A Multiplexed System for Quantitative Comparisons of Chromatin Landscapes.

Genome-wide profiling of histone modifications can provide systematic insight into the regulatory elements and programs engaged in a given cell type. However, conventional chromatin immunoprecipitation and sequencing (ChIP-seq) does not capture quantitative information on histone modification levels, requires large amounts of starting material, and involves tedious processing of each individual sample. Here, we address these limitations with a technology that leverages DNA barcoding to profile chromatin quantitatively and in multiplexed format. We concurrently map relative levels of multiple histone modifications across multiple samples, each comprising as few as a thousand cells. We demonstrate the technology by monitoring dynamic changes following inhibition of p300, EZH2, or KDM5, by linking altered epigenetic landscapes to chromatin regulator mutations, and by mapping active and repressive marks in purified human hematopoietic stem cells. Hence, this technology enables quantitative studies of chromatin state dynamics across rare cell types, genotypes, environmental conditions, and drug treatments.

Arthroplasty Surgeons Differ in Their Intraoperative Soft Tissue Assessments: A Study in Human Cadavers to Quantify Surgical Decision-making in TKA.

BACKGROUND: In TKA, soft tissue balancing is assessed through manual intraoperative trialing. This assessment is a physical examination via manually applied forces at the ankle, generating varus and valgus moments at the knee while the surgeon visualizes the lateral and medial gaps at the joint line. Based on this examination, important surgical decisions are made that influence knee stability, such as choosing the polyethylene insert thickness. Yet, the applied forces and the assessed gaps in this examination represent a qualitative art that relies on each surgeon's intuition, experience, and training. Therefore, the extent of variation among surgeons in conducting this exam, in terms of applied loads and assessed gaps, is unknown. Moreover, whether variability in the applied loads yields different surgical decisions, such as choice of insert thickness, is also unclear. Thus, surgeons and developers have no basis for deciding to what extent the applied loads need to be standardized and controlled during a knee balance exam in TKA. QUESTIONS/PURPOSES: (1) Do the applied moments in soft tissue assessment differ among surgeons? (2) Do the assessed gaps in soft tissue assessment differ among surgeons? (3) Is the choice of insert thickness associated with the applied moments? METHODS: Seven independent human cadaveric nonarthritic lower extremities from pelvis to toe were acquired (including five females and two males with a mean age of 73 ± 7 years and a mean BMI of 25.8 ± 3.8 kg/m 2 ). Posterior cruciate ligament substituting (posterior stabilized) TKA was performed only on the right knees. Five fellowship-trained knee surgeons (with 24, 15, 15, 7, and 6 years of clinical experience) and one chief orthopaedic resident independently examined soft tissue balance in each knee in extension (0° of flexion), midflexion (30° of flexion), and flexion (90° of flexion) and selected a polyethylene insert based on their assessment. Pliable force sensors were wrapped around the leg to measure the loads applied by each surgeon. A three-dimensional (3D) motion capture system was used to measure knee kinematics and a dynamic analysis software was used to estimate the medial and lateral gaps. We assessed (1) whether surgeons applied different moments by comparing the mean applied moment by surgeons in extension, midflexion, and flexion using repeated measures (RM)-ANOVA (p < 0.05 was assumed significantly different); (2) whether surgeons assessed different gaps by comparing the mean medial and lateral gaps in extension, midflexion, and flexion using RM-ANOVA (p < 0.05 was assumed significantly different); and (3) whether the applied moments in extension, midflexion, and flexion were associated with the insert thickness choice using a generalized estimating equation (p < 0.05 was assumed a significant association). RESULTS: The applied moments differed among surgeons, with the largest mean differences occurring in varus in midflexion (16.5 Nm; p = 0.02) and flexion (7.9 Nm; p < 0.001). The measured gaps differed among surgeons at all flexion angles, with the largest mean difference occurring in flexion (1.1 ± 0.4 mm; p < 0.001). In all knees except one, the choice of insert thickness varied by l mm among surgeons. The choice of insert thickness was weakly associated with the applied moments in varus (ß = -0.06 ± 0.02 [95% confidence interval -0.11 to -0.01]; p = 0.03) and valgus (ß = -0.09 ± 0.03 [95% CI -0.18 to -0.01]; p= 0.03) in extension and in varus in flexion (ß = -0.11 ± 0.04 [95% CI -0.22 to 0.00]; p = 0.04). To put our findings in context, the greatest regression coefficient (ß = -0.11) indicates that for every 9-Nm increase in the applied varus moment (that is, 22 N of force applied to the foot assuming a shank length of 0.4 m), the choice of insert thickness decreased by 1 mm. CONCLUSION: In TKA soft tissue assessment in a human cadaver model, five surgeons and one chief resident applied different moments in midflexion and flexion and targeted different gaps in extension, midflexion, and flexion. A weak association between the applied moments in extension and flexion and the insert choice was observed. Our results indicate that in the manual assessment of soft tissue, changes in the applied moments of 9 and 11 Nm (22 to 27 N on the surgeons' hands) in flexion and extension, respectively, yielded at least a 1-mm change in choice of insert thickness. The choice of insert thickness may be more sensitive to the applied moments in in vivo surgery because the surgeon is allowed a greater array of choices beyond insert thickness. CLINICAL RELEVANCE: Among five arthroplasty surgeons with different levels of experience and a chief resident, subjective soft tissue assessment yielded 1 to 2 mm of variation in their choice of insert thickness. Therefore, developers of tools to standardize soft tissue assessment in TKA should consider controlling the force applied by the surgeon to better control for variations in insert selection.

