Motion type and knee articular conformity influenced mid-flexion stability of a single radius knee prosthesis.

PURPOSE: Single radius knee implants were introduced to reduce the level of paradoxical anterior femoral translation (AFT) during mid-flexion after total knee arthroplasty. Findings from clinical and experiment studies are inconsistent, which may be due to the different loading conditions and articular conformities of the knee implants studied. The aim of this study is to analyze how variations in these two factors affect the mid-flexion stability of a single radius knee prosthesis. METHODS: Six daily activities (walking, stair ascent, stair descent, sit-to-stand, pivot turn and crossover turn), and three articular conformity ratios (low, moderate and high) were considered. The resulting AFTs from the 18 finite element models were analyzed. RESULTS: For low conformity knees, the worst case activity (the greatest AFT) was sit-to-stand with an AFT of 6.2 mm, while for the moderate conformity the worst case was crossover turn and pivot turn. For high conformity, all activities produced a relatively small AFT ranging from 0 mm to 1.8 mm, which more closely resembles natural knee motion. In addition, no AFT was recorded during stair ascent for all three conformities (low, moderate, high). CONCLUSIONS: This study demonstrated that the amount of AFT is highly dependent on the activity being undertaken and the articular conformity of the knee prosthesis, and the worst case activity depends on the knee conformity. The clinical relevance of this study is that it offers valuable information towards the design of improved knee prostheses and selection of knee implants for clinical use. LEVEL OF EVIDENCE: II.

The impact of variations in input directions according to ISO 14243 on wearing of knee prostheses.

ISO 14243 is the governing standard for wear testing of knee prostheses, but there is controversy over the correct direction of anterior-posterior (AP) displacement and loading and the correct direction of tibial rotation (TR) angles and torque. This study aimed to analyze how altering the direction of AP and TR affected wear on the tibial insert. Modifications to the conditions specified in ISO 14243-1 and ISO 14243-3 were also proposed. As such, five loading conditions were applied to FEA models of a knee prosthesis: (1) Modified ISO 14243-3 with positive AP displacement and TR angle, (2) ISO 14243-3:2004 with negative AP displacement and positive TR angle, (3) ISO 14243-3:2014 with positive AP displacement and negative TR angle, (4) Modified ISO 14243-1 with positive AP load and TR torque, and (5) ISO 14243-1:2009 with negative AP load and positive TR torque. This study found that changing the input directions for AP and TR according to ISO 14243-1 and 14243-3 had an influence on the wear rate and wear contours on the tibial insert model. However, the extent of wear varies depending on the design features of the tibial insert and shape of the input curves. For displacement control according to ISO 14243-3, changing the direction of AP displacement had a marked influence on the wear rate (272.77%), but changing the direction of TR angle had a much lower impact (2.17%). For load control according to ISO 14243-1, reversing the AP load (ISO 14243-1:2009) only increased the wear rate by 6.73% in comparison to the modified ISO 14243-1 conditions. The clinical relevance of this study is that the results demonstrate that tibial wear is affected by the direction of application of AP and TR. Incorrect application of the loading conditions during the design stage may lead to an ineffective preclinical evaluation and could subsequently influence implant longevity in clinical use.

Is the posterior cruciate ligament necessary for medial pivot knee prostheses with regard to postoperative kinematics?

PURPOSE: Excellent clinical and kinematical performance is commonly reported after medial pivot knee arthroplasty. However, there is conflicting evidence as to whether the posterior cruciate ligament should be retained. This study simulated how the posterior cruciate ligament, post-cam mechanism and medial tibial insert morphology may affect postoperative kinematics. METHODS: After the computational intact knee model was validated according to the motion of a normal knee, four TKA models were built based on a medial pivot prosthesis; PS type, modified PS type, CR type with PCL retained and CR type with PCL sacrificed. Anteroposterior translation and axial rotation of femoral condyles on the tibia during 0°-135° knee flexion were analyzed. RESULTS: There was no significant difference in kinematics between the intact knee model and reported data for a normal knee. In all TKA models, normal motion was almost fully restored, except for the CR type with PCL sacrificed. Sacrificing the PCL produced paradoxical anterior femoral translation and tibial external rotation during full flexion. CONCLUSION: Either the posterior cruciate ligament or post-cam mechanism is necessary for medial pivot prostheses to regain normal kinematics after total knee arthroplasty. The morphology of medial tibial insert was also shown to produce a small but noticeable effect on knee kinematics. LEVEL OF EVIDENCE: V.

In vitro study of haematoporphyrin monomethyl ether-mediated sonodynamic effects on C6 glioma cells.

OBJECTIVES: To study the cytotoxicity induced by haematoporphyrin monomethyl ether (HMME)-mediated sonodynamic therapy (SDT) on C6 glioma cells. METHODS: The potent photosensitizer HMME was used as the sensitizer. Rat C6 glioma cells were incubated with HMME (10 microg/mL) in the dark for 2 h and then subjected to ultrasound treatment at 1.0 MHz and 0.5 W/cm2 for 2 min. The growth inhibition rate at different time points after SDT was determined by MTT assay. The apoptotic rate and cell circle profiles were examined with flow cytometry. Fine structures were observed with transmission electron microscope (TEM). The sonodynamic effect on the glioma cells was also studied in the absence or presence of various reactive oxygen species (ROS) scavengers. RESULTS: The growth inhibition rate of C6 glioma cells after SDT significantly increased. SDT also increased the apoptosis and proliferation rate (APR). TEM examination showed the morphological features of apoptosis or necrosis. The addition of NaN(3) showed a strong protective effect again SDT. CONCLUSIONS: Our data indicated that SDT could kill C6 glioma cells in vitro and possibility through induction of apoptosis and necrosis. Singlet oxygen ((1)O2) may play an important role in SDT.