Mid-term results of an anatomic total knee replacement design.

INTRODUCTION: A significant proportion of patients remain dissatisfied following total knee arthroplasty (TKA) surgery. Reasons for this are unclear. Contemporary implants seek to mirror innate anatomy. Such innovations are necessarily subject to scrutiny to validate their use. The Zimmer-Biomet Persona® Personalized Knee system is such an anatomic TKA. This work seeks to establish medium term survival data and patient reported outcomes for this implant. METHODS: This was a cohort study of prospectively collected data on all patients undergoing Persona TKA at our institution. Patients were managed using a standardised protocol for intra- and post-operative care. Survivorship data were collected using our National Joint Registry and corroborated with local data. Range of motion, Oxford Knee Score (OKS) and patient satisfaction were recorded at six weeks and one year post-operatively. Hip-knee-ankle radiographs were used to record pre- and post-operative alignment. RESULTS: Data were collected for 749 knees in 679 patients. Overall survivorship was 99.0% at a mean 5.35 years, with seven patients undergoing revision surgery during the study period. Significant improvements in the OKS (mean 20.7 points) and range of motion were observed (mean 104.6° at one year). 94.9% of patients were satisfied at one year. Mean correction was to a mechanical femoro-tibial angle of 0.8° varus. CONCLUSIONS: We demonstrate excellent medium term survival of the Persona TKA in this large cohort, coupled with improvements in patient reported outcomes, range of motion and patient satisfaction at one year which compare favourably to other implants.

Is the mechanical function of meniscal tissue altered in osteoarthritic knees?

BACKGROUND: Deteriorating meniscal function is thought to play a role in knee osteoarthritis. Meniscal proteoglycans maintain mechanical stiffness of the tissue through electrostatic effects. This study aimed to investigate whether the mechanical properties of macroscopically intact meniscus are preserved in osteoarthritis. METHODS: Discs of lateral meniscal tissue two millimetres thick and of five millimetres diameter from osteoarthritic knees and from healthy donors were placed within a confined compression chamber, mounted in a materials testing machine and bathed in isotonic 0.14M PBS, hypotonic deionised water or hypertonic 3M PBS. Following equilibrium, a 10% ramp compressive strain was applied followed by a 7200 second hold. Resultant stress relaxation curves were fitted to a nonlinear poroviscoelastic model with strain dependent permeability using finite element modelling to determine mechanical parameters. All samples were assayed for proteoglycan content. Comparison of results was undertaken using multivariate ANOVA. RESULTS: Thirty samples from osteoarthritic knees and 18 samples from healthy donors were tested. No significant differences in mechanical parameters or proteoglycan content was observed between groups. In both groups Young's modulus (E) was significantly greater, and zero-strain permeability significantly reduced, in samples tested in deionised water compared to samples tested in 0.14M or 3M PBS (all p < 0.05). CONCLUSION: Mechanical parameters of intact lateral meniscus in osteoarthritic knees are similar to those found in healthy knees. Proteoglycan concentration and their electrostatic contribution to mechanical stiffness of the meniscus is maintained in menisci derived from osteoarthritic knees. Whilst macroscopic tears in the meniscal ultrastructure may contribute to osteoarthritis, intact meniscal tissue maintains its function.

Perioperative air travel increases the risk of venous thromboembolism following lower limb arthroplasty.

PURPOSE: Venous thromboembolism (VTE) is a significant complication following lower limb arthroplasty (LLA). There is a paucity of evidence with regard to air travel following LLA. Orthopaedic surgeons are often asked by patients regarding air travel following LLA, and there is a need for evidence to guide these patients. METHODS: This was a retrospective cohort study. We identified two cohorts, one travelling to and from the hospital by air and another, by land. All patients received routine preoperative and post-operative care, and thromboprophylaxis, as per our hospital guidelines. We collected baseline demographics, ASA score and incidence of VTE at 90 days using local patient records and a national joint registry. We also recorded data on flight time and overland distance of travel. RESULTS: Two hundred and forty-three patients travelled by air; mean flight time was 74 min. In total, 5498 patients travelled a mean 25.3 miles over land to the hospital. No differences in baseline demographics or ASA score were observed. Four patients developed a VTE in the flight group, with 32 patients suffering a VTE in the control group. There was a significant difference in the VTE rate between the flight and control groups (p < 0.05); the relative risk of developing a VTE in the flight group was 2.85. CONCLUSIONS: In our cohort, perioperative short haul air travel is associated with an increased risk of VTE at 90 days following LLA. Orthopaedic surgeons must ensure that their patients are cognizant of the risks associated with perioperative air travel and take measures to minimise these risks.