Anatomy education in US Medical Schools: before, during, and beyond COVID-19.

BACKGROUND: Anatomy education in US medical schools has seen numerous changes since the call for medical education reform in 2010. The purpose of this study was to survey US medical schools to assess recent trends in anatomy education, the impact of the COVID-19 pandemic on anatomy teaching, and future directions of medical school anatomy curricula. METHODS: We sent a 29-item survey to anatomy course directors of 145 AAMC-associated allopathic medical schools inquiring about their schools' anatomy curricula. The survey contained objective discrete questions concerning the curricula changes preceding COVID-19 and those directly related to COVID-19. We also asked subjective and open-ended questions about the impact of COVID-19 and future directions of anatomy education. RESULTS: A total of 117/143 course directors (82%) completed the survey. Most schools (60%) reported a major change to their anatomy course within the past five years, including a decrease in total course time (20%), integration of anatomy into other courses (19%), and implementation of a "flipped classroom" (15%) teaching style. Due to COVID-19, there was a decrease in the fraction of course time dedicated to "hands-on" learning (p < 0.01) and teaching of clinical correlates (p = 0.02) and radiology (p < 0.01). Most course directors (79%) reported that COVID-19 had a negative impact on quality of learning due to decreased interactive or in-person (62%) learning and lack of dissection (44%). Incorporation of virtual-reality applications or 3D anatomy software (23%) and a decrease in cadaver dissection (13%) were the most common future anticipated changes. CONCLUSION: The constraints conferred by COVID-19 highlight the importance of maximizing interactive learning in the discipline of anatomy. In an era of social distancing and decreased emphasis on conventional anatomy dissection, adaptations of new technologies and teaching modalities may allow for traditional educational rigor to be sustained.

Perioperative Use of Antifibrotic Medications Associated With Lower Rate of Manipulation After Primary TKA: An Analysis of 101,366 Patients.

BACKGROUND: Several commonly prescribed medications have known antifibrotic properties and have been shown to reduce postoperative scar formation in other clinical areas, but it is unknown whether the use of such medications perioperatively in patients undergoing TKA may improve rates of postoperative stiffness. METHODS: A large US employer-sponsored healthcare database (Truven Marketscan) was queried for patients who underwent elective primary TKA for primary osteoarthritis between 2015-2019. Demographic information and comorbidities were recorded, along with whether patients were prescribed one of several medications with known antifibrotic properties during the three months before or after surgery. RESULTS: Complete data were available for 101,366 patients undergoing TKA, of which 4,536 underwent MUA (4.5%). Perioperative use of any antifibrotic medication was associated with a lower likelihood of undergoing MUA (P < .001). When controlling for age, sex, comorbidities, opioid use, length of stay, among other variables, perioperative use of specific ACE inhibitors (OR 0.91, CI 0.84-1, P = .042), COX-2 inhibitors (OR 0.88, CI 0.81-0.96, P = .002), and angiotensin II receptor blockers, specifically losartan (OR 0.80, CI 0.70-0.91, P = .007) all remained significantly associated with lower rates of MUA. CONCLUSION: This study, spanning over a hundred thousand primary TKA procedures over a recent five-year period, demonstrates an association between perioperative use of specific medications with antifibrotic properties and a decreased rate of MUA. These data will help inform future studies aimed to prospectively evaluate the potential of antifibrotic medications in preventing postoperative stiffness in high-risk patients undergoing knee arthroplasty.

A Mid-Level Constrained Insert Reduces Coupled Axial Rotation but Not Coronal Mid-Flexion Laxity Induced by Joint Line Elevation in Posterior-Stabilized Total Knee Arthroplasty: A Computational Study.

