Restoring more natural kinematics is crucial for the success of knee TKA. The relative size of the tibia to the femur may differ in each patient and requires the possibility to combine different tibia sizes for a given femur size. Therefore, TKA systems need to be designed to allow for different size combinations. In literature some report higher revision rates when the femoral size is greater than the tibia, while others find no impact of the size mismatch on the clinical outcome. The tibio-femoral kinematics resulting from different size combinations has not been analyzed yet. The Columbus Deep Dish implant (Aesculap, Tuttlingen, Germany) is designed to allow a full size compatibility. Therefore we hypothesized that the kinematics would not be affected by the different size combinations. The goal of this study was to investigate the impact on kinematics of different tibio-femoral size combinations with the Columbus Deep Dish implant. 6 fresh frozen cadavers were tested in a force controlled well established knee rig after implantation of a cruciate retaining, fixed bearing Columbus Deep Dish TKA (Aesculap, Tuttlingen, Germany). Femoro-tibial kinematics were recorded while performing a loaded squat from 30° to 130°. Specifically developed and manufactured inlays allowed simulating different tibia sizes on each bone/tibial implant. For each cadaver, a total of 4 different tibia sizes were tested (1 original size, 3 simulated different sizes). Tibio-femoral internal/external rotation and antero-posterior translation of the medial and of the lateral condyles were computed for all size combinations. The kinematics obtained with the simulated sizes were compared to the kinematics obtained with the original inlay. For each flexion angle from 30° to 130°, the difference between the rotation (resp. translation) obtained with the original inlay was subtracted from the rotation obtained with the simulated tibia size. The mean value and standard deviation of the differences were computed.Objectives
Methods
Revision total hip arthroplasty is often associated with acetabular bone defects. In most cases, assessment of such defects is still qualitative and biased by subjective interpretations. Three-dimensional imaging techniques and novel anatomical reconstructions using statistical shape models (SSM) allow a more impartial and quantitative assessment of acetabular bone defects [1]. The objectives of this study are to define five clinically relevant parameters and to assess 50 acetabular bone defects in a quantitative way. Anonymized CT-data of 50 hemi-pelvises with acetabular bone defects were included in the study. The assessment was based on solid models of the defect pelvis (i.e. pelvis with bone defect) and its anatomical reconstruction (i.e. native pelvis without bone defect) (Fig.1A). Five clinically relevant parameters were defined: (1) Bone loss, defined by subtracting defect pelvis from native pelvis. (2) Bone formation, defined by subtracting native pelvis from defect pelvis. Bone formation represents bone structures, which were not present in the native pelvis (e.g. caused by remodeling processes around a migrated implant). (3) Ovality, defined by the length to width ratio of an ellipse fitted in the defect acetabulum. A ratio of 1.0 would represent a circular acetabulum. (4) Lateral center-edge angle (LCE angle), defined by the angle between the most lateral edge of the cranial roof and the body Z-axis, and (5) implant migration, defined by the distance between center of rotation (CoR) of the existing implant and CoR of native pelvis (Fig. 1B).Introduction
Methods
It is well-known that wear debris generated by metal-on-metal hip replacements leads to aseptic loosening. This process starts in the local tissue where an inflammatory reaction is induced, followed by an periprosthetic osteolysis. MOM bearings generate particles as well as ions. The influence of both in human bodies is still the subject of debate. For instance hypersensitivity and high blood metal ion levels are under discussion for systemic reactions or pseudotumors around the hip replacement as a local reaction. The exact biopathologic mechanism is still unknown. The aim of this study was to investigate the impact of local injected metal ions and metal particles. We used an established murine inflammation model with Balb/c mice and generated three groups. Group PBS (control group, n=10) got an injection of 50µl 0.1 vol% PBS-suspension, Group MI (Metal-ion, n=10) got an injection of 50µl metal ion suspension at a concentration of 200µg/l and Group MP (Metal-particles, n=10) got an injection of 50µl 0.1 vol% metal particle suspension each in the left knee. After incubation for 7 days the mice were euthanized and the extraction of the left knee ensued. Followed by immunhistochemical treatment with markers of inflammation that implied TNFα, IL-6, IL-1β, CD 45, CD 68, CD 3, we counted the positive cells in the synovial layer in the left knees by light microscopy, subdivided into visual fields 200× magnified. The statistical analysis was done with Kruskal-Wallis test and a post hoc Bonferroni correction.Introduction
