Aims

A novel enhanced cement fixation (EF) tibial implant with deeper cement pockets and a more roughened bonding surface was released to market for an existing total knee arthroplasty (TKA) system.This randomized controlled trial assessed fixation of the both the EF (ATTUNE S+) and standard (Std; ATTUNE S) using radiostereometric analysis.

With the rising rates, and associated costs, of total knee arthroplasty (TKA), enhanced clarity regarding patient appropriateness for TKA is warranted. Towards addressing this gap, we elucidated in qualitative research that surgeons and osteoarthritis (OA) patients considered TKA need, readiness/willingness, health status, and expectations of TKA most important in determining patient appropriateness for TKA. The current study evaluated the predictive validity of pre-TKA measures of these appropriateness domains for attainment of a good TKA outcome.

This prospective cohort study recruited knee OA patients aged 30+ years referred for TKA at two hip/knee surgery centers in Alberta, Canada. Those receiving primary, unilateral TKA completed questionnaires pre-TKA assessing TKA need (WOMAC-pain, ICOAP-pain, NRS-pain, KOOS-physical function, Perceived Arthritis Coping Efficacy, prior OA treatment), TKA readiness/willingness (Patient Acceptable Symptom State (PASS), willingness to undergo TKA), health status (PHQ-8, BMI, MSK and non-MSK comorbidities), TKA expectations (HSS KR Expectations survey items) and contextual factors (e.g., age, gender, employment status). One-year post-TKA, we assessed for a ‘good outcome’ (yes/no), defined as improved knee symptoms (OARSI-OMERACT responder criteria) AND overall satisfaction with TKA results. Multiple logistic regression, stepwise variable selection, and best possible subsets regression was used to identify the model with the smallest number of independent variables and greatest discriminant validity for our outcome. Receiver Operating Characteristic (ROC) curves were generated to compare the discriminative ability of each appropriateness domain based on the ‘area under the ROC curve’ (AUC). Multivariable robust Poisson regression was used to assess the relationship of the variables to achievement of a good outcome.

f 1,275 TKA recipients, 1,053 (82.6%) had complete data for analyses (mean age 66.9 years [SD 8.8]; 58.6% female). Mean WOMAC pain and KOOS-PS scores were 11.5/20 (SD 3.5) and 52.8/100 (SD 17.1), respectively. 78.1% (95% CI 75.4–80.5%) achieved a good outcome. Stepwise variable selection identified optimal discrimination was achieved with 13 variables. The three best 13-variable models included measures of TKA need (WOMAC pain, KOOS-PS), readiness/willingness (PASS, TKA willingness), health status (PHQ-8, troublesome hips, contralateral knee, low back), TKA expectations (the importance of improved psychological well-being, ability to go up stairs, kneel, and participate in recreational activities as TKA outcomes), and patient age. Model discrimination was fair for TKA need (AUC 0.68, 95% CI 0.63-0.72), TKA readiness/willingness (AUC 0.61, 95% CI 0.57-0.65), health status (AUC 0.59, 95% CI 0.54-0.63) and TKA expectations (AUC 0.58, 95% CI 0.54-0.62), but the model with all appropriateness variables had good discrimination (AUC 0.72, 95% CI 0.685-0.76). The likelihood of achieving a good outcome was significantly higher for those with greater knee pain, disability, unacceptable knee symptoms, definite willingness to undergo TKA, less depression who considered improved ability to perform recreational activities or climb stairs ‘very important’ TKA outcomes, and lower in those who considered it important that TKA improve psychological wellbeing or ability to kneel.

Beyond surgical need (OA symptoms) and health status, assessment of patients’ readiness and willingness to undergo, and their expectations for, TKA, should be incorporated into assessment of patient appropriateness for surgery.

Knee arthroscopy with debridement is commonly performed to treat osteoarthritis and degenerative meniscal tears in older adults; however robust evidence does not support sustained benefit from this procedure. Current Canadian guidelines advise against its use as first line treatment. Characterizing the use of this low value procedure will facilitate efforts to maximize quality of care, minimize harm and decrease healthcare costs. We sought to understand:

Data were derived from National Ambulatory Care Reporting System (NACRS), the Discharge Abstract Database (DAD) and the National Physician Database for years 2011-12 to 2019-20. The study included all elective knee arthroscopies (CCI codes 1.VG.80.DA,1.VG.80.FY and 1.VG.87.DA) performed in day surgery and acute care settings in 9 provinces and 3 territories of Canada. Quebec was not included in the analysis due to different reporting methods. We set a threshold of 60 years of age at which it would be highly unlikely that a patient would undergo arthroscopy to treat anything other than osteoarthritis or degenerative meniscal tear. Trends at national and provincial levels were analyzed using regression. Costs were estimated separately using the 2020 case mix groups (CMG) and comprehensive ambulatory care classification system (CACS) methodologies. Surgeons were classified by decade of graduation from medical school (1989 and prior, 1990-99, 2000-09 and 2010+) and categorized based on the proportion of their patient population who were above (“high proportion inappropriate”) or below (“low proportion inappropriate”) the overall national proportion of ≥ 60 years of age.

