Compliant Intramedullary Stems for Joint Reconstruction.

The longevity of current joint replacements is limited by aseptic loosening, which is the primary cause of non-infectious failure for hip, knee, and ankle arthroplasty. Aseptic loosening is typically caused either by osteolysis from particulate wear, or by high shear stresses at the bone-implant interface from over-constraint. Our objective was to demonstrate feasibility of a compliant intramedullary stem that eliminates over-constraint without generating particulate wear. The compliant stem is built around a compliant mechanism that permits rotation about a single axis. We first established several models to understand the relationship between mechanism geometry and implant performance under a given angular displacement and compressive load. We then used a neural network to identify a design space of geometries that would support an expected 100-year fatigue life inside the body. We additively manufactured one representative mechanism for each of three anatomic locations, and evaluated these prototypes on a KR-210 robot. The neural network predicts maximum stress and torsional stiffness with 2.69% and 4.08% error respectively, relative to finite element analysis data. We identified feasible design spaces for all three of the anatomic locations. Simulated peak stresses for the three stem prototypes were below the fatigue limit. Benchtop performance of all three prototypes was within design specifications. Our results demonstrate the feasibility of designing patient- and joint-specific compliant stems that address the root causes of aseptic loosening. Guided by these results, we expect the use of compliant intramedullary stems in joint reconstruction technology to increase implant lifetime.

Racial Disparities in Rates of Revision and use of Modern Features in Total Knee Arthroplasty, a National Registry Study.

BACKGROUND: The purpose of our study was to investigate the association of race and ethnicity with rates of modern implant use and postoperative outcomes in total knee arthroplasty (TKA) using the American Academy of Orthopaedic Surgeons American Joint Replacement Registry. METHODS: Adult TKAs from 2012 to 2020 were queried from the American Joint Replacement Registry. A total of 1,121,457 patients were available for analysis for surgical features and 1,068,210 patients for analysis of outcomes. Mixed-effects multivariable logistic regression models were used to examine the association of race with each individual surgical feature (unicompartmental knee arthroplasty (UKA) and robotic-assisted TKA (RA-TKA)) and 30- and 90-day readmission. A proportional subdistribution hazard model was used to model the risk of revision TKA. RESULTS: On multivariate analyses, compared to White patients, Black (odds ratio (OR): 0.52 P < .0001), Hispanic (OR 0.75 P < .001), and Native American (OR: 0.69 P = .0011) patients had lower rates of UKA, while only Black patients had lower rates of RA-TKA (OR = 0.76 P < .001). White (hazard ratio (HR) = 0.8, P < .001), Asian (HR = 0.51, P < .001), and Hispanic-White (HR = 0.73, P = .001) patients had a lower risk of revision TKA than Black patients. Asian patients had a lower revision risk than White (HR = 0.64, P < .001) and Hispanic-White (HR = 0.69, P = .011) patients. No significant differences existed between groups for 30- or 90-day readmissions. CONCLUSION: Black, Hispanic, and Native American patients had lower rates of UKA compared to White patients, while Black patients had lower rates of RA-TKA compared to White, Asian, and Hispanic patients. Black patients also had higher rates of revision TKA than other races.

Lower Rates of Ceramic Femoral Head Use in Non-White Patients in the United States, a National Registry Study.

