Objectives. The Attune total knee arthroplasty (TKA) has been used in over 600 000 patients worldwide. Registry data show good clinical outcome; however, concerns over the cement-tibial interface have been reported. We used retrieval analysis to give further insight into this controversial topic. Methods. We examined 12 titanium (Ti) PFC Sigma implants, eight cobalt-chromium (CoCr) PFC Sigma implants, eight cobalt-chromium PFC Sigma rotating platform (RP) implants, and 11 Attune implants. We used a peer-reviewed digital imaging method to quantify the amount of cement attached to the backside of each tibial tray. We then measured: 1) the size of tibial tray thickness, tray projections, peripheral lips, and undercuts; and 2) surface roughness (Ra) on the backside and keel of the trays. Statistical analyses were performed to investigate differences between the two designs. Results. There was no evidence of cement attachment on any of the 11 Attune trays examined. There were significant differences between Ti and CoCr PFC Sigma implants and Attune designs (p < 0.05); however, there was no significant difference between CoCr PFC Sigma RP and Attune designs (p > 0.05). There were significant differences in the design features between the investigated designs (p < 0.05). Conclusion. The majority of the earliest PFC Sigma designs showed evidence of cement, while all of the retrieved Attune trays and the majority of the RP PFC trays in this study had no cement attached. This may be attributable to the design differences of these implants, in particular in relation to the cement pockets. Our results may help explain a controversial aspect related to cement attachment in a recently introduced TKA design. Cite this article: A. Cerquiglini, J. Henckel, H. Hothi, P. Allen, J. Lewis, A. Eskelinen, J. Skinner, M. T. Hirschmann, A. J. Hart. Analysis of the Attune tibial tray backside: A comparative retrieval study. Bone Joint Res 2019;8:136–145. DOI: 10.1302/2046-3758.83.BJJ-2018-0102.R2

Aims. The extensive variation in axial rotation of tibial components can lead to coronal plane malalignment. We analyzed the change in coronal alignment induced by tray malrotation. Methods. We constructed a computer model of knee arthroplasty and used a virtual cutting guide to cut the tibia at 90° to the coronal plane. The virtual guide was rotated axially (15° medial to 15° lateral) and with posterior slopes (0° to 7°). To assess the effect of axial malrotation, we measured the coronal plane alignment of a tibial tray that was axially rotated (25° internal to 15° external), as viewed on a standard anteroposterior (AP) radiograph. Results. Axial rotation of the cutting guide induced a varus-valgus malalignment up to 1.8° (for 15° of axial rotation combined with 7° of posterior slope). Axial malrotation of tibial tray induced a substantially higher risk of coronal plane malalignment ranging from 1.9° valgus with 15° external rotation, to over 3° varus with 25° of internal rotation. Coronal alignment of the tibial cut changed by 0.07° per degree of axial rotation and 0.22° per degree of posterior slope (linear regression, R. 2. > 0.99). Conclusion. While the effect of axial malalignment has been studied, the impact on coronal alignment is not known. Our results indicate that the direction of the cutting guide and malalignment in axial rotation alter coronal plane alignment and can increase the incidence of outliers. Cite this article: Bone Joint J 2020;102-B(6 Supple A):43–48

Aims. The aim of this study was to investigate whether wear and backside deformation of polyethylene (PE) tibial inserts may influence the cement cover of tibial trays of explanted total knee arthroplasties (TKAs). Methods. At our retrieval centre, we measured changes in the wear and deformation of PE inserts using coordinate measuring machines and light microscopy. The amount of cement cover on the backside of tibial trays was quantified as a percentage of the total surface. The study involved data from the explanted fixed-bearing components of four widely used contemporary designs of TKA (Attune, NexGen, Press Fit Condylar (PFC), and Triathlon), revised for any indication, and we compared them with components that used previous generations of PE. Regression modelling was used to identify variables related to the amount of cement cover on the retrieved trays. Results. A total of 114 explanted fixed-bearing TKAs were examined. This included 76 used with contemporary PE inserts which were compared with 15 used with older generation PEs. The Attune and NexGen (central locking) trays were found to have significantly less cement cover than Triathlon and PFC trays (peripheral locking group) (p = 0.001). The median planicity values of the PE inserts used with central locking trays were significantly greater than of those with peripheral locking inserts (205 vs 85 microns; p < 0.001). Attune and NexGen inserts had a characteristic pattern of backside deformation, with the outer edges of the PE deviating inferiorly, leaving the PE margins as the primary areas of articulation. Conclusion. Explanted TKAs with central locking mechanisms were significantly more likely to debond from the cement mantle. The PE inserts of these designs showed characteristic patterns of deformation, which appeared to relate to the manufacturing process and may be exacerbated in vivo. This pattern of deformation was associated with PE wear occurring at the outer edges of the articulation, potentially increasing the frictional torque generated at this interface. Cite this article: Bone Joint J 2021;103-B(12):1791–1801

