), Stryker. He is in leadership role in American Association of Hip and Knee Surgeons, Hip Society, Knee Society. Also has stocks in CERAS Health, MirrorAR, Peerwell, USMI.R.E.D. is a board member of Baltimore City Medical Society. He reports research support from : Biocomposites, Inc.; CyMedica Orthopedics; DePuy Synthes Product, Inc.; Flexion Therapeutics; Microport; Orthopedics, Inc.; Orthofix, Inc.; Patient-Centered Outcomes Research Institute (PCORI); Smith & Nephew; Stryker; Tissue Gene; and United Orthopedic Corporation.G.S. reports royalties from Biomet, Springer, Zimmer and consulting fee from 3M, Biomet, KCI, Zimmer. Also Payment or honoraria from 3M, Biomet, Next Science and stocks from Enhanced medical nutrition, Force Therapeutics, ROM Tech., (Thieme. All rights reserved.)

Periprosthetic patella fractures are a rare complication that can lead to severe disability following total knee arthroplasty (TKA). There are several factors that increase the risk of this injury, including patient comorbidities, anatomic considerations, and surgical technique. With these factors limiting healing ability in the area, periprosthetic patellar fractures can pose a major challenge to treat, with potentially lasting morbidity for affected patients. These fractures can occur at any time following TKA and are classified based on their associated implant stability and disruption of the extensor mechanism using the Ortiguera and Berry classification system. Each of the three types of fractures can be managed in their own unique way; however, outcomes remain poor, and the complication rates remain high regardless of fracture type. This article provides an overview of the current literature and the recommended management of periprosthetic patella fractures., Competing Interests: None declared., (Thieme. All rights reserved.)

One of the critical steps in total knee arthroplasty is femoral component positioning and sizing. Historically, there was wider variability between femoral component sizes, necessitating the concepts of anterior referencing (AR) and posterior referencing (PR). With the introduction of smaller increments between sizes, the concept of anatomic referencing has been introduced to replace AR and PR. The intent of this study was to validate the concept of anatomic referencing and show that with 2 mm increments in femoral sizes, the femoral component can be placed flush to the anterior cortex while maintaining posterior condylar offset (PCO). Digital surface models were created using 515 femurs from an established computed tomography database. Virtual bone resections, component sizing and placement were performed assuming neutral mechanical axis and a cartilage thickness of 2 mm. The appropriately sized femoral component, which had 2 mm incremental sizes, was placed flush with the anterior cortex with restoration of the PCO. The anterior-posterior distance from the posterior surface of the component to the medial and lateral surfaces of the posterior condylar cartilage were measured. The medial condyle was the limiting condyle in the majority of cases (73%). The average medial gap after appropriate femoral component matching was 0.6 mm (0.39-1.41 mm) across all sizes. The overall average condylar gap was 1.02 mm. The most common femoral component was a size 7 (57.2 mm) and the average femoral AP width was 55.9 mm. Anatomic referencing with an implant system that has 2-mm increments in femoral component sizing provides an alternative to AR and PR without compromise. Anatomic referencing allows for perfect alignment of the anterior flange of the femoral component to the anterior cortex of the femur while restoring the native PCO to within 1 mm. This avoids having to choose between AR or PR when in between femoral sizes., Competing Interests: J.B. reports being a board member of Orthopaedic Research Society. Stocks Zimmer Biomet. G.R.S. reports royalties from Zimmer Biomet. Consulting fee from Zimmer Biomet, 3M KCI, and Canary. Payment or honoraria from Zimmer Biomet and 3M KCI. Participation on a Advisory Board of Canary and Enhanced Medical Nutrition. Stocks of ROM Tech, KAT Robotics, and Enhanced Medical Nutrition., (Thieme. All rights reserved.)

