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.

Total hip arthroplasty (THA) is one of the most successful and commonly performed surgical interventions worldwide. Based on registry data, at one-year post THA, implant survivorship is nearly 100% and patient satisfaction is 90%. A novel, porous coated acetabular implant was introduced in Europe and Australia in 2007. Several years after its introduction, warnings were issued for the system when used with metal-on-metal bearings due to adverse local tissue reaction, with one study reporting a 24% failure rate (Dramis et al. 2014). A subsequent 2018 study by Teoh et al. showed that the acetabular system had a survival rate of 98.9% at five years when used with conventional polyethylene or ceramic bearing surfaces. The current study was conducted to determine the safety and effectiveness of the acetabular system using standard highly-crosslinked polyethylene (XLPE) and ceramic liners at five-year follow-up. Our hypothesis was that the acetabular system would exhibit survivorship comparable to other acetabular components on the market at five-year follow-up.

A prospective, non-randomized study was conducted from February 2009 to June 2017 at eight sites in Canada and the USA. One hundred fifty-five hips were enrolled and 148 hips analyzed after THA indicated for degenerative arthritis. At five-year follow-up, 103 subjects remained for final analysis. All patients received a zero, three, or multi-hole R3 acetabular shell with Stiktite porous coating (Smith & Nephew, Inc., Memphis, TN, USA). Standard THA surgical techniques were employed, with surgical approach and either of a XLPE or ceramic bearing surface chosen at the discretion of the surgeon. The primary outcome was revision at five-years post-op with secondary outcomes including the Harris Hip Score (HHS), Hip Disability and Osteoarthritis Outcome Score (HOOS), Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC), radiographic analysis, and post-operative adverse events. Data and outcomes were analyzed using summary statistics with 95% confidence intervals, t-tests, and Wilcoxon Rank tests.

At five-year follow-up the overall success rate was 97.14% (95% CI: 91.88–100). When analyzed by liner type, the success rate was 96.81% (95% CI: 90.96–99.34) for polyethylene (n=94) and 100% (95% CI: 71.51–100) for ceramic (n=11), with no significant difference between either liner type (p=1). There were three revisions during the study (1.9%), two for femoral stem revision post fracture, and one for deep infection. The HHS (51.36 pre-op, 94.50 five-year), all 5 HOOS sub-scales, and WOMAC (40.9 pre-op, 89.13 five-year) scores all significantly improved (p < 0 .001) over baseline scores at all follow-up points. One (0.7%) subject met the criteria for radiographic failure at one-year post-op but did not require revision. Six (1.8%) of the reported adverse events were considered related to the study device, including four cases of squeaking, one bursitis, and one femur fracture.

Results from this five-year, multicenter, prospective study indicate good survivorship for this novel, porous coated acetabular system. The overall survivorship of 97.14% at five-year follow-up is comparable to that reported for similar acetabular components and aligns with previous analyses (Teoh et al. 2018).

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).

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.

Introduction

Detailed analysis of retrieved total hip replacements (THRs) is valuable for assessing implant and material successes and failures. Reduction of bearing wear and corrosion and fretting of the head-neck trunnion is essential to implant durability and patient health. This research quantifies and characterizes taper and bearing surface damage on retrieved oxidized zirconium THRs.

Non-large head Metal-on-metal (MoM) hip replacements were seen as a solution to concerns about implant wear in younger patients. Mid-term loosening of once well-fixed hydroxyapatite (HA) coated femoral stems was recently observed in select MoM patients upon revision surgery. Accordingly, an implant retrieval study was undertaken to examine the incidence of aseptic loosening of in HA-coated femoral stems with MoM, ceramic on ceramic (CoC) and metal on polyethylene (MoP) bearing couples.

A single-centre implant retrieval lab reviewed 44 hydroxyapatite (HA)-coated titanium wedge taper stems of the same design retrieved over a period of 9 years. Ten were MoM articulations, 23 MoP and 11 CoC. Head sizes ranged from 28 to 40 with only four 40mm heads, all of which were MoM. Reason for revision, duration of implantation, femoral head size, patient age and body mass index was recorded for each retrieval. Goldberg corrosion scores were determined for the taper surfaces of each retrieval, with ‘0’ indicating no corrosion and ‘3’ indicating severe corrosion. Logistic regression analysis, Wilcoxan Rank Sum and Fischer's exact test were used for statistical analysis.

Aseptic loosening was the listed reason for revision in 18 of 44 cases. MoM bearing was associated with increased probability of aseptic loosening (Odds ratio 7.1 (95%CI 1.1–47.0) p=0.042). Severity of corrosion was also associated with aseptic loosening (Odds ratio 2.75 (95%CI 1.1–6.6) p=0.02). Head size and patient age had no correlation. Median time to revision of implants for aseptic loosening was 4.5 years (range: 4.2–7.0 years) for MoM versus 1.4 years (range: 0.3–3.0) for other bearing couples (p=0.004). Aseptic loosening was categorised as early (<=2 years) or mid-term (>2 years). No MoM hips were revised for aseptic loosening in the first 2 years while 8 of the 11 mid-term revisions had MoM articulations (p=0.004). Taper corrosion was more severe in mid-term aseptic loosing cases (p=0.049).

MoM HA-coated hip replacements appear to be associated with increased mid-term aseptic loosening compared to other bearing couples. Patients with MoM HA-coated hip replacements should be monitored regularly beyond the initial 1 to 2 years following surgery. Future analyses will examine the presence and progression of femoral radiolucency prior to revision surgery to determine an approximate timeline of stem loosening in this patient cohort. This research highlights the importance of implant retrieval programs to assess post-revision implant characteristics for early identification of possible device issues.

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.