BACKGROUND: The purpose of our study was to investigate the association of race and ethnicity with the use of the newest technology and postoperative outcomes in total hip arthroplasty (THA) using the American Academy of Orthopaedic Surgeons (AAOS) American Joint Replacement Registry (AJRR). METHODS: Adult THA procedures were queried from the AJRR from 2012 to 2020. A mixed-effects multivariate regression model was used to evaluate the association of race and ethnicity with the use of the newest technology (ceramic femoral head, dual-mobility implant, and robotic assist) at 30-day, and 90-day readmission. A proportional subdistribution hazard model was used to model a risk of revision THA. RESULTS: There were 85,188 THAs with complete data for an analysis of outcomes and 103,218 for an analysis of ceramic head usage. The median length of follow-up was 37.9 months (interquartile range [IQR] 21.6 to 56.3 months). In multivariate models, compared to White non-Hispanic patients, Black (odds ratio [OR] 0.79, 95% confidence interval [CI] 0.69-0.92, P < .001), Hispanic (OR 0.76, CI 0.59-0.99, P = .037), Asian (OR 0.74, CI 0.55-1.00, P = .045), and Native American (OR 0.52, CI 0.30-0.87, P = .004) patients all had significantly lower rates of ceramic head use in THA. Compared to White non-Hispanic patients, Asian (hazard ratio [HR] 0.39, CI 0.18-0.86, P = .008) and Hispanic (HR 0.43, CI 0.19-0.98, P = .043) patients had significantly lower rates of revision. No differences in 30-day or 90-day readmission rates were seen. CONCLUSION: Black, Hispanic, Native American, and Asian patients had lower rates of ceramic head use in THA when compared to White patients. These differences did not translate into worse clinical outcomes on a short-term follow-up. In fact, Asian patients had lower revision rates compared to non-Hispanic White patients. Additional study is necessary to evaluate the long-term consequence of lower ceramic head use in non-White patients in the United States.

Utilization trends and outcomes of computer-assisted navigation in spine fusion in the United States.

BACKGROUND CONTEXT: Computer-assisted navigation (CAN) has emerged in spine surgery as an approach to improve patient outcomes. While there is substantial evidence demonstrating improved pedicle screw accuracy in CAN as compared to conventional spinal fusion (CONV), there is limited data regarding clinical outcomes and utilization trends in the United States. PURPOSE: The purpose of this study was to determine the utilization rates of CAN in the United States, identify patient and hospital trends associated with both techniques, and to compare their results. STUDY DESIGN: Retrospective review of national database. PATIENT SAMPLE: Nationwide Inpatient Sample (NIS), United States national database. OUTCOME MEASURES: CAN utilization, mortality, medical complications, neurologic complications, discharge destination, length of hospital stay, cost of hospital stay. METHODS: The NIS database was queried to identify patients undergoing spinal fusion with CAN or CONV. CAN and CONV utilization were tracked by year and anatomic location (cervical, thoracic, lumbar/lumbosacral). Patient demographics, hospital characteristics, index length of stay (LOS), and cost of stay (COS) were compared between the cohorts. After multivariate adjustment, index hospitalization clinical outcomes were compared. RESULTS: A total of 4,275,413 patients underwent spinal fusion surgery during the study period (2004 to 2014). CONV was performed in 98.4% (4,208,068) of cases and CAN was performed in 1.6% (67,345) of cases. The utilization rate of CAN increased from 0.04% in 2004 to 3.3% in 2014. Overall, CAN was performed most commonly in the lumbar/lumbosacral region (70.4%) compared to the cervical (20.4%) or thoracic (9.2%) regions. When normalized to region-specific rates of fusion with any technique, the proportional utilization of CAN was highest in the thoracic spine (2.7%), followed by the lumbar/lumbosacral (2.2%) and cervical (0.9%) regions. CAN utilization was positively correlated with patient factors including increasing age and number of medical comorbidities. Multivariate adjusted clinical outcomes demonstrated that compared to CONV, CAN was associated with a statistically significant decreased risk of mortality (0.28% vs 0.31%, OR=0.67, 95% CI: 0.46-0.97, p=.035) and increased risk of blood transfusions (9.1% vs 6.7%, OR=1.19, 95% CI: 1.02-1.39, p=.032). However, there was no difference in risk of neurologic complications. CAN patients had an increased average LOS (4.44 days vs. 3.97 days, p<.0001) and average COS ($34,669.49 vs $26,784.62, p<.0001) compared to CONV patients. CONCLUSIONS: CAN utilization increased in the United States from 2004-2014. Use of CAN was proportionately higher in the thoracic and lumbar/lumbosacral regions and in older patients with more comorbidities. Given the continued trend towards increased CAN utilization, large-scale studies are needed to determine the impact of this technology on long-term clinical outcomes.