The number of knee arthroscopies decreased by 37% (42,785 in 2011-12 to 27,034 in 2019-20) overall and 39% (11,103 in 2011-12 to 6,772 in 2019-20) in those 60 years and older (p 25% of patients 60 years and older. Fifty four percent of surgeons who graduated prior to 1989 were considered high proportion inappropriate, whereas only 30.1% of surgeons who graduated in 2010 or later were considered high proportion inappropriate (p < 0 .0001).

Knee arthroscopy continues to be a common procedure in patients over 60 despite strong evidence for lack of benefit. Lower rates in this population in some provinces are encouraging for potential opportunity for improvement. Efforts at practice change should be targeted at surgeons in practice the longest. Canada spends over $12,000,000 per year on this procedure, decreasing its use could allow these resources to be directed to other areas of orthopaedics that provide higher value care.

In Canada, hip and knee replacements are each among the top three surgeries performed annually. In 2020, surgeries across the country were cancelled in response to the COVID-19 pandemic. We examined the impact on these joint replacement surgeries throughout the year.

Using the Discharge Abstract Database and National Ambulatory Care Reporting System, we developed a dataset of all 208,041 hip and knee replacements performed in Canada (except from Quebec) between January 1, 2019 to December 31, 2020. We compared patient and surgical characteristics (including sex, age, main diagnosis, and type of surgery (planned/urgent, primary/revision, inpatient/day surgery) in 2020 to 2019.

In 2020, hip and knee replacements volumes decreased by 18.8% compared to 2019. In April and May 2020, hip and knee replacements fell by 69.4% and 93.8%, respectively, compared to the same period in 2019. During those months, 66.5% of hip replacements were performed to treat hip fracture versus 20.2% in April and May 2019, and 64.5% of knee replacements were primaries versus 93.0% in April and May 2019. Patterns by patient age group and sex were similar compared to 2019. These patterns were similar across all provinces. By the summer, planned surgeries resumed across the country and volumes mostly returned to pre-pandemic monthly levels by the end of the year. We also found that there was an increase in the proportion of hip and knee replacements done as day surgery, with 4% in 2020 versus 1% in 2019, and patients undergoing day surgery replacement for osteoarthritis were older, with a median age of 64 for hip patients and 65 for knee patients, versus 63 for both joints the previous year.

As a result of the COVID-19 pandemic, there was a notable drop in 2020 of hip and knee replacements performed in Canada. With the demand for joint replacements continuing to grow, the resulting backlog will have an immediate, significant impact on wait lists and patient quality of life. The shift to a greater proportion of joint replacements performed as day surgeries may have an effect on patient outcomes as well shifts in access to care. It will be important to continue monitor patient outcomes following day surgery and the impact on patients for which day surgery was not an option.

Increased collection of patient-reported outcome measures (PROM) in registries enables international comparison of patient-centered outcomes after knee and hip replacement. We aimed to investigate 1) variations in PROM improvement, 2) the possible confounding factor of BMI, and 3) differences in comorbidity distributions between registries.

Registries affiliated with the International Society of Arthroplasty Registries (ISAR) or OECD membership countries were invited to report aggregate EQ-5D, OKS, OHS, HOOS-PS and KOOS-PS values. Eligible patients underwent primary total, unilateral knee or hip replacement for osteoarthritis within three years and had completed PROMs preoperatively and either 6 or 12 months postoperatively, excluding patients with subsequent revisions. For each PROM cohort, Chi-square tests were performed for BMI distributions across registries and 12 predefined PROM strata (male/female, age 20-64/65-74/>75, high or low preoperative PROM scores). Comorbidity distributions were reported for available comorbidity indexes.

Thirteen registries from 9 countries contributed data, n~130000 knee (range 140 to 79848) and n~113000 hip (range 137 to 85281). Mean EQ-5D index values (10 registries) ranged from 0.53 to 0.71 (knee) and 0.50 to 0.70 (hips) preoperatively and 0.78 to 0.85 (knee) and 0.83 to 0.87 (hip) postoperatively. Mean OKS (6 registries) ranged from 19.3 to 23.6 preoperatively and 36.2 to 41.2 postoperatively. Mean OHS (7 registries) ranged from 18.0 to 23.2 preoperatively and 39.8 to 44.2 postoperatively. Four registries reported KOOS-PS and three reported HOOS-PS. Proportions of patients with BMI >30 ranged from 35 to 62% (10 knee registries) and 16 to 43% (11 hip registries). For both knee and hip registries, distributions of patients across six BMI categories differed significantly among registries (p30 were for patients in the youngest age groups (20 to 64 and 65 to 74 years) with the lowest baseline scores. Additionally, females with lowest preoperative PROM scores had highest BMI. These findings were echoed for the OHS and OKS cohorts. Proportions of patients with ASA scores ≥3 ranged from 7 to 42% (9 knee registries) and 6 to 35% (8 hip registries).