Survivorship and Patient-Reported Outcomes of an Uncemented Vitamin E-Infused Monoblock Acetabular Cup: A Multicenter Prospective Cohort Study.

BACKGROUND: Addition of vitamin E to polyethylene is theorized to reduce the potential for oxidative wear in acetabular components. This paper presents a multicenter prospective cohort study that reports on outcomes from use of a Vitamin E-infused highly cross-linked polyethylene acetabular cup. METHODS: Patients were recruited across nine medical institutions. Clinical outcome measures recorded were the Harris Hip Score, visual analogue score for pain and satisfaction. Evidence of implant loosening or osteolysis was collected radiologically. Cup survival and reasons for revision in relevant cases were also recorded. Data collection was undertaken preoperatively, at 6-12 weeks, 6 months, 1 year, 2 years, and 5 years. A total of 675 patients were recruited, with 450 cases available at final review. Data regarding cup survival was available to 8 years and 9 months postoperatively. RESULTS: Improvements in both the Harris Hip Score and visual analogue score for pain and satisfaction were recorded at all time points, with these being maintained through the length of follow-up. In total, 89% of cups were implanted within the Lewinnek safe zone. A lucent line was identified in one case, with no evidence of acetabular osteolysis observed throughout the follow-up period. Cup survival was 98.9% at 8 years and 9 months. No revisions for aseptic loosening were observed. CONCLUSIONS: The use of a vitamin E-infused polyethylene acetabular cup demonstrates reassuring patient-reported outcomes, radiological measures, and cup survival at medium to long-term follow-up.

A new landmark for measuring tibial component rotation after total knee arthroplasty.

BACKGROUND: Existing methods for assessment of total knee arthroplasty (TKA) component rotation on computed tomography (CT) scans are complex, especially in relation to the tibial component. Anecdotal evidence from our practice pointed towards a potential new landmark. The study aims were to check the prevalence of this landmark, define tibial component rotation in relation to it and demonstrate its reliability. METHODS: Two hundred and eleven CTs undertaken following TKA were reviewed for presence of the landmark. A protocol to measure tibial component rotation in relation to this landmark was developed and the rotation measured using this method and Berger's protocol. Thirty one of the 211 CT scans were measured twice by two observers. Reliability was calculated using the Intraclass Correlation Coefficient (ICC). RESULTS: The new landmark of a flat area on the lateral cortex of the tibia inferior to the tibial component was identified on all scans. Median tibial component rotation measured using our protocol was 0.0°â€¯±â€¯5.4° and -9.2°â€¯±â€¯5.5° using Berger's protocol. Intra-observer reliability with the new method was excellent (ICCs of 0.899 and 0.871) and inter-observer reliability was good (ICCs of 0.734 and 0.836). CONCLUSIONS: The new landmark had a very high prevalence and could be used to define tibial component rotation. This measurement of tibial component rotation had acceptable reliability. This landmark has potential for use in the radiological assessment of tibial component rotation following TKA. Further work is required to determine its relationship to anatomical structures and symptoms of tibial component mal-rotation.

The ionic contribution of proteoglycans to mechanical stiffness of the meniscus.

Load transmission is an important function of the meniscus. In articular cartilage, proteoglycans help maintain hydration via negatively charged moieties. We aimed to investigate the influence of electrostatic effects on stiffness of meniscal tissue. Circular discs from bovine menisci of 8 mm diameter and 5 mm thickness were placed within a confined compression chamber. The apparatus was bathed in distilled water, 0.14 M PBS or 3 M PBS before being subjected to 5% ramp compressive strain and held for 300s. FEBio software was used to fit resultant relaxation curves to a non-linear poroviscoelastic model with strain dependent Holmes-Mow permeability. Analysis was conducted using one-way ANOVA with Tukey post-hoc analysis. 10 samples were tested in each solution. Significant differences (p < 0.05) were observed between the values for Young's modulus, zero strain dependent permeability and the viscoelastic coefficient for samples tested in 3 M PBS as compared to deionised water/0.14 M PBS. No significant differences were observed in the strain dependent/stiffening coefficients or the relaxation time. Approximately 79% of the stiffness of the meniscus appears attributable to ionic effects. Ionic effects play a significant role in the mechanical stiffness of the meniscus. It is important to include the influence of ionic effects when developing mathematical models of this tissue.

Risk Factors for Surgical Site Infection Following Lower Limb Arthroplasty: A Retrospective Cohort Analysis of 3932 Lower Limb Arthroplasty Procedures in a High Volume Arthroplasty Unit.

