Fixed or mobile-bearing total knee arthroplasty

Fixed and mobile-bearing in total knee arthroplasty are still discussed controversially. In this article, biomechanical and clinical aspects in both fixed and mobile-bearing designs were reviewed. In biomechanical aspect, the mobile-bearing design has proved to provide less tibiofemoral contact stresses under tibiofemoral malalignment conditions. It also provides less wear rate in in-vitro simulator test. Patients with posterior stabilized mobile-bearing knees had more axial tibiofemoral rotation than patients with posterior stabilized fixed-bearing knees during gait as well as in a deep knee-bend activity. However, in clinical aspect, the mid-term or long-term survivorship of mobile-bearing knees has no superiority over that of fixed-bearing knees. The theoretical advantages for mobile-bearing design to provide a long-term durability have not been demonstrated by any outcome studies. Finally, the fixed-bearing design with all-polyethylene tibial component is suggested for relatively inactive, elder people. The mobile-bearing design is suggested for younger or higher-demand patients due to the potential for reduced polyethylene wear and more normal kinematics response after joint replacement. For younger surgeon, the fixed-bearing design is suggested due to less demand for surgical technique. For experienced surgeon, one familiar surgical protocol and instrumentation is suggested rather than implant design, either fixed-bearing or mobile-bearing

Does Posterior Tibial Slope Influence Knee Kinematics in Medial Stabilized TKA?

Background: During total knee arthroplasty (TKA), one of the key alignment factors to pay attention to is the posterior tibial slope (PTS). The PTS clearly influences the kinematics of the knee joint but must be adapted to the coupling degree of the specific TKA design. So far, there is hardly any literature including clear recommendations for how surgeons should choose the PTS in a medial stabilized (MS) TKA. The aim of the present study is to investigate the effects of different degrees of PTS on femorotibial kinematics in MS TKA. Materials and Methods: An MS TKA was performed in seven fresh-frozen human specimens successively with 0 degrees, 3 degrees, and 6 degrees of PTS. After each modification, weight-bearing deep knee flexion (30-130 degrees) was performed, and femorotibial kinematics were analyzed. Results: A lateral femoral rollback was observed for all three PTS modifications. With an increasing PTS, the tibia was shifted more anteriorly on the lateral side (0 degrees PTS anterior tibial translation -9.09 (+/- 9.19) mm, 3 degrees PTS anterior tibial translation -11.03 (+/- 6.72) mm, 6 degrees PTS anterior tibial translation 11.86 (+/- 9.35) mm). No difference in the tibial rotation was found for the different PTS variants. All PTS variants resulted in internal rotation of the tibia during flexion. With a 3 degrees PTS, the design-specific medial rotation point was achieved more accurately. Conclusions: According to our findings, we recommend a PTS of 3 degrees when implanting the MS prosthesis used in this study

No differences in in vivo kinematics between six different types of knee prostheses

Purpose: The aim of this study was to compare a broad range of total knee prostheses with different design parameters to determine whether in vivo kinematics was consistently related to design. The hypothesis was that there are no clear recognizable differences in in vivo kinematics between different design parameters or prostheses. Methods: At two sites, data were collected by a single observer on 52 knees (49 subjects with rheumatoid arthritis or osteoarthritis). Six different total knee prostheses were used: multi-radius, single-radius, fixed-bearing, mobilebearing, posterior-stabilized, cruciate retaining and cruciate sacrificing. Knee kinematics was recorded using fluoroscopy as the patients performed a step-up motion. Results: There was a significant effect of prosthetic design on all outcome parameters; however, post hoc tests showed that the NexGen group was responsible for 80% of the significant values. The range of knee flexion was much smaller in this group, resulting in smaller anterior-posterior translations and rotations. Conclusion: Despite kinematics being generally consistent with the kinematics intended by their design, there were no clear recognizable differences in in vivo kinematics between different design parameters or prostheses. Hence, the differences in design parameters or prostheses are not distinct enough to have an effect on clinical outcome of patients.Biomechanical EngineeringMechanical, Maritime and Materials Engineerin

