Incremental costs of fragility fractures: a population-based matched -cohort study from Ontario, Canada.

Using a matched cohort design, the 1-year excess cost of incident fragility fractures at any site was $26,341 per patient, with 43% of total excess costs attributed to hospitalization. The high economic burden of fractures in Ontario underscores the urgency of closing the secondary fracture prevention gap. INTRODUCTION: This retrospective real-world observational study was conducted to document the incremental costs associated with fragility fractures in Ontario, Canada. METHODS: Patients aged >65 years with an index fragility fracture occurring between January 2011 and March 2015 were identified from administrative databases and matched 1:1 to a cohort of similar patients without a fracture. Healthcare resource utilization data were extracted from healthcare records and associated costs were calculated on a per-patient level and for the province of Ontario. Costs were presented as 2017 Canadian dollars. RESULTS: The eligible cohort included 115,776 patients with a fragility fracture. Of these, 101,773 patients were successfully matched 1:1 to a non-fracture cohort. Overall, hip fractures (n = 31,613) were the most common, whereas femur fractures (n = 3002) were the least common type. Hospitalization and continuing care/home care/long-term care accounted for more than 60% of 1-year direct costs, whereas 5% was attributed to medication costs. First-year costs per patient in the fracture cohort were approximately threefold higher versus the non-fracture cohort (mean $37,362 versus $11,020, respectively). The incremental first-year direct healthcare costs of fragility fractures for the province of Ontario were calculated at $724 million per year. CONCLUSIONS: Fragility fractures were associated with a threefold increase in overall mean healthcare costs per patient compared to patients without fractures. With an aging population, there is an urgent need for improved prevention strategies for patients at high-risk of fracture to decrease the economic burden of fragility fractures on the Canadian healthcare system.

Understanding why people do or do not engage in activities following total joint replacement: a longitudinal qualitative study.

OBJECTIVE: Numerous studies report large and significant improvements in basic mobility and activities of daily living following total hip or knee replacement (TJR). Nevertheless, quantitative research has shown minimal increase in participation in activities that benefit overall health. This study explored why people do or do not engage in activities following hip or knee TJR. METHOD: This was a longitudinal qualitative study. Sampling was guided by constructivist grounded theory and data collected using open-ended, semi-structured interviews. Participants were recruited using maximum variation sampling based on age, sex and joint replaced (hip or knee). Data were analysed using a constant comparative approach and coded for thematic patterns and relationships from which overarching themes were constructed. RESULTS: Twenty-nine patients participated in interviews prior to, and 8 and 18 months post following TJR. A high degree of variability with regard to participants' return to activities was found and five emergent themes were identified that accounted for this variability. These themes highlight the importance of issues beyond medical factors alone, such as socio-cultural factors that partially determine participants' participation in activity following TJR. CONCLUSION: Findings suggest that multi-faceted experiences impact participation in activity following TJR. These experiences include changes in identity and lifestyle that preclude a 'return to normal'. There is an urgent need for supports to increase people's activity post-TJR in order to facilitate enhancement of post-surgery levels of engagement. Approaches that take into consideration more personalized interventions may be critical to promoting healthy aging in people with TJR.

Co-morbidities in elderly patients with hip fracture: recommendations of the ISFR-IOF hip fracture outcomes working group.

INTRODUCTION: Hip fractures are the second leading cause of hospitalization in the aged and by 2041, epidemiologists forecast an increase in economic cost to $2.4 billion. The hip patient population often presents with comorbidities causing these patients to receive less aggressive medical treatment and have a low quality of life. We believe that physical function is a patient-important outcome for many medical and surgical interventions. The functional co-morbidity index (FCI), unlike prior co-morbidity indices, was developed with physical function as an outcome instead of being designed for administrative purposes or to predict mortality. Our objective was to evaluate the perceptions of practitioners in hip fracture care about the impact of comorbidities on physical function as primary outcome. METHODS: We piloted and then distributed a self-administered survey to members of the International Society for Fracture Repair hip fracture outcomes working group. For each of the 18 diagnoses included in the FCI index, we asked in our survey whether the presence of the co-morbidity and whether the severity of the co-morbidity was perceived to impact physical function in patients following a hip fracture. RESULTS: Seventeen out of 20 respondents completed the questionnaire. The presence and severity of arthritis was 'strongly' believed to predict physical function in those with hip fracture (69 and 85.7 %, respectively). Respondents 'agreed' (range 53-73 %) that 10/18 diagnoses would predict changes in physical function following hip fracture treatment. Whereas, 63 % of the practitioners'strongly disagreed' that diabetes types I and II would change physical function scores. Furthermore, dementia was listed as an additional diagnosis that would affect physical function. CONCLUSION: The FCI may provide a useful instrument to predict functional outcome after hip fracture; however, the index may need to be modified for this specific population.