BACKGROUND: Surgeons may resect additional distal femur during primary posterior-stabilized (PS) total knee arthroplasty (TKA) to correct a flexion contracture. However, the resultant joint line elevation (JLE) increases mid-flexion laxity. We determined whether a mid-level constraint (MLC) insert reduced mid-flexion laxity after JLE. METHODS: Six computational knee models were developed using computed tomography scans and average soft tissue properties yielding balanced extension gaps but with a 10° flexion contracture. Distal femoral resections of +2 and +4 mm were simulated with PS and MLC inserts. Varus-valgus ±10 Nm moments were applied at 30°, 45°, and 60° of flexion. Coronal laxity (the sum of varus-valgus angulation) and coupled axial rotation (the sum of internal/external rotation) were measured and compared between insert models. RESULTS: At 30° of flexion, coronal laxities with the PS insert at the +2 and +4 mm resections averaged 7.9° ± 0.6° and 11.3° ± 0.6°, respectively, and decreased by 0.8° (P = .06) and 1.0° (P = .07), respectively, with the MLC insert. PS rotational laxities at the +2 and +4 mm resections averaged 11.1° ± 3.9° and 12.5° ± 4.6°, respectively, and decreased by 5.6° (P = .01) and 7.1° (P = .02), respectively, with the MLC insert. Similar patterns were observed at 45° and 60° of flexion. CONCLUSION: With additional distal femoral resections to alleviate a flexion contracture, utilizing an MLC insert substantially reduced coupled axial rotation but had a minimal impact on coronal laxity compared to a PS insert. Efforts should be taken to avoid JLE in primary total knee arthroplasty as even MLC inserts may not mitigate coronal laxity.

Projected Economic Burden of Periprosthetic Joint Infection of the Hip and Knee in the United States.

BACKGROUND: In addition to the significant morbidity and mortality associated with periprosthetic joint infection (PJI), the cost of treating PJI is substantial. Prior high-quality national estimates of the economic burden of PJI utilize data up to 2009 to project PJI growth in the United States through 2020. Now in the year 2020, it is appropriate to evaluate these past projections and incorporate the latest available data to better understand the current scale and burden of PJI in the United States. METHODS: The Nationwide Inpatient Sample (2002-2017) was used to identify rates and associated inpatient costs for primary total knee arthroplasty (TKA) and total hip arthroplasty (THA) and PJI-related revision TKA and THA. Poisson regression was utilized to model past growth and project future rates and cost of PJI of the hip and knee. RESULTS: Using the most recent data, the combined annual hospital costs related to PJI of the hip and knee were estimated to be $1.85 billion by 2030. This includes $753.4 million for THA PJI and $1.1 billion for TKA PJI, in that year. Increases in PJI costs are mainly attributable to increases in volume. Although the growth in incidence of primary THA and TKA has slowed in recent years, the incidence of PJI and the cost per case of PJI remained relatively constant from 2002 to 2017. DISCUSSION: Understanding the current and potential future financial burden of PJI for surgeons, patients, and healthcare systems is essential. There is an urgent need for efficacious preventive strategies in reducing rates of PJI after THA and TKA.

Analysis of Hip and Knee Reconstruction Questions on the Orthopedic In-Training Examination.

BACKGROUND: It is vital for orthopedic residents and residency programs to have a current understanding of the materials and resources utilized on the Orthopedic In-Training Examination (OITE) to tailor resident educational curricula accordingly. This study presents an updated analysis of the hip and knee section of the OITE. METHODS: All OITE questions related to hip and knee reconstruction over six examinations between 2014 and 2019 were analyzed for topic, subtopic, taxonomy, imaging modalities, resident performance, and references. RESULTS: There were 166 hip and knee reconstruction questions of 1600 OITE questions (10.4%) over a six-year period. The most commonly tested topics include mechanical properties of total knee and hip implants (10.8%), instability after THA (10.8%), periprosthetic fracture (10.2%), and prosthetic joint infection (10.2%). A total of 362 references were cited from 68 different sources. The most common sources were JOA, JBJS, JAAOS, and CORR, which were collectively responsible for 68% of all citations. There was an average publication lag of 7.1 years, with 75% of all citations falling within 10 years of the question date. Compared with a prior analysis from 2005 and 2009, there were significantly more complex multistep questions regarding treatment and fewer one-step knowledge recall questions (P = .003). Similarly, recent tests had significantly more questions involving interpretation of radiographs (55%, P < .001) and advanced imaging (9.6%, P < .001), compared with a decade ago. CONCLUSIONS: The OITE continues to evolve over time, incorporating recent literature and topics. The current analysis identifies high-yield topics and resources that can guide resident preparation for the OITE hip and knee section.

The Effectiveness of Closed-Incision Negative-Pressure Therapy Versus Silver-Impregnated Dressings in Mitigating Surgical Site Complications in High-Risk Patients After Revision Knee Arthroplasty: The PROMISES Randomized Controlled Trial.