Historically, anterior referencing and posterior referencing are two specific techniques that surgeons can use for proper sizing of the femoral component in total knee arthroplasty (TKA). In this review, we introduce the concept of "anatomic referencing" which has become useful with more incremental sizes of the femoral component to more perfectly match the native anatomy of each patient and reduce overstuffing of the patellofemoral joint and medial-lateral (ML) overhang. Fifty consecutive TKA cases were reviewed where the novel anatomic referencing technique was used. Lateral radiographic projections were obtained preoperatively and postoperatively. The posterior condylar offset (PCO) was evaluated on the lateral radiographs by measuring the distance between the tangent line of the femoral diaphysis posterior cortex and the posterior condylar margin. PCO ratio (PCOR) was calculated by dividing the PCO by the distance between the posterior condylar border and a tangent line along the anterior cortex of the femoral diaphysis. Forty-five patients (50 TKAs) were reviewed. Average age of the patients was 70.34, range: 47-91. There were 19 males and 26 females reviewed in this series. On average, the delta PCOR was 0.022 (standard deviation = 0.032; min: -0.049, max: 0.082). When grouping our results into three main groups: < -0.03, -0.03 to 0.03, and > 0.03, we found that 62% fell within the -0.03 to 0.03 range. There was no statistically significant difference in delta PCOR between standard and narrow implants ( p  = 0.418). The proposed novel anatomic referencing technique has allowed for proper sizing of patients' femurs in the anteroposterior and ML direction while avoiding component overhang or the need for component downsizing to obtain a proper ML fit. This radiographic review confirmed this to be a highly accurate and reproducible technique., Competing Interests: None declared., (Thieme. All rights reserved.)

Competing Interests: None declared.

An estimated 10 to 15% of total knee arthroplasties (TKAs) are implanted for a diagnosis of arthritis when a valgus deformity is present. There are various techniques and considerations that must be considered for a successful TKA in a patient with a valgus deformity. This article provides a detailed summary of the anatomy, pathology, bone preparation, soft tissue management, implant selection, and complications when performing a TKA in a patient with valgus deformity., Competing Interests: None declared., (Thieme. All rights reserved.)

Accurately predicting component sizing in total knee arthroplasty (TKA) can ensure appropriate implants are readily available, avoiding complications from malsizing while also reducing cost by improving workflow efficiency through a reduction in instrumentation. This study investigated the utility of demographic variables to reliably predict TKA component sizes. A retrospective chart review of 337 patients undergoing primary TKA was performed. Patient characteristics (age, sex, race, height, weight) were recorded along with implant and shoe size. Correlation between shoe size and TKA component size was assessed using Pearson's correlation coefficient and linear regression analysis using three models: (A) standard demographic variables, (B) shoe size, and (C) combination of both models. Shoe size demonstrated the strongest correlation with femoral anteroposterior (FAP) ( p  < 0.001) followed by height ( p  < 0.001). Conversely, height exhibited the strongest correlation with tibial mediolateral (TML) ( p  < 0.001) followed by shoe size ( p  < 0.001). Model C was able to correctly predict both the femur and tibia within one and two sizes in 83.09 and 98.14% of cases, respectively. Individually, model C predicted the FAP within one and two sizes in 83.09 and 96.14% of cases, and the TML in 98.81 and 100% of cases, respectively. A patient's shoe size demonstrates a strong correlation to the TKA implant size, and when combined with standard demographic variables the predictive reliability is further increased. Here, we present a predictive model for implant sizing based solely on easily attainable demographic variables, that will be useful for preoperative planning to improve surgical efficiency. LEVEL OF EVIDENCE:  II, Diagnostic., Competing Interests: G.R.S. receives royalties from Zimmer Biomet. personal fees from Zimmer Biomet, 3M KCL, ROM Tech, and FORCE therapeutics, outside the submitted work. The rest authors declare no conflict of interest., (Thieme. All rights reserved.)