Understanding osteoporosis and fractures: an introduction to the use of qualitative research.

BACKGROUND: Qualitative research has been recognized in recent years as a field of inquiry used to understand people's beliefs, attitudes, behaviors, culture or lifestyle. While quantitative results are challenging to apply in everyday practice, the qualitative paradigm can be useful to fill in a research context that is poorly understood or ill-defined. It can provide an in-depth study of interactions, a way to incorporate context, and a means to hear the voices of participants. Understanding experiences, motivation, and beliefs can have a profound effect on the interpretation of quantitative research and generating hypotheses. In this paper, we will review different qualitative approaches that healthcare providers and researchers may find useful to implement in future study designs, specifically in the context of osteoporosis and fracture. METHODS: We will provide insight into the qualitative paradigm gained from the osteoporosis literature on fractures using examples from the database Scopus. Five prominent qualitative techniques (narratives, phenomenology, grounded theory, ethnography, and case study) can be used to generate meanings of the social and clinical world. DISCUSSION AND CONCLUSION: We have highlighted how these strategies are implemented in qualitative research on osteoporosis and fractures and are anchored to specific methodological practices. We focus on studies that explore patient psychosocial experiences of diagnosis and treatment, cultural boundaries, and interprofessional communication. After reviewing the research, we believe that action research, that is not frequently used, could also effectively be used by many professions to improve programs and policies affecting those dealing with osteoporosis issues.

The importance of perceived helplessness and emotional health in understanding the relationship among pain, function, and satisfaction following revision knee replacement surgery.

OBJECTIVE: Little is known about the relationships among pain, function, psychological variables like perceived helplessness and emotional health, and patient satisfaction in people with revision knee replacement surgery. We hypothesized that pain and function would have a direct association with satisfaction as well as an indirect association through patient perceptions of helplessness and emotional health. DESIGN: This longitudinal study included 145 participants undergoing revision knee replacement surgery. Demographic data and expectation of benefit from surgery were recorded prior to surgery. The Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC), the Arthritis Helplessness Scale (AHS) and the Mental Component Scale (MCS) of the SF-36 (emotional health) were collected prior to and 2 years post-surgery. Satisfaction was recorded 2 years post-surgery. Regression analyses were conducted to test for mediation effects of helplessness and MCS. RESULTS: Participants were on average 69 years old and 54% were women. Participants were satisfied with the results of the surgery (mean ± standard deviation (SD) = 70.42 ± 31.46). Less pain and functional disability were associated with increased patient satisfaction and, the effect of pain or function was also mediated through helplessness whereby more pain and disability were associated with perceptions of helplessness and helplessness was associated with lower satisfaction. MCS did not mediate the relationship of pain and function with satisfaction. CONCLUSION: Helplessness plays an important role in understanding patient satisfaction. Interventions aimed at improving patient outcome should target not only pain and function but also should address strategies to support people in managing following knee revision surgery to maximize satisfaction with outcome.

The impact of wait time on patient outcomes in knee and hip replacement surgery: a scoping review protocol.