BACKGROUND: Revision total knee arthroplasty (rTKA) is associated with significant risk of wound-related morbidity. The present study aimed to evaluate the 1) efficacy of closed-incision negative-pressure therapy (ciNPT) vs silver-impregnated antimicrobial dressing (AMD) in mitigating postoperative surgical site complications (SSCs), 2) the effect of ciNPT vs AMD on certain postoperative health utilization parameters, and on 3) patient-reported outcomes (PROs) improvement at 90-day postoperative follow-up. METHODS: This multicenter randomized controlled trial was conducted between December 2017 and August 2019. Patients ≥22 years, at high risk for SSC, and receiving rTKA with full exchange and reimplantation of new prosthetic components or open reduction and internal fixation of periprosthetic fractures were screened for inclusion. Eligible patients were randomized to receive a commercially available ciNPT system or a silver-impregnated AMD (n = 147, each) for minimum of 5-day duration. Primary outcome was the 90-day incidence of SSCs with stratification in accordance with revision type (aseptic/septic). Secondary outcomes were the 90-day health care utilization parameters (readmission, reoperation, dressing changes, and visits) and PROs. RESULTS: Of 294 patients randomized (age: 64.9 ± 9.0 years, female: 59.6%), 242 (82.0%) patients completed the study (ciNPT: n = 124; AMD: n = 118). The incidence of 90-day SSCs was lower for the ciNPT cohort (ciNPT: 3.4% vs AMD: 14.3%; odds ratio (OR): 0.22, 95% confidence interval (0.08, 0.59); P = .0013). Readmission rates (3.4% vs 10.2%, OR: 0.30(0.11, 0.86); P = .0208) and mean dressing changes (1.1 ± 0.3 vs 1.3 ± 1.0; P = .0003) were lower with ciNPT. The differences in reoperation rates, number of visits, and PRO improvement between both arms were not statistically significant (P > .05). CONCLUSION: ciNPT is effective in reducing the 90-day postoperative SSCs, readmission, and number of dressing changes after rTKA. Recommending routine implementation would require true-cost analyses.

An Updated Analysis of the Pediatric Section of the Orthopaedic In-Training Examination.

BACKGROUND: An updated analysis of the pediatrics section of the Orthopaedic In-Training Examination (OITE) is helpful for resident education and preparation for the OITE. The purpose of this study is to provide an updated evaluation of the pediatric category of the OITE, and to explore trends in question topics and taxonomy compared with the previously published analysis from 2011 to 2014. METHODS: Five years (2015-2019) of OITE questions, answers, and references were reviewed. The number of pediatric questions per year was recorded, and questions were subcategorized based on topic tested. The presence or absence of imaging or a clinical photograph was noted. Each question was also assigned a cognitive taxonomy level, based on a previously published classification system. RESULTS: The percentage of pediatric questions on the 2015-2019 OITEs averaged 11.4% compared with 12.6% from 2011 to 2014 (P=0.349). The 3 most commonly tested pediatric topics were general trauma (17.8%), elbow trauma (13.2%), and genetic disorders/syndromes (11.2%). There was a significant increase in questions that required diagnosis and interpretation (27.6% vs. 8%, P<0.001) and a slight but not significant decrease in the questions requiring simple knowledge recall (26.3% vs. 35.5%, P=0.120) and decisions about management (46.1% vs. 56.5%, P=0.077). Overall, 65% of questions utilized clinical photographs or imaging studies compared with 62% from 2011 to 2014 (P=0.621). The most common references were the Journal of Pediatric Orthopaedics, Journal of American Academy of Orthopaedic Surgeons, and Journal of Bone and Joint Surgery. Textbooks were cited less frequently than in the past. CONCLUSIONS: While the percentage of pediatric questions on the OITE has remained consistent over time, the percentage of questions requiring diagnosis and interpretation has increased. In addition, questions testing genetic disorders/syndromes have become more prevalent in recent years. The most commonly cited resources were high-impact journal articles, with textbooks cited less frequently than in previous years. CLINICAL RELEVANCE: Knowledge of the most frequently tested topics and resources cited may assist orthopaedic residents in preparing for the OITE and orthopaedic faculty to focus didactic sessions on the most commonly tested topics.

Operative time greater than 120 minutes is associated with increased pulmonary and thromboembolic complications following revision total hip arthroplasty.

BACKGROUND: The aim of this study was to determine the impact of operative time on the development of early postoperative complications in patients undergoing revision total hip arthroplasty (THA). METHODS: In this retrospective cohort study, data were collected through the American College of Surgeons National Quality Improvement Program Database. All patients who underwent revision THA between 2007 and 2016 were identified and stratified into groups based on operative time|: 0-60 min, 61-120 min, 121-180 min, and > 180 min. The incidence of early postoperative adverse events with 30 days, including cardiac, pulmonary, renal, septic, thromboembolic, urinary tract, and wound complications, death, length of stay > 7 days, and unplanned return to the operating room were collected. The complications rates following revision THA were evaluated with univariate and multivariate analyses with significance set at p < 0.05. RESULTS: A total of 6271 revision THA patients were included for analysis. Patients who had > 120 min of operative time had a significantly increased risk of the development of pulmonary (OR: 1.339; 95% CI: 1.08-1.661; p = 0.008) and thromboembolic complications (OR: 1.34; 95% CI: 1.053-1.707; p = 0.017) and also had an extended length of stay greater than 7 days (OR: 1.413; 95% CI: 1.295-1.541; p < 0.001). CONCLUSIONS: Increased operative time (> 120 min) during revision THA is associated with increased risk of pulmonary and thromboembolic complications, and prolonged hospitalizations (greater than seven days).