Total knee arthroplasty (TKA) in cases of complex deformity (e.g., ligamentous laxity, posttraumatic arthritis) may require prostheses with inherent varus-valgus stability greater than that of traditional posterior stabilized or cruciate-retaining implants. Here, we investigate the clinical and radiographic outcomes of TKA using a midlevel constraint (MLC) prosthesis. A retrospective review of 53 patients (62 knees) who underwent primary TKA with an MLC implant was performed. Short tibial stem extensions were utilized in 49 knees, and 13 knees received no stem extension. Mean follow-up time was 31.6 months (standard deviation [SD] = 10.0, range = 24-53). Preoperative and postoperative range of motion (ROM) were assessed. Plain radiographs were reviewed for alignment, radiolucent lines, component loosening, and osteolysis. Patients who developed postoperative arthrofibrosis underwent manipulation under anesthesia (MUA). Failure was defined as instability, component loosening, or need for revision surgery. Mean ROM significantly improved from 114.1 degrees (SD = 19.7 degrees) preoperatively to 123.5 degrees (SD = 12.2 degrees) at final follow-up ( t  = -3.43, p  = 0.001). Thirty-seven knees initially presented with varus deformity (mean = 7.5 degrees, SD = 4.8 degrees), whereas 23 had valgus deformity (mean = 10.6 degrees, SD = 6.5 degrees), and 2 knees had neutral alignment. Following surgery, mean alignment was 4.3 degrees valgus (SD = 1.7 degrees, range = 0-8 degrees), representing a statistically significant improvement ( t  = 5.29, p  < 0.001). Six patients (9.7%) developed arthrofibrosis requiring MUA, which was irrespective of baseline ROM ( p  = 0.92) and consistent with 12% incidence reported in the literature. There were no significant differences in postoperative ROM ( t  = 0.38, p  = 0.71), alignment ( t  = -0.22, p  = 0.83), or incidence of arthrofibrosis (χ 2  = 0.07, p  = 0.79) between short-stemmed and nonstemmed implants. There was no radiographic evidence of radiolucent lines, component loosening, or osteolysis in any patients. No patients required revision surgery. Use of an MLC prosthesis with primary femoral component in TKA resulted in satisfactory clinical and radiographic results with no evidence of component loosening, osteolysis, instability, or need for revision at minimum 2-year follow-up., Competing Interests: G.R.S. reports royalties from Zimmer Biomet; consulting fees from Zimmer Biomet, 3M KCI; payment from Zimmer Biomet, 3M KCI; leadership or fiduciary role from Operation Walk USA; stock from ROM Tech, Force Therapeutics. Rest authors declare no conflict of interest., (Thieme. All rights reserved.)

As the number of total knee arthroplasties (TKAs) increases, it is reasonable to expect the number of revision TKAs (rTKAs) to rise in parallel. The patient-related and societal burdens of rTKA are poorly understood. Therefore, the purpose of this study was to determine temporal changes in: (1) the incidence of rTKA; (2) patient and hospital characteristics; (3) complications, hospital lengths of stay (LOSs), and discharge dispositions; and (4) costs, charges, and payer types. All patients who underwent rTKA between 2009 and 2016 were identified from the National Inpatient Sample database using International Classification of Diseases, Ninth Revision and Tenth Revision codes and were studied. Univariate analyses were performed to compare the incidence of rTKA, patient and hospital characteristics, LOS and discharge dispositions, as well as costs, charges, and payer types. A multivariate logistic regression model was built to compare the odds of complications in 2009 and 2016. Over our study period, there was a 4.3% decrease in the incidence of rTKA. The mean age of patients who underwent rTKA was 65 years and a majority were female (58%). Mean hospital LOS decreased from 4.1 days in 2009 to 3.3 days in 2016 ( p  < 0.001). The rate of several complications decreased significantly over our study period including myocardial infarction, cardiac arrest, transfusion, pneumonia, urinary tract infection, and mortality. A significantly lower percentage of rTKA patients were discharged to a skilled nursing facility in 2016 (26.5%) compared with 2009 (31.6%; p  < 0.001). There was an 18.7% increase in the mean costs, and a 43.3% increase in the mean charges ( p  < 0.001). Over the study period, there was a decrease in the incidence of rTKAs. Despite potential improvements in primary TKA, the burden associated with rTKA remains large. This report can be used to help educate medical providers about outcomes that may result from a primary and/or revised TKA., Competing Interests: G.R.S. reports personal fees from Acelity, personal fees from Biomet, personal fees from Convatec, other from Force Therapeutics, personal fees from Medtronic, other from Operation Walk USA, grants and personal fees from Pacira, personal fees from Zimmer, outside the submitted work. R.E.D. reports grants from Flexion Therapeutics, grants from Orthofix, grants from Stryker, grants from TissueGene, grants from United Orthopedics, outside the submitted work. M.A.M. reports personal fees from Cymedica, personal fees from Flexion Therapeutics, grants and personal fees from Johnson & Johnson, other from Peerwell, personal fees from Pfizer, grants, personal fees, and other from Stryker, grants and personal fees from TissueGene, other from USMI, outside the submitted work. All the other authors report no conflict of interest., (Thieme. All rights reserved.)