BACKGROUND: Total hip and total knee replacement surgery are in high demand, leading to long wait times for many patients. While on the waiting list, patients may experience worsening pain, reduced mobility, and deteriorating health. Given that long wait times are common for lower joint replacement surgery, it is important to understand how patient health changes during the wait period and whether this impacts patient outcomes after surgery. The aim of this scoping review will be to identify and describe the evidence regarding the impact of wait time on patient outcomes for patients who undergo total knee and total hip replacement surgery. METHODS: This scoping review was designed with guidance from the Joanna Briggs Institute Manual for Evidence Synthesis, and results will be reported following the Preferred Reporting Items for Systematic Reviews and Meta-Analyses extension for scoping reviews. EMBASE, Medline, PubMed, Scopus, CINAHL, and Cochrane electronic databases will be searched for English language articles published after 1999. Studies of adult patients with osteoarthritis undergoing primary knee or hip replacement surgery, which measure patient outcomes over the wait period for surgery, will be included. Two independent reviewers will screen titles and abstracts followed by full article review. Data will be extracted by two reviewers using a standardized form. Outcomes assessed during the wait period will be identified and described in tables. Factors associated with changes in health status during the wait period will be qualitatively described. DISCUSSION: This review will map the evidence regarding wait times for lower extremity joint replacement surgery. Better understanding of how the impact of wait times on patient health status is measured over the perioperative period will inform future research on wait times. SCOPING REVIEW REGISTRATION: Registered with Open Science Framework, Feb 14, 2021 DOI: https://doi.org/10.17605/OSF.IO/MV4FS.

The trajectory of recovery and the inter-relationships of symptoms, activity and participation in the first year following total hip and knee replacement.

OBJECTIVE: Primary total hip (THR) and knee (TKR) replacement outcomes typically include pain and function with a single time of follow-up post-surgery. This research evaluated the trajectory of recovery and inter-relationships within and across time of physical impairments (PI) (e.g., symptoms), activity limitations (AL), and social participation restrictions (PR) in the year following THR and TKR for osteoarthritis. DESIGN: Participants (hip: n=437; knee: 494) completed measures pre-surgery and at 2 weeks, 1, 3, 6 and 12 months post-surgery. These included PI (Hip Disability and Osteoarthritis Outcome Score (HOOS)/Knee Injury and Osteoarthritis Outcome Score (KOOS) symptoms and Chronic Pain Grade); AL (HOOS/KOOS activities of daily living and sports/leisure activities); and, PR (Late Life Disability and the Calderdale community mobility). Repeated measures analysis of variance (RANOVA) was used to evaluate the trajectory of recovery of outcomes and the inter-relationships of PI, AL and PR were evaluated using path analysis. All analyses were adjusted for age, sex, obesity, THR/TKR, low back pain and mood. RESULTS: THR: age 31-86 years with 55% female; TKR: age 35-88 years with 65% female. Significant improvements in outcomes were observed over time. However, improvements were lagged over time with earlier improvements in PI and AL and later improvements in PR. Within and across time, PI was associated with AL and AL was associated with PR. The magnitude of these inter-relationships varied over time. CONCLUSION: Given the lagged inter-relationship of PI, AL and PR, the provision and timing of interventions targeting all constructs are critical to maximizing outcome. Current care pathways focusing on short-term follow-up with limited attention to social and community participation should be re-evaluated.

The biomechanical effect of changes in cancellous bone density on synthetic femur behaviour.

Biomechanical researchers increasingly use commercially available and experimentally validated synthetic femurs to mimic human femurs. However, the choice of cancellous bone density for these artificial femurs appears to be done arbitrarily. The aim of the work reported in this paper was to examine the effect of synthetic cancellous bone density on the mechanical behaviour of synthetic femurs. Thirty left, large, fourth-generation composite femurs were mounted onto an Instron material testing system. The femurs were divided evenly into five groups each containing six femurs, each group representing a different synthetic cancellous bone density: 0.08, 0.16, 0.24, 0.32, and 0.48 g/cm3. Femurs were tested non-destructively to obtain axial, lateral, and torsional stiffness, followed by destructive tests to measure axial failure load, displacement, and energy. Experimental results yielded the following ranges and the coefficient of determination for a linear regression (R2) with cancellous bone density: axial stiffness (range 2116.5-2530.6N/mm; R2 = 0.94), lateral stiffness (range 204.3-227.8N/mm; R2 = 0.08), torsional stiffness (range 259.9-281.5N/mm; R2 = 0.91), failure load (range 5527.6-11 109.3 N; R2 = 0.92), failure displacement (range 2.97-6.49 mm; R2 = 0.85), and failure energy (range 8.79-42.81 J; R2 = 0.91). These synthetic femurs showed no density effect on lateral stiffness and only a moderate influence on axial and torsional stiffness; however, there was a strong density effect on axial failure load, displacement, and energy. Because these synthetic femurs have previously been experimentally validated against human femurs, these trends may be generalized to the clinical situation. This is the first study in the literature to perform such an assessment.