This study was to evaluate the stability of a delta keel tibial tray using a block prosthesis and to determine whether a long intramedullary stem is a necessary adjunct to augment construct stability. An experimental technique was used employing strain gauges and deflection transducers to assess the stiffness and principle strains conferred to human cadaveric tibiae under various axial loading conditions. As a control measure, tests were conducted in the absence of any bone loss, and repeated in a simulated bone defect treated with a metal block. The latter was analysed with and without augmentation of the tibial tray with an intramedullary stem. With axial loading of 2000N, the tray and block configuration resulted in 21% less proximal bone strain than the tray alone. The combined tray, block and stem resulted in 35% less proximal bone strain than the tray alone. Using the tray and block produced 1.06 times more deflection of the tibial tray and using the tray, block and stem 1.03 times more deflection of the tibial tray than the tray alone in the absence of a bony defect. There was no statistical difference in overall construct stability (p < 0.05) despite the large strain-offsetting effect recorded using the tibial tray in conjunction with the block and stem. These results suggest that isolated bone defects that can be dealt with using a single block and modern standard tibial tray may not require additional supplementation with a long intramedullary stem

We wanted to know if a mobile bearing Total Knee Arthroplasty was able to cope with rotation of the tibial tray about the femoral prosthesis, by studying the tibio-femoral and patello-femoral joints. This was a kinematic study that used a mobile bearing TKA mounted on a jig that allowed rotation of the tibial tray. The TKA was moved through a 90° range of flexion and we used photography to record the effects at the tibio-femoral and patello-femoral joints. We found that with a fixed tibia, increasing the degree of external rotation increased the degree of medial femoral condyle lift off from the polyethylene insert which was complete at 25° of tibial tray external rotation. The lift off increased with the degree of flexion. The patello-femoral joint remained congruent. If the rotated tibial tray was mounted on a tibia that was allowed to freely rotate, it led to congruity at the tibio-femoral joint. Now we found that there was medial facet impingement and lateral facet lift off of the patella button in extension and flexion. We concluded that this mobile bearing prosthesis did not cope well with rotation of the tibial tray. The relatively low congruency at the tibio-femoral articulation meant that there was a reduced “driving force” at the tibio-femoral joint resulting in less than adequate rotation of the mobile polyethylene insert. We feel that the tibial tray must be placed in neutral to the femoral prosthesis and failure to do so will result in abnormal polyethylene loading that would increase wear and may culminate in early prosthesis revision

The problem of early mechanical stability and late biological osseointegration of the tibial component is still a debated issue in total knee arthroplasty. We are among those authors that stress the necessity of cementing the tibial component to avoid the risk of failure due to the high torque stresses at this interface. In fact while on the femoral edge a good stability can be achieved even in uncemented implants, the stability of traditional tibial components is harder to obtain even in cemented implants. To solve this problem it has been proposed to use additional devices such as screws, pegs or keels to better fix the tibial plateau. Tantalum monobloc tibial tray is a new answer to this problem. It consists in a cement-less tibial tray made of porous tantalum with monobloc polyethylene. Chemical, physical and biological properties of the raw tantalum are very similar to those of titanium. Porosity of the processed material is 80% (2–3 times compared to plasma spray, beads and fiber mesh coatings) and pores, which diameter is 650 mm, are fully interconnected in the whole bulk of the implant. This trabecular spongy structure, that is not a coating, allows the bone at the interface to deeply grow into the pores, and to achieve optimal stability. In addiction, the fusion of polyethylene into the tantalum mesh completely abolish the back side wear problem. With this technology is yet in use an acetabular component, with which we have a 5 years experience in 150 implants, and now is available a new tibial plateau; the first implant in Europe was performed in our department. Despite our short series and follow up (6 implants in 2 months) the properties of porous tantalum, already tested in acetabular implants, represent an alternative to the traditional ways of tibial tray fixation

All polyethylene tibial components (APT) for total knee joint replacement have been recently reintroduced due to their past success and cost savings with respect to knee designs with a metal backed tibial tray (MBT). However, isolated cases of collapse of the medial bone in APT designs have been observed by the authors prompting this investigation. The objective of this study was to investigate the stress/strain distribution within the cancellous bone for the APT and MBT systems, particularly looking at the effects of coverage of the tray over the proximal tibia in each design. A three-dimensional finite element model of the proximal tibia implanted with a tibia tray was generated. An elliptical cylindrical tibia tray with a peg was modeled as being perfectly bonded to a PMMA layer on the superior surface of the cancellous and cortical bone. Gap size between the edge of the tray and outer of the cancellous bone, was introduced in the medial direction. Load was applied on the superior surface of the tibial insert in the medial side. Two lift-off loading cases were used, a low load of 800N (1 body-weight) and a high load of 3200N (4 x BW), both on the medial side. Permanent plastic deformation and collapse was allowed only in the cancellous bone, while all other materials were modeled elastically. Under low load conditions within the elastic limit, introducing a gap between the tray and the cortical bone produced a stress/strain intensity in the cancellous bone beneath the edge of the tray. The strain in the cancellous bone within the APT design was generally 3 times greater than the MBT design, however, peak strain values were similar at the edge of the tray. Whilst the strain increased with the introduction of a gap the resulting strain was not sensitive to the gap size for both designs. Under high load conditions, permanent plastic deformation and bone collapse were observed in the cancellous bone at the edge of the tibial tray in both designs where a gap was introduced. The maximum strain in the cancellous bone was found to be more sensitive to the gap size for the APT design than the MBT design. This can be contributed to the difference in the load transfer through the cancellous bone in the two designs. The MBT design with the more rigid tibial tray transfered higher load through the outer cortical bone than the APT design. The less rigid APT design resulted in progressive collapse of the cancellous bone beneath the tray. Particularly significant was the volume of highly stressed cancellous bone which was 4 times greater in the APT design compared to the MBT design. The results suggest that coverage may be a more important parameter for the APT design than the MBT design. The APT design may, therefore, be more suited to patients with better bone quality

