Rate Of Resurfacing Research Articles

Global Trends in Patellar Resurfacing From 2004 to 2022

BackgroundInternational rates of patellar resurfacing in primary total knee arthroplasty (TKA) are highly variable. This study sought to determine how trends in patellar resurfacing rates have changed between 2004 and 2022. In addition, we investigated how modern rates of revision have varied between resurfaced and unresurfaced patellae in primary TKA among national joint registries. MethodsData between 2004 and 2022 was obtained either from the publicly available joint registry annual reports, a literature review, or via direct correspondence with registry personnel in Sweden, New Zealand, Australia, the United States, Norway, the United Kingdom, the Netherlands, Switzerland, Canada, and India. Only English language national joint registries or data via direct correspondence with registry administrators were utilized. Additionally, the 10-year cumulative risk of revision TKA with and without patellar resurfacing was pulled from those registries that had this data available. ResultsThere were persistent differences in the rates of patellar resurfacing among countries. Australia documented a 40% increase in patellar resurfacing rates, while other countries demonstrated modest or little change in resurfacing rates. This may indicate that surgeons are making the decision to resurface based on national TKA revision rates. The average rates of patellar resurfacing in primary TKA ranged from 4% in Sweden to 94% in the United States. Canada, the United States, Australia, and Switzerland documented a lower risk of revision when the patella was resurfaced, while Sweden, conversely, showed a higher risk of revision with resurfacing. ConclusionsRates of patellar resurfacing in primary TKA were highly variable among countries, as were rates of change over time. It appears that the optimal patellar resurfacing strategy may depend mostly on unique patient factors and surgeon expertise. Future studies should attempt to elucidate the individual patient characteristics that contribute to increased risks of revision or anterior knee pain to determine who will most benefit from patellar resurfacing in primary TKA.

Total knee arthroplasty following lateral closing-wedge high tibial osteotomy versus primary total knee arthroplasty: a propensity score matching study

BackgroundThe disparity in patient-reported outcomes between total knee arthroplasty (TKA) following high tibial osteotomy (HTO) and primary TKA has yet to be fully comprehended. This study aims to compare the patient-reported outcomes, radiological parameters and complication rates between TKA following HTO and primary TKA.MethodsSixty-five patients who underwent TKA following lateral closing-wedge HTO were compared to a matched group of primary TKA at postoperative 6-months and 1-year. Between-group confounders of age, gender, smoking status, Body Mass index, preoperative Numeric Rating Scale (NRS) pain in rest, Knee injury and Osteoarthritis Outcome Score-Physical function Shortform (KOOS-PS), EuroQol five-dimensional (EQ-5D) overall health score, and Oxford Knee Score (OKS) were balanced by propensity score matching. Patient-reported outcome measures were NRS pain in rest, KOOS-PS, EQ-5D overall health score, and OKS. Radiological parameters were femorotibial angle, medial proximal tibial angle, anatomical lateral distal femoral angle, posterior tibial slope, and patellar height assessed by Insall-Salvati ratio. The complication rates of TKA were compared between the two groups. The HTO survival time, the choice of staple removal before or during TKA in patients who underwent TKA following HTO patients, and the rate of patellar resurfacing were assessed. The p value < 0.0125 indicates statistical significance after Bonferroni correction.ResultsAfter propensity score matching, no significant between-group differences in the patient-reported outcome measures, radiographical parameters and complication rates were found (p > 0.0125). In the TKA following HTO group, with an average HTO survival time of 8.7 years, staples were removed before TKA in 46 patients (71%) and during TKA in 19 patients, and 11 cases (17%) had patella resurfacing. In the primary TKA group, 15 cases (23%) had patella resurfacing.ConclusionThe short-term assessment of TKA following HTO indicates outcomes similar to primary TKA. A previous HTO does not impact the early results of subsequent TKA, suggesting that the previous HTO has minimal influence on TKA outcomes.Level of evidenceIII, cohort study.