The biomechanics of plate fixation of periprosthetic femoral fractures near the tip of a total hip implant: cables, screws, or both?

Femoral shaft fractures after total hip arthroplasty (THA) remain a serious problem, since there is no optimal surgical repair method. Virtually all studies that examined surgical repair methods have done so clinically or experimentally. The present study assessed injury patterns computationally by developing three-dimensional (3D) finite element (FE) models that were validated experimentally. The investigation evaluated three different constructs for the fixation of Vancouver B1 periprosthetic femoral shaft fractures following THA. Experimentally, three bone plate repair methods were applied to a synthetic femur with a 5 mm fracture gap near the tip of a total hip implant. Repair methods were identical distal to the fracture gap, but used cables only (construct A), screws only (construct B), or cables plus screws (construct C) proximal to the fracture gap. Specimens were oriented in 15 degrees adduction to simulate the single-legged stance phase of walking, subjected to 1000 N of axial force, and instrumented with strain gauges. Computationally, a linearly elastic and isotropic 3D FE model was developed to mimic experiments. Results showed excellent agreement between experimental and FE strains, yielding a Pearson linearity coefficient, R2, of 0.92 and a slope for the line of best data fit of 1.06. FE-computed axial stiffnesses were 768 N/mm (construct A), 1023 N/mm (construct B), and 1102 N/mm (construct C). FE surfaces stress maps for cortical bone showed Von Mises stresses, excluding peaks, of 0-8 MPa (construct A), 0-15 MPa (construct B), and 0-20 MPa (construct C). Cables absorbed the majority of load, followed by the plates and then the screws. Construct A yielded peak stress at one of the empty holes in the plate. Constructs B and C had similar bone stress patterns, and can achieve optimal fixation.

The biomechanics of plate repair of periprosthetic femur fractures near the tip of a total hip implant: the effect of cable-screw position.

Optimal surgical positioning of cable-screw pairs in repairing periprosthetic femur fractures near the tip of a total hip implant still remains unclear. No studies in the literature to date have developed a fully three-dimensional finite element (FE) model that has been validated experimentally to assess these injury patterns. The aim of the present study was to evaluate the biomechanical performance of three different implant-bone constructs for the fixation of periprosthetic femoral shaft fractures following total hip arthroplasty. Experimentally, three bone-plate repair configurations were applied to the periprosthetic synthetic femur fractured with a 5 mm gap near the tip of a total hip implant. Constructs A, B, and C, respectively, had successively larger distances between the most proximal and the most distal cable-screw pairs used to affix the plate. Specimens were oriented in 15 degrees adduction, subjected to 1000 N of axial force to simulate the single-legged stance phase of walking, and instrumented with strain gauges. Computationally, a linearly elastic and isotropic three-dimensional FE model was developed to mimic the experimental setup. Results showed excellent agreement between experimental versus FE analysis strains, yielding a Pearson linearity coefficient, R2, of 0.90 and a slope for the line of best data fit of 0.96. FE axial stiffnesses were 601 N/mm (Construct A), 849 N/mm (Construct B), and 1359 N/mm (Construct C). FE surface stress maps for cortical bone showed maximum von Mises values of 74 MPa (Construct A), 102 MPa (Construct B), and 57 MPa (Construct C). FE stress maps for the metallic components showed minimum von Mises values for Construct C, namely screw (716MPa), cable (445MPa), plate (548MPa), and hip implant (154MPa). In the case of good bone stock, as modelled by the present synthetic femur model, optimal fixation can be achieved with Construct C.

Outcome assessment in hip fracture: evaluation of the practicality of commonly-used outcomes in hip fracture studies.