PROM-score improvement varies between international registries, which may be partially explained by differences in age, sex and preoperative scores. BMI and comorbidity may be relevant to adjust for.

This study used model-based radiostereometric analysis (MBRSA) to compare migration of a recently introduced cementless hip stem to an established hip stem of similar design. Novel design features of the newer hip stem included a greater thickness of hydroxyapatite coating and a blended compaction extraction femoral broach.

Fifty-seven patients requiring primary total hip arthroplasty (THA) were enrolled at a single centre. Patients were randomized to receive either an Avenir collarless stem and Trilogy IT cup (ZimmerBiomet) or a Corail collarless stem and Pinnacle cup (DePuy Synthes) via a posterior or lateral approach. Both stems are broach-only femoral bone preparation. RSA beads (Halifax Biomedical) were inserted into the proximal femur during surgery. Patients underwent supine RSA imaging a 6 weeks (baseline), 6, 12, and 24 months following surgery. The primary study outcome was total subsidence of the hip stem from baseline to 24 months as well as progression of subsidence between 12 and 24 months. These values were compared against published migration thresholds for well-performing hip stems (0.5mm). The detection limit, or precision, of MBRSA was calculated based on duplicate examinations taken at baseline. Patient reported outcome measures were collected throughout the study and included the Oxford-12 Hip Score (OHS), EuroQoL EQ-5D-5L, Hip Osteoarthritis Score (HOOS) as well as visual analogue scales (VAS) for thigh pain and satisfaction. Analysis comprised of paired and unpaired t-tests with significance set at p≤0.05.

Forty-eight patients (30 males) were included for analysis; 7 patients received a non-study hip stem intra-operatively, 1 patient suffered a traumatic dislocation within three weeks of surgery, and 1 patient died within 12 months post-surgery. RSA data was obtained for 45 patients as three patients did not receive RSA beads intra-operatively. Our patient cohort had a mean age of 65.9 years (±;7.2) at the time of surgery and body mass index of 30.5 kg/m2 (±;5.2). No statistical difference in total stem migration was found between the Avenir and Corail stems at 12 months (p=0.045, 95%CI: −0.046 to 0.088) and 24 months (p=0.936, 95% CI: −0.098 to 0.090). Progression of subsidence from 12-24 months was 0.011mm and 0.034mm for the Avenir and Corail groups which were not statistically different (p=0.163, 95%CI: −0.100 to 0.008) between groups and significantly less than the 0.5mm threshold (pNo statistically significant differences existed between study groups for any pre-operative function scores (p>0.05). All patients showed significant functional improvement from pre- to post-surgery and no outcome measures were different between study groups with exception of EQ-5D-5L health visual analogue scale at 12 months which showed marginally superior (p=0.036) scores in the Avenir group. This study was not powered to detect differences in clinical outcomes.

This study has demonstrated no statistical difference in subsidence or patient-reported outcomes between the Corail hip stem and the more recently introduced Avenir hip stem. This result is predictable as both stems are of a triple-tapered design, are coated with hydroxyapatite, and utilize a broach-only bone preparation technique. Both stem designs demonstrate migration below 0.5mm suggesting both are low-risk for aseptic loosening in the long-term.

Recent registry data from around the world has strongly suggested that using cemented hip hemiarthroplasty has lower revision rates compared to cementless hip hemiarthroplasty for acute femoral neck hip fractures. The adoption of using cemented hemiarthroplasty for hip fracture has been slow as many surgeons continue to use uncemented stems. One of the reasons is that surgeons feel more comfortable with uncemented hemiarthroplasty as they have used it routinely. The purpose of this study is to compare the difference in revision rates of cemented and cementless hemiarthroplasty and stratify the risk by surgeon experience. By using a surgeons annual volume of Total Hip Replacements performed as an indicator for surgeon experience. The Canadian Joint Replacement Registry Database was used to collect and compare the outcomes to report on the revision rates based on surgeon volume.

This is a large Canadian Registry Study where 68447 patients were identified for having a hip hemiarthroplasty from 2012-2020. This is a retrospective cohort study, identifying patients that had cementless or cemented hip hemiarthroplasty. The surgeons who performed the procedures were linked to the procedure Total Hip Replacement. Individuals were categorized as experienced hip surgeons or not based on whether they performed 50 hip replacements a year. Identifying high volume surgeon (>50 cases/year) and low volume (<50 cases/year) surgeons. Hazard ratios adjusted for age and sex were performed for risk of revision over this 8-year span. A p-value <0.05 was deemed significant.