Using Io's Sulfur Isotope Cycle to Understand the History of Tidal Heating

AbstractStable isotope fractionation of sulfur offers a window into Io's tidal heating history, which is difficult to constrain because Io's dynamic atmosphere and high resurfacing rates leave it with a young surface. We constructed a numerical model to describe the fluxes in Io's sulfur cycle using literature constraints on rates and isotopic fractionations of relevant processes. Combining our numerical model with measurements of the 34S/32S ratio in Io's atmosphere, we constrain the rates for the processes that move sulfur between reservoirs and model the evolution of sulfur isotopes over time. Gravitational stratification of SO2 in the upper atmosphere, leading to a decrease in 34S/32S with increasing altitude, is the main cause of sulfur isotopic fractionation associated with loss to space. Efficient recycling of the atmospheric escape residue into the interior is required to explain the 34S/32S enrichment magnitude measured in the modern atmosphere. We hypothesize this recycling occurs by SO2 surface frost burial and SO2 reaction with crustal rocks, which founder into the mantle and/or mix with mantle‐derived magmas as they ascend. Therefore, we predict that magmatic SO2 plumes vented from the mantle to the atmosphere will have lower 34S/32S than the ambient atmosphere, yet are still significantly enriched compared to solar‐system average sulfur. Observations of atmospheric variations in 34S/32S with time and/or location could reveal the average mantle melting rate and hence whether the current tidal heating rate is anomalous compared to Io's long‐term average. Our modeling suggests that tides have heated Io for &gt;1.6 Gyr if Io today is representative of past Io.

Low effective ultraviolet exposure ages for organics at the surface of Enceladus

The saturnian moon Enceladus presents a remarkable opportunity in our solar system for searching for evidence of life, given its habitable ocean and plume that deposits organic-bearing ocean material onto the surface. Organic ocean material could be sampled by a lander mission at Enceladus. It is of interest to understand the amount of relatively pristine, unaltered organics present on the surface, given the ultraviolet (UV) and plasma environment. Here, we investigate UV penetration into Enceladus’s surface and the resultant effective exposure ages for various regions, using the UV reflectance spectrum of Enceladus as measured by the Hubble Space Telescope and considering the rate of resurfacing by plume fallout. In high plume fallout regions near the south pole, plume grains are buried by fresher grains within years, resulting in low levels of exposure to solar UV, which penetrates only ~100 micrometers. Regions at latitudes south of ~40°S can have exposure ages <100 years, translating to relatively high abundances of pristine organic material preserved in the regolith.

The tectonics and volcanism of Venus: New modes facilitated by realistic crustal rheology and intrusive magmatism

To explain Venus’ young surface age and lack of plate tectonics, Venus’ tectonic regime has often been proposed to be either an episodic-lid regime with global lithospheric overturns, or an equilibrium resurfacing regime with numerous volcanic and tectonic activities. Stratigraphic analysis suggests that Venus’ surface tectonics could be a combination of these two end-member models with a global resurfacing event that created most of the crust followed by tectonic and volcanic activities until now. Recent analyses of Venus’ satellite images also suggest widespread lithospheric mobility in the lowland basins that does not fit the episodic-lid tectonic regime. Here, we use global 2-D thermochemical convection models with realistic parameters, including rheology (dislocation creep, diffusion creep, and plastic yielding), an experiment-based plagioclase (An75) crustal rheology, and intrusive magmatism, to investigate the tectonics and mantle evolution of Venus. We find that surface tectonics is strongly affected by crustal rheology. With a “weak” plagioclase-rheology crust, models exhibit episodic overturns but with continuously high surface mobility and high distributed surface strain rates between overturns, leading to a new tectonic regime that we name “deformable episodic lid”. On the other hand, olivine-crustal-rheology models exhibit either standard episodic-lid tectonics, i.e. with mobility that is high during overturns and near zero between overturns, or stagnant-lid tectonics, i.e. with near-zero mobility over the entire model time. In models with plagioclase-rheology crust, magmatic resurfacings are short-lived and randomly located, leading to a rather uniform resurfacing rate. Also, a combination of plagioclase crustal rheology and dislocation creep can weaken the lithosphere sufficiently to facilitate lithospheric overturns without applying plastic yielding. Internally, the composition-dependent density profile results in a “basalt barrier” at the mantle transition zone, which strongly affects Venus’ mantle evolution. Only strong plumes can penetrate this basalt barrier and cause global lithospheric overturns. This basalt barrier also causes global internal episodic overturns that generate global volcanic resurfacing in stagnant-lid models, which suggests a new resurfacing mechanism that does not involve lithospheric overturns. We name this regime “stagnant episodic-volcanic-resurfacing”. Results in models with plagioclase crustal rheology and low eruption efficiencies best fit current estimates of crustal thickness, surface age, and tectonic structures based on observations of Venus. The crustal thickness in models with an olivine-rheology crust is limited by the basalt–eclogite phase transition and is higher than observation-based estimates. Higher intrusion rates better fit these estimates, as models with high eruption efficiency predict very low surface age (< 100 Myr).

