Introduction. Unicompartmental knee arthroplasty (UKA) in patients with isolated medial osteoarthritis of the knee is nowadays a standard procedure with good results, especially with the minimally-invasive approach. However, the survival rate of the unicompartmental knee prostheses is inferior to that of total knee prostheses. Therefore, further studying of UKA is still necessary. In most mobile bearing designs the femoral component has a spherical surface and therefore its positioning is not crucial. The role of the tibial slope in UKA has not been investigated so far. The manufacturers recommend tibial slopes with values between 10° positive slope and 5° negative slope. Most surgeons try to reconstruct the anatomical slope with a high failure by measuring the slope on x-rays. The aim of this study was to investigate the influence of the tibial slope on the wear rate of a medial UKA. Materials and methods. In vitro wear simulation of medial mobile bearing unicompartmental knee prosthesis with a spherical femoral surface (Univation ®) was performed with a customized four-station servo-hydraulic knee wear simulator (EndoLab GmbH, Thansau, Germany) reproducing exactly the walking cycle as specified in ISO 14243–1:2002(E). The tibial tray was inserted with 2 different medial tibial slopes: 0°, 8° (n=3 for each group). The lateral tibial slope of the space-holder was not changed (0° for every group). We performed a total of 5 million cycles for every different slope, the gravimetric wear rate was determined gravimetrically using an analytical balance every 500 000 cycles according to the ISO 14243–2. Results. The wear rate in the 0° slope group was 3.46±0.59 mg/million cycles, and in the 8° slope group it was 0.99±0.42 mg/million cycles. The difference between the 0° tibial slope group and the 8° tibial slope group was highly significant (p<0.01, alternate t-test). Discussion. An increase of the tibial slope leads to a reduced wear rate in a mobile bearing UKA. Therefore, a higher tibial slope should be recommended for mobile bearing UKA. However, the influence on the ligaments has to be considered as a higher tibial slope leads to an increased strain on the anterior cruciate ligament. This influences needs to be investigated in further studies before a definite optimal range for the tibial slope can be recommended

Introduction. Minimally invasive implanted unicompartmental knee arthroplasty (UKA) leads to excellent functional results. Due to the reduced intraoperative visibility it is difficult to remove extruded bone cement particles, as well as bone particles generated through the sawing. These loose third body particles are frequently found in minimally invasive implanted UKA. The aim of this study was to analyse the influence of bone and cement particles on the wear rate of unicompartmental knee prostheses in vitro. Material & Methods. Fixed- bearing unicompartmental knee prostheses (n = 3; Univation F®, Aesculap, Tuttlingen) were tested with a customized four-station servo-hydraulic knee wear simulator (EndoLab GmbH, Thansau, Germany) reproducing exactly the walking cycle as specified in ISO 14243-1:2002. After 5.0 million cycles crushed cortical bone chips were added to the test fluid for 1.5 million cycles to simulate bone particles, followed by 1.5 million cycles blended with PMMA- particles (concentration of the third-body particles: 5g/l; particle diameter: 0.5- 0.7 mm). Every 500 000 cycles the volumetric wear rate was measured (ISO 14243-2) and the knee kinematics were recorded. For the interpretation of the test results we considered four different phases: breaking in- (during the first 2.0 million cycles), the steady state- (from 2.0 million to 5 million cycles), bone particle- and cement particle phase. Finally, a statistical analysis was carried out to verify the normal distribution (Kolmogorov-Smirnov test), followed by direct comparisons to differentiate the volumetric wear amount between the gliding surfaces (paired Student's t-test, p<0.05). Results. The wear rate was 12.5±0.99 mm. 3. /mio. cycles in the breaking-in phase and decreased during the steady state phase to 4.4±0.91 mm. 3. /mio cycles (not significant, p = 0,3). The bone particles did not have any influence on the wear rate (3.0±1.27 mm. 3. /mio cycles; p = 0,83) compared to the steady state phase. The cement particles, however, lead to a significantly higher wear rate compared to the steady state phase (25.0±16.93 mm. 3. /mio cycles; p<0.05). Discussion. To our knowledge this is the first study demonstrating that free cement debris which can be found after minimally invasive implanted UKA increases significantly the wear- rate. Bone particles generated for instance through sawing during implantation, however, had no influence on the prostheses wear rate. Our Data suggests, that it is extremely important to remove all the extruded cement debris accurately during implantation in order to avoid a higher wear rate which could result in an early loosening of the prostheses