INTRODUCTION: Elderly patients are at a major risk for a first hip fracture. The decrease in bone mineral density may account for 60-85% of the variability in fracture risk. Other contributing factors for hip fractures include cognitive impairment as well as impaired mobility and visual depth perception. Dizziness and poor or fair self-perceived health care characteristics are predictive of a second hip fracture. In general, patients over the age of 65 years admitted to a geriatric rehabilitation unit after proximal hip fracture have complex multiple interacting pathologies with 78% having significant co-morbidity. Because of the added co-morbidity, we believed that the choice of outcome assessment in hip fracture studies would reflect the practical qualities of an instrument. The purpose of our study was to evaluate the practicality of functional outcome instruments found in the current literature in the elderly following postoperative hip fracture. METHODS: We coded the instruments according to the International Classification of Functioning, Disability and Health conceptual framework. 24 different instruments measuring Body Function, 13 instruments evaluating Activity and Participation and 8 composite scores were identified. Practicality was evaluated using four dimensions: respondent burden, examiner burden, score distribution and format compatibility. RESULTS: All instruments evaluating Body Function were performance-based and used exclusively in rehabilitation trials. Performance-based instruments also correlated with a high score in examiner and respondent burden. Surgical trials mostly adopted the Harris hip score which was rated low in examiner and respondent burden. The SF-36 was rated with an adequate score distribution but low in format compatibility. DISCUSSION AND CONCLUSION: An instrument with low respondent burden and minimal examiner burden demonstrated better potential for being applicable in randomized trials with elderly hip fracture patients presenting with co-morbidities. In the future we believe that practical qualities should also be considered when developing or utilizing instruments.

The effect of load application rate on the biomechanics of synthetic femurs.

Biomechanical investigations are increasingly using commercially available synthetic femurs as surrogates for human cadaveric femurs. However, the rate of force application in testing these artificial femurs appears to be chosen arbitrarily without much consideration to their visco-elastic time-dependent nature. The aim of this study, therefore, was to examine the effect of loading rate on the mechanical behaviour of synthetic femurs. Ten left, medium, fourth-generation composite femurs (Model 3403, Pacific Research Laboratories, Vashon, WA, USA) were fixed distally into cement-filled steel cubic chambers for mounting into a mechanical tester. In randomized order, each of the ten femurs was loaded at rates of 1, 2.5, 5, 7.5, 10, 20, 30, 40, 50, and 60 mm/min to obtain axial, lateral, and torsional stiffness. Axial stiffness showed an aggregate average value of 1742.7 +/- 174.7 N/mm with a high linear correlation with loading rate (R2 = 0.80). Lateral stiffness yielded an aggregate average value of 56.9 +/- 10.2 N/mm and was linearly correlated with loading rate (R2 = 0.85). Torsional stiffness demonstrated an aggregate average value of 176.9 +/- 14.5 N/mm with a strong linear correlation with loading rate (R2 = 0.59). Despite the high correlations between stiffness and speed, practically this resulted in an overall average difference between the lowest and highest stiffness of only 4 per cent. Moreover, no statistical comparisons between loading rates for axial, lateral, or torsional test modes showed differences (p > or = 0.843). Future biomechanical investigators utilizing these synthetic femurs need not be concerned with loading rate effects over the range tested presently. This is the first study in the literature to perform such an assessment.

The biomechanics of a validated finite element model of stress shielding in a novel hybrid total knee replacement.

This study proposes a novel hybrid total knee replacement (TKR) design to improve stress transfer to bone in the distal femur and, thereby, reduce stress shielding and consequent bone loss. Three-dimensional finite element (FE) models were developed for a standard and a hybrid TKR and validated experimentally. The Duracon knee system (Stryker Canada) was the standard TKR used for the FE models and for the experimental tests. The FE hybrid device was identical to the standard TKR, except that it had an interposing layer of carbon fibre-reinforced polyamide 12 lining the back of the metallic femoral component. A series of experimental surface strain measurements were then taken to validate the FE model of the standard TKR at 3000 N of axial compression and at 0 degreeof knee flexion. Comparison of surface strain values from FE analysis with experiments demonstrated good agreement, yielding a high Pearson correlation coefficient of R(2)= 0.94. Under a 3000N axial load and knee flexion angles simulating full stance (0O degree, heel strike (200 degrees, and toe off (600 degrees during normal walking gait, the FE model showed considerable changes in maximum Von Mises stress in the region most susceptible to stress shielding (i.e. the anterior region, just behind the flange of the femoral implant). Specifically, going from a standard to a hybrid TKR caused an increase in maximum stress of 87.4 per cent (O0 degree from 0.15 to 0.28 MPa), 68.3 per cent (200 degrees from 1.02 to 1.71 MPa), and 12.6 per cent (600 degrees from 2.96 to 3.33 MPa). This can potentially decrease stress shielding and subsequent bone loss and knee implant loosening. This is the first report to propose and biomechanically to assess a novel hybrid TKR design that uses a layer of carbon fibrereinforced polyamide 12 to reduce stress shielding.