Outcomes and Survivorships of Total Knee Arthroplasty Comparing Resurfaced and Unresurfaced Patellae

BackgroundThe decision to resurface the patella in total knee arthroplasty (TKA) is controversial. While there is some consensus that leaving the patella unresurfaced increases risk of reoperation, there is conflicting evidence about patient reported outcomes or indications for resurfacing. This study sought to determine recent rates of patellar resurfacing, examine factors affecting rates of resurfacing, and analyze the associations between patellar resurfacing and both revision rates and patient-reported outcome measures (PROMs). MethodsThe American Joint Replacement Registry was used to identify primary TKAs performed for osteoarthritis between 2012 and 2021. Cases were classified as resurfaced patella and unresurfaced patella (URP). Outcomes analyzed included trends in patellar resurfacing, factors influencing rate of resurfacing, revision rates, operative time, and 2 PROMs. ResultsRates of patellar resurfacing decreased and rates of URP increased significantly faster in ambulatory surgery centers and among high volume surgeons. Operative time was significantly lower in URP versus resurfaced patella (88.15 versus 89.90 minutes). The URP were significantly more likely to require revision surgery (odds ratio = 1.206 (1.078, 1.35), P = .0011). There was no significant difference in the likelihood of achieving the minimal clinically important difference in PROMs between resurfaced and nonresurfaced TKAs at 1 year (odds ratio = 1.060 (0.710, 1.581), P = .7755). ConclusionThere was no difference in minimal clinically important difference between resurfaced and URPs and no clinically relevant difference in operative time. However, URPs were more likely to require revision surgery. Therefore, the decision not to resurface should be made carefully considering the known risk of revision and the uncertain benefit.

Rare primary patellar resurfacing does not lead to more secondary patellar resurfacing: analysis of 70,014 primary total knee arthroplasties in the Dutch Arthroplasty Register (LROI).

Background and purposeCurrent literature provides no conclusive evidence in support of a patellar resurfacing vs. non-resurfacing regime. Therefore, we compared the incidence of secondary patellar resurfacing among hospitals using 3 different primary patellar resurfacing regimes in the Netherlands. Secondarily we identified patient and surgical characteristics associated with primary patellar resurfacing and secondary patella resurfacing following non-resurfaced primary total knee arthroplasty (TKA).Patients and methodsWe used data from 2014–2016 of the Dutch Arthroplasty Register. Hospitals were divided into rare (0–10%), selective (>10% to 90%), and usually primary patellar resurfacing (>90%) regimes. We performed a logistic regression analysis for associated factors of primary patellar resurfacing in the selective resurfacing subgroup and for secondary patellar resurfacing in the rare resurfacing subgroup.ResultsThe rate of primary resurfacing was 5.2% for the rare and 36% for the selective patellar resurfacing regimes, with similar secondary patellar resurfacing (1.1% vs. 0.9%). Predictors for primary patellar resurfacing were being female (OR 1.3) and younger (50–59 years, OR 1.4). The PS prosthesis design had a higher OR (4.1) than the CR design. Younger age (50–59 years, OR 1.5) and PS prosthesis (OR 2.7) were significant predictors of secondary patellar resurfacing. Particular surgical systems have a higher rate of primary and secondary patellar resurfacing.InterpretationLow rates of secondary patellar resurfacing in hospitals with a rare resurfacing regime indicate that this regime does not lead to more secondary patellar resurfacing then selective resurfacing. In the Dutch orthopedic community primary and secondary patellar resurfacing is associated with using a posterior stabilizing design, being younger, and using particular TKA systems.