Community transmission of type 2 poliovirus after cessation of trivalent oral polio vaccine in Bangladesh: an open-label cluster-randomised trial and modelling study.

BACKGROUND: Trivalent oral polio vaccine (tOPV) was replaced worldwide from April, 2016, by bivalent types 1 and 3 oral polio vaccine (bOPV) and one dose of inactivated polio vaccine (IPV) where available. The risk of transmission of type 2 poliovirus or Sabin 2 virus on re-introduction or resurgence of type 2 poliovirus after this switch is not understood completely. We aimed to assess the risk of Sabin 2 transmission after a polio vaccination campaign with a monovalent type 2 oral polio vaccine (mOPV2). METHODS: We did an open-label cluster-randomised trial in villages in the Matlab region of Bangladesh. We randomly allocated villages (clusters) to either: tOPV at age 6 weeks, 10 weeks, and 14 weeks; or bOPV at age 6 weeks, 10 weeks, and 14 weeks and either one dose of IPV at age 14 weeks or two doses of IPV at age 14 weeks and 18 weeks. After completion of enrolment, we implemented an mOPV2 vaccination campaign that targeted 40% of children younger than 5 years, regardless of enrolment status. The primary outcome was Sabin 2 incidence in the 10 weeks after the campaign in per-protocol infants who did not receive mOPV2, as assessed by faecal shedding of Sabin 2 by reverse transcriptase quantitative PCR (RT-qPCR). The effect of previous immunity on incidence was also investigated with a dynamical model of poliovirus transmission to observe prevalence and incidence of Sabin 2 virus. This trial is registered at ClinicalTrials.gov, number NCT02477046. FINDINGS: Between April 30, 2015, and Jan 14, 2016, individuals from 67 villages were enrolled to the study. 22 villages (300 infants) were randomly assigned tOPV, 23 villages (310 infants) were allocated bOPV and one dose of IPV, and 22 villages (329 infants) were assigned bOPV and two doses of IPV. Faecal shedding of Sabin 2 in infants who did not receive the mOPV2 challenge did not differ between children immunised with bOPV and one or two doses of IPV and those who received tOPV (15 of 252 [6%] vs six of 122 [4%]; odds ratio [OR] 1·29, 95% CI 0·45-3·72; p=0·310). However, faecal shedding of Sabin 2 in household contacts was increased significantly with bOPV and one or two doses of IPV compared with tOPV (17 of 751 [2%] vs three of 353 [1%]; OR 3·60, 95% CI 0·82-15·9; p=0·045). Dynamical modelling of within-household incidence showed that immunity in household contacts limited transmission. INTERPRETATION: In this study, simulating 1 year of tOPV cessation, Sabin 2 transmission was higher in household contacts of mOPV2 recipients in villages receiving bOPV and either one or two doses of IPV, but transmission was not increased in the community as a whole as shown by the non-significant difference in incidence among infants. Dynamical modelling indicates that transmission risk will be higher with more time since cessation. FUNDING: Bill & Melinda Gates Foundation.

Analysis of vaccination campaign effectiveness and population immunity to support and sustain polio elimination in Nigeria.

BACKGROUND: The world is closer than ever to a polio-free Africa. In this end-stage, it is important to ensure high levels of population immunity to prevent polio outbreaks. Here, we introduce a new method of assessing vaccination campaign effectiveness and estimating immunity at the district-level. We demonstrate how this approach can be used to plan the vaccination campaigns prospectively to better manage population immunity in Northern Nigeria. METHODS: Using Nigerian acute flaccid paralysis surveillance data from 2004-2014, we developed a Bayesian hierarchical model of campaign effectiveness and compared it to lot-quality assurance sampling data. We then used reconstructed sero-specific population immunity based on campaign history and compared district estimates of immunity to the occurrence of confirmed poliovirus cases. RESULTS: Estimated campaign effectiveness has improved across northern Nigeria since 2004, with Kano state experiencing an increase of 40 % (95 % CI, 26-54 %) in effectiveness from 2013 to 2014. Immunity to type 1 poliovirus has increased steadily. On the other hand, type 2 immunity was low and variable until the recent use of trivalent oral polio vaccine. We find that immunity estimates are related to the occurrence of both wild and vaccine-derived poliovirus cases and that campaign effectiveness correlates with direct measurements using lot-quality assurance sampling. Future campaign schedules highlight the trade-offs involved with using different vaccine types. CONCLUSIONS: The model in this study provides a novel method for assessing vaccination campaign performance and epidemiologically-relevant estimates of population immunity. Small-area estimates of campaign effectiveness can then be used to evaluate prospective campaign plans. This modeling approach could be applied to other countries as well as other vaccine preventable diseases.