Surgical site infections (SSIs) are among the most prevalent and devastating complications following lower extremity total joint arthroplasty (TJA). Strategies to reduce the rates can be divided into preoperative, perioperatives, and postoperative measures. A multicenter trial is underway to evaluate the efficacy of implementing a bundled care program for SSI prevention in lower extremity TJA including: (1) nasal decolonization; (2) surgical skin antisepsis; (3) antimicrobial incise draping; (4) temperature management; and (5) negative-pressure wound therapy for selected high-risk patients. The purposes of this systematic review were to provide a background and then to summarize the available evidence pertaining to each of these SSI-reduction strategies with special emphasis on total knee arthroplasty. A systematic review of the literature was conducted in accordance with the 2009 Preferred Reporting Items for Systematic Reviews and Meta-Analyses statement guidelines. Five individual literature searches were performed to identify studies evaluating nasal decolonization temperature management, surgical skin antisepsis, antimicrobial incise draping, and negative-pressure wound therapy. The highest level of evidence reports was used in each product review, and if there were insufficient arthroplasty papers on the particular topic, then papers were further culled from the surgical specialties to form the basis for the review. There was sufficient literature to assess all of the various prophylactic and preventative techniques. All five products used in the bundled program were supported for use as prophylactic agents or for the direct reduction of SSIs in both level I and II studies. This systematic review showed that various pre-, intra-, and postoperative strategies are efficacious in decreasing the risks of SSIs following lower extremity TJA procedures. Thus, including them in the armamentarium for SSI-reduction strategies for hip and knee arthroplasty surgeons should decrease the incidence of infections. We expect that the combined use of these products in an upcoming study will support these findings and may further enhance the reduction of total knee arthroplasty SSIs in a synergistic manner., Competing Interests: M.A.M. is a board or committee member for The Knee Society and The Hip Society, receives research support from National Institutes of Health, and is on the editorial board for the Journal of Arthroplasty, Journal of Knee Surgery, Surgical Technology International, and Orthopaedics. Dr. Mont also receives company support from 3M, Centrexion, Ceras Health, Flexion Therapeutics, Johnson & Johnson, Kolon TissueGene, NXSCI, Pacira, Pfizer-Lily, Skye Biologics, SOLVD Health, Smith & Nephew, Stryker, MirrorAR, Peerwell, US Medical Innovations, RegenLab, Medicus Works LLC, Up-to Date, and Wolters Kluwer Health — Lippincott Williams & Wilkins.G.R.S. receives royalties and/or is a consultant for Zimmer Biomet, 3M KCI, Elsevier, Springer, Thieme, and World Scientific. He has stock options in Force Therapeutics and ROM Tech. G.R.S. is also on the editorial board for the Journal of Knee Surgery and is a board member for Operation Walk USA. The rest authors declare no conflict of interest., (Thieme. All rights reserved.)

Early identification and treatment of Staphylococcus aureus ( S. aureus ) nasal colonization can reduce the risk of prosthetic joint infection. The purpose of this study was to evaluate patient-specific predictors for S. aureus nasal colonization in total joint arthroplasty patients to aid in preoperative screening protocols. A total of 2,147 arthroplasty patients who were preoperatively screened for S. aureus nasal colonization were retrospectively reviewed. Factors analyzed consisted of procedure type, primary diagnosis, gender, ethnicity, body mass index, the presence of chronic obstructive pulmonary disease, obstructive sleep apnea, hypertension, diabetes mellitus, use of immunosuppression medication, smoking history, and chronic kidney disease. Univariate and multivariate analyses were performed with significance p  < 0.05 and 95% confidence intervals. Overall, 3.7% (79) of our cohort tested positive for methicillin-resistant Staphylococcus aureus (MRSA), and 23.2% (493) tested positive for methicillin-sensitive Staphylococcus aureus (MSSA). Independent predictors for MRSA colonization were of Hispanic ethnicity ( p  = 0.001, odds ratio [OR] 13.98, confidence interval [CI] 2.97-65.76), immunosuppression medication use ( p  = 0.006, OR 2.82, CI 1.35-5.87), and revision total hip arthroplasty (THA) procedure ( p  < 0.001, OR 7.51, CI 2.58-21.89). Independent predictors for MSSA colonization were body mass index (BMI) >35 ( p  = 0.002, OR 1.57, CI 1.19-2.1). Variables were found to be protective against MSSA colonization including female gender ( p  = 0.012, OR 0.76, CI 0.61-0.94), age 60 to 69 ( p  = 0.025, OR 0.75, CI 0.58-0.96), and age 70 to 79 ( p  = 0.002, OR 0.63, CI 0.47-0.84). Age, Hispanic ethnicity, gender, revision THA, use of immunosuppression medication, and elevated BMI were independent risk factors for S. aureus nasal colonization., Competing Interests: G.R.S. reports personal fees from Zimmer Biomet, personal fees from 3M KCI, personal fees from Convatec, personal fees from Metronic, outside the submitted work., (Thieme. All rights reserved.)