Material and Methods
Metal on metal bearings are used especially in hip resurfacing. On the one hand, small bone preserving implants can be used. On the other hand recent studies found a variety of local and systemic side effects, for instance the appearance of pseudotumors, that are explained by pathologic biological reaction of the metal wear debris. The detailed mechanisms are still not understood until now. Thus it was the aim of this study to investigate the local reaction of metal wear particles and metal ions in a murine model. The hypothesis was that mainly metal ions provoke adverse histopathological reactions in vivo. Three groups, each with 10 Balb / c mice were generated. Group A: injection of a 50 µl metal ion suspension at a concentration of 200 µg / l in the left knee. Group B: injection of a 50 µl 0,1 vol% metal particle suspension into the left knee joint. Group C (control group): injection of a 50 µl of 0,1 vol% PBS-suspension in the left knee. Incubation for 7 days, followed by euthanasia of the animals by intracardiac pentobarbital. The left and right knee, the lungs, kidneys, liver and spleen were removed. Histologic paraffin sections in 2 microns thickness were made, followed by HE (overview staining) and Movat (Pentachrom staining) staining. The histologic analysis was a done by a light microscopic evaluation of the subdivided visual fields at 200× magnification.Introduction
Material and Methods
The complex process of inflammation and osteolysis due to wear particles still is not understood in detail. So far, Ultra-high-molecular-weight-polyethylene (UHMWPE) is the bearing material of choice in knee arthroplasty and revision knee arthroplasty, but there is a growing demand for alternative bearing materials with improved wear properties. Lately, increasing interest developed in the use of natural and carbon-fiber-reinforced-poly-ether-ether-ketones (CFR-PEEK). While there is a lack of data concerning the effects of CFR-PEEK particles on human tissue, the effects of such wear debris The aim of this study was to analyze human tissue containing CFR-PEEK as well as UHMWPE wear debris. The authors hypothesized no difference between the used biomaterials because of similar size parameters of the wear particles in a prior knee simulator study of this implant. Synovial tissue samples of 10 patients while knee revision surgery of a rotating hinge knee implant design (Enduro®, Aesculap, Germany) were achieved. The tibial inserts of this design were made from UHMWPE (GUR 1020), whereas the bushings and flanges are made of CFR-PEEK containing 30% polyacrylonitrile (PAN) based carbon fibers (PEEK-Optima LT1, Invibio Ltd. Thornton-Cleveleys, UK). In a prior The tissue was fixed with 4% paraformaldehyde, embedded in paraffin, sliced into 2 µm thick sections stained with hematoxylin and eosin in a standard process. A modified panoptical staining (preincubation in propylenglycol; >3h; 35°C) was also done which stained the UHMWPE particles turquoise. The study was approved by the ethics committee of the local university.Introduction
Methods and Materials
Despite consequent advancement in Total Knee Arthroplasty (TKA) up to 20% of patients are not satisfied after having been operated. Beside correct implantation, the design of the TKA-system is supposed to be a key factor of a successful TKA. Consequently it has been tried to restore natural kinematics by the design of the prosthesis. A medially stabilized design therefore is supposed to allow a lateral translation with a medial pivot. Our study compared posterior stabilized (PS) with medially stabilized (MS) TKA-design in terms of kinematics, femorotibial and patellofemoral contact patterns in vitro.Introduction
Objectives