Does Change in ESR and CRP Guide the Timing of Two-stage Arthroplasty Reimplantation?

BACKGROUND: Two-stage reimplantation arthroplasty is a commonly used approach for treating chronic periprosthetic joint infections. A prereimplantation threshold value of erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP) to determine infection eradication and the proper timing of reimplantation remains ill defined. We theorized that rather than a specific numeric threshold, a percentage of improvement in these serology markers might improve diagnostic accuracy in determining the timing of reimplantation. QUESTION/PURPOSES: We investigated if (1) the percent, or delta, change in ESR and CRP values from preresection to prereimplantation ([INCREMENT]ESR, [INCREMENT]CRP) is a useful marker of infection eradication and (2) whether the initial PJI causative organism (resistant, nonresistant, or culture-negative) is associated with serum ESR and CRP values before and after treatment with an antibiotic spacer and parenteral antibiotic therapy. METHODS: We retrospectively reviewed 300 patients, nine of whom were lost to followup, treated with a two-stage revision THA or TKA protocol between 2005 and 2014 from two separate institutional arthroplasty registries. Serum ESR and CRP values were recorded at two designated points: (1) preresection and (2) after 6 weeks of intravenous antibiotic therapy with a drug-eluting spacer and completion of an organism-specific intravenous antibiotic regimen. Patient records were reviewed electronically for causative species of infection, revision surgeries, and recurrent/persistent infection based on Musculoskeletal Infection Society criteria for a minimum of 2 years. Forty-eight of 291 patients (16%) underwent a revision procedure for recurrent or persistent infection, whereas 31 patients (10%) were revised for noninfectious reasons. The [INCREMENT]ESR, [INCREMENT]CRP, culture results, and patient demographics were recorded and analyzed with receiver operator curves controlling for American Society of Anesthesiologists (ASA) class. RESULTS: Receiver operator characteristic area under the curves (AUC) demonstrated that both the [INCREMENT]ESR (AUC = 0.581) and [INCREMENT]CRP (AUC = 0.539) percentages were poor markers of recurrent or persistent infection. When comparing preresection with prereimplantation values, the median percent [INCREMENT]ESR was 50% (interquartile range [IQR], 17%-77%) for those patients who remained infection-free versus 59% (IQR, 29%-78%) for those who developed reinfection (p = 0.540). The median percent [INCREMENT]CRP was 77% (IQR, 47%-92%) for those patients who remained infection-free versus 79% (IQR, 46%-95%) for those who experienced reinfection (p = 0.634). Although no significant differences were found between organism type and CRP values at the two time points, the preresection ESR level was higher in patients infected with resistant bacteria (median, 69; IQR, 60%-85%) compared with nonresistant organisms (median, 55; IQR, 33%-83%; p = 0.020). CONCLUSIONS: The percent change in serum ESR and CRP inflammatory markers before and after two-stage reimplantation for PJI was not associated with reinfection risk when controlling for ASA class. Although a return to normal serology infrequently occurs before reimplantation, [INCREMENT]ESR and [INCREMENT]CRP provide no additional diagnostic accuracy to determine the timing of reimplantation. Furthermore, the pre- and postresection serology values have no meaningful relationship to resistant or nonresistant pathogens. Decisions for reimplantation must take into account multiple variables rather than a specific threshold change in serum inflammatory markers. LEVEL OF EVIDENCE: Level III, diagnostic study.

Posterior condylar bone resection and femoral implant thickness vary by up to 3 mm across implant systems: implications for flexion gap balancing.

PURPOSE: The purpose of this study was to evaluate the thickness of medial and lateral posterior femoral condylar bone resected with five implant systems using posterior referencing jigs set at 3° of external rotation. The hypothesis was that posterior condylar resection thickness on the medial side would be equal to the thickness of the femoral implant posteriorly, regardless of implant system. METHODS: Posterior referencing femoral sizers were used on right femur sawbones models for five different implant systems. Each sawbones model was sized using a femoral sizer for the specific implant system. Sizing guides were set at 3° of external rotation for the right femur. Each system's 4-in-1 cutting block was then used to make posterior condylar cuts. The thicknesses of the cut bones were measured using a manual calliper. RESULTS: The amount of bone resected from both medial (P = 0.0004) and lateral (P < 0.0001) posterior condyles differed significantly across the five implant systems. The mean thickness of bone resected from the posteromedial femoral condyle ranged from 9.4 ± 0.5 to 12.4 ± 0.9 mm. The mean thickness of the posterolateral condyle cut ranged from 6.7 ± 0.6 to 10.2 ± 0.3 mm. The difference in thicknesses between the bone resection from the posteromedial condyle and the implant thickness of the posterior condyles ranged from 0.6 to 2.9 mm. CONCLUSIONS: The thickness of bone removed from the posterior femoral condyles varied by up to 3 mm across the five TKA implant systems. For each system, the posteromedial condyle resection was larger than the thickness of the posterior condyle of the actual implant. As the difference between the posterior bone resection and the implant thickness increases, the flexion gap will likely loosen and should be accounted for during gap balancing. In commonly used knee implant systems, resected bone is greater than implant thickness and may lead to flexion instability.

