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

Introduction

Beneath infection, instability and malalignment, aseptic tibial component loosening remains a major cause of failure in total knee arthroplasty (TKA) [1]. This emphasizes the need for stable primary and long-term secondary fixation of tibial baseplates. To evaluate the primary stability of cemented tibial baseplates, different pre-clinical test methods have been undergone: finite element analysis [2], static push-out [3,4] or dynamic compression-shear loading [5] until interface failure. However, these test conditions do not reflect the long-term endurance under in vivo loading modes, where the tibial baseplate is predominantly subjected to compression and shear forces in a cyclic profile [5,6].

To distinguish between design parameters the aim of our study was to develop suitable pre-clinical test methods to evaluate the endurance of the implant-cement-bone interface fixation for tibial baseplates under severe anterior (method I) and internal-external torsional (method II) shear test conditions.

Introduction. The results of the original mobile bearing Oxford unicompartmental knee replacement (UKR) in the lateral compartment have been disappointing because of high dislocation rates (11%). This original implant used a flat bearing articulation on the tibial tray. To address the issue of dislocation a new implant (domed tibia with biconcave bearing to increase entrapment) was introduced with a modified surgical technique. The aim of this study was to compare the risk of dislocation between a domed and flat lateral UKR. Methods. Separate geometric computer models of an Oxford mobile bearing lateral UKR were generated for the two types of articulation between the tibial component and the meniscal bearing: Flat-on-flat (flat) and Concave-on-convex (domed). Each type of mobile bearing was used to investigate three distinct dislocation modes observed clinically: lateral to medial dislocation, with the bearing resting on the tray wall (L-M-Wall); medial to lateral dislocation, out of the joint space (M-L); anterior to posterior dislocation, out of the joint space (A-P). A size C tray and a medium femoral component and bearing were used in all models. The femoral component, tibial tray and bearing were first aligned in a neutral position. For each dislocation the tibial tray was restrained in all degrees of freedom. The femoral component was restrained from moving in the anterior-posterior directions and in the medial-lateral directions. The femoral component was also restrained from rotating about the anterior-posterior, medial-lateral and superior-inferior directions. This meant that the femoral component was only able to move in the superior-inferior direction. Different bearing sizes were inserted into the model and the effect that moving the femoral component medially and laterally had on the amount of distraction required to cause bearing dislocation was investigated. Results. The average femur distraction to allow bearing dislocation in the A-P, M-L and L-M-wall directions was 1.62 mm (27%), 0.51 mm (26%) and 1.2 mm (24%) greater respectively for the domed bearing. There was a 3% increase in femoral distraction required to cause L-M-Wall dislocation, per increment of bearing thickness for both the domed and lateral bearings. There was on average a 7% increase in femoral distraction required to cause L-M-Wall dislocation per mm increment of medial femoral component movement. Discussion. Dislocation over the tray wall is a particular clinical problem and using a domed bearing can lead to an increased required femoral distraction of between 25% and 37%. This may be significant during everyday activities and demonstrates that the new domed design should reduce the incidence of bearing dislocation by increasing the amount of entrapment. Increasing the thickness of the bearing has a small effect on the distraction required to allow bearing dislocation. Lateral placement of the femoral component markedly reduced the femoral distraction required for bearing dislocation over the tray wall. Medial placement of the femoral component is advisable so long as impingement with the tray wall is avoided