For high volume surgeons, cementless fixation had a higher revision risk than cemented fixation, HR 1.29 (1.05-1.56), p=0.017. This pattern was similar for low volume surgeons, with cementless fixation having a higher revision risk than cemented fixation, HR 1.37 (1.11-1.70) p=0.004 We could not detect a difference in revision risk for cemented fixation between low volume and high volume surgeons; at 0-1.5 years the HR was 0.96 (0.72-1.28) p=0.786, and at 1.5+ years the HR was 1.61 (0.83-3.11) p=0.159. Similarly, we could not detect a difference in revision risk for cementless fixation between low volume and high volume surgeons, HR 1.11 (0.96-1.29) p=0.161

Using large registry data, cemented hip hemiarthroplasty has a significant lower revision rate than the use of cementless stems even when surgeons are stratified to high and low volume. Low volume surgeons who use uncemented prostheses have the highest rate of revision. The low volume hip surgeon who cements has a lower revision rate than the high volume cementless surgeon. The results of this study should help to guide surgeons that no matter the level of experience, using a cemented hip hemiarthroplasty for acute femoral neck fracture is the safest option. That high volume surgeons who perform cementless hemiarthroplasty are not immune to having revisions due to their technique. Increased training and education should be offered to surgeons to improve comfort when using this technique.

Recent registry data from around the world has strongly suggested that using cemented hip hemiarthroplasty has lower revision rates compared to cementless hip hemiarthroplasty for acute femoral neck hip fractures. The adoption of using cemented hemiarthroplasty for hip fracture has been slow as many surgeons continue to use uncemented stems. One of the reasons is that surgeons feel more comfortable with uncemented hemiarthroplasty as they have used it routinely. The purpose of this study is to compare the difference in revision rates of cemented and cementless hemiarthroplasty and stratify the risk by surgeon experience. By using a surgeons annual volume of Total Hip Replacements performed as an indicator for surgeon experience. The Canadian Joint Replacement Registry Database was used to collect and compare the outcomes to report on the revision rates based on surgeon volume.

This is a large Canadian Registry Study where 68447 patients were identified for having a hip hemiarthroplasty from 2012-2020. This is a retrospective cohort study, identifying patients that had cementless or cemented hip hemiarthroplasty. The surgeons who performed the procedures were linked to the procedure Total Hip Replacement. Individuals were categorized as experienced hip surgeons or not based on whether they performed 50 hip replacements a year. Identifying high volume surgeon (>50 cases/year) and low volume (<50 cases/year) surgeons. Hazard ratios adjusted for age and sex were performed for risk of revision over this 8-year span. A p-value <0.05 was deemed significant.

For high volume surgeons, cementless fixation had a higher revision risk than cemented fixation, HR 1.29 (1.05-1.56), p=0.017. This pattern was similar for low volume surgeons, with cementless fixation having a higher revision risk than cemented fixation, HR 1.37 (1.11-1.70) p=0.004 We could not detect a difference in revision risk for cemented fixation between low volume and high volume surgeons; at 0-1.5 years the HR was 0.96 (0.72-1.28) p=0.786, and at 1.5+ years the HR was 1.61 (0.83-3.11) p=0.159. Similarly, we could not detect a difference in revision risk for cementless fixation between low volume and high volume surgeons, HR 1.11 (0.96-1.29) p=0.161

Using large registry data, cemented hip hemiarthroplasty has a significant lower revision rate than the use of cementless stems even when surgeons are stratified to high and low volume. Low volume surgeons who use uncemented prostheses have the highest rate of revision. The low volume hip surgeon who cements has a lower revision rate than the high volume cementless surgeon. The results of this study should help to guide surgeons that no matter the level of experience, using a cemented hip hemiarthroplasty for acute femoral neck fracture is the safest option. That high volume surgeons who perform cementless hemiarthroplasty are not immune to having revisions due to their technique. Increased training and education should be offered to surgeons to improve comfort when using this technique.

Aims

Orthopaedic surgeries are complex, frequently performed procedures associated with significant haemorrhage and perioperative blood transfusion. Given refinements in surgical techniques and changes to transfusion practices, we aim to describe contemporary transfusion practices in orthopaedic surgery in order to inform perioperative planning and blood banking requirements.

Revision is a key negative outcome of joint replacements. The purpose of this abstract is to present revision risk curves for hip and knee replacements based on the most recently available national data sources. Having a better understanding of determinants of revision risk can help inform clinical and health care system improvements.