The complex cellular mechanisms of the aseptic loosening of total joint arthroplasties still remain not completely understood in detail. Especially the role of adherent endotoxins in this process remains unclear, as lipopolysaccharides (LPS) are known to be very potent modulators of the cell response on wear particle debris. Contributing factors on the LPS affinity of used orthopedic biomaterials as their surface roughness have to be investigated. The aim of this study was to evaluate the affinity of LPS on the surface roughness of different biomaterials Cubes with a side length from ultra-high-molecular-weight-polyethylene (UHMWPE), crosslinked polytethylene (XPE), carbon fibre reinforced poly-ether-ether-ketone (CFR-PEEK), titanium, titanium alloy, Polymethyl methacrylate (PMMA), implant steel (CoCr) and instrument steel (BC) were produced (figure 1). Cubes of each material have been produced with a rough and a smooth surface. Before the testings, all cubes and used materials were treated with E-Toxa-Clean(®) to eliminate pre-existing LPS on the used surfaces. The cubes were then fixed on the cap of a glass that was filled with a LPS solution with a concentration of 5 IE/ml. After 30 minutes the cube was removed and the LPS concentration in the supernatant was measured. The endotoxin content of each sample was evaluated by a Limulus Amoebocyte Lysate (LAL) - Test (Lonza, Verviers, Belgium). The detection level of endotoxin was set at < 0.005 EU/ml diluted 1/10.Introduction
Materials and methods
A pain free motion of the patella after total knee arthroplasty (TKA) is still a challenge for surgeons and TKA-designers today. After TKA, the restricted guidance of the patella and kinematic alterations of the femorotibial joint results in increased retropatellar pressure and unphysiological patellar tracking. The alignment of the prosthetic components can influence patellofemoral stresses and tracking of the patella. The aim of this study was to demonstrate the consequences of different alignments of the tibial baseplate on patellar stress and knee kinematics. Different alignments of the tibial baseplate were simulated with five different UHMWPE-Inlets. Inserts with medial and lateral translation (±3mm; Figure 1A) as well as internal and external rotation (±3°; Figure 1B) were manufactured. Original inlays were used to define the neutral position. Eight human knee specimens without TKA were tested in a custom made knee rig. This rig mimics a loaded squat from approximately 20°−120° of flexion under six degrees of freedom in the knee joint. Retropatellar pressure (IScan, Tekscan, USA) as well as knee kinematics (CMS 20, Zebris, Germany) were recorded during squatting. Afterwards, TKA components were implanted in a neutral position via subvastus approach in tibia first technique. Each of the 5 tibial inlets was tested consecutively with the knee rig under the same conditions. Results were compared using mixed effects models with a random intercept per specimen. Component alignment as well as moving direction (flexion/extension) and flexion degree were defined as fixed effects in our model (SPSS, IBM, USA). After TKA in neutral position, retropatellar peak pressure increased by 0.71MPa (p<0.01), femorotibial rollback was reduced (−2.24mm; p<0.01) and the patella kinematics, in particular patella flexion (−2.02°; p<0.01) and rotation (−0.97°; p<0.01), were changed during squatting. Compared to the neutral position, internal rotation of the tibial baseplate increased retropatellar pressure by 0.20 MPa, while an external rotation provided a reduction of −0.24 MPa (p<0.01). In contrast a medialization or lateralization showed no effect on retropatellar pressure (p=0.09). Both, rotation and translation of the tibial baseplate influenced tibiofemoral kinematics significantly. A reduction of the femorotibial rollback was measured in external alignment (rotation and lateral translation; both p<0.01). An internal rotation showed more femoral rollback (0.93mm p<0.01). Patellar kinematics was changed primarily by component translation rather than rotation. A lateralisation of the tibial baseplate resulted in a medial shift of the patella by −0.43mm and vice versa (p<0.01). Rotation of the tibial baseplate had no influence on the patella shift (p=0.8) The findings in this study suggest that the alignment of the tibial baseplate influences patellar biomechanics significantly in vitro. An external rotation of the tibial baseplate decreased retropatellar pressure and patella kinematics tend more to the in situ situation of a natural knee. An internal alignment of the tibial baseplate seems to reconstruct natural tibiofemoral rollback in parts. However, studies (i.e. Nicoll et al.) show higher anterior knee pain by an internal alignment and a higher rollback after TKA might lead to higher wear.