Model versus measured detrital zircon age signatures of the early Earth

The scarcity of Archean (4.0–2.5 Ga) rocks on Earth limits our ability to analyse when plate tectonics began and what tectonic mode may have preceded it. Proposed times for the initiation of plate tectonics range from the Hadean eon (>4 Ga) to the Neoproterozoic era (ca 1.0–0.5 Ga), before which the Earth may have been dominated by stagnant-lid regimes that cooled through volcanic advection, partial crustal convection, and/or conduction. Here, we use various 1D numerical simulations of potential geodynamic states of the early Earth to predict detrital zircon age patterns. We find that different Archean tectonic modes yield contrasting temporal differences between zircon crystallization ages and respective maximum depositional ages of the sediments from which the detrital zircons were sourced (we have termed such age differences ‘ΔtDZ’). We compare these predictions with a global compilation of detrital zircon age data from >400 Archean (meta)sedimentary units, including new data from six samples from the Pilbara Craton, Western Australia. Combined, the data show significantly increased contributions from high ΔtDZ detrital zircons after ca 3.4 Ga. For the Pilbara Craton, 90% of the detrital zircons in each of two >3.4 billion-year-old metasedimentary samples have crystallization ages that are ≤110 million years older than the maximum age of deposition (we use ‘ΔtDZ90’ to denote such age differences hereafter). The ΔtDZ90 of Pilbara strata formed at ca 3.29–3.27, 3.24–3.18 and ca 2.95 Ga show successively larger ΔtDZ90 values of ca 270, 290 and 570 million years, respectively. Globally, pre-3.4 billion-year-old samples show a low mean ΔtDZ90 of around 70 million years, but a mean of around 320 million years for 3.40–2.80 billion-year-old samples. Samples with >90% of zircons featuring >250 million year ΔtDZ values only occur at or after ca 3.23 Ga. These results are consistent with a significant slow-down in the rate of volcanic resurfacing, and increasing contributions of detritus from basins associated with exhumation and/or volcanic quiescence after ca 3.4 Ga. Compared with detrital zircon age predictions, our findings are best explained by a transition from volcanism-dominated stagnant-lid modes to one increasingly dominated by subduction over the period 3.4–3.2 Ga, with the emergence of plate tectonics within this period or at some time thereafter.

Secondary Patellar Resurfacing in TKA: A Combined Analysis of Registry Data and Biomechanical Testing.

The German Arthroplasty registry (EPRD) has shown that different prosthesis systems have different rates of secondary patellar resurfacing: four years after implantation, the posterior-stabilized (PS) Vega prosthesis has a 3.2% risk of secondary patellar resurfacing compared to the cruciate-retaining (CR) Columbus prosthesis at 1.0% (both Aesculap AG, Tuttlingen, Germany). We hypothesized that PS implants have increased retropatellar pressure and a decreased retropatellar contact area compared to a CR design, which may lead to an increased likelihood of secondary patellar resurfacing. Eight fresh frozen specimens (cohort 1) were tested with an established knee rig. In addition, a possible influence of the registry-based patient collective (cohort 2) was investigated. No significant differences were found in patient data–cohort 2-(sex, age). A generally lower number of PS system cases is noteworthy. No significant increased patella pressure could be detected with the PS design, but a lower contact area was observed (cohort 1). Lower quadriceps force (100°–130° flexion), increased anterior movement of the tibia (rollback), greater external tilt of the patella, and increasing facet pressure in the Vega PS design indicate a multifactorial cause for a higher rate of secondary resurfacing which was found in the EPRD patient cohort and might be related to the PS’ principle function.

The Patellar Resurfacing in Total Knee Prosthesis: Indications for Bone Stock and Patellar Morphology.

The patellar resurfacing is still a controversial and unresolved problem. The choice to use the patellar resurfacing in the total knee prosthesis (TKP) is decided by the surgeon's experience; he analyzes the thickness, the shape, consumption of the surface and he chooses the use of patellar resurfacing or to limit itself to cheiloplasty, denervation, or often to the release of the lateral wing ligament. He also assesses the metabolic state of the bone linked to Osteoporosis and the potential fragility of the joint and kneecap in particular. Bone loss after total knee arthroplasty (TKP) may lead to periprosthetic fractures that are associated with significant costs (morbidity, economic, etc.) and pose a challenge to operative fixation. The literature doesn't express a definitive judgment on the two options, since the results can be overlapped on average. Each option has advantages and disadvantages to be considered in the overall balance of the patellar operation. In reality, however, this technical choice requires more consolidated decision-making criteria so as to minimize the incidence of post-surgical femoral-patellar pain syndrome, the second cause of failure, which frequently leads to revision of the implant. The balance between experience and evidence can be a compromise in the choice of surgery. The experience documented in the literature must identify the parameters capable of constructing an algorithm aimed not only at the secondary resurfacing rate, but at the overall clinical evaluation. This has implications also for the rehabilitation of these patients after surgery.