Popliteus impingement after TKA may occur with well-sized prostheses

To determine the mechanisms and extents of popliteus impingements before and after TKA and to investigate the influence of implant sizing. The hypotheses were that (1) popliteus impingements after TKA may occur at both the tibia and the femur, and (2) even with an apparently well-sized prosthesis, popliteal tracking during knee flexion is modified compared to the preoperative situation. The location of the popliteus in three cadaver knees was measured using computed tomography, before and after implantation of plastic TKA replicas, by injecting the tendon with radiopaque liquid. The pre- and post-operative positions of the popliteus were compared from full extension to deep flexion using normosized, oversized, and undersized implants (one size increments). At the tibia, TKA caused the popliteus to translate posteriorly, mostly in full extension: 4.1 +/- 2 mm for normosized implants, and 15.8 +/- 3 mm with oversized implants, but no translations were observed when using undersized implants. At the femur, TKA caused the popliteus to translate laterally at deeper flexion angles, peaking between 80A degrees and 120A degrees: 2 +/- 0.4 mm for normosized implants and 2.6 +/- 0.5 mm with oversized implants. Three-dimensional analysis revealed prosthetic overhang at the posterosuperior corner of normosized and oversized femoral components (respectively, up to 2.9 mm and 6.6 mm). A well-sized tibial component modifies popliteal tracking, while an undersized tibial component maintains more physiologic patterns. Oversizing shifts the popliteus considerably throughout the full arc of motion. This study suggests that both femoro- and tibio-popliteus impingements could play a role in residual pain and stiffness after TKA

Valutazione cinematica intraoperatoria con utilizzo del navigatore e postoperatoria con rsa dinamica nelle protesi totali di ginocchio

Restoring a correct implant kinematics and providing a good ligament balance and patellar tracking is mandatory to improve clinical and functional outcome after a Total Knee Replacement. Surgical navigation systems are a reliable and accurate tool to help the surgeon in achieving these goals. The aim of the present study was to use navigation system with an intra-operative surgical protocol to evaluate and determine an optimal implant kinematics during a Total Knee Replacement

Cruciate retaining and cruciate substituting ultra-congruent insert

The posterior cruciate ligament (PCL) conservation and the polyethylene insert constraint in total knee arthroplasty (TKA) are still debated. The PCL is one of the primary stabilizers of the joint, but cruciate retaining (CR) implants have the disadvantage of a difficult balancing of the PCL. Postero-stabilized (PS) implants were introduced to reduce this problem. However, also the PS implants have some disadvantages, due to the cam-mechanism, such as high risk of cam-mechanism polyethylene wear. To minimize the polyethylene wear of the cam-mechanism and the bone sacrifice due to the intercondylar box, different types of inserts were developed, trying to increase the implant conformity and to reduce stresses on the bone-implant interface. In this scenario ultra-congruent (UC) inserts were developed. Those inserts are characterized by a high anterior wall and a deep-dished plate. This conformation should guarantee a good stability without the posterior cam. Few studies on both kinematic and clinical outcomes of UC inserts are available. Clinical and radiological outcomes, as well as kinematic data are similar between UC mobile bearing (MB) and standard PS MB inserts at short to mid-term follow-up. In this manuscript biomechanics and clinical outcomes of UC inserts will be described, and they will be compared to standard PS or CR inserts

Failure of Primary Total Knee Arthroplasty: Establishing a Baseline for Retrieval Analysis Using Well-Functioning Necropsy Specimens