We explored revision risk of primary joint replacement stratified by key clinical, prosthesis, and surgeon-level factors using data from three databases managed by CIHI: the Canadian Joint Replacement Registry (CJRR), the Discharge Abstract Database, and the National Ambulatory Care Reporting System. To investigate early revisions, we used Kaplan-Meier analysis stratified by demographic factors to determine the risk of revision within up to five years of primary surgery. This analysis identified the primary cohort from the CJRR from April 1, 2012 to March 31, 2017 and was limited to mandatory reporting provinces (British Columbia, Manitoba and Ontario) to ensure maximal coverage of prosthesis information. Bearing surface was obtained from the International Prosthesis Library maintained by the International Consortium of Orthopaedic Registries (ICOR) and the International Society of Arthroplasty Registers (ISAR).

The total revision risk cohort contained 283,620 primary surgeries, of which 5,765 (2%) had at least one revision. For total hip arthroplasties, revision risk at the end of the follow-up period did not differ by age, by sex or across bearing surface (metal on cross-linked polyethylene [XLPE], ceramic on XLPE, ceramic on ceramic, metal on non-cross-linked polyethylene). For hemiarthroplasties in hip fracture patients, cement fixation was significantly associated with decreased revision risk. Surgeon volume had a positive effect on survivorship with cementless fixation (2.7% at one year [95% CI 2.3%, 3.1%] for high-volume vs 3.2% [2.7%, 3.7%] for low-volume). However, surgeon volume did not have an effect on survivorship with cemented fixation (2% at one year [95% CI 1.3%, 2.6%] for high-volume vs. 2% [1.4%, 2.6%] for low-volume). For total knee replacements, revision risk increased with decreasing age and male sex. For patients aged 75 and older, four-year revision risks were 1.5% (95% CI 1.3%, 1.7%) for women and 2.0% (1.7%, 2.3%) for men, but for patients under 55 years old, they were 4.3% (3.7%, 5%) for women and 5.9% (4.9%, 6.9%) for men. Additional results from the upcoming 2019 CJRR annual report, including data up to March 31, 2018, will be presented.

Revisions represent a key failure of the primary replacement, they are costly to the health care system and negatively affect patients' quality of life. CJRR's coverage is currently 72%, increased coverage and follow-up time will allow increasingly comprehensive reporting on hip and knee prostheses in Canada. Future work in this area involves exploring additional prosthesis attributes for stratification of revision risk curves and calculation of hazards ratios adjusted by age and sex.

The Canadian Institute for Health Information (CIHI) and the Organisation for Economic Co-operation and Development (OECD) have partnered to advance international patient-reported outcome measures (PROMs) collection and reporting standards for hip and knee arthroplasty. This project is part of the OECD's Patient-Reported Indicator Survey (PaRIS) initiative, which aims to address the need for internationally comparable patient-reported outcome and experience measures in order to better monitor health system performance and drive continuous improvement. PROMs are in varying stages of implementation across OECD health systems, with differences in collection and reporting practices across existing programs.

CIHI and the OECD are leading an international working group for PROMs in hip and knee replacement surgery in order to build consensus on PROMs data collection standards and develop indicators for international reporting. Working group members include patient representatives, clinicians, national arthroplasty registries, the International Society of Arthroplasty Registries (ISAR), experts in PROMs measurement, and government representatives of several OECD member countries. Activities of the working group focus on two main priorities: 1) Use existing PROMs programs to maximize pilot comparable reporting in OECD's Health at a Glance 2019 report, and 2) Advance new PROMs standards and data collection to maximize comparable reporting beyond Health at a Glance 2019.

An environmental scan of PROMs in hip and knee arthroplasty found that a number of countries are collecting this data, however, there are variations in survey instruments as well as administration and reporting methods within and across countries. As part of priority 1, the working group has achieved consensus on a number of aspects around pilot reporting. The project is compiling data from existing PROMs programs in order to report results in the Health at a Glance 2019 publication.

For priority 2, the most notable challenge is establishing an agreement across countries on common survey tools, as well as a minimum data set that works for all, given the disparities of existing collection across countries. Many international programs lack the flexibility to change PROMs tools or collections methods, and have concerns regarding the break in trend for PROMs data within their own countries if they were to change methods. The project is exploring the use of crosswalks and other opportunities for comparable reporting, such as the use of single-item anchor questions. To date, the working group continues to develop consensus on international standards for PROMs collection and reporting. Results of the international consensus building and work to date will be shared.

PROMs incorporate the patient's perspective into the delivery of treatments and care – such as hip and knee arthroplasty – that aim to improve a patient's quality of life. Alignment of standards in PROMs collection across countries will make comparable data available for reporting, in order to inform quality improvement initiatives within health systems to provide better care for patients. CIHI and the OECD will continue to work with member countries to develop international data collection and reporting standards for PROMs, and encourage the adoption of common approaches across countries.