Introduction: Tibial component loosening is a common mode of failure in modern total knee arthroplasty and is thus a common cause for revision knee surgery. Direct bone ingrowth of press fit knee prosthesis has been deemed an important prerequisite for long-lasting implant fixation and thus clinical success in both primary and revision TKA whether for cemented or uncemented stems. To achieve good long term biological stabilization, initial secure mechanical stability, (i.e. minimising tibial tray and stem motion with respect to the tibia,) is vital. A lack of initial stability can lead to resorption of bone at the implant-tissue interface and can consequently result in loosening and failure of the prosthesis. Obtaining adequate tibial fixation is difficult in revision patients as often there is insufficient bone stock in the proximal tibia. A longer stem is often recommended with revision surgery as a central stem should guide the migration of the tibial component so that it occurs predominantly along the vertical axis, thus minimising the risk of recurrent malalignment and loosening due to tilting of the tibial tray. It is also thought that the presence of a third rigid peg helps to reduce inducible displacements by anchoring the new implant in robust cancellous bone. However there is no consensus on the length of central stem should be to achieve the best load transfer and fixation and although the use of long stems on the tibial component is advocated, in revision TKA involving bone grafting and augmentation. The effect of the tibial stem length in other cases has received contradictory evaluations. This research deals with an experimentally evaluate the effect that central stem lengths on the initial micromotion of the tibial tray in two revision tibial defects. This is being investigated by measurement of the bone-implant interface motion of the tibial stem. Method: Composite bones were resected with an extramedullary jig. Three common revision defects were compared 1) no defect requiring no repair(primary); 2) T1 defect requiring bone impaction grafting; 3) T2A requiring augmentation. Three stem configurations were analysed in conjunction with these defects 1) no stem; 2) short 40mm stem; 3) long 80mm stem. Four LVDTs were positioned anteriorly, posteriorly, medially and laterally around the tray and were used to measure the movement of the tibial tray with respect to the tibia. The bones were potted and subjected to axial loading simulating 1– 6 times body weight for 3500 cycles at 1 Hz. Results: The longer stemmed press fit implants were associated with slightly higher levels of micromotion compared to the “no stem press fit” trays in the primary and T2A defects. This could be due to the fact that cutting errors are accentuated by a longer stem and can cause increased levels of posterior lift off. For bone impaction grafting it seems that a stem sufficiently long to by-pass the defect should be used. The proximal surface cemented trays presented more stable fixation with the inducible displacement between the no stem and stemmed groups being negligible. Subsidence of the tibial tray was reduced marginally by using a longer stem

Introduction. Initial large-scale clinical studies of porous tantalum implants have been generally promising with well-fixed implants and few cases of loosening [1–3]. An initial retrieval study suggests increased bone ingrowth in a modular tibial tray design compared to the monoblock design [4]. Since micromotion at the bone-implant interface is known to influence bone ingrowth [5], the goal of this study was to determine the effect of implant design, bone quality and activity type on micromotion at the bone-implant interface, through FE modeling. Patients & Methods. Our case-specific FE model of bone was created from CT data (68 year-old female, right tibia, Fig-1). Isotropic properties of cortical and trabecular bone were derived from the calibrated CT data. Modular and monoblock porous tantalum tibial implants were virtually placed in the tibia following surgical guidelines. All models parts were 3D meshed with 4-noded tetrahedral elements (MSC.MARC-Mentat 2013, MSC Software Corporation, USA). Frictional contact was applied to the bone-tantalum interface (µ=0.88) and UHWMPE-Femoral condyle interface (µ=0.05) with all other interfaces bonded. Loading was applied to simulate walking, standing up and descending stairs. For each activity, a full load cycle [6] was applied to the femoral condyles in incremental steps. The direction and magnitude of micromotions were calculated by tracking the motions of nodes of the bone, projected onto the tibial tray. Micromotions were calculated parallel to the implant surface (shear), and perpendicularly (tensile). We report the maximum (resultant) micromotion that occurred during a cycle of each activity. The bone properties were varied to represent a range in BMD (−30%BMD, Norm, +30%BMD). We compared design type, bone quality and activity type considering micromotion below 40 µm to be favorable for bone ingrowth [5]. Results. The modular tibial tray showed lower shear micromotion than the monoblock design for shear micromotion (Fig-2). Tensile micromotion was similar between the two designs (Fig-2). Lower bone quality resulted in higher shear micromotion for the modular tibial tray design. The effect of lower bone quality on shear micromotion was less apparent for the monoblock tibial tray design. For both designs, change in the bone quality had minimal effect on the tensile micromotion. For both designs, standing up and descending stairs showed lower micromotion than walking for both the tensile and shear micromotion (Fig-3). The monoblock design showed higher micromotion for standing up and descending stairs compared to the modular design (Fig-3). Discussion. In our analysis, activity type had the highest effect on micromotion. Additionally, the modular design showed lower shear micromotion than the monoblock. Although the designs were similar for the the modular and monoblock implants, the difference in micromotion, representing the initial stability of the implant, may partially explain why retrieved modular porous tantalum tibial trays had higher bone ingrowth than the monoblock design