Large-scale studies evaluating the effects of Parkinson's disease (PD) on primary total knee arthroplasty (TKA) are limited. The purpose of this study was to determine if PD patients undergoing primary TKA have increased: (1) medical complications; (2) implant-related complications; (3) readmission rates; and (4) costs. A query was performed using an administrative claims database. The study group consisted of all patients undergoing primary TKA who had a history of PD. Matched non-PD patients undergoing primary TKA served as a control group. The query yielded 72,326 patients (PD = 18,082; matching cohort = 54,244). Pearson's chi-square tests, logistic regression analyses, and Welch's t- tests were used to test for significance between the cohorts. Primary TKA patients who had PD were found to have greater incidences and odds of medical complications (4.21 vs. 1.24%; odds ratio [OR]: 3.50, 95% confidence interval [CI]: 3.15-3.89, p <  0.0001) and implant-related complications (5.09 vs. 3.15%; OR: 1.64, 95% CI: 1.51-1.79, p <  0.0001) compared with the matching cohort. Additionally, the rates and odds of 90-day readmission were higher (16.29 vs. 12.66%; OR:1.34, p <  0.0001) and episodes of care costs were significantly greater ($17,105.43 vs. $15,252.34, p   <  0.0001) in patients who had PD. Results demonstrate that PD patients undergoing primary TKA had higher incidences of medical and implant-related complications. They also had increased 90-day readmission rates and costs compared with controls. The findings of this study should be used in risk stratification and should inform physician-patient discussion but should not be arbitrarily used to deny access to care., Competing Interests: M.A.M. reports other from The Journal of Knee Surgery, outside the submitted work. The rest authors declare no conflict of interest., (Thieme. All rights reserved.)

Competing Interests: None declared.

As the volume of primary total knee arthroplasties continues to rise, so will the volume of revision arthroplasties. Bone loss is commonly encountered in revision surgery and must be managed appropriately to optimize outcomes. The concept of zonal fixation highlights the importance of attaining secure fixation within each of the three major osseous zones: the epiphysis, the metaphysis, and the diaphysis. While each zone is important, the metaphysis carries particular significance. The development of new implants such as metaphyseal cones and sleeves has greatly expanded the orthopedic surgeon's armamentarium to allow for solid metaphyseal fixation in virtually every case., Competing Interests: None declared., (Thieme. All rights reserved.)

With an expected increase in total knee arthroplasty (TKA) procedures, revision TKA (rTKA) procedures continue to be a burden on the United States health care system. The evolution of surgical techniques and prosthetic designs has, however, provided a paradigm shift in the etiology of failure mechanisms of TKA. This review can shed light on the current reasons for revision, which may lead to insights on how to improve outcomes and lower future revision risks. We will primarily focus on the epidemiology of rTKA in the present time, but we will also review this in the context of various time periods to see how the field has evolved. We will review rTKAs: 1) prior to 1997; 2) between 1997 and 2000; 3) between 2000 and 2012; and 3) in the modern era since 2012. We will further subdivide each of the sections into reasons for early (first 2 years after index procedure) versus late revisions (greater than 2 years after index procedure). In doing so, it was determined that prior to 1997, the most prevalent causes of failure were infection, patella failure, polyethylene wear, and aseptic loosening. After a major shift of failure mechanisms was described by Sharkey et al, polyethylene wear and aseptic loosening became the leading causes for revision. However, with the improved manufacturing technology and implant design, polyethylene wear was replaced with aseptic loosening and infection as the leading causes of failure between 2000 and 2012. Since that time, in the modern era of TKA, mechanical loosening and infection have taken over the most prevalent causes for failure. Hopefully, with continued developments in component design and surgical techniques, as well as increased focus on infection reduction methods, the amount of rTKA procedures will decline., Competing Interests: M.A.M. is a board or committee member for The Knee Society and The Hip Society, receives research support from National Institutes of Health, and is on the editorial board for the Journal of Arthroplasty, Journal of Knee Surgery, Surgical Technology International, and Orthopaedics. He also receives company support from 3M, Centrexion, Ceras Health, Flexion Therapeutics, Johnson & Johnson, Kolon TissueGene, NXSCI, US Medical Innovations, Pacira, Pfizer-Lily, Skye Biologics, SOLVD Health, Smith & Nephew, Stryker, CERAS Health, MirrorAR, Peerwell, US Medical Innovations, Johnson & Johnson, RegenLab, TissueGene, Stryker, Medicus Works LLC, Up-to Date, Wolters Kluwer Health–Lippincott Williams & Wilkins, Journal of Arthroplasty, Journal of Knee Surgery, Orthopedics, Surgical Techniques International; AAHKS, Knee Society, and Hip Society. Dr. Giles R. Scuderi receives royalties and/or is a consultant for Zimmer Biomet, 3M KCI, Elsevier, Springer, Thieme, and World Scientific. He has stock options in Force Therapeutics and ROM Tech. G.R.S. is also on the editorial board for the Journal of Knee Surgery and is a board member for Operation Walk USA. All other authors have no conflicts of interest to disclose., (Thieme. All rights reserved.)