The purpose of this study was to examine the influence of weight-bearing on the measurement of in vivo wear of total knee replacements using model-based RSA at 1 and 2 years following surgery.

Model-based RSA radiographs were collected for 106 patients who underwent primary TKR at a single institution. Supine RSA radiographs were obtained post-operatively and at 6-, 12-, and 24-months. Standing (weight-bearing) RSA radiographs were obtained at 12-months (n=45) and 24-months (n=48). All patients received the same knee design with a fixed, conventional PE insert of either a cruciate retaining or posterior stabilized design. Ethics approval for this study was obtained.

In order to assess in vivo wear, a highly accurate 3-dimensional virtual model of each in vivo TKA was developed. Coordinate data from RSA radiographs (mbRSA v3.41, RSACore) were applied to digital implant models to reconstruct each patient's replaced knee joint in a virtual environment (Geomagic Studio, 3D Systems). Wear was assessed volumetrically (digital model overlap) on medial and lateral condyles separately, across each follow-up. Annual rate of wear was calculated for each patient as the slope of the linear best fit between wear and time-point. The influence of weight-bearing was assessed as the difference in annual wear rate between standing and supine exams. Age, BMI, and Oxford-12 knee improvement were measured against wear rates to determine correlations.

Weight bearing wear measurement was most consistent and prevalent in the medial condyle with 35% negative wear rates for the lateral condyle. For the medial condyle, standing exams revealed higher mean wear rates at 1 and 2 years, supine, 16.3 mm3/yr (SD: 27.8) and 11.2 mm3/yr (SD: 18.5) versus standing, 51.3 mm3/yr (SD: 55.9) and 32.7 mm3/yr (SD: 31.7). The addition of weight-bearing increased the measured volume of wear for 78% of patients at 1 year (Avg: 32.4 mm3/yr) and 71% of patients at 2 years (Avg: 48.9 mm3/yr). There were no significant (95% CI) correlations between patient demographics and wear rates.

Volumetric, weight-bearing wear measurement of TKR using model-based RSA determined an average of 33 mm3/yr at 2 years post-surgery for a modern, non-cross-linked polyethylene bearing. This value is comparable to wear rates obtained from retrieved TKRs. Weight-bearing exams produced better wear data with fewer negative wear rates and reduced variance. Limitations of this study include: supine patient imaging performed at post-op, no knee flexion performed, unknown patient activity level, and inability to distinguish wear from plastic creep or deformation under load. Strengths of this study include: large sample size of a single TKR system, linear regression of wear measurements and no requirement for implanted RSA beads with this method. Based on these results, in vivo volumetric wear of total knee replacement polyethylene can be reliably measured using model-based RSA and weight-bearing examinations in the short- to mid–term. Further work is needed to validate the accuracy of the measurements in vivo.

Introduction

Total hip arthroplasty (THA) is a highly successful procedure achieving excellent clinical outcomes beyond 10 years post-surgery. With exception of periprosthetic infection, dislocation is the most common cause of failure in THA. A novel reverse total hip (RTH) replacement has been developed to address dislocation through reversal of the typical THA articulation in which a femoral cup and acetabular ball interlock at the extremes of motion to enhance mechanical stability in all planes. The purpose of this study was to assess the safety and efficacy of this novel RTH in a series of 22 patients and to monitor implant fixation using radiostereometric analysis (RSA).

Background

The anatomy of the human knee is very different than the tibiofemoral surface geometry of most modern total knee replacements (TKRs). Many TKRs are designed with simplified articulating surfaces that are mediolaterally symmetrical, resulting in non-natural patterns of motion of the knee joint [1]. Recent orthopaedic trends portray a shift away from basic tibiofemoral geometry towards designs which better replicate natural knee kinematics by adding constraint to the medial condyle and decreasing constraint on the lateral condyle [2]. A recent design concept has paired this theory with the concept of guided kinematic motion throughout the flexion range [3]. The purpose of this study was to validate the kinematic pattern of motion of the surface-guided knee concept through in vitro, mechanical testing.

Purpose

The purpose of this study was to examine the influence of weight-bearing on the measurement of in vivo wear of total knee replacements using model-based RSA at 1 and 2 years following surgery.

Hospital type is an indicator for structures and processes of care. The effect of hospital type on hip fracture in-hospital mortality is unknown. We determine whether hip fracture in-hospital mortality differs according to hospital type.

We retrieved records of hip fracture for 167,816 patients aged 65 years and older, who were admitted to a Canadian acute hospital between 2004 and 2012. For each hospital type we measured and compared the cumulative incidence of in-hospital death by in-patient day, accounting for discharge as a competing event.