Subsurface architecture of alpine icy debris fans: Integration of ground-penetrating radar and surface observations in Alaska and New Zealand

Icy debris fans (IDFs) are extremely dynamic supraglacial landforms at the mouths of bedrock catchments between valley glaciers and icecaps. Recent studies quantified the nature, pace, and volume of mass flow processes contributing ice and sediment to IDFs by integrating field observations, drone and time-lapse imagery, and terrestrial laser scanning. New geophysical data presented herein characterize the subsurface architecture of IDFs along the McCarthy Glacier in Alaska and the Douglas, La Perouse, and Mueller Glaciers in New Zealand. Ground Penetrating Radar (GPR) profiles and soundings from field surveys during 2013–2015 provide stratigraphic evidence of the following subsurface processes important in the delivery of ice/sediment through IDFs to glaciers: (1) transitional merging of fan IDF deposits with valley glacier ice in cirque settings, (2) progressive rotation (slumping) of IDF deposits preserved in the hanging walls of downfan-dipping crevasses/faults, (3) progradation of IDF deposits onto valley glaciers, and (4) buttressing of IDF deposits along the margins of valley glaciers. The GPR-based variations in subsurface architecture/processes are attributable to previously documented variations in ice/sediment supply from overlying icecaps/nevés and topographic interaction with valley glacier junctions.GPR profiles document major depositional units separated by prominent reflectors, interpreted as annual ablation lag surfaces where lithic sediments are relatively concentrated. Most IDFs contain less than five depositional units, which may reflect the transitory nature of ice/sediment in these dynamic landforms. The uppermost depositional package on IDFs revealed by GPR is interpreted as deposition from the year preceding the GPR survey because it appears unconsolidated and lacks diffractions common in ice imaged in older (lower) units. The thickness of the upper package is typically less than or equal to the thickness of new deposits recorded by time-lapse cameras spread evenly over fan surfaces, which is expected accounting for compaction and ablation.The new geophysical datasets, together with previous surface observations, bear directly on managing hazards and evaluating glacial budgets in alpine regions. In particular, documentation of progressive rotation, buttressing, and progradation in IDF subsurface stratigraphies indicates protracted episodes of landform instability during deglaciation, consistent with previous surface observations documenting exceptionally high rates of depositional resurfacing and slumping. GPR-based evidence for subsurface deformation suggests ice/sediment is transferred to valley glaciers through IDFs. This interpretation is supported by previous visual evidence, including surface sliding/glacial flow and exceptionally high rates of deposition on IDFs coeval with little change in fan size. Integrating the role of IDFs in glacier budget models may result in forecasting a lower rate of deglaciation than traditionally recognized for some glaciers decoupled from icecaps.

Early Results From the American Joint Replacement Registry: A Comparison With Other National Registries

BackgroundThe American Joint Replacement Registry (AJRR) was created to capture knee and hip arthroplasty data in the United States. The purpose of this study was to compare early reports from the AJRR to other national registries to identify topics for future analysis. MethodsHip and knee arthroplasty data were extracted from the AJRR, Australia, New Zealand, United Kingdom, Norway, and Sweden from 2014 to 2016. Hip arthroplasty data including femoral and acetabular fixation, bearing surface, head size, dual-mobility bearings, resurfacing, and revision burden were compared. Knee arthroplasty data including polyethylene type, unicondylar arthroplasty, mobile bearings, cruciate-retaining implants, patella resurfacing, and revision burden were compared. Registry characteristics and patient demographics were reported using descriptive statistics. ResultsIn 2016, the AJRR captured 28% of arthroplasty procedures performed in the United States compared with 95%-98.3% among other registries. Cementless femoral fixation was 96.7% in the AJRR compared with 21.8%-63.4%. Ceramic and 36-mm heads were most common in AJRR; all other registries reported that metal and 32-mm heads were most popular. Dual-mobility articulations were used in 8% of primary and 28% of revision total hip arthroplasty procedures in the AJRR. The AJRR reported a unicondylar knee arthroplasty rate of 3.2% compared with 5.1%-13.3% in other registries, but the highest rates of posterior-stabilized total knee arthroplasties (48.5% compared to 8.2%-28.7%) and patella resurfacing (93.9% compared to 2.4%-51.6%). ConclusionSeveral differences in hip and knee arthroplasty practices exist between the United States and other countries. Future studies should focus on understanding why differences in practice trends exist and assess outcomes associated with these practices. Level of EvidenceLevel III, retrospective.