Introduction. Total knee arthroplasty (TKA) is an effective treatment for end-stage osteoarthritis of the knee. While many patients have positive functional and pain outcomes following primary TKA, a subset of patients have suboptimal outcomes, such as unexplained pain or aseptic loosening of the implant components necessitating revision of the index procedure. The understanding of the exact etiology of these suboptimal outcomes of primary TKA is in its infancy. In order to elucidate the etiology of failure in primary TKAs, a baseline for the factors contributing to arthroplasty failure and dissatisfaction must first be established. The purpose of this study was to investigate the relationship between soft tissue laxity, inflammatory cytokine concentrations, tissue metal concentrations, and wear scores of well-functioning implants retrieved from cadaveric specimens to determine the role of each of these factors in implant survivorship. It was hypothesized that decreased joint laxity would increase metal concentrations in the periprosthetic tissue, that cytokines specifically tied to the innate immune system would be elevated in laxer joints, and, lastly, that elevated inflammatory cytokines in the synovial fluid would be associated with elevated periprosthetic tissue metal concentrations. Methodology. A total of 33 cadaveric specimens with primary TKA were obtained from two sources, the Medical Education and Research Institute (Memphis, TN) and RestoreLife USA (Elizabethton, TN), as part of institution review board approved multi-institutional orthopaedic retrieval program. Prior to testing and retrieval, fluoroscopically-assisted radiographs were taken to assess if any evidence of radiolucencies were present and all replacements were determined to be well-fixed per the images. Synovial fluid was then aspirated from the joint, processed, and stored in a -80˚C freezer. Each specimen was mounted into a custom knee testing platform and the IE rotation, varus-valgus (VV) deflection, and AP translation was measured at 0˚, 30˚, 60˚, and 90˚ of flexion. After collection of the laxity data, tissue samples were collected from the supra- and infra-patellar regions, the medial and lateral gutter, and from the tibia. The polyethylene inserts were assessed for wear on the condylar, backside, and stabilizing post surfaces, when applicable, and the femoral condyle was assessed for damage. A bead-based multiplex assay using the Luminex MAGPIX platform (R&D Systems, Minneapolis, MN) was performed on the synovial aspirates for simultaneous detection of various inflammatory cytokines including: IL-1β, IL-6, MCP-1, and MIP-3α. Inductively coupled plasma mass spectrometry (ICP-MS) was performed at Brooks Applied Labs (Bothel, WA) on the periprosthetic tissue samples for determination of tissue cobalt (Co), chromium (Cr), and titanium (Ti) concentrations. Finally, statistical analysis was conducted using SigmaPlot (Systat Software, Chicago, IL) to elucidate whether any correlations existed between the aforementioned factors. Results. Decreased IE laxity at full extension was inversely correlated with increased Co concentrations in the periprosthetic tissues (ρ=-0.64, p=0.02) with a sample size (n) of 13 and a 95% confidence interval (CI) from -0.88 to -0.14. At 90° of flexion, anterior laxity was inversely correlated with Co concentrations (ρ=-0.66, p=0.03, n=11, 95% CI: -0.90 vi to -0.10). At 60° of flexion, anterior laxity was inversely correlated with Cr concentrations (ρ=-0.63, p=0.03, n=13, 95% CI: -0.88 to -0.12). Anterior laxity at 90° of flexion was also inversely correlated with Cr concentrations (ρ=-0.81, p=0.003, n=11, 95% CI: -0.95 to -0.41). Lastly, posterior laxity at 90° of flexion was inversely correlated with Cr concentrations in the periprosthetic tissues (ρ=-0.74, p=0.01, n=11, 95% CI: -0.93 to -0.25). At 60° of flexion, IE rotational laxity was inversely correlated with IL-1β concentrations (ρ=-0.55, p=0.02, n=18, 95% CI: -0.81 to -0.11). At 60° of flexion, VV laxity was inversely correlated with TNF-α concentrations (ρ=-0.78, p=2x10-4 , n=14, 95% CI -0.93 to -0.43). Additionally, VV laxity was inversely correlated with IL-1β concentrations (ρ=-0.48, p=0.04, n=18, 95% CI: -0.77 to -0.02) at 60° of flexion. At full extension, VV laxity was inversely correlated with IL-6 concentrations (ρ=-0.46, p=0.04, n=19, 95% CI: -0.76 to -0.01). Anterior laxity was directly correlated with IL-6 concentrations (ρ=0.53, p=0.02, n=18, 95% CI: 0.08 to 0.80) at 90° of flexion. Additionally, anterior laxity was directly correlated with MCP-1 concentrations (ρ=0.62, p=0.006, n=18, 95% CI: 0.22 to 0.84) at 90° of flexion. Cr was inversely correlated with IL-6 (ρ=-0.52, p=0.01, n=21, 95% CI: -0.78 to -0.11). Cr was also inversely correlated with MIP-3α (ρ=-0.46, p=0.04, n=21, 95% CI: -0.74 to -0.04). Discussion. The specimens included in this study consisted of primary TKA implants that were retrieved at necropsy and were determined to be well-fixed per fluoroscopic analysis. The first objective of this study was to establish a baseline of different factors that likely contribute to failure of primary total knee replacements. This study provided semi-quantitative assessment of wear of the condylar surface, backside surface, and stabilizing post, when applicable, and of damage to the bearing surface of the femoral components. Joint laxity was measured using a custom knee testing platform that had been previously studied and utilized in published journal articles and theses. Inflammatory cytokine profiles in the synovial fluid samples were presented and measureable levels of metal debris was found in the periprosthetic tissue samples. The second objective of this study was to determine if any significant relationships arose in correlation analysis of the latter three aforementioned factors. An inverse trend was observed between joint laxity and tissue metal concentrations, such that decreased laxity induced metal release from the implant components. A direct trend was observed specifically between increased anteroposterior laxity and elevated inflammatory cytokines. Lastly, an inverse trend was found between decreased tissue metal concentrations and increased inflammatory cytokines. The third, and future, objective of this study is to utilize these measurements and observations for comparison with failed implants retrieved at time of revision. While some meaningful relationships were observed in this study, there were several limitations that must be noted. Firstly, this study had a relatively small sample size. Secondly, the cohort included a wide range of implants including cruciate-retaining, posterior-stabilized, fixed bearing, mobile bearing, monoblock, and modular designs fabricated from different material