Introduction. The goal of tibial tray placement in total knee arthroplasty (TKA) is to maximize tibial surface coverage while maintaining proper rotation. Maximizing tibial surface coverage without component overhang reduces the risk of tibial subsidence. Proper tibial rotation avoids excess risk of patellar maltracking, knee instability, inappropriate tibial loading, and ligament imbalance. Different tibial tray designs offer varying potential in optimizing the relationship between tibial surface coverage and rotation. Patient specific instrumentation (PSI) generates customized guides from an MRI- or CT-based preoperative plan for use in TKA. The purpose of the present study was to utilize MRI information, obtained as part of the PSI planning process, to determine, for anatomic, symmetric, and asymmetric tibial tray designs, (1) which tibial tray design achieves maximum coverage, (2) the impact of maximizing coverage on rotation, and (3) the impact of establishing neutral rotation on coverage. Methods. In this prospective comparative study, MR images for 100 consecutive patients were uploaded into Materialise™ PSI software that was used to evaluate characteristics of tibial component placement. Tibial component rotation and surface coverage was analyzed using the preoperative planning software. Anatomic (Persona™), symmetric (NexGen™), and asymmetric (Natural-Knee II™) designs from a single manufacturer (Zimmer™) were evaluated to assess the relationship of tibial coverage and tibial rotation. Tibial surface coverage, defined as the proportion of tibial surface area covered by a given implant, was measured using Adobe Photoshop™ software (Figure 1). Rotation was calculated with respect to the tibial AP axis, which was defined as the line connecting the medial third of the tibial tuberosity and the PCL insertion. Results. When tibial surface coverage was maximized, the anatomic tray compared to the symmetric/asymmetric trays showed significantly higher surface coverage (82.1% vs 80.4/80.1%; p<0.01), significantly less deviation from the AP axis (0.3° vs 3.0/2.4°; p<0.01), and a significantly higher proportion of cases within 5° of the AP axis (97% vs 73/77%). When constraining rotation to the AP axis, the anatomic tray showed significantly higher surface coverage compared to the symmetric/asymmetric trays (80.8% vs 76.3/75.8%; p<0.01). No significant differences were found between symmetric and asymmetric trays. Discussion. We found that the anatomic tibial tray resulted in significantly higher tibial coverage with significantly less deviation from the AP axis compared to the symmetric and asymmetric trays. When rotation was constrained to the AP axis, the anatomic tray resulted in significantly higher tibial coverage than the symmetric and asymmetric trays. Tibial rotation is recognized as an important factor in the success of a total knee replacement. Maximizing coverage with the least compromise in rotation is the goal for tibial tray design. In this study, the anatomic tibia seemed to optimize the relationship between tibial surface coverage and rotation. This study additionally illustrates the way by which advanced preoperative planning tools (ie. MRI/computer reconstructions) allow us to obtain valuable information with regard to implant design

Introduction. Backside wear of polyethylene (PE) inlays in fixed-bearing total knee replacement (TKR) generates high number of wear debris, but is poorly studied in modern plants with improved locking mechanisms. Aim of study. Retrieval analysis of PE inlays from contemporary fixed bearing TKRs - to evaluate the relationship between backside wear and liner locking mechanism and material type and roughness of the tibial tray. Methods. MATERIAL. We included five types of implants, revised after min. 12 months (14–71): three models with a peripheral locking rim and two models with a dove-tail locking mechanism. Altogether this study included 15 inlays were removed from TKRs with CoCr alloy tray with a roughened surface and a peripheral locking lip liner (Stryker Triathlon, Ra 5,61 µm), 9 from CoCr trays with peripheral locking lip and untreated surface (Aesculap Search, Ra 0,81 µm), 13 from Ti alloy trays with peripheral locking lip and untreated surface (DePuy PFC Sigma 0,61 µm), 11 from Ti alloy trays with untreated surface and dovetail locking mechanism (Zimmer NexGen, 0,34 µm), and 9 from iplants with a Ti alloy tibial tray with mirror polished surface and dovetail locking mechanism (Smitn&Nephew Genesis II, 0,11 µm). METHODS. Wear of bearing surface and back side of retrieved inlays was examined in 10 sectors under a light microscope. Seven modes of wear were analysed and quantified according to the Hood scale: surface deformation, pitting, embedded third bodies, pitting, scratching, burnishing (polishing), abrasion and delamination. Damage of inlays caused by backside wear was also evaluated using scanning electron microscopy (SEM). Roughness of tibial tray was evaluated using a contact profilometer. Results. We found no differences between wear scores on the articulating surface in all group, they did not correlate with backside wear scores in all groups as well. Compared to all other groups, backside wear scores were significantly higher in implants with untreated Ti alloy tibial tray (P<0,001 Wilcoxon test). Lowest wear rates were found in implants from both Ti and CoCr alloys and peripheral locking rim. Interestingly there was no difference between wear of implants with polished and untreated surface (Fig. 1). SEM analysis demonstrated different wear modes in implants with dovetail mechanism and peripheral rim. The first group demonstrated signs of gross rotational instability, with severe abrasion with an arch-shaped pattern and delaminated PE (Fig 2). In one design we observed severe extrusion of PE into screw holes of the tibial tray. Inlays from trays with peripheral rim presented two types of wear: flattening of machining marks or protrusion of the material caused by the rough surface (Fig 3). Conclusions. This study demonstrates that backside wear is still a problem in modern TKR. Our findings suggest that it is predominantly affected by type of locking mechanism (with peripheral rim performing better), to a lesser extent by surface roughness of the tibial component, while material type does not seem to play an important role. This study was funded by a grant from the National Science Centre nr 2012/05/D/NZ5/01840. To view tables/figures, please contact authors directly