A Parameterization for Volcanic Heat Flux in Heat Pipe Planets

AbstractRocky planets with high levels of internal heat production experience high rates of melting and extensive volcanic resurfacing in the heat pipe mode of planetary heat transport. On Earth, this took place prior to the onset of plate tectonics during the first billion or more years. The extraction of melt from a planetary mantle affects the mantle dynamics, the temperature structure of the interior, the viscosity of mantle material, and the timescales of thermal equilibration in the mantle, and therefore, developing a quantitative parameterization for heat transport by volcanism is necessary to calculate the thermal histories of terrestrial planets efficiently. In this work, we develop a quantitative parameterization of heat transport in planetary mantles including the effect of melting. The heat flux due to melting, the internal temperature of the mantle, the temperature of the lid base, the lid thickness, and the heat flux due to conduction were calculated using the parameterization for different cases of solidus gradient and surface melting temperatures, and the values were compared with the results of numerical simulations for validation. The good fit achieved (&lt;15% relative error) over a large range of melt fluxes with no additional parameters indicates that the parameterization usefully and accurately models the process of mantle convection including melting.

Patellar Resurfacing in Total Knee Arthroplasty: A Cost-Effectiveness Analysis

BackgroundThis study estimates the cost-effectiveness of patellar resurfacing in total knee arthroplasty (TKA). MethodsWe conducted a cost-effectiveness analysis using a decision analytic model representing a hypothetical TKA cohort, with or without patellar resurfacing, using data from the 2014 Australian Registry. The model represents 3 possible postoperative health states: (1) well, (2) patellofemoral pain, or (3) serious adverse event (any event resulting in a revision). Our effectiveness outcome was the quality-adjusted life year, from published utility scores. We estimated cost-effectiveness from a Canadian public healthcare payer perspective. Costs and quality of life were valued in 2015 United States dollars and discounted annually at 5%. ResultsOur results suggest that TKA with resurfacing is cost-effective compared to nonresurfacing. Unresurfacing the patellae resulted in higher costs ($13,296.63 vs $12,917.01) and lower quality-adjusted life year (5.37 vs 6.01) at 14 years. Sensitivity analysis suggests that if rates of secondary resurfacing are <0.5%, there was no cost difference. ConclusionOver 14 years postoperative, patellar resurfacing appears to be cost-effective, due to higher revision rates for unresurfaced TKA. Although our results suggest resurfacing improves quality of life, our model is limited by the availability and validity of long-term utility outcomes reported for TKA. Our cost-effectiveness analysis showed superiority of the resurfacing compared to retention of the patella.

Should the patella be resurfaced in distal femoral replacement after distal femoral resection?

In the article published by Etchebehere et al. in Journal of Bone and Joint Surgery, April 2016, the authors described a retrospective review of the clinical and radiological outcomes in 108 patients with distal femoral tumour who underwent distal femoral resection and endoprosthetic reconstruction (1). Sixty patients had patellar resurfacing and 48 had not. The mean duration of follow-up was 4.5 years. Due to its retrospective nature, selection bias is almost unavoidable in the study: the non-resurfacing group was more than 10 years younger than the resurfacing group. Patellar resurfacing rate was significantly higher in one model of prosthesis (Finn, 77%) than the other one (GMRS, 23%). It was also more common in surgery performed through lateral approach (83%) than the medial approach (17%).

The need for secondary resurfacing is affected by trochlear height in total knee arthroplasty.