Development of an instrumented customizable total knee prosthesis for experimental tests.

Total knee arthroplasty (TKA) has revolutionized the life of millions of patients and it is the most efficient treatment in cases of osteoarthritis. The increase in life expectancy has lowered the average age of the patient, which requires a more enduring and performing prosthesis. To improve the design of implants and satisfying the patient's needs, a deep understanding of the knee Biomechanics is needed. To overcome the uncertainties of numerical models, recently instrumented knee prostheses are spreading. The aim of the thesis was to design and manifacture a new prototype of instrumented implant, able to measure kinetics and kinematics (in terms of medial and lateral forces and patellofemoral forces) of different interchangeable designs of prosthesis during experiments tests within a research laboratory, on robotic knee simulator. Unlike previous prototypes it was not aimed for industrial applications, but purely focusing on research. After a careful study of the literature, and a preliminary analytic study, the device was created modifying the structure of a commercial prosthesis and transforming it in a load cell. For monitoring the kinematics of the femoral component a three-layers, piezoelettric position sensor was manifactured using a Velostat foil. This sensor has responded well to pilot test. Once completed, such device can be used to validate existing numerical models of the knee and of TKA and create new ones, more accurate.It can lead to refinement of surgical techniques, to enhancement of prosthetic designs and, once validated, and if properly modified, it can be used also intraoperatively

Changes in knee kinematics reflect the articular geometry after arthroplasty

We hypothesized changes in rotations and translations after TKA with a fixed-bearing anterior cruciate ligament (ACL)-sacrificing but posterior cruciate ligament (PCL)-retaining design with equal-sized, circular femoral condyles would reflect the changes of articular geometry. Using 8 cadaveric knees, we compared the kinematics of normal knees and TKA in a standardized navigated position with defined loads. The quadriceps was tensed and moments and drawer forces applied during knee flexion-extension while recording the kinematics with the navigation system. TKA caused loss of the screw-home; the flexed tibia remained at the externally rotated position of normal full knee extension with considerably increased external rotation from 63° to 11° extension. The range of internal-external rotation was shifted externally from 30° to 20° extension. There was a small tibial posterior translation from 40° to 90° flexion. The varus-valgus alignment and laxity did not change after TKA. Thus, navigated TKA provided good coronal plane alignment but still lost some aspects of physiologic motion. The loss of tibial screw-home was related to the symmetric femoral condyles, but the posterior translation in flexion was opposite the expected change after TKA with the PCL intact and the ACL excised. Thus, the data confirmed our hypothesis for rotations but not for translations. It is not known whether the standard navigated position provides the best match to physiologic kinematics