The effort to reduce overall healthcare costs may affect more complex patients, as their pre- and postoperative care can be substantially involved. Therefore, the purpose of this study was to use a large nationwide insurance database to compare (1) costs, (2) reimbursements, and (3) net losses of 90-day episodes of care (EOC) for total knee arthroplasty (TKA) patients according to Elixhauser's Comorbidity Index (ECI) scores. All TKAs performed between 2005 and 2014 in the Medicare Standard Analytic Files were extracted from the database and stratified based on ECI scores, ranging from 1 to 5. ECI 1 patients served as the control cohort, while ECI 2, 3, 4, and 5 patients were considered study cohorts. Each study cohort and control cohort were matched based on age and sex, resulting in a total of 715,398 patients included for analysis. Total EOC costs, reimbursements, and total net losses (defined as total EOC costs minus total EOC reimbursements) were compared between the cohorts. Overall, total EOC costs increased with ECI. For example, compared with the matched ECI 1 cohorts, the total EOC costs for ECI 5 patients ($56,589.19 vs. $51,747.54) were significantly greater ( p  < 0.01). Although reimbursements increased with increasing ECI, so did net losses. The net losses for ECI 5 patients were greater than that for ECI 1 patients ($42,309.39 vs. $40,007.82). The bundled payments for care improvement (BPCI) and comprehensive care for joint replacement (CJR) are alternative payment models that might de-incentivize treatment of more complex patients. Our study found that despite increasing reimbursements, overall costs, and therefore net losses, were greater for more complex patients with higher ECI scores., Competing Interests: G.S. reports other from Convatec, Acelity, Biomet, Medtronic, Pacira, Zimmer, Force Therapeutics, Springer, Elsevier, Thieme, World Scientific, and Operation Walk USA, outside the submitted work. A.M. reports other from Stryker, Journal of Arthroplasty, and American Academy of Orthopedic Surgeons, outside the submitted work. M.R. reports other from Stryker, Orthosensor, Smith and Nephew, outside the submitted work. M.A.M. reports other from Stryker, Microport, DJ Orthopedics, Johnson and Johnson, Medical Compression Systems, Merz, Orthosensor, Pacira, Sage Products, Tissue Gene, US Medical Innovations, National Institutes of Health (National Institute of Arthritis and Musculoskeletal and Skin Diseases [NIAMS] and National Institute of Child Health and Human Development [NICHD]), Ongoing Care Solutions, American Journal of Orthopedics, Journal of Arthroplasty, Journal of Knee Surgery, Orthopedics, Surgical Technology International, American Academy of Orthopedic Surgeons, outside the submitted work., (Thieme. All rights reserved.)