Introduction. Unicompartmental Knee Replacement (UKR) is an appealing alternative to Total Knee Replacement (TKR) when the patient has isolated compartment osteoarthritis (OA). A common observation post-operatively is radiolucency between the tibial tray wall and the bone. In addition, some patients complain of persistent pain following implantation with a UKR; this may be related to elevated bone strains in the tibia. The aim of this study was to investigate the mechanical environment of the tibia bone adjacent to the tray wall, following UKR, to determine whether this region of bone resorbs, and how altering the mechanical environment affects tibia strains. Materials and methods. A finite element (FE) model of a cadaver tibia implanted with an Oxford UKR was used in this study, based on a validated model. A single static load, measured in-vivo during a step-up activity was used. There was a 1 mm layer of cement surrounding the keel in the cemented UKR, and the cement filled the cement pocket. In accordance with the operating procedure, no cement was used between the tray wall and bone. For the cementless UKR a layer of titanium filled the cement pocket. An intact tibia was used to compare to the cemented and cementless UKR implanted tibiae. The tibia was sectioned by the tray wall, defining the radiolucency zone (parallel to the vertical tray wall, 2 mm wide with a volume of 782.5 mm. 3. ), corresponding to the region on screened x-rays where radiolucencies are observed. Contact mechanics algorithms were used between all contacting surfaces; bonded contact was also introduced between the tray wall and adjacent bone, simulating a mechanical tie between them. Strain energy density (SED), was compared between the intact and implanted tibia for the radiolucency zone. Equivalent strains were compared on the proximal tibia between the intact and implanted tibia models. Forty patients (20 cemented, 20 cementless) who had undergone UKR were randomly selected from a database, and assessed for radiolucency. Results. The SED in the radiolucency zone was 80% lower in the cemented and cementless tibia, compared to the intact tibia, without a mechanical tie between the tibial tray wall and adjacent bone. When a mechanical tie was introduced the SED in the radiolucency zone was 35% higher in the cemented and cementless tibia, compared to the intact tibia. The strain on the proximal tibia was reduced by 20% when a mechanical tie was used between the tray wall and adjacent bone. Radiolucency at the tray wall was observed in all forty radiographs examined. Discussion. This work has presented a static snapshot of the load being carried through the proximal tibia following implantation with an Oxford UKR. It has been shown that by introducing a mechanical tie between the tibial tray wall and the adjacent bone, the SED in the region observed to have radiolucency is increased; this has the potential of reducing the likelihood of a radiolucency occurring in that region. Moreover, the strain observed in the proximal tibia was reduced when a mechanical tie was introduced, which may reduce the incidence of pain following implantation with a UKR. It is recommended that integration between the bone and the tray wall is important for UKR

Ultra-high molecular weight polyethylene (UHMWPE) is a commonly used as bearing material in joint replacement devices. UHMWPE implants can be hard to see on a standard X-ray because UHMWPE does not readily attenuate X-rays. Radiopaque UHMWPE would enable direct imaging of the bearing both during and after surgery, providing in vivo assessment of bearing position, dislocation or fracture, and potentially a direct measure of wear. The X-ray attenuation of UHMWPE was increased by diffusing an FDA approved contrast agent (Lipiodol) into UHMWPE parts (Zaribaf et al, 2018). The aim of this study was to evaluate the optimal level of radiopacity for a UHMWPE bearing. Samples of un-irradiated medical grade UHMWPE (GUR 1050) were machined into 4mm standard medium Oxford Unicompartmental bearings. Samples were immersed in Lipiodol Ultra Fluid (Guerbert, France) at elevated temperatures (85 °C, 95 °C and 105 °C) for 24 h to achieve three different levels of radiopacity. A phantom set-up was used for X-ray imaging; the phantom contained two perspex rods to represent bone, with the metallic tibial tray and polyethylene bearing fixed to the end of one rod and the metallic femoral component fixed to the other rod. Radiographs of the samples were taken (n=5) with the components positioned in full extension. To ensure consistency, the images of all the samples were taken simultaneously alongside an untreated part. The results of our ongoing study demonstrate that the radiopacity of UHMWPE can be enhanced using Lipiodol and the parts are visible in a clinical radiographs. The identification of the optimal treatment from a clinical perspective is ongoing; we are currently running a survey with clinicians to find the consensus on the optimal radiopacity taking into account the metallic components and alignment. Future work will involve a RSA study to assess the feasibility of measuring wear directly from the bearing