Quantifying the impact of expanded age group campaigns for polio eradication.

A priority of the Global Polio Eradication Initiative (GPEI) 2013-2018 strategic plan is to evaluate the potential impact on polio eradication resulting from expanding one or more Supplementary Immunization Activities (SIAs) to children beyond age five-years in polio endemic countries. It has been hypothesized that such expanded age group (EAG) campaigns could accelerate polio eradication by eliminating immunity gaps in older children that may have resulted from past periods of low vaccination coverage. Using an individual-based mathematical model, we quantified the impact of EAG campaigns in terms of probability of elimination, reduction in polio transmission and age stratified immunity levels. The model was specifically calibrated to seroprevalence data from a polio-endemic region: Zaria, Nigeria. We compared the impact of EAG campaigns, which depend only on age, to more targeted interventions which focus on reaching missed populations. We found that EAG campaigns would not significantly improve prospects for polio eradication; the probability of elimination increased by 8% (from 24% at baseline to 32%) when expanding three annual SIAs to 5-14 year old children and by 18% when expanding all six annual SIAs. In contrast, expanding only two of the annual SIAs to target hard-to-reach populations at modest vaccination coverage-representing less than one tenth of additional vaccinations required for the six SIA EAG scenario-increased the probability of elimination by 55%. Implementation of EAG campaigns in polio endemic regions would not improve prospects for eradication. In endemic areas, vaccination campaigns which do not target missed populations will not benefit polio eradication efforts.

Predictive spatial risk model of poliovirus to aid prioritization and hasten eradication in Nigeria.

BACKGROUND: One of the challenges facing the Global Polio Eradication Initiative is efficiently directing limited resources, such as specially trained personnel, community outreach activities, and satellite vaccinator tracking, to the most at-risk areas to maximize the impact of interventions. A validated predictive model of wild poliovirus circulation would greatly inform prioritization efforts by accurately forecasting areas at greatest risk, thus enabling the greatest effect of program interventions. METHODS: Using Nigerian acute flaccid paralysis surveillance data from 2004-2013, we developed a spatial hierarchical Poisson hurdle model fitted within a Bayesian framework to study historical polio caseload patterns and forecast future circulation of type 1 and 3 wild poliovirus within districts in Nigeria. A Bayesian temporal smoothing model was applied to address data sparsity underlying estimates of covariates at the district level. RESULTS: We find that calculated vaccine-derived population immunity is significantly negatively associated with the probability and number of wild poliovirus case(s) within a district. Recent case information is significantly positively associated with probability of a case, but not the number of cases. We used lagged indicators and coefficients from the fitted models to forecast reported cases in the subsequent six-month periods. Over the past three years, the average predictive ability is 86 ± 2% and 85 ± 4% for wild poliovirus type 1 and 3, respectively. Interestingly, the predictive accuracy of historical transmission patterns alone is equivalent (86 ± 2% and 84 ± 4% for type 1 and 3, respectively). We calculate uncertainty in risk ranking to inform assessments of changes in rank between time periods. CONCLUSIONS: The model developed in this study successfully predicts districts at risk for future wild poliovirus cases in Nigeria. The highest predicted district risk was 12.8 WPV1 cases in 2006, while the lowest district risk was 0.001 WPV1 cases in 2013. Model results have been used to direct the allocation of many different interventions, including political and religious advocacy visits. This modeling approach could be applied to other vaccine preventable diseases for use in other control and elimination programs.