Introduction. Post-operative clinical outcomes of TKA are dependent on a multitude of surgical and patient-specific factors. Malrotation of the femoral and/or tibial component is associated with pain, accelerated wear of the tibial insert, joint instability, and unfavorable patellar tracking and dislocation. Using the transepicondylar axis to guide implantation of the femoral component is considered to be an accurate anatomical reference and is widely used. However, no gold standard currently exists with respect to ensuring optimal rotation of the tibial tray. Literature has suggested that implantation methods, which reference the tibial tubercle, reduce positioning outliers with more consistency than other anatomical landmarks. Therefore, the purpose of this evaluation is to use data collected from intraoperative sensors to assess the true rotational accuracy of using the mid-medial third of the tibial tubercle in 98 TKAs. Methods. The data for this evaluation was retrieved from 98 consecutive patients who underwent primary TKA from the same highly experienced surgeon. Femoral component rotation was verified in every case via the use of the Whiteside line, referencing the transepicondylar axis, and confirming appropriate patellar tracking. Tibial tray rotation was initially established by location of the mid-medial third of the tibial tubercle. Rotational adjustments of the tibial tray were evaluated in real-time, as the surgeon corrected any tibiofemoral incongruency and tray malpositioning. The initial and final angles of tibial tray rotation were captured with intraoperative video feed, and recorded. A z-test of differences between pre- and post-rotational correction was performed to assess the statistical significance of malrotation present in this cohort. Results. All patients in this study received a primary TKA, using the mid-medial third of the tibial tubercle to dictate tibial tray rotation. After the sensor-equipped tibial insert was implanted, it was shown that 63.1% of patients exhibited unfavorable rotation. Of those patients, 70% were shown to have internal rotation; 30% were shown to have external rotation. The average malrotation of the tibial tray deviated from a neutral position by 6.3° ± 4.3°, ranging from 0.5° to 19.2°. The z-test of differences yielded a p-value <0.0001, indicating that the proportion of malrotation was statistically significant. The 95% confidence interval of this cohort was calculated to be between 44.8% and 71.8% of malrotation. Discussion. Malrotation in TKA isassociated with poor clinical outcomes. While no gold standard anatomic landmark currently exists for positioning the tibial tray, the mid-medial third of the tibial tubercle is widely used as a reference. However, the data from this evaluation demonstrates that, not only is this landmark insufficient for establishing optimal rotation (p < 0.0001), but that it had guided the surgeon to an average of 6.3° outside of the optimized implant congruency zone. The large confidence interval indicates that the rotational alignment of the tibial tray—based on the location of the mid-medial third of the tibial tubercle—is not only inaccurate, but also highly variable. Based on this intraoperative sensor data, we suggest that care should be taken when utilizing the tibial tubercle as the sole rotational landmark for the tibial tray

Abstract. Introduction. At our national explant retrieval unit, we identified an unusual pattern of backside-deformation on polyethylene (PE) inserts of contemporary total-knee-replacements (TKRs). The PE backside's margins were inferiorly deformed in TKRs with central-locking trays. We reported that this backside-deformation appeared to be linked to tray debonding. Moreover, recent studies have shown high-rate of tray debonding in PS NexGen TKRs. Therefore, we hypothesised that backside deformation on PS inserts may be more than on CR inserts. Methodology. We used peer-reviewed techniques to analyse changes in the bearing (wear rate) and backside surfaces (deformation) of PE inserts using coordinate measuring machines [N=61 NexGen (CR-39 and PS-22) TKRs with non-augmented-trays]. Multiple regression was used to determine which variable had the greatest influence on backside-deformation. The amount of cement cover on trays was quantified as a %of the total surface using Image-J software. Results. There was no statistically significant difference (p=0.238) in median (IQR) wear rate of the CR PEs 18 (12–28) mm. 3. /year and PS PEs 14 (8–20) mm. 3. /year. The PE backside-deformation median (IQR) of PS [297(242–333) µm] was significantly higher (p=0.011), when compared with CR [241(161–259) µm]. Multiple regression modelling showed that duration in-vivo (p=0.037), central-clearance between insert and tray (p<0.001) and constraint (p=0.003) were significantly associated with PE backside-deformation. 27(69%) of CR and 20(91%) PS exhibited ≤10% of cement cover on tray. Conclusion. This explant study showed backside-deformation on PS inserts was more than on CR inserts. Therefore, indicating a high-rate of tibial tray debonding in PS compared to CR NexGen TKRs