When performing total knee replacement (TKR), surgeons must select a size of tibial component tray that most closely matches the anatomy of the proximal tibia. As implants are available in a limited range of sizes, it may be necessary to slightly under or oversize the component. There are concerns overhang could lead to pain from irritation of soft tissues, and underhang could lead to subsidence and failure. 154 TKRs at 1- or 5-year follow up were reviewed prospectively. Oxford Knee Score (OKS), WOMAC and SF-12 was recorded along with pain scores. Scaled radiographs were reviewed and grouped into perfect sizing (78 TKRs, 50.6%), underhang in isolation (48 TKRs, 31.1%), minor overhang 1–3 mm (10 TKRs, 6.49%) or major overhang >3 mm (18 TKRs, 11.7%). There was no significant difference in the SF-12 (p=0.356), post-operative OKS (p=0.401) or WOMAC (p=0.466) score. For the OKS, there was no difference for the scores collected at 1 year (p=0.176) or at 5 years (p=0.883). Pre-operative OKS was well matched between the groups (p=0.152). There was no significant difference in the improvement in OKS from pre-operative scores (p=0.662). There was no significant difference in either the OKS or WOMAC pain scores (p=0.237 and 0.542 respectively). There was no significant association of medial overhang with?medial knee pain (p=1.000) or lateral overhang with lateral knee pain (p=0.569) when compared to the group of patients with a well sized tibial component. Our results suggest that tibial component overhang or underhang has no detrimental affect on outcome or pain scores. Surgeons should continue to select the tibial component that most closely fits the rim of the proximal tibia while accepting slight overhang if necessary due to the potential longer-term complications of subsidence and premature failure with an undersized tibial tray

Achieving deep flexion after total knee replacement remains a challenge. In this study we compared the soft-tissue tension and tibiofemoral force in a mobile-bearing posterior cruciate ligament-sacrificing total knee replacement, using equal flexion and extension gaps, and with the gaps increased by 2 mm each. The tests were conducted during passive movement in five cadaver knees, and measurements of strain were made simultaneously in the collateral ligaments. The tibiofemoral force was measured using a customised mini-force plate in the tibial tray. Measurements of collateral ligament strain were not very sensitive to changes in the gap ratio, but tibiofemoral force measurements were. Tibiofemoral force was decreased by a mean of 40% (. sd. 10.7) after 90° of knee flexion when the flexion gap was increased by 2 mm. Increasing the extension gap by 2 mm affected the force only in full extension. Because increasing the range of flexion after total knee replacement beyond 110° is a widely-held goal, small increases in the flexion gap warrant further investigation

Summary Statement. Our data suggest that postoperative component positioning in TKA with PSPG is not consistent with pre-operative software planning. More studies are needed to rule out possible learning curve in this study. Introduction. Patient specific positioning guides (PSPGs) in TKA are based on MRI or CT data. Preoperatively, knee component positions can be visualised in 3-dimensional reconstructed images. Software allows anticipation of component position. From software planning PSPGs are manufactured and those PSPGs represent intra-operative component alignment. To our knowledge, there are no studies comparing pre-operative software planning with post-operative alignment. Aim of this study is to investigate the correlation between pre-operative planning of component positioning and the post-operative achieved alignment with PSPG technique. Patients & Methods. The first 25 TKA (cemented Vanguard® Complete Knee System, Biomet) with PSPG (Signature™ Biomet) performed at Telemark Hospital in 2009–2010 and the first 17 TKA with PSPG performed at Oslo University Hospital in 2010–2011 were included. A postoperative CT scanning and measurement protocol was used (Perth protocol). CT measurements were performed by 2 independent observers and comparative with pre-operative software (Materialise) planning. Component position angles of femur and tibia were measured. Mechanical axis for both femoral and tibial component angles in all planes was defined as zero degrees. Target angle for femoral component in sagittal plane was set to 2,8 degrees flexion on average and for the tibial tray to 3 degrees of posterior slope. Tibial rotation was in most cases obtained by using extra-medullary guide and therefore not included in this study. Results. In respectively coronal, sagittal and axial plane the femoral component angle was on average 1.2° in varus, SD 1.6 (1.7° valgus −4.5° varus), 4.4° in flexion, SD 3.9 (17.3° flexion −1.6° extension) and 0.5° in external rotation, SD 0.1 (2.3° internal rotation −4.3° external rotation). For the tibial component angle the component was on average 0,5° in varus (3.5° valgus −7.3° varus) and 3.7° posterior slope, SD 2.3 (8.8° flexion −2.4° extension). Intra-class correlation (ICC) between the 2 independent observers was for femoral component in coronal, sagittal and axial plane 0.85, 0.93 and 0.63 and tibial component in coronal and sigittal plane 0.94 and 0.95. Discussion/Conclusion. We expected that our measurements would be close to the pre-operative values. Although the mean values of post-operative measurements are close to pre-operative software planning, we found a considerable spread. Possible explanation might be error levels in pre-operative wrong identification of landmarks from MRI and/or different identification of bony landmarks on CT and intra-operative errors. All measurements were performed from the first Signatures performed in both hospitals. An early learning curve might explain some of the outliers. Time between manufacturing date and performed operation was in most cases several months, but less than the advocated 6 months. This time gap can theoretically provide a less proper fit in some cases due to slight change of anatomy in a progressive osteoarthritis. Our data suggest that postoperative positioning is not consistent with preoperative planning. This may be caused by the an early learning curve. It is uncertain whether this inconsistency is of clinical relevance. More data is necessary to prove any benefit of PSPG compared to existing procedures for TKA