Introduction

This retrieval analysis study consisted of two goals. The first goal was to determine if there was a difference in the corrosion and fretting damage along the taper interface between large femoral heads in comparison to monopolar hemiarthroplasty heads. The second goal was to examine if the diameter of monopolar hemiarthroplasty heads can influence corrosion and fretting damage along the taper interface.

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.

Ceramic-on-ceramic (C-C) total hip replacements (THRs) are an attractive option for young, active patients [1, 2]. However, more clinical data is necessary to establish the reasons of failure of contemporary C-C THRs in vivo. The objective of the present study was to assess the surface damage on retrieved C-C THRs and determine possible influential factors that may explain their in vivo performance. Thirty-five C-C retrievals of material type Biolox® forte (n=28) and Biolox® delta (n=7) (CeramTec AG, Plochingen, Germany) were collected after a mean of 3.7 ± 3.2 years in vivo. Semi-quantitative surface damage assessment [3] was performed on all retrievals to obtain both a damage score (DS) (Fig. 1). Contact profilometry was performed on the retrieved femoral heads to characterize the type of surface damage (metal transfer, stripe wear). Scanning electron microscope (SEM) images were obtained from two femoral heads displaying areas of typical surface damage. The implantation period correlated with the damage score (DS) of the femoral heads (R=0.573, p<0.001) and the acetabular cups (R=0.592, p<0.001). However, the metal transfer DS of the femoral heads did not correlate with implantation period (R=0.185, p=0.29). Surface roughness of metal-transfer areas were positively skewed (additive metal transfer) while the stripe damage areas were negatively skewed (grain removal), as evidenced by SEM analysis. Stripe damage was observed on both the Biolox® forte and Biolox® delta retrieved femoral heads; however, the extent of grain removal appeared less severe on the Biolox® delta retrieved femoral heads due to their overall smaller grain size (Fig. 2). Inclination angles > 45° was associated with a greater DS rate [DS/time of implantation], which had also been suggested elsewhere [4]. Four patients reported squeaking in their C-C THRs; one of which was a 54 yr-old male patient who completed three full marathons with his implant. In this his case, the DS for this retrieval was below average, with metal-transfer being the only macroscopic damage feature. Fracture of the acetabular liner occurred in three patients, all of which had malpositioned components. Metal-transfer on the ceramic surface could possibly cause a local break down of the fluid film and may facilitate, in addition to an increased inclination angle, stripe damage via an adhesive wear mechanism. Therefore, direct contact between the Ti-alloy acetabular shell and the ceramic femoral head should be avoided at primary surgery. C-C THRs remain an attractive option for young, active patients, but care must be taken during implantation to appropriately position the acetabular cup and to avoid unwanted metal-transfer as such alteration at the bearing interface may change implant tribology.

Revision of fractured ceramic-on-ceramic total hip replacements with a cobalt-chromium (CoCr) alloy-on-polyethylene articulation can facilitate metallosis and require further expensive revision surgery [1–3]. In the present study, a fifty-two year old male patient suffered from fatal cardiomyopathy after undergoing revision total hip arthroplasty. The patient had received a polyethylene-ceramic acetabular liner and a ceramic femoral head as his primary total hip replacement. The polyethylene-ceramic sandwich acetabular liner fractured in vivo after 58 months and the patient underwent his first revision surgery where he received a Vitamin E stabilized acetabular Polyethylene (PE) liner and a CoCr alloy femoral head with documented synovectomy at that time. After 15 months, the patient was admitted to hospital in cardiogenic shock, with retrieval of the bearing components. Before the second revision surgery, peak serum cobalt levels measured 6,521 μg/L, 78-times greater than serum cobalt levels of 83μg/L associated with cobalt poisoning [4]. Serum titanium levels found in the patient measured 17.5 μg/L) normal, healthy range 0–1.4 μg/L). The retrieved CoCr alloy femoral head had lost a total of 28.3g (24% or an estimated amount of 102 × 10⁻⁹ wear particles (∼2 μm diameter) [1]) within 16 months of in vivo service. Despite initiating a cobalt chelating therapy, the patients' cardiac left ventricular ejection fraction remained reduced at 6%. This was followed by multi-organ failure, and ultimately the patient passed away shortly after being taken off life support. Embedded ceramic particles were found on the backside and articular surfaces of the Vitamin E-stabilized PE acetabular liner. Evidence of fretting wear on the titanium (Ti) alloy acetabular shell was present, possibly explaining the increased serum Ti levels. Scanning electron microscopy and energy dispersive X-ray analyses confirmed Ti alloy transfer on the embedded ceramic particles on the backside PE liner surface and CoCr alloy transfer on the embedded ceramic particles on the articular PE liner surface. A fractured ceramic-on-ceramic total hip replacement should not be revised to a CoCr alloy-on-polyethylene articulation irrespective of concurrent synovectomy [5] as it can cause severe, third-body wear to the CoCr alloy femoral head that can lead to metallosis with fatal, systemic consequences.

Purpose

Radiostereometric Analysis (RSA) is a well developed imaging technique used to estimate implant fixation of orthopaedic implants in randomized clinical trials. The precision of RSA depends on a number of factors including image quality related to the individual modality properties. This study assesses the precision of RSA with a novel Digital Radiography (DR) system compared to a CR imaging system using different imaging techniques. Additionally, the study assesses the precision of locating beads embedded in a modified spine pedicle screw.

Introduction

Radiostereometric Analysis (RSA) is an imaging method that is increasingly being utilized for monitoring fixation of orthopaedic implants in randomized clinical trials. Extensive RSA research has been conducted over the last 35+ years using standard clinical x-ray acquisition modalities that irradiate screen/film media or Computed Radiography (CR) plates. The precision of RSA can depend on a number of factors including modality image quality.