The goal of tibial tray placement in total knee arthroplasty (TKA) is to maximise tibial surface coverage while maintaining proper rotation. Maximising tibial surface coverage without component overhang reduces the risk of tibial subsidence. Proper tibial rotation avoids excess risk of patellar maltracking, knee instability, inappropriate tibial loading, and ligament imbalance. Different tibial tray designs offer varying potential in optimising the relationship between tibial surface coverage and rotation. Patient specific instrumentation (PSI) generates customised guides from an MRI- or CT-based preoperative plan for use in TKA. The purpose of the present study was to utilise MRI information, obtained as part of the PSI planning process, to determine, for anatomic, symmetric, and asymmetric tibial tray designs, (1) which tibial tray design achieves maximum coverage, (2) the impact of maximising coverage on rotation, and (3) the impact of establishing neutral rotation on coverage. MR images for 100 consecutive patients were uploaded into Materialise™ PSI software that was used to evaluate characteristics of tibial component placement. Tibial component rotation and surface coverage was analysed using the preoperative planning software. Anatomic (Persona™), symmetric (NexGen™), and asymmetric (Natural-Knee II™) designs from a single manufacturer (Zimmer™) were evaluated to assess the relationship of tibial coverage and tibial rotation. Tibial surface coverage, defined as the proportion of tibial surface area covered by a given implant, was measured using Adobe Photoshop™ software. Rotation was calculated with respect to the tibial AP axis, which was defined as the line connecting the medial third of the tibial tuberosity and the PCL insertion. When tibial surface coverage was maximised, the anatomic tray compared to the symmetric/asymmetric trays showed significantly higher surface coverage (82.1% vs 80.4/80.1%; p<0.01), significantly less deviation from the AP axis (0.3° vs 3.0/2.4°; p<0.01), and a significantly higher proportion of cases within 5° of the AP axis (97% vs 73/77%). When constraining rotation to the AP axis, the anatomic tray showed significantly higher surface coverage compared to the symmetric/asymmetric trays (80.8% vs 76.3/75.8%; p<0.01). No significant differences were found between symmetric and asymmetric trays. We found that the anatomic tibial tray resulted in significantly higher tibial coverage with significantly less deviation from the AP axis compared to the symmetric and asymmetric trays. When rotation was constrained to the AP axis, the anatomic tray resulted in significantly higher tibial coverage than the symmetric and asymmetric trays. Tibial rotation is recognised as an important factor in the success of a total knee replacement. Maximising coverage with the least compromise in rotation is the goal for tibial tray design. In this study, the anatomic tibia seemed to optimise the relationship between tibial surface coverage and rotation. This study additionally illustrates the way by which advanced preoperative planning tools (ie. MRI/computer reconstructions) allow us to obtain valuable information with regard to implant design

Aims: Should the tibial tray be rotated about the femoral component of a total knee arthroplasty? Literature review provides evidence commending rotation and neutral alignment. We wanted to provide evidence to help this debate. Method: We developed a knee jig allowing full range of movement of a knee arthoplasty. Under compression, we studied the isolated effect of tibial tray rotation about the femoral prosthesis in þxed and mobile bearing prostheses. We photographed the tibio-femoral and patello-femoral articulations. Results: A mobile bearing prosthesis at 15 degrees of tray rotation suffered posteromedial and anterolateral polyethylene impingement. At 25 degrees, the medial femoral component lifted off. The þxed bearing prosthesis showed similar polyethylene impingement, but no femoral condyle lift off. In both prostheses, tray rotation increased lateral patella facet loading, which increased with knee ßexion. Conclusion: Mobile bearing prosthesis was less tolerant than þxed bearing prosthesis to tibial tray rotation. Rotation caused polyethylene impingement, which would generate wear debris. Patella tracking was not improved by tibial tray rotation. The mobile bearing prosthesis is less congruent at the tibio-femoral articulation. Therefore there is less Òdriving forceÒ to rotate the polyethylene to align it to the femoral component, when the tray is rotated. We recommend the tibial tray be aligned to the femoral prosthesis in neutral

Aims: To evaluate the effect of tapered pegs in reducing tibial tray tilt and subsidence in closed cell foam. Methods: 1. Foam validation was carried out using a load frame (Instron) to establish its static and fatigue behaviour. 2. Subsidence and tilt tests: Three brass peg sets of varying length and matching surface area were designed. Four identical pegs of each set were fixed with screws to an IBII tibial tray and testing was performed using the load frame and the closed cell foam. Results: Foam validation revealed an average strength of 0.65±0.01 MPa in compression and 1.53±0.02 MPa in tension and an average stiffness of 40.2±1.5 Mpa in compression and 50.4±1.06 Mpa in tension. Subsidence tests revealed a significant increase in the total load producing 0.2mm subsidence with pegs ( p< 0.0053) and no significant difference for 1 and 2mm (p> 0.1). Tilt tests revealed a significant increase in the total load producing 0.2mm tilt with the medium and short pegs ( p < 0.008 & < 0.042 respectively) and no significant difference for 1 and 2mm (p> 0.1). Conclusions: The foam analogue material shows similar behaviour to cancellous bone in both static and dynamic tests and suggests that polymer foams are a good analogue material to cancellous bone. The addition of tapered conical pegs to the tibial tray increases its resistance to initial subsidence while initial tilt resistance is increased only with the medium and short pegs. Combining tilt and subsidence resistance, the medium pegs perform most favourably