Compared with nonelective total knee arthroplasties (TKAs), elective procedures have more time for preoperative planning, which allows for potentially improved patient optimization, risk factor modification, and patient education. The purpose of this study was to (1) determine nationwide trends in operative times and (2) evaluate associations between surgery type, elective or nonelective, with respect to (a) operative times, (b) length of stay (LOS), (c) discharge dispositions, (d) 30-day postoperative complications, (e) reoperations, and (f) readmissions. The American College of Surgeons National Surgical Quality Improvement Program (ACS-NSQIP) database was queried for all primary TKAs performed between 2011 and 2016. This yielded 209,178 cases which were stratified into elective and nonelective cases. Elective cases were those in which patients were brought from their normal living environment for scheduled procedures. One-way ANOVA (analysis of variance) was used to evaluate associations between operative times and year of surgery. Multivariate linear and logistic regression models adjusted for surgery year and patient factors (age, sex, BMI [body mass index], and ASA [American Society of Anesthesiologists] score) were used to evaluate associations of surgery type with peri- and postoperative outcomes. A significant inverse correlation between operative times and operative year was observed ( p  < 0.001). Mean operative times and LOS were significantly shorter in elective cases compared with nonelective cases (93 vs. 112 minutes, p  < 0.005; 3 vs. 5 days, p  < 0.001). Multivariate analysis showed these associations remained significant even after adjusting for potential confounders ( p  < 0.001). Compared with the nonelective cohort, patients in the elective cohort were more likely to be discharged home (74 vs. 69%, p  < 0.001). Nonelective patients had higher rates of pneumonia (0.7 vs. 0.3%, p  = 0.005), organ-space surgical site infections (SSI; 0.4 vs. 0.2%, p  = 0.004), transfusions (10.9 vs. 6.5%, p  < 0.001), sepsis (0.6 vs. 0.2%, p  = 0.001), and septic shock (0.2 vs. 0.1%, p  = 0.005) compared with elective patients. These associations remained significant with multivariate logistic regression. This study demonstrated that preoperative planning can help shorten operative times and LOS as well as reduce complication and reoperation rates. Alongside the direct advantages identified in this study, potential greater effects include superior patient outcomes and reduced health care costs., Competing Interests: Dr. G.R.S. reports other from Acelity, Biomet, Convatec, Force Therapeutics, Medtronic, Operation Walk U.S.A., Pacira, Springer, Elsevier, ThiemeWorld Scientific, and Zimmer, outside the submitted work. Dr. J.T.M. reports other from AAOS, AAHKS, Corin, DePuy, Invuity, Stryker, Think Surgical, and null, outside the submitted work. Dr. M.A.M. reports other from Abbott, Cymedica, DJ Orthopaedics, Johnson & Johnson, Malinckrodt, Microport, Ongoing Care Support, Orthosensor, Pacira, Peerwell, Performance Dynamics, Sage, Stryker, TissueGene, outside the submitted work. The remaining authors declare no conflict of interest related to this article., (Thieme Medical Publishers 333 Seventh Avenue, New York, NY 10001, USA.)

Total knee arthroplasty (TKA) is recognized as one of the most successful surgical procedures performed today. One of the most common and dreaded complications of TKA is postoperative infection. To prevent infections, it is critical to identify patients at high risk through analyzing their risk factors, and help in addressing them prior to surgery. The effort to prevent infection must be carried through every step of the surgical process, from preoperative counseling to intraoperative measures and postoperative protocols. Hair removal, the application of antiseptics, the utilization of antibiotics, barbed sutures, smart dressings, and antibacterial washes are some of the avenues surgeons may explore to help prevent infection., Competing Interests: None., (Thieme Medical Publishers 333 Seventh Avenue, New York, NY 10001, USA.)

Although it is well known that patients with preoperative hemoglobin levels <13.0 g/dL are at a higher risk for requiring postoperative transfusions, the ideal blood management strategy for this group of patients remains unclear. This study compared preoperative autologous donation with preoperative administration of epoetin alfa as a method to maximize perioperative hemoglobin levels and minimize blood transfusions in these high-risk patients undergoing total knee arthroplasty (TKA). Results show that both preoperative autologous donation and epoetin alfa were successful in decreasing the need for allogeneic blood transfusions following TKA in high-risk patients. Epoetin alfa was more effective in maximizing perioperative hemoglobin levels.

This study determined the accuracy of plain radiography in detecting osteolytic lesions around total knee prostheses compared to multi-detector computed tomography (CT). Thirty-one patients diagnosed with periprosthetic osteolysis by multi-detector CT after total knee arthroplasty (TKA) were studied. Computed tomography for each patient was retrospectively reviewed in a blinded fashion. The plain radiographs for each patient that had been obtained prior to CT were reviewed in the same manner. The results of the CT were compared with the results of the radiographs. The number, size, and location of the lesions were compared. The multi-detector CT detected 48 lesions in 31 knees: 40 tibial lesions, 4 femoral lesions, and 4 patellar lesions. Radiographic diagnosis was made in 6 of the 40 tibial lesions, 2 of the 4 femoral lesions, and 0 of the 4 patellar lesions. Plain radiographs are inadequate for evaluating periprosthetic osteolysis in TKA with only 8 (17%) of 48 lesions detected by multi-detector CT visible on the standard radiographs. Multi-detector CT provides the surgeon with a diagnostic and preoperative planning tool when osteolysis is suspected.