The treatment of bony defects of the tibia at the time of revision total knee replacement is controversial. The place of compacted morsellised bone graft is becoming established, particularly in contained defects. It has previously been shown that the initial stability of impaction-grafted trays in the contained defects is equivalent to that of an uncemented primary knee replacement. However, there is little biomechanical evidence on which to base a decision in the treatment of uncontained defects. We undertook a laboratory-based biomechanical study comparing three methods of graft containment in segmental medial tibial defects and compared them with the use of a modular metal augment to bypass the defect.

Using resin models of the proximal tibia with medial defects representing either 46% or 65% of the medial cortical rim, repair of the defect was accomplished using mesh, cement or a novel bag technique, after which impaction bone grafting was used to fill the contained defects and a tibial component was cemented in place. As a control, a cemented tibial component with modular metal augments was used in identical defects. All specimens were submitted to cyclical mechanical loading, during which cyclical and permanent tray displacement were determined.

The results showed satisfactory stability with all the techniques except the bone bag method. Using metal augments gave the highest initial stability, but obviously lacked any potential for bone restoration.

The biomechanics of the patellofemoral joint can become disturbed during total knee replacement by alterations induced by the position and shape of the different prosthetic components. The role of the patella and femoral trochlea has been well studied. We have examined the effect of anterior or posterior positioning of the tibial component on the mechanisms of patellofemoral contact in total knee replacement. The hypothesis was that placing the tibial component more posteriorly would reduce patellofemoral contact stress while providing a more efficient lever arm during extension of the knee.

We studied five different positions of the tibial component using a six degrees of freedom dynamic knee simulator system based on the Oxford rig, while simulating an active knee squat under physiological loading conditions. The patellofemoral contact force decreased at a mean of 2.2% for every millimetre of posterior translation of the tibial component. Anterior positions of the tibial component were associated with elevation of the patellofemoral joint pressure, which was particularly marked in flexion > 90°.

From our results we believe that more posterior positioning of the tibial component in total knee replacement would be beneficial to the patellofemoral joint.

The use of impaction bone grafting during revision arthroplasty of the hip in the presence of cortical defects has a high risk of post-operative fracture. Our laboratory study addressed the effect of extramedullary augmentation and length of femoral stem on the initial stability of the prosthesis and the risk of fracture.

Cortical defects in plastic femora were repaired using either surgical mesh without extramedullary augmentation, mesh with a strut graft or mesh with a plate. After bone impaction, standard or long-stem Exeter prostheses were inserted, which were tested by cyclical loading while measuring defect strain and migration of the stem.

Compared with standard stems without extramedullary augmentation, defect strains were 31% lower with longer stems, 43% lower with a plate and 50% lower with a strut graft. Combining extramedullary augmentation with a long stem showed little additional benefit (p = 0.67). The type of repair did not affect the initial stability. Our results support the use of impaction bone grafting and extramedullary augmentation of diaphyseal defects after mesh containment.