The purpose of the study was to compare the rate of secondary resurfacing in a consecutive series of five different total knee arthroplasty (TKA) systems. It was our hypothesis that different TKA design features such as sulcus angle or trochlear height influence the rate of secondary resurfacing. A retrospective study was performed on data from patients who underwent TKA without primary patellar resurfacing from 2004 to 2012 in an university-affiliated hospital. The study cohort included 784 TKA patients (m:f=302:482, mean age at surgery±SD 71±10). Five different cruciate-retaining TKA systems were used consecutively (Group A, Triathlon, Stryker, Switzerland (n=296), Group B, PFC Sigma, DepuySynthes, Switzerland (n=215), Group C, LCS, DepuySynthes, Switzerland (n=81), Group D, Balansys, Mathys, Switzerland (n=128), Group E, Duracon, Stryker, Switzerland (n=64)). Data were retrospectively obtained from hospital archives. Patients demographics, age at surgery, type of TKA were noted. In addition, TKA component position was assessed on radiographs with respect to "The knee society total knee arthroplasty roentgenographic evaluation and scoring system" (TKA-RESS). Pearson Chi-square test was used to compare differences between groups (p<0.05). There were no significant differences between the groups in terms of age, gender, and radiological outcomes. Twenty-six of 784 patients (3.3%) underwent secondary resurfacing due to patellofemoral pain. In group A 4/296 patients (1.4%), in group B 15/215 patients (7%), in group C 5/81 patients (6.2%), in group D 1/128 patients (0.8%), in group E 1/64 patients (1.6%) underwent secondary patellar resurfacing during follow-up. Significantly higher rates of secondary patellar resurfacing were seen in groups B and C when compared to the others (p<0.001). It was found that the trochlear height in these TKA was higher than in the others. Based on the findings of this study, trochlear height influences the need for secondary patellar resurfacing. The resurfacing rate ranged from 1 to 7%, with the highest rate in the PFC Sigma TKA. Therapeutic study, Level III.

High energy electron sintering of icy regoliths: Formation of the PacMan thermal anomalies on the icy Saturnian moons

The so-called ‘PacMan’ features on the leading hemispheres of the icy Saturnian moons of Mimas, Tethys and Dione were initially identified as anomalous optical discolorations and subsequently shown to have greater thermal inertia than the surrounding regions. The shape of these regions matches calculated deposition contours of high energy plasma electrons moving opposite to the moon’s orbital direction, thus suggesting that electron interactions with the grains produce the observed anomalies. Here, descriptions of radiation-induced diffusion processes are given, and various sintering models are considered to calculate the rate of increase in the contact volume between grains in an icy regolith. Estimates of the characteristic sintering timescale, i.e. the time necessary for the thermal inertia to increase from that measured outside the anomalous regions to that within, are given for each of the moons. Since interplanetary dust particle (IDP) impact gardening and E-ring grain infall would be expected to mix the regolith and obscure the effects of high energy electrons, sintering rates are compared to rough estimates of the impact-induced resurfacing rates. Estimates of the sintering timescale determined by extrapolating laboratory measurements are below ∼0.03 Myr, while the regolith renewal timescales are larger than ∼0.1 Myr, thus indicating that irradiation by the high energy electrons should be sufficient to form stable thermal anomalies. More detailed models developed for sintering of spherical grains are able to account for the radiation-induced anomalies on Mimas and Tethys only if the regoliths on those bodies are relatively compact and composed of small (≲ 5 µm) grains or grain aggregates, and/or the grains are highly non-spherical with surface defect densities in the inter-grain contact regions that are much higher than expected for crystalline water ice grains at thermal equilibrium. These results are consistent with regolith thermal conductivity models which can only be reconciled with spacecraft observations if the contacts between grains are assumed to have much lower thermal conductance than predicted for idealized grains. The strength of the anomalies on Tethys and Dione appear to be limited by E-ring grain infall, while on Mimas IDP gardening limits the strength of the anomaly. The smaller flux of more deeply penetrating high energy (>1 MeV) electrons on Dione can account for the small thermal inertia differences measured there. Determining regolith sintering rates and the corresponding effect on thermal conductivity can, in principle, provide an independent constraint on the regolith grain geometries and exposure timescales for icy bodies.

International Rates of Patellar Resurfacing in Primary Total Knee Arthroplasty, 2004-2014