The cumulative incidence of in-hospital death at in-patient day 30 was lowest for teaching hospital admissions (7.3%) and highest for small community hospital admissions (11.5%). The adjusted odds of in-hospital death were 12% (95% CI 1.06–1.19), 25% (95% CI 1.17–1.34), and 64% (95% CI 1.50–1.79) higher for large, medium, and small community hospital versus teaching hospital admissions. The adjusted odds of nonoperative death were 1.6 times (95% CI 1.42–1.86), and 3.4 times (95% CI 2.96–3.94) higher for medium and small community hospital versus teaching hospital admissions. The adjusted odds of postoperative death were 14% (95% CI 1.07–1.22) and 20% (95% CI 1.10–1.31) higher at large and medium community hospitals versus teaching hospitals. The adjusted odds of postoperative death were largest at small community hospitals but the confidence interval crossed 1 (OR = 1.25, 95% CI 0.92–1.70).

A higher proportion of hip fracture patients die at non-teaching compared to teaching hospitals accounting for length of stay. Higher mortality at small community hospitals may reflect disparities in access to resources and delay to treatment.

Articulation of the polyethylene (PE) insert between the metal femoral and tibial components in total knee replacements (TKR) results in wear of the insert which can necessitate revision surgery. Continuous PE advancements have improved wear resistance and durability increasing implant longevity. Keeping up with these material advancements, this study utilises model-based radiostereometric analysis (mbRSA) as a tool to measure in vivo short-term linear PE wear to thus predict long-term wear of the insert.

Radiographic data was collected from the QEII Health Sciences Centre in Halifax, NS. Data consisted of follow-up RSA examinations at post-operative, six-, 12-, and 24-month time periods for 72 patients who received a TKR. Implanted in all patients were Stryker Triathlon TKRs with a fixed, conventional PE bearing of either a cruciate retaining or posterior stabilised design. Computer-aided design (CAD) implant models were either provided by the manufacturer or obtained from 3D scanned retrieved implants. Tibial and femoral CAD models were used in mbRSA to capture pose data in the form of Cartesian coordinates at all follow-ups for each patient. Coordinate data was manually entered into a 3D modeling software (Geomagic Studio) to position the implant components in virtual space as presented in the RSA examinations. PE wear was measured over successive follow-ups as the linear change in joint space, defined as the shortest distance between the tibial baseplate and femoral component, independently for medial and lateral sides. A linear best-fit was applied to each patient's wear data; the slope of this line determined the annual wear rate per individual patient. Wear rates were averaged to provide a mean rate of in vivo wear for the Triathlon PE bearing.

Mean linear wear per annum across all 72 patients was 0.088mm/yr (SD: 0.271 mm/yr) for the medial condyle and 0.032 mm/yr (SD: 0.230 mm/yr) for the lateral condyle. Cumulative linear wear at the 2-year follow-up interval was 0.207mm (SD: 0.565mm) and 0.068mm (SD: 0.484mm) for the medial and lateral condyles, respectively.

Linear PE wear measurements using mbRSA and Geomagic Studio resulted in 0.056mm/yr additional wear on the medial condyle than the lateral condyle. Large standard deviations for yearly wear rates and cumulative measurements demonstrate this method does not yet exhibit the accuracy needed to provide short-term in vivo wear measurement. Inter-patient variability from RSA examinations is likely a source of error when dealing with such small units of measure. Further analysis on patient age and body mass index may eliminate some variability in the data to improve accuracy. Despite high standard deviations, the results from this research are in proximity to previously reported linear wear measurements 0.052mm/yr and 0.054mm/yr. Linear wear analysis will continue upon completion of >100 patients, in addition to volumetric PE wear over the entire articulating surface.

Modular total hip arthroplasty (MTHA) stems were introduced in order to provide increased intra-operative flexibility for restoring hip biomechanics, improving stability and potentially reducing revision risk. However, the additional interface at the neck-body junction provides another location for corrosion or mechanical failure of the stem. To delineate the mid term revision risk of MTHA stems, we examined data from the Canadian Joint Replacement Registry (CJRR) at the Canadian Institute for Health Information (CIHI).

Kinectiv, Profemur and Rejuvenate modular stems were identified from CJRR records submitted between 2004 and 2014. Revision status was determined by examining the discharge abstract database (DAD) also housed by CIHI, which collects information on all revisions, regardless of whether the procedure was submitted to CJRR.

A total of 2446 modular stems were identified with a mean follow up of 4.2 years (range 0 to 10). Their usage peaked in 2012 (the first year of mandatory CJRR form submission for BC, ON and MB), and dropped rapidly thereafter. A total of 155 (6.3%) were revised. This consisted of 5/301 Kinectiv (1.7%), 141/2050 ProFemur (6.9%), and 9/96 Rejuvenate (9.4%) stems. As a group, this falls below the National Institute for Clinical Excellence (NICE) guidelines of 95% survival at 10 years.