The effect of the screw pull-out rate on cortical screw purchase in unreamed and reamed synthetic long bones.

Orthopaedic fracture fixation constructs are typically mounted on to human long bones using cortical screws. Biomechanical studies are increasingly employing commercially available synthetic bones. The aim of this investigation was to examine the effect of the screw pull-out rate and canal reaming on the cortical bone screw purchase strength in synthetic bone. Cylinders made of synthetic material were used to simulate unreamed (foam-filled) and reamed (hollow) human long bone with an outer diameter of 35 mm and a cortex wall thickness of 4 mm. The unreamed and reamed cylinders each had 56 sites along their lengths into which orthopaedic cortical bone screws (major diameter, 3.5 mm) were inserted to engage both cortices. The 16 test groups (n = 7 screw sites per group) had screws extracted at rates of 1 mm/ min, 5 mm/min, 10 mm/min, 20 mm/min, 30 mm/min, 40 mm/min, 50 mm/min, and 60 mm/ min. The failure force and failure stress increased and were highly linearly correlated with pull-out rate for reamed (R2 = 0.60 and 0.60), but not for unreamed (R2 = 0.00 and 0.00) specimens. The failure displacement and failure energy were relatively unchanged with pull-out rate, yielding low coefficients for unreamed (R2 = 0.25 and 0.00) and reamed (R2 = 0.27 and 0.00) groups. Unreamed versus reamed specimens were statistically different for failure force (p = 0.000) and stress (p = 0.000), but not for failure displacement (p = 0.297) and energy (0.054 < p < 1.000). This is the first study to perform an extensive investigation of the screw pull-out rate in unreamed and reamed synthetic long bone.

The effect of cortex thickness on intact femur biomechanics: a comparison of finite element analysis with synthetic femurs.

Biomechanical studies on femur fracture fixation with orthopaedic implants are numerous in the literature. However, few studies have compared the mechanical stability of these repair constructs in osteoporotic versus normal bone. The present aim was to examine how changes in cortical wall thickness of intact femurs affect biomechanical characteristics. A three-dimensional, linear, isotropic finite element (FE) model of an intact femur was developed in order to predict the effect of bicortical wall thickness, t, relative to the femur's mid-diaphyseal outer diameter, D, over a cortex thickness ratio range of 0 < or = t/D < or = 1. The FE model was subjected to loads to obtain axial, lateral, and torsional stiffness. Ten commercially available synthetic femurs were then used to mimic 'osteoporotic' bone with t/D = 0.33, while ten synthetic left femurs were used to simulate 'normal' bone with t/D = 0.66. Axial, lateral, and torsional stiffness were measured for all femurs. There was excellent agreement between FE analysis and experimental stiffness data for all loading modes with an aggregate average percentage difference of 8 per cent. The FE results for mechanical stiffness versus cortical thickness ratio (0 < or = t/D < or = 1) demonstrated exponential trends with the following stiffness ranges: axial stiffness (0 to 2343 N/mm), lateral stiffness (0 to 62 N/mm), and torsional stiffness (0 to 198 N/mm). This is the first study to characterize mechanical stiffness over a wide range of cortical thickness values. These results may have some clinical implications with respect to appropriately differentiating between older and younger human long bones from a mechanical standpoint.

The biomechanics of the T2 femoral nailing system: a comparison of synthetic femurs withfinite element analysis.