Due to increased life expectancy of human population, the amount of total knee replacements (TKR) is expected to increase. TKR reached a high grade of quality and safety, but most often it fail because of aseptic implant loosening caused by polyethylene (PE) wear debris. Wear is generated at the articulating surfaces, e.g. caused by three body particles, like bone fragments or bone cement particles. The aim of this experimental study was to compare the wear of tibial PE inserts combined with metallic and ceramic femoral components at three body wear situation induced by polymethylmethacrylate (PMMA) and zirconia (ZrO2) particles from the bone cement. Wear testing was performed for 5 Mio load cycles, using tibial standard PE inserts combined with the same CR femoral component, in two different materials, Cobalt Chromium (CoCrMo) and Biolox delta ® ceramic (Multigen Plus Knee System, Lima Corporate, Italy). A knee wear simulator, according to ISO 14243 (EndoLab GmbH, Rosenheim, Germany), was used to carry out the tests. The tests were performed in temperature-controlled test chambers at 37 °C, containing calf serum with a protein content of 30 g/l. Polymethylmethacrylate (PMMA) and zirconia (ZrO2) bone cement particles (Palacos R ®) were manufactured to a size of 30 μm. The three body particles were added at all stations onto the articulating surface of the tibial PE insert (7mg per condyle) at every 500,000 cycles. Wear was determined gravimetrically and the surfaces of tibial inserts were analysed by scanning electron microscope (SEM) after finishing the 5 million cycles. Furthermore, roughness of the PE insert surfaces and the articulating surfaces of the different femoral components were detected and the PE wear particles were analysed by SEM. The average gravimetrical wear rates of the tibial PE inserts in combination with CoCr and Biolox delta ® ceramic femoral components amounted to 6.4 ± 0.9 mg and 2.6 ± 0.4 mg per million cycles, respectively. Beside bone cement particles on the articulating surface of the PE inserts, polished surfaces and scratches were detected by SEM. In comparison to the untreated surfaces of the PE inserts at both material pairings the surface roughness at the articulating areas showed deep scratches and polished regions. Analyses of the metallic femoral components showed scratches at the articulating surfaces, none on ceramics. The present study pointed out the effect of femoral component material in an abrasive three body wear situation on the wear properties of TKR. The wear simulator tests showed that wear of PE inserts under three body wear conditions, in combination with ceramic femoral components, was significantly lower than with metallic femoral components. With regard to anti-allergic properties, ceramic femoral components are promising products for TKR

Introduction. The options for the treatment of the young active patient with unicompartmental symptomatic osteoarthritis and pre-existing Anterior Cruciate Ligament (ACL) deficiency are limited. Patients with ACL deficiency and end-stage medial compartment osteoarthritis are usually young and active. The Oxford Unicompartmental Knee Replacement (UKA) is a well established treatment option in the management of symptomatic end-stage medial compartmental osteoarthritis, but a functionally intact ACL is a pre-requisite for its satisfactory outcome. If absent, high failure rates have been reported, primarily due to tibial loosening. Previously, we have reported results on a consecutive series of 15 such patients in whom the ACL was reconstructed and patients underwent a staged or simultaneous UKA. The aim of the current study is to provide an update on the clinical and radiological outcomes of a large, consecutive cohort of patients with ACL reconstruction and UKA for the treatment of end-stage medial compartment osteoarthritis and to evaluate, particularly, the outcome of those patients under 50. Methods. This study presents a consecutive series of 52 patients with ACL reconstruction and Oxford UKA performed over the past 10 years (mean follow-up 3.4 years). The mean age was 51 years (range: 36–67). Procedures were either carried out as Simultaneous (n=34) or Staged (n=18). Changes in clinical outcomes were measured using the Oxford Knee Score (OKS), the change in OKS (OKS=Post-op − Pre-op) and the American Knee Society Score (AKSS). Fluoroscopy assisted radiographs were taken at each review to assess for evidence of loosening, radiolucency progression, (if present), and component subsidence. Results. Five year survival was 90%. At last follow-up, the mean outcome scores for the group were: OKS 40 (SD: 8.3), objective AKSS 77 (SD: 16.1), functional AKSS 93 (SD: 13.7) and OKS of 11. Complications were recorded in three patients, (one early infection requiring a two-stage revision, a bearing dislocation and progression of OA in the lateral compartment). 25 patients, whose procedure occurred under the age of 50, had mean outcome scores of: OKS 38 (SD: 7.7), objective AKSS 73 (SD: 20.2), functional AKSS 93 (SD: 11.9) and OKS 12. No patients had radiological evidence of component loosening. Discussion and Conclusion. This study has demonstrated that combined ACL reconstruction and Oxford UKA provide good medium-term clinical and radiological results. The mobile bearing used in the Oxford knee minimises wear and our radiographic study has seen no suggestions of loosening