One hundred thirty five patients with osteoarthritis who underwent total knee arthroplasty (TKA) were evaluated to determine whether specific pre- and postoperative variables were correlated with the postoperative range of motion. Age, sex, pre- and postoperative range of motion, pre- and postoperative Knee Society scores, intraoperative patellar thickness before and after resurfacing, pre- and postoperative radiographic patellar height (as determined by the Insall-Salvati and Blackburn-Peel ratios), and preoperative radiographic alignment were recorded for each patient. Regression analysis was performed to identify whether any variables were correlated with the postoperative range of motion or Knee Society scores. The only variable that was significantly correlated with postoperative range of motion was the preoperative range of motion. This study suggests that among the variables evaluated, the preoperative range of motion was the only significant predictor of postoperative range of motion.

Fifty-seven patients who underwent 65 primary TKAs between 1993-1994 were retrospectively studied to identify the technical challenges and pitfalls associated with patellar resurfacing and to improve patellar tracking during total knee arthroplasty (TKA). Average patient age was 69 years. All surgeries were performed by a single surgeon (J.N.I), and the same prosthesis was used in all patients. Intraoperatively, attention was paid to avoid femoral and tibial component malrotation and prevent overstuffing of the patellofemoral joint. Preoperative limb alignment was varus in 42 knees, neutral in 6 knees, and valgus in 17 knees. Average pre-resection patellar thickness measured 23.8 mm and post-resection thickness averaged 21.5 mm. No patella-prosthesis composite was thicker than the native patella. Two (3%) knees required a formal lateral release to improve patellar tracking at surgery. Average follow-up for 53 patients (61 knees) was 5 years. At latest follow-up, 4 (6%) patients reported mild anterior knee pain, 5 (7%) patients reported pain with stairs, and 2 (3%) patients had knee crepitus without pain. No dislocations or recurrent subluxations occurred. No patient required revision surgery for patellofemoral complication. Awareness of the anatomic variability, attention to component rotation, and restoration of the normal patellar height improves patellar tracking and minimizes patellofemoral instability following TKA.

Flexion and extension gap heights were measured in 50 consecutive primary posterior-stabilized total knee arthroplasties (TKAs) to determine whether posterior cruciate ligament (PCL) release or re-establishment of the posterior condylar recess increased gap width. After PCL release, a slight symmetrical increase was noted in both gaps. In extension, gap width increased on average 1.3 mm and 1 mm in the medial and lateral compartments, respectively. The same pattern was observed in flexion, averaging 1.3 mm medially and 1.3 mm laterally. Another increase in the two gaps was observed after the posterior condylar osteophytes were removed and the posterior recess was re-established. The gaps in extension increased, with respect to the base-line value, on average 1.8 mm medially and 1.8 mm laterally, whereas flexion increased an average 2 mm medially and 2.2 mm laterally. No statistical differences were noted between flexion and extension gaps. No independent differences between the flexion and extension gaps were found in any surgical phase. Posterior cruciate ligament removal and re-establishment of posterior condylar recess does not require additional consideration in gap balancing during posterior-stabilized TKA.

Although the results of TKR are highly successful at long-term follow-up, failures occur. One of the more frequent causes of failure is instability. In distinction to instability in the medial-lateral plane, AP instability in flexion has been poorly described until recently. Although acquired ligamentous incompetence can occur, particularly with cruciate retaining prostheses, many cases of flexion instability result from an intraoperative failure to create symmetric balanced flexion and extension spaces. In primary TKR, use of a well-designed posterior stabilized prosthesis and creation of symmetric balanced flexion and extension gaps should minimize the incidence of postoperative flexion instability. If flexion instability occurs, the role of nonoperative treatment is limited. In most cases, revision TKR using the same basic principles is required. When symmetric flexion and extension spaces cannot be produced intraoperatively in complex primary or revision surgery, use of a more constrained articulation, such as a constrained condylar prosthesis or hinged prosthesis, is required.