Aims We rotated the tibial tray, of a fixed and mobile bearing, total knee arthroplasty and studied the effects on the patellofemoral and tibiofemoral joints, when the arthroplasty was placed through a range of movement. Method and results A specially designed jig allowed us to put the knee arthroplasty under 100N of compression using a single pulley system. We rotated the tibial platform in isolation, in 5° increments of external rotation. At each position, the arthroplasty was put through 90° of flexion. We studied the PFC fixed bearing prosthesis and the LCS, PCL substituting rotating platform pros-thesis manufactured by Johnson & Johnson. We used a translucent custom femoral component for each type. This allowed us to observe dye at the femoral component articulations, recording the results using digital photography. The mobile bearing prosthesis was surprisingly more sensitive to tibial tray external rotation. It suffered antero-lateral and posteromedial point loading on the polyethylene tray from 5–15° of tray rotation. Further increase caused the medial femoral component to lift off the polyethylene tray at 25° of rotation resulting in lateral femoral component loading. Simultaneously, there was lateral patella facet loading with medial facet lift off at the patellofemoral joint. The fixed bearing prosthesis did not experience impingement until 10° of rotation. At 25° of external tray rotation, there was posteromedial and antero-lateral point loading on the polyethylene but no lift off. The patellofemoral joint showed superior pole loading of the patella button but no medial/lateral loading. Conclusion External tibial tray rotation caused polyethylene point loading in a knee arthroplasty. This would increase wear debris generation and aseptic loosening rates. Tray rotation does not improve patellofemoral tracking. We advise neutral alignment of the tibial tray to the femoral prosthesis. The mobile bearing prosthesis was more sensitive because the polyethylene tray could not rotate to confer the optimum tibiofemoral alignment

Aim of the study: To prove that tapered pegs are effective in reducing tibial tray subsidence in vitro and that this effect is related to the dimensions of these pegs. Methods: The peg designs were drawn up mathematically to allow for a unified surface area – Three different designs were used. The pegs were made from cobalt chrome, were conical in shape with a cut off tip and had a variable base and height and an equal surface area. These pegs were fixed with screws to an IB 11 HA coated tibial tray. Wet foam was used as bone substitute, this is an open cell foam that is fairly fragile but has the benefit of being constant and is cheap and readily available. This foam is not desired to have cancellous bone characteristics but is useful in observing the relative effect of adding these pegs. Two different settings in vivo were mimicked: that of a tibial tray and pegs resting fully on cancellous bone, in which case a central vertical force was applied, and that of the tray resting on the cortex on one side with a lateral vertical force applied over the other side in both the proud and flush setting (2& 4 pegs respectively). The investigation was undertaken using a home made system allowing a crude estimate of the forces producing initial subsidence, which was identified by initial fracture of the foam, and total subsidence which was identified as total failure of the foam. Each test was carried out three times. Controls were carried out on the tray with no pegs and on the pegs individually before attaching these to the tray and repeating the tests for each design. Results: Using this crude approach, the mean control force for total subsidence of the pegs was as follows: Short with wide base 550.3 g (± 45.3 g), medium length and base 475.6 g (± 24.25 g), long with narrow base 364.5 g (± 24.25 g). The mean control force for initial subsidence of the tray without pegs when subjected to a vertical central force was 4.3 kg (4–4.5 ± 0.27 kg) and the total subsidence force for the tray was 7.32 Kg (5.5–8, ± 0.84 kg). The mean central vertical force for initial subsidence of the tray with the tapers mounted was 7.16 kg (7–7.5 ± 0.28), for the short wide pegs, 5.33 kg (5–5.5 ± 0.28) for the medium pegs and 5.33 kg (5–6 ± 0.57) for the long pegs. The mean central vertical force for total subsidence of the tray with the tapers mounted was 9 kg (8.5–9.5 ± 0.5) for the short wide pegs, 9.8 kg (8–11 ± 1.6) for the medium pegs and 9.6 kg (8.5–11.5 ± 1.6) for the long pegs. The mean lateral control force for total subsidence of the proud tray with pegs resting on the wooden ledge was 5 kg (4–6 ± 0.75). The mean lateral vertical force for total subsidence with all pegs mounted was 7.16 kg (7–7.5 ± 0.28) for the short pegs, 5.8 kg (5.5–6 ± 0.28) for the medium pegs and 5.5 (5.5–5.6 ± 0.05) for the long pegs. No definite initial subsidence force could be identified. The mean lateral control force for total subsidence of the flush tray resting on the wooden ledge was 13.16 kg (12.5–14 ± 0.76). The mean lateral vertical force for total subsidence with pegs mounted on the foam side was 12.3 kg (11.5–13 ± 0–76) for the short pegs, 13.5 kg (12–15.5 ± 1.8) for the medium pegs and 13.83 kg (12–15.5 ± 1.7) for the long pegs. Again no definite initial subsidence force could be identified. Conclusion: The addition of tapered conical pegs to the tibial tray increases the resistance to subsidence when subjected to a central vertical force with the tray sitting fully on foam. The initial subsidence resistance was more marked in the case of the short wide variety. In the case of the tray resting on the hard edge and a lateral force applied, the proud tray showed improved resistance to total subsidence with the short pegs while the flush tray did not show improvement with pegs and was marginally worse with the short pegs. This is probably due to a higher margin of observer error