Intramedullary nails are commonly used to repair femoral fractures. Fractures in normal healthy bone often occur in the young during motor vehicle accidents. Although clinically beneficial, bone refracture and implant failure persist. Large variations in human femur quality and geometry have motivated recent experimental use of synthetic femurs that mimic human tissue and the development of increasingly sophisticated theoretical models. Four synthetic femurs were fitted with a T2 femoral nailing system (Stryker, Mahwah, New Jersey, USA). The femurs were not fractured in order to simulate post-operative perfect union. Six configurations were created: retrograde nail with standard locking (RS), retrograde nail with advanced locking 'off' (RA-off), retrograde nail with advanced locking 'on' (RA-on), antegrade nail with standard locking (AS), antegrade nail with advanced locking 'off' (AA-off), and antegrade nail with advanced locking 'on' (AA-on). Strain gauges were placed on the medial side of femurs. A 580 N axial load was applied, and the stiffness was measured. Strains were recorded and compared with results from a three-dimensional finite element (FE) model. Experimental axial stiffnesses for RA-off (771.3 N/mm) and RA-on (681.7 N/mm) were similar to intact human cadaveric femurs from previous literature (757 + 264 N/mm). Conversely, experimental axial stiffnesses for AS (1168.8N/mm), AA-off (1135.3N/mm), AA-on (1152.1 N/mm), and RS (1294.0 N/mm) were similar to intact synthetic femurs from previous literature (1290 +/- 30 N/mm). There was better agreement between experimental and FE analysis strains for RS (average percentage difference, 11.6 per cent), RA-on (average percentage difference, 11.1 per cent), AA-off (average percentage difference, 13.4 per cent), and AA-on (average percentage difference, 16.0 per cent), than for RA-off (average percentage difference, 33.5 per cent) and AS (average percentage difference, 32.6 per cent). FE analysis was more predictive of strains in the proximal and middle sections of the femur-nail construct than the distal. The results mimicked post-operative clinical stability at low static axial loads once fracture healing begins to occur.

Same-day and delayed hospital discharge are associated with worse outcomes following total knee arthroplasty.

AIMS: To evaluate the influence of discharge timing on 30-day complications following total knee arthroplasty (TKA). PATIENTS AND METHODS: We identified patients aged 18 years or older who underwent TKA between 2005 and 2016 from the American College of Surgeons' National Surgical Quality Improvement Program (NSQIP) database. We propensity score-matched length-of-stay (LOS) groups using all relevant covariables. We used multivariable regression to determine if the rate of complications and re-admissions differed depending on LOS. RESULTS: Our matched cohort consisted of 76 246 TKA patients (mean age 67 years (sd 9)). Patients whose LOS was zero and four days had an increased risk of major complications by an odds ratio (OR) of 1.8 (95% confidence interval (CI) 1.0 to 3.2) and 1.5 (95% CI 1.2 to 1.7), respectively, compared with patients whose LOS was two days. Patients whose LOS was zero, three, and four days had an increased risk of minor complications (OR 1.8 (95% CI 1.3 to 2.7), 1.2 (95% CI 1.0 to 1.4), and 1.6 (95% CI 1.4 to 1.9), respectively), compared with patients whose LOS was two days. In addition, a LOS of three days increased the risk of re-admission by an OR of 1.2 (95% CI 1.0 to 1.3), and a LOS of four days increased the risk of re-admission by an OR of 1.5 (95% CI 1.3 to 1.6), compared with a LOS of two days. CONCLUSION: Patients discharged on days one to two postoperatively following TKA appear to have reduced major and minor complications compared with discharge on the day of surgery, or on days three to four. Prospective clinical data are required to confirm these findings. Cite this article: Bone Joint J 2019;101-B(7 Supple C):70-76.

Duration of surgery affects the risk of complications following total hip arthroplasty.

AIMS: The aim of this study was to assess the influence of operating time on 30-day complications following total hip arthroplasty (THA). PATIENTS AND METHODS: We identified patients aged 18 years and older who underwent THA between 2006 and 2016 from the American College of Surgeons National Surgical Quality Improvement Program (NSQIP) database. We identified 131 361 patients, with a mean age of 65 years (sd 12), who underwent THA. We used multivariable regression to determine if the rate of complications and re-admissions was related to the operating time, while adjusting for relevant covariables. RESULTS: The mean operating time decreased from 118.3 minutes (29.0 to 217.0) in 2006, to 89.6 minutes (20.0 to 240.0) in 2016. After adjustment for covariables, operating times of between 90 and 119 minutes increased the risk of minor complications by 1.2 (95% confidence interval (CI) 1.1 to 1.3), while operating times of between 120 and 179 minutes increased the risk of major complications by 1.4 (95% CI 1.3 to 1.6) and minor complications by 1.4 (95% CI 1.2 to 1.5), and operating times of 180 minutes or more increased the risk of major complications by 2.1 (95% CI 1.8 to 2.6) and minor complications by 1.9 (95% CI 1.6 to 2.3). There was no difference in the overall risk of complications for operating times of between 20 and 39, 40 and 59, or 60 and 89 minutes (p > 0.05). Operating times of between 40 and 59 minutes decreased the risk of re-admission by 0.88 (95% CI 0.79 to 0.97), while operating times of between 120 and 179 minutes, and of 180 minutes or more, increased the risk of re-admission by 1.2 (95% CI 1.1 to 1.3) and 1.6 (95% CI 1.3 to 1.8), respectively. CONCLUSION: These findings suggest that an operating time of more than 90 minutes may be an independent predictor of major and minor complications, as well as re-admission, following THA, and that an operating time of between 40 and 90 minutes may be ideal. Prospective studies are required to confirm these findings. Cite this article: Bone Joint J 2019;101-B(6 Supple B):51-56.