Neither Anterior nor Posterior Referencing Consistently Balances the Flexion Gap in Measured Resection Total Knee Arthroplasty: A Computational Analysis.

BACKGROUND: Whether anterior referencing (AR) or posterior referencing (PR) produces a more balanced flexion gap in total knee arthroplasty (TKA) using measured resection remains controversial. Our goal was to compare AR and PR in terms of (1) medial and lateral gaps at full extension and 90° of flexion, and (2) maximum medial and lateral collateral ligament (MCL and LCL) forces in flexion. METHODS: Computational models of 6 knees implanted with posterior-stabilized TKA were virtually positioned with both AR and PR techniques. The ligament properties were standardized to achieve a balanced knee at full extension. Medial-lateral gaps were measured in response to varus and valgus loading at full extension and 90° of flexion; MCL and LCL forces were estimated during passive flexion. RESULTS: At full extension, the maximum difference in the medial-lateral gap for both AR and PR was <1 mm in all 6 knee models. However, in flexion, only 3 AR and 3 PR models produced a difference in medial-lateral gap <2 mm. During passive flexion, the maximum MCL force ranged from 2 N to 87 N in AR and from 17 N to 127 N in PR models. The LCL was unloaded at >25° of flexion in all models. CONCLUSION: In measured resection TKA, neither AR nor PR better balance the ligaments and produce symmetrical gaps in flexion. Alternative bone resection techniques and rotation alignment targets are needed to achieve more predictable knee balance.

Patient Attitudes Toward Resident and Fellow Participation in Orthopedic Surgery.

BACKGROUND: Residents' and fellows' participation in orthopedic surgery is a potential source of anxiety and concern for patients. The purpose of this study was to determine patients' attitudes toward trainee involvement in orthopedic surgery, surgeons as educators, and disclosure of trainee involvement. METHODS: Three hundred two consecutive patients with preoperative and postoperative appointments at three arthroplasty practices in academic medical centers were surveyed with an anonymous, self-administered questionnaire. The questionnaire was developed in consultation with an expert in survey design. RESULTS: Two hundred thirty-four patients completed the questionnaire (response rate 77.5%). Respondents were 60.5% female, 79.6% white, 66.5% privately insured, and 82.8% had at least some college education. About 65.9% of the respondents felt that surgeons who teach are better surgeons. Nearly all felt residents and fellows should perform surgeries as part of their education (94.1% and 95.3%, respectively). However, 39.7% of the respondents were not satisfactory with a second-year resident assisting in their own surgery. Patients dissatisfied with their most recent orthopedic surgery were more likely to respond that they did not want residents helping with their surgery. Respondents agreed that resident or fellow involvement in surgery should be disclosed (92.2% and 90.1%, respectively). CONCLUSIONS: Insured and educated patients in the United States overwhelmingly desire disclosure of trainee involvement in their surgery. To address the need for orthopedic training in the context of a patient population that is not fully comfortable with trainee involvement in their own surgery, an open discussion between patients and surgeons regarding trainees' roles may be the best course of action.

Femoral Component External Rotation Affects Knee Biomechanics: A Computational Model of Posterior-stabilized TKA.