Introduction:. Appropriate transverse rotation of the tibial component is critical to achieving a balance of tibial coverage and proper tibio-femoral kinematics in total knee replacement (TKR), yet no consensus exists on the best anatomic references to determine rotation. Historically, surgeons have aligned the tibial component to the medial third of the tibial tubercle. 1. , but recent literature suggests this may externally rotate the tibial component relative to the femoral epicondylar axis (ECA) and that the medial border of the tubercle is more reliable. 2. Meanwhile, some TKR components are designed with asymmetry of the tibial tray assuming that maximizing component coverage of the resected tibia will result in proper alignment. The purpose of this study was to determine how different rotational landmarks and natural variation in osteoarthritic patient anatomy may affect asymmetry of the resected tibial plateau. Methods:. Pre-operative computed-tomography scans were collected from 14,791 TKR patients. The tibia and femur were segmented and anatomic landmarks identified: tibial mechanical axis, medial third and medial border of the tibial tubercle, PCL attachment site, and the surgical ECA of the femur. Virtual surgery was performed with an 8-mm resection (referencing the high side) made perpendicular to the tibial mechanical axis in the frontal plane, with 3° posterior slope, and transversely aligned with three different landmarks: the ECA, the medial border, and medial third of the tubercle. In each of these rotational alignments, the relative asymmetry of the medial and lateral plateaus was calculated (Medial AP/Lateral AP) (Fig. 1). Results:. Rotational alignment of the tibial component to the ECA, medial border, and medial third of the tubercle resulted in progressive external rotation of the tibial tray on the bone. Alignment to the medial border and medial third of the tubercle resulted in average 0.9° ± 5.7° and 7.8° ± 5.3° external rotations of the tray relative to the ECA, respectively (Fig. 2). Greater external rotation of the tibial implant relative to the bone increased the appearance of tibial asymmetry (Fig. 3). Referencing the medial border and medial third of the tubercle resulted in apparent tibial bone asymmetry of 1.10 ± 0.10 and 1.12 ± 0.10, respectively. Discussion:. Assuming the ECA is the appropriate rotational reference to re-establish appropriate kinematics. 2. , alignment to the medial border of the tubercle resulted in the most favorable tray alignment. However, there was a great deal of variation between the relative position of the ECA and the tubercle across the patient population. Rotational alignment to either the medial border or medial third of the tubercle resulted in external tray alignment relative to the ECA of greater than 3 degrees for 36% and 84% of patients, respectively. In addition, increased tray asymmetry (broader medial plateau) necessitates relative external rotation of the tray on the bone reducing the flexibility of intra-operative rotational adjustment. Tray asymmetry greater than 1.10 (the asymmetry of the resected tibia when aligned to the ECA) may result in external mal-rotation for a significant portion of the patient population

Introduction:. Adequate coverage of the resected tibial plateau with the tibial tray is necessary to reduce the theoretical risk of tibial subsidence after primary total knee arthroplasty (TKA). Maximizing tibial coverage is balanced against avoiding excessive overhang of the tray causing soft tissue irritation, and establishing proper tray alignment improving implant longevity and patella function. 1. Implant design factors, including the number of tray sizes, tray shape, and tray asymmetry influence the ability to cover the tibial plateau. 2. Furthermore, rotating platform (RP) tray designs decouple restoring proper tibial rotation from maximizing tibial coverage, which may enhance the ability to maximize coverage. The purpose of the current study was to assess the ability of five modern tray designs (Fig. 1), including symmetric, asymmetric, fixed-bearing, and RP designs, to maximize coverage of the tibial plateau across a large patient population. Methods:. Lower limb computed-tomography scans were collected from 14,791 TKA patients and the tibia was segmented. Virtual surgery was performed with an 8-mm tibial resection (referencing the high side) made perpendicular to the tibial mechanical axis in the frontal plane, with 3° posterior slope, and aligned transversely to the medial third of the tibial tubercle. An automated algorithm placed the largest possible tray on the plateau, optimizing the ML and AP placement (and I-E rotation for the RP tray), to minimize overhang. The largest sized tray that fit the plateau with less than 2-mm of tray overhang was identified for each of the five implant systems. The surface area of the tibial tray was divided by the area of the resected plateau and the percentage of patients with greater than 85% plateau coverage was calculated. Results:. The percentage of patients with greater than 85% plateau coverage across the tray designs ranged from 17.0% to 61.4% (Fig. 1). The tray with the greatest number of size options (Tray 4, 10 sizes) had the best coverage among the fixed-bearing trays. The RP variant of the same tray had the best overall coverage. Tibial asymmetry did not significantly improve the overall tibial coverage across the patient distribution for both asymmetric designs. Incorporating a broader medial condyle improved fit along the posterior medial corner for Tray 2, but increased the average under-hang along the posterior lateral plateau offsetting any improvement in total coverage. Discussion:. This analysis represents the most comprehensive assessment of tray coverage to date across a large TKA-patient population. Large variations exist in the size and shape of the proximal tibia among TKA patients. 3. Developing a tray design which provides robust coverage despite this variation remains challenging. This analysis suggests that tibial asymmetry may not robustly improve coverage. Conversely, incorporating an increased number of tray sizes and utilizing an RP implant to decouple coverage from alignment may provide the most reliable solution for maximizing coverage across the patient population