BackgroundPatella resurfacing is performed in >80% of primary total knee arthroplasties (TKAs) in the United States, yet far fewer patellae are resurfaced internationally. Recent registry data have begun to question the long-held belief that patellar resurfacing yields lower revision rates. Multiple current meta-analyses have not shown a difference in patient satisfaction, anterior knee pain, or knee society scores based on patellar resurfacing. MethodsWe sought to determine how the rates of patellar resurfacing have changed over the past 10 years worldwide (2004-2014). Data were abstracted from the annual reports of 7 national joint registries, literature review, or via direct correspondence with registry administrators. ResultsAverage rates of patellar resurfacing from 2004 to 2014 ranged from 4% (Norway) to 82% (United States). The largest decrease in resurfacing rates was in Sweden (15%-2%), whereas the biggest increase was in Australia (44%-59%). In 2010, only 48,367 of 137,813 (35%) primary TKAs from all registries outside the United States were resurfaced. Meta-analyses have demonstrated no difference in anterior knee pain or satisfaction scores but do consistently report increased revision rates for unresurfaced patellae. Recent Swedish registry data, however, showed a reverse trend toward higher revision rates after resurfacing. ConclusionDespite recent registry data and meta-analyses demonstrating equivalent outcomes among resurfaced and unresurfaced patellae in primary TKA, worldwide trends in patellar resurfacing have changed little over the past decade. Most countries outside the United States continue to resurface a much smaller proportion of patellae.

Does prosthesis design affect the need for secondary resurfacing in total knee arthroplasty?

Aims and Objectives:The purpose of this retrospective consecutive study was to compare the rate of secondary resurfacing in consecutive series of five different TKA systems. It was our hypothesis that different brands of TKA show different rates of secondary resurfacing.Materials and Methods:A retrospective study was performed on data from patients who underwent TKA without primary patellar resurfacing from 2004 to 2012 in an university affiliated hospital. The study cohort included 784 patients (m:f=302:482, mean age at surgery±SD 71±10) operated with TKA during this period. Five different cruciate-retaining TKA systems were used in consecutives series. These were the following: A) Triathlon, Stryker, Switzerland (n=296), B) PFC Sigma, DepuySynthes, Switzerland (n=215), C) LCS, DepuySynthes, Switzerland (n=80), D) Balansys, Mathys, Bettlach, Switzerland (n=129), E) Duracon, Stryker, Switzerland (n=64). Data was retrospectively obtained from our different hospital archives. Patients demographics, age at surgery, type of total knee arthroplasty were noted. In addition, the data were screened for a secondary resurfacing in each patient. On anterior-posterior, lateral and skyline view radiographs different measurements were performed. TKA component position was assessed on radiographs with respect to "The knee society total knee arthroplasty roentgenographic evaluation and scoring system (TKA-RESS). Pearson Chi square test was used to compare differences between groups (p<0.05). There was no significant difference between the groups in terms of age, gender, and radiological outcomes.Results:Twenty-six of 784 patients (3.3%) underwent secondary resurfacing due to patellofemoral pain during follow-up. In group A four of 296 patients (1.4%), in group B fifteen of 215 patients (7%), in group C four of 80 patients (5%), in group D two of 129 patients (1.6%), in group E one of 64 patients (1.6%) underwent secondary patellar resurfacing during follow-up. There was a statistically significant difference between group B and A, D and E as well as between group C and A, D and E (p<0.001).Conclusion:Prosthesis design influences the need for secondary resurfacing of the patella. It was shown that the rate ranges from 1 to 7%. The highest rate for secondary resurfacing was found in the PFC Sigma TKA.

Patellar resurfacing complications in total knee arthroplasty

The ideal management of the patella during total knee arthroplasty (TKA) is still controversial. Patellar retention is generally associated with an increased rate of anterior knee pain; however, patient satisfaction is similar in cases of replacement or retention. When the patella is replaced, potential severe complications can occur. Aim of this study was to retrospectively review results of a continuous series of patients having been treated with TKA and patella resurfacing. The charts of 1,600 consecutive total knee prostheses were analysed to evaluate the rate of patellar resurfacing. All implants were posterior stabilized; 310 patients having received a patellar replacement were reviewed at follow-up (FU) examination. Complete physical examination as well as administration of the Hospital for Special Surgery (HSS) score was performed. X-rays analysis included weightbearing anteroposterior (AP) and lateral views of the injured knee and bilateral skyline views at 30° flexion. Two hundred and eighty patients were available for clinical and imaging investigation at an average FU of 96 (58-144) months. Mean age at the time of surgery was 70 (62-80) years. Mean HSS score was 85.9 ± 7.6. The overall rate of patellofemoral complications was 7% (19 cases); 13 patients claimed anterior knee pain, five had symptomatic patellar maltracking and one had patellar component loosening. Our data are in accordance with those available in the literature. Recent meta-analyses demonstrated lower risk of re-operation after patellar resurfacing. However, when complications of the resurfaced patella occur, they can be potentially catastrophic events.