BACKGROUND: The correct amount of external rotation of the femoral component during TKA is controversial because the resulting changes in biomechanical knee function associated with varying degrees of femoral component rotation are not well understood. We addressed this question using a computational model, which allowed us to isolate the biomechanical impact of geometric factors including bony shapes, location of ligament insertions, and implant size across three different knees after posterior-stabilized (PS) TKA. QUESTIONS/PURPOSES: Using a computational model of the tibiofemoral joint, we asked: (1) Does external rotation unload the medial collateral ligament (MCL) and what is the effect on lateral collateral ligament tension? (2) How does external rotation alter tibiofemoral contact loads and kinematics? (3) Does 3° external rotation relative to the posterior condylar axis align the component to the surgical transepicondylar axis (sTEA) and what anatomic factors of the femoral condyle explain variations in maximum MCL tension among knees? METHODS: We incorporated a PS TKA into a previously developed computational knee model applied to three neutrally aligned, nonarthritic, male cadaveric knees. The computational knee model was previously shown to corroborate coupled motions and ligament loading patterns of the native knee through a range of flexion. Implant geometries were virtually installed using hip-to-ankle CT scans through measured resection and anterior referencing surgical techniques. Collateral ligament properties were standardized across each knee model by defining stiffness and slack lengths based on the healthy population. The femoral component was externally rotated from 0° to 9° relative to the posterior condylar axis in 3° increments. At each increment, the knee was flexed under 500 N compression from 0° to 90° simulating an intraoperative examination. The computational model predicted collateral ligament forces, compartmental contact forces, and tibiofemoral internal/external and varus-valgus rotation through the flexion range. RESULTS: The computational model predicted that femoral component external rotation relative to the posterior condylar axis unloads the MCL and the medial compartment; however, these effects were inconsistent from knee to knee. When the femoral component was externally rotated by 9° rather than 0° in knees one, two, and three, the maximum force carried by the MCL decreased a respective 55, 88, and 297 N; the medial contact forces decreased at most a respective 90, 190, and 570 N; external tibial rotation in early flexion increased by a respective 4.6°, 1.1°, and 3.3°; and varus angulation of the tibia relative to the femur in late flexion increased by 8.4°, 8.0°, and 7.9°, respectively. With 3° of femoral component external rotation relative to the posterior condylar axis, the femoral component was still externally rotated by up to 2.7° relative to the sTEA in these three neutrally aligned knees. Variations in MCL force from knee to knee with 3° of femoral component external rotation were related to the ratio of the distances from the femoral insertion of the MCL to the posterior and distal cuts of the implant; the closer this ratio was to 1, the more uniform were the MCL tensions from 0° to 90° flexion. CONCLUSIONS: A larger ratio of distances from the femoral insertion of the MCL to the posterior and distal cuts may cause clinically relevant increases in both MCL tension and compartmental contact forces. CLINICAL RELEVANCE: To obtain more consistent ligament tensions through flexion, it may be important to locate the posterior and distal aspects of the femoral component with respect to the proximal insertion of the MCL such that a ratio of 1 is achieved.

Posterior tibial slope impacts intraoperatively measured mid-flexion anteroposterior kinematics during cruciate-retaining total knee arthroplasty.

PURPOSE: Posterior tibial slope (PTS) for cruciate-retaining (CR) total knee arthroplasty (TKA) is usually pre-determined by the surgeon. Limited information is available comparing different choices of PTS on the kinematics of the CR TKA, independent of the balancing of the extension gap. This study hypothesized that with the same balanced extension gap, the choice of PTS significantly impacts the intraoperatively measured kinematics of CR TKA. METHODS: Navigated CR TKAs were performed on seven fresh-frozen cadavers with healthy knees and intact posterior cruciate ligament (PCL). A custom designed tibial baseplate was implanted to allow in situ modification of the PTS, which altered the flexion gap but maintained the extension gap. Knee kinematics were measured by performing passive range of motion (ROM) tests from full extension to 120° of flexion on the intact knee and CR TKAs with four different PTSs (1°, 4°, 7°, and 10°). The measured kinematics were compared across test conditions to assess the impact of PTS. RESULTS: With a consistent extension gap, the change of PTS had significant impact on the anteroposterior (AP) kinematics of the CR TKA knees in mid-flexion range (45°-90°), but not so much for the high-flexion range (90°-120°). No considerable impacts were found on internal/external (I/E) rotation and hip-knee-ankle (HKA) angle. However, the findings on the individual basis suggested the impact of PTS on I/E rotation and HKA angle may be patient-specific. CONCLUSIONS: The data suggested that the choice of PTS had the greatest impact on the mid-flexion AP translation among the intraoperatively measured kinematics. This impact may be considered while making surgical decisions in the context of AP kinematics. When using a tibial component designed with "center" pivoting PTS, a surgeon may be able to fine tune the PTS to achieve proper mid-flexion AP stability.

Rates and Risk Factors of Conversion Hip Arthroplasty After Closed Reduction Percutaneous Hip Pinning for Femoral Neck Fractures-A Population Analysis.

BACKGROUND: Closed reduction with percutaneous pinning (CRPP) for nondisplaced or valgus impacted femoral neck fractures is a relatively low-risk operation that can produce excellent union rates in some patients; however, failure can occur in selected patients requiring conversion to arthroplasty. The primary aim of this study was to perform a population-level analysis to determine the rate and timeframe of conversion from CRPP to total hip arthroplasty (THA) or hemiarthroplasty. METHODS: The PearlDiver database was queried from 2007-2015 for all patients who underwent CRPP for a femoral neck fracture. Survival analysis was used to evaluate the rate of conversion of CRPP to hemiarthroplasty or THA. Risk factors for conversion arthroplasty were identified using a multivariable cox proportional hazards model that included patient demographics and comorbidities. RESULTS: There were 5122 patients in the Humana database and 4840 patients in the Medicare database that were included in analysis. At 5 years after CRPP, the conversion rate was 10.0% in the Medicare patients and 10.8% in the Humana patients. Risk factors for undergoing conversion from CRPP to arthroplasty in the Medicare cohort included preexisting diagnoses of pulmonary and/or circulatory comorbidities, peripheral vascular disease, hypertension, hypothyroidism, and metastatic cancer. In the Humana cohort, the only risk factors were male gender and acute blood loss anemia. CONCLUSION: Although CRPP remains a successful operation in elderly patients and patients with certain comorbidities, failure of CRPP for the treatment of a femoral neck fracture is high at approximately 10%-11%, which is much higher than reported failure rates for THA in the same population. Patients with femoral neck fractures being considered for CRPP should be counseled about the possibility of further surgery.