Cancellous bone screw purchase: a comparison of synthetic femurs, human femurs, and finite element analysis.

Biomechanical assessments of orthopaedic fracture fixation constructs are increasingly using commercially available analogues such as the fourth-generation composite femur (4GCF). The aim of this study was to compare cancellous screw purchase directly between these surrogates and human femurs, which has not been done previously. Synthetic and human femurs each had one orthopaedic cancellous screw (major diameter, 6.5 mm) inserted along the femoral neck axis and into the spongy bone of the femoral head to a depth of 30 mm. Screws were removed to obtain pull-out force, shear stress, and energy values. The three experimental study groups (n = 6 femurs each) were the 4GCF with a 'solid' cancellous matrix, the 4GCF with a 'cellular' cancellous matrix, and human femurs. Moreover, a finite element model was developed on the basis of the material properties and anatomical geometry of the two synthetic femurs in order to assess cancellous screw purchase. The results for force, shear stress, and energy respectively were as follows: 4GCF solid femurs, 926.47 +/- 66.76 N, 2.84 +/- 0.20 MPa, and 0.57 +/- 0.04 J; 4GCF cellular femurs, 1409.64 +/- 133.36 N, 4.31 +/- 0.41 MPa, and 0.99 +/- 0.13 J; human femurs, 1523.29 +/- 1380.15N, 4.66 +/- 4.22 MPa, and 2.78 +/- 3.61J. No statistical differences were noted when comparing the three experimental groups for pull-out force (p = 0.413), shear stress (p = 0.412), or energy (p = 0.185). The 4GCF with either a 'solid' or 'cellular' cancellous matrix is a good biomechanical analogue to the human femur at the screw thread-bone interface. This is the first study to perform a three-way investigation of cancellous screw purchase using 4GCFs, human femurs, and finite element analysis.

A biomechanical assessment of the coupling of torsion and tension in the human scapholunate ligament.

The mechanical behaviour of human scapholunate ligaments is not well described in the literature with regard to torsion. In this study, intact scapholunate specimens were mechanically tested in torsion to determine whether a simultaneous tensile load was generated. Human intact scapholunate specimens (n = 19) were harvested. The scaphoid and lunate bones were potted in square chambers using epoxy cement, while the interposing ligament remained exposed. Each specimen was mounted rigidly in a specially designed test jig and remained at a fixed axial length during all tests. Specimens were subjected to a torsional load regime that included cyclic preconditioning, ramp-up, stress relaxation, ramp-down, rest, and torsion to failure. Torque and axial tension were monitored simultaneously. The relationship between torsion and tension was determined. Graphs of torque versus tension were generated, from which outcome measures were extracted. Tests demonstrated a clear relationship between applied torsion and the resulting generation of tension for the ligament during ramp-up (torsion-to-tension ratio, 38.86 +/- 29.00 mm; linearity coefficient R2 = 0.89 +/- 0.15; n = 19), stress relaxation (torsion-to-tension ratio, 23.43 +/- 15.84 mm; R2 = 0.90 +/- 0.09; n = 16), and failure tests (torsion-to-tension ratio, 38.81 +/- 26.39mm; R2 = 0.77 +/- 0.20; n = 16). No statistically significant differences were detected between the torsion-to-tension ratios (p = 0.13) or between the linearity (R2) of the best-fit lines (p > 0.085). A strongly coupled linear relationship between torsion and tension for the scapholunate ligament was exhibited in all test phases. This may suggest interplay between these two parameters in the stabilization of the ligament during normal motion and for injury cascades.