While MTHA stems were introduced to improve outcomes and reduce revision risk, our findings of a 6.3% revision risk at a mean follow up of 4.2 years does not appear to support this.

The wear particles released from the polyethylene (PE) tibial insert of modular total knee replacements (TKRs) have been shown to cause wear particle induced osteolysis, which may necessitate revision surgery [1]. Wear occurs at the backside surface of the PE insert of modular TKRs, resulting from the relative movement between the PE insert and the tibial tray [2]. Wear particles generated from the backside surface of the PE insert have been shown to be smaller in size than those originating from the articular surface [1], and may therefore have increased biological activity and osteolytic potential [3-4]. The ability to predict backside micromotion and contact pressure by finite element simulation has previously been demonstrated by O'Brien et al. [6-7]. Although the effect of insert thickness on articular surface contact pressure has been investigated [5], the effects of insert thickness on backside contact pressures, backside micromotion, and wear has not received adequate attention. Brandt et al. [2] has suggested that increased insert thickness was associated with increased backside damage (Fig. 1). In the present study, finite element simulations were conducted using the Sigma - Press Fit Condylar TKR (Sigma-PFC®, DePuy Orthopedics Inc., Warsaw, IN) with inserts of different insert thickness ranging between 5, 10, 15, 20 and 25 mm. The TKRs were simulated under ISO 14343-2 [8]. A non-linear PE material model was implemented by means of the J2-plasticity theory [6] and the effects of insert thickness on backside micromotion and contact pressure were analyzed. At the peak loading of the simulated gait cycle (time=13%), the 5 mm thick PE insert showed a greater backside peak contact pressure than the 25 mm thickness PE insert. Increasing insert thickness from 5 mm to 25 mm lead to approximately 15% greater peak micromotion at the modular interface (Fig. 2). This effect may be attributed to the ability of the PE material to distribute the load more evenly through deformation at the modular interface and reduce micromotion for thinner inserts. It is suggested that increased insert thickness results in increased moments at the modular interface that could lead to increased backside wear in silico. Although an increase in PE insert thickness was only associated with a moderate increase in backside micromotion in the present study, it was deemed likely that backside micromotion could be accelerated for thicker inserts in vivo as the PE locking mechanism has been shown to degrade after extended implantation periods.

Femoral components with an oxidized zirconium-niobium (OxZr) gradient ceramic surface (Oxinium, Smith & Nephew, Memphis, TN) were introduced as an alternative to cobalt-chromium (CoCr) alloy femoral components for the purpose of PE wear reduction in total knee replacements [1]. In the present study, the surface damage and clinical performance of both CoCr alloy and OxZr femoral components were investigated. By matching CoCr alloy and OxZr femoral components for clinical factors, as done by Heyse et al. [2], the surface damage on retrieved CoCr alloy and OxZr femoral component was assessed. Twenty-six retrieved cobalt-chromium (CoCr) alloy femoral components were matched with twenty-six retrieved oxidized zirconium (OxZr) femoral components for implantation period, body-mass index, patient gender, implant type (cruciate ligament retaining/substituting), and polyethylene insert thickness. Detailed surface profilometry was performed on retrieved femoral condyles in areas that had not been damaged by gouging [3] with the specific purpose of investigating the in vivo wear behaviour of undamaged OxZr surface. In addition, the cumulative survivorships were calculated for patients who had received CoCr alloy or OxZr femoral components from our orthopaedic database. In order to identify factors that affect the clinical performance of CoCr alloy and OxZr femoral components, the findings from the retrieval analysis and the survivorship analysis were combined. The Rp, Rpm, and Rpk-values for the retrieved CoCr alloy femoral components were found significantly higher than the Rp, Rpm, and Rpk-values for the retrieved OxZr femoral components (p ≤ 0.031). The roughness parameters values (Ra, Rq, Rz, Rp, Rpm, Rpk, Rv, and Rsk) for the retrieved CoCr alloy femoral components were found significantly higher than the values of the new, never implanted CoCr alloy femoral components (p ≥ 0.001). The surface roughness was higher on the medial condyles than the lateral condyles of the retrieved CoCr alloy femoral components; such a difference was not observed on the retrieved OxZr femoral components. The OxZr bearing surface appeared to protect the femoral components from abrasive wear in vivo. At 8.5-years follow up, the cumulative survivorship for the CoCr alloy femoral components (98%) was not found to be statistically significantly different (p = 0.343, Breslow test) from the OxZr femoral components (97.5%). Therefore, OxZr femoral components appeared to possess low wear characteristics and could be particularly suitable for younger, heavier patients to ensure long-term durability.