Risk of Ischemic Stroke After Perioperative Atrial Fibrillation in Total Knee and Hip Arthroplasty Patients.

BACKGROUND: To determine if new-onset perioperative atrial fibrillation during arthroplasty represents a benign response to intraoperative cardiac stress or is a risk factor for stroke, we evaluated the subsequent risk of ischemic stroke in patients with new-onset atrial fibrillation occurring during primary total knee arthroplasty (TKA) and total hip arthroplasty (THA). METHODS: Discharge data of all adult patients undergoing primary TKA or THA from 1997 to 2013 were queried via the New York Statewide Planning and Research Cooperative System database to find patients with new-onset perioperative atrial fibrillation. These patients were then followed up over time to determine their risk of ischemic stroke. RESULTS: Of the 312,636 TKA and 215,610 THA unique patient admissions, 3646 (0.7%) had a diagnosis of new-onset perioperative atrial fibrillation. The cohort of patients with this finding was 58.9% female with an average age of 73.6 years and higher prevalence of vascular risk factors. Adjusting for validated stroke risk factors, the risk of ischemic stroke within 1 year after THA or TKA in patients with new-onset atrial fibrillation was 2.7 times higher than in those without a history of atrial fibrillation (odds ratio: 2.7, 95% confidence interval: 1.5-4.8). Hospital length of stay and charges for patients with new-onset atrial fibrillation were also greater than patients with either a prior diagnosis or no diagnosis of atrial fibrillation. CONCLUSION: New-onset atrial fibrillation during TKA and THA may indicate risk of ischemic stroke following surgery that should warrant medical follow-up and may increase hospital length of stay and charges.

Readability of Patient Education Materials From the Web Sites of Orthopedic Implant Manufacturers.

BACKGROUND: Prior studies indicate that orthopedic patient education materials are written at a level that is too high for the average patient. The purpose of this study was to assess the readability of online patient education materials provided by orthopedic implant manufacturers. METHODS: All patient education articles available in 2013 from the web sites of the 5 largest orthopedic implant manufacturers were identified. Each article was evaluated with the Flesch-Kincaid (FK) readability test. The number of articles with readability ≤ the eighth-grade level (average reading ability of US adults) and the sixth-grade level (recommended level for patient education materials) was determined. Mean readability levels of each company's articles were compared using analysis of variance (significance set at P < .05). RESULTS: A total of 581 articles were reviewed from the 5 largest implant manufacturers. The mean overall FK grade level was 10.9 (range, 3.8-16.1). Only 58 articles (10%) were written ≤ the eighth-grade level, and only 13 (2.2%) were ≤ the sixth-grade level. The mean FK grade level was significantly different among groups (Smith & Nephew = 12.0, Stryker = 11.6, Biomet = 11.3, DePuy = 10.6, Zimmer = 10.1; P < .0001). CONCLUSION: The majority of patient education materials from implant manufacturers are written at a level too high to be comprehended by the average patient. Future efforts should be made to improve the readability of orthopedic patient education materials.

Quantifying Pelvic Motion During Total Hip Arthroplasty Using a New Surgical Navigation Device.

BACKGROUND: Accurate cup positioning is one of the most challenging aspects of total hip arthroplasty (THA). Undetected movement of the patient during THA surgery can lead to inaccuracies in cup anteversion and inclination, increasing the potential for dislocation and revision surgery. Investigations into the magnitude of patient motion during THA are not well represented in the literature. METHODS: We analyzed intraoperative pelvic motion using a novel navigation device used to assist surgeons with cup position, leg length, and offset during THA. This device uses an integrated accelerometer to measure motion in 2 orthogonal degrees of freedom. We reviewed the data from 99 cases completed between February and September 2016. RESULTS: The mean amount of pitch recorded per patient was 2.7° (standard deviation, 2.2; range, 0.1°-9.9°), whereas mean roll per patient was 7.3° (standard deviation, 5.5; range, 0.3°-31.3°). Twenty-one percent (21 of 99) of patients demonstrated pitch of >4°. Sixty-nine percent (68 of 99) of patients demonstrated >4° of roll, and 25% (25 of 99) of patients demonstrated roll of ≥10°. CONCLUSION: Our findings indicate that while the majority of intraoperative motion is <4°, many patients experience significant roll, with a large proportion rolling >10°. This degree of movement has implications for acetabular cup position, as failure to compensate for this motion can result in placement of the cup outside the planned safe zone, thus, increasing the potential for dislocation. Further study is warranted to determine the effect of this motion on cup position, leg length, and offset.