BACKGROUND: Surgical site infection (SSI) is a debilitating complication of lower limb arthroplasty with significant morbidity and increased costs. Numerous risk factors are associated with SSI. METHODS: In an effort to identify novel risk factors for SSI, we undertook a retrospective cohort study of 1832 primary total hip arthroplasties and 2100 primary total knee arthroplasties performed in our high volume arthroplasty unit over a 2-year period. RESULTS: Two risk factors were identified for SSI following total hip arthroplasty: body mass index ≥30 and peri-operative blood transfusion. Eight risk factors were identified for SSI following total knee arthroplasty: hypertension, peri-operative blood transfusion, skin closure using 2-octyl cyanoacrylate, use of oral steroids, reduced serum mean cell volume, reduced mean cell hemoglobin, elevated serum neutrophil count, and use of warfarin or rivaroxaban for venous thromboembolism prophylaxis. CONCLUSIONS: Our work proposes a number of previously undocumented risk factors in relation to SSI. Further investigation is required to ascertain the magnitude of their effect.

Non-pharmacological interventions for caregivers of stroke survivors.

BACKGROUND: A substantial component of care is provided to stroke survivors by informal caregivers. However, providing such care is often a new and challenging experience and has been linked to a number of adverse outcomes. A range of interventions targeted towards stroke survivors and their family or other informal caregivers have been tested in randomised controlled trials (RCTs).  OBJECTIVES: To evaluate the effect of interventions targeted towards informal caregivers of stroke survivors or targeted towards informal caregivers and the care recipient (the stroke survivor). SEARCH STRATEGY: We searched the Cochrane Stroke Group Trials Register (March 2011), CENTRAL (The Cochrane Library Issue 2010, Issue 4), MEDLINE (1950 to August 2010), EMBASE (1980 to December 2010), CINAHL (1982 to August 2010), AMED (1985 to August 2010), PsycINFO (1967 to August 2010) and 11 additional databases. In an effort to identify further published, unpublished and ongoing studies, we searched conference proceedings and trials registers, scanned reference lists of relevant articles and contacted authors and researchers. There were no language restrictions. SELECTION CRITERIA: We included RCTs if they evaluated the effect of non-pharmacological interventions (compared with no care or routine care) on informal caregivers of stroke survivors. We included trials of interventions delivered to stroke survivors and informal caregivers only if the stroke survivor and informal caregiver were randomised as a dyad. We excluded studies which included stroke survivors and caregivers if the stroke survivors were the primary target of the intervention. DATA COLLECTION AND ANALYSIS: Two review authors selected studies for inclusion, independently extracted data and assessed methodological quality. We sought original data from trialists. We categorised interventions into three groups: support and information, teaching procedural knowledge/vocational training type interventions, and psycho-educational type interventions. The primary outcome was caregivers' stress or strain. We resolved disagreements by consensus. MAIN RESULTS: Eight studies, including a total of 1007 participants, met our inclusion criteria. We did not pool the results of all the studies because of substantial methodological, statistical and clinical heterogeneity. For caregivers' stress or strain we found no significant results within categories of intervention, with the exception of one single-centre study examining the effects of a 'vocational training' type intervention which found a mean difference between the intervention and comparator group at the end of scheduled follow-up of -8.67 (95% confidence interval -11.30 to -6.04, P < 0.001) in favour of the 'teaching procedural knowledge' type intervention group. AUTHORS' CONCLUSIONS: It was not possible to carry out a meta-analysis of the evidence from RCTs because of methodological, clinical and statistical heterogeneity. One limitation across all studies was the lack of a description of important characteristics that define the informal caregiver population. However, 'vocational educational' type interventions delivered to caregivers prior to the stroke survivor's discharge from hospital appear to be the most promising intervention. However, this is based on the results from one, small, single-centre study.  

Generation of histo-anatomically representative models of the individual heart: tools and application.

This paper presents methods to build histo-anatomically detailed individualized cardiac models. The models are based on high-resolution three-dimensional anatomical and/or diffusion tensor magnetic resonance images, combined with serial histological sectioning data, and are used to investigate individualized cardiac function. The current state of the art is reviewed, and its limitations are discussed. We assess the challenges associated with the generation of histo-anatomically representative individualized in silico models of the heart. The entire processing pipeline including image acquisition, image processing, mesh generation, model set-up and execution of computer simulations, and the underlying methods are described. The multifaceted challenges associated with these goals are highlighted, suitable solutions are proposed, and an important application of developed high-resolution structure-function models in elucidating the effect of individual structural heterogeneity upon wavefront dynamics is demonstrated.