Influence of Patella thickness on Patellofemoral pressure in total knee Arthroplasty

Background Patellofemoral complications are one of the major issues after total knee arthroplasty (TKA). Excessive patellofemoral joint pressure is associated with complications after TKA surgery, and the amount of patellar osteotomy has a direct effect on patellofemoral joint pressure. The purpose of this study was to evaluate the influence of patella thickness on patellofemoral pressure in TKA. Methods Five freshly frozen cadavers were operated with a custom-made Stryker posterior stabilizing type knee joint prosthesis. Patellofemoral joint pressure was measured using a pressure sensor, with the knee joint flexed from 90 to 110 degrees, and with patellar thickness of − 2 mm to + 4 mm. Results Increasing or decreasing patellar thickness significantly increased or decreased patellofemoral pressure. Regarding knee flexion angle, patellofemoral pressure increased with increasing patellar thickness at all flexion angles, but the pressure increase was greatest at 90 degrees of knee flexion and smallest at 110 degrees. Conclusions The amount of patellar osteotomy influences the patellofemoral pressure. Surgeons should avoid increasing patella thickness, since the resulting increased patellofemoral pressure may reduce knee joint function.

Influence of Patella Thickness on Patellofemoral Pressure in Total Knee Arthroplasty

Background: Patellofemoral complications are one of the major issues after total knee arthroplasty (TKA). Excessive patellofemoral joint pressure is associated with complications after TKA surgery, and the amount of patellar osteotomy has a direct effect on patellofemoral joint pressure. The purpose of this study was to evaluate the influence of patella thickness on patellofemoral pressure in TKA.Methods. Five freshly frozen cadavers were operated with a custom-made Stryker posterior stabilizing type knee joint prosthesis. Patellofemoral joint pressure was measured using a pressure sensor, with the knee joint flexed from 90 to 110 degrees, and with patellar thickness of -2mm to +4mm.Results: Increasing or decreasing patellar thickness significantly increased or decreased patellofemoral pressure. Regarding knee flexion angle, patellofemoral pressure increased with increasing patellar thickness at all flexion angles, but the pressure increase was greatest at 90 degrees of knee flexion and smallest at 110 degrees.Conclusions: The amount of patellar osteotomy influences the patellofemoral pressure. Surgeons should avoid increasing patella thickness, since the resulting increased patellofemoral pressure may reduce knee joint function.

Influence of Different Patellofemoral Design Variations Based on Genesis II Total Knee Endoprosthesis on Patellofemoral Pressure and Kinematics

In total knee arthroplasty (TKA), patellofemoral groove design varies greatly and likely has a distinct influence on patellofemoral biomechanics. To analyse the selective influence, five patellofemoral design variations were developed based on Genesis II total knee endoprosthesis (original design, being completely flat, being laterally elevated, being medially elevated, and both sides elevated) and made from polyamide using rapid prototyping. Muscle-loaded knee flexion was simulated on 10 human knee specimens using a custom-made knee simulator, measuring the patellofemoral pressure distribution and tibiofemoral and patellofemoral kinematics. The measurements were carried out in the native knee as well as after TKA with the 5 design prototypes. The overall influence of the different designs on the patellofemoral kinematics was small, but we found detectable effects for mediolateral tilt (p<0.05 for 35°–80° flexion) and translation of the patella (p<0.045 for 20°–65° and 75°–90°), especially for the completely flat design. Considering patellofemoral pressures, major interindividual differences were seen between the designs, which, on average, largely cancelled each other out. These results suggest that the elevation of the lateral margin of the patellofemoral groove is essential for providing mediolateral guidance, but smooth contouring as with original Genesis II design seems to be sufficient. The pronounced interindividual differences identify a need for more patellofemoral design options in TKA.

Patellofemoral and tibiofemoral forces during knee extension: simulations to strength training and rehabilitation exercises

Introduction: Limited evidence has been shown on ways to optimize the mechanical design of machines in order to minimize knee loads. Objective: This study compared six computer simulated models of open kinetic knee extension exercises for patellofemoral pressure and tibiofemoral forces. Methods: A musculoskeletal model of the lower limb was developed using six different cam radius to change resistive forces. A default machine, a constant cam radius, a torque-angle model, a free-weight model and two optimized models were simulated. Optimized models reduced cam radius at target knee flexion angles to minimize knee forces. Cam radius, human force, tibiofemoral compressive and shear force, and patellofemoral pressure were compared for the six models using data from five knee flexion angles. Results: Large reductions in cam radius comparing the free-weight model to other models (73-180%) were limited to the large human force for the constant cam model to other models (9-36%). Larger human force (13 -36%) was estimated to perform knee extension using a constant cam radius compared other models without large effects in knee joint forces. Conclusion: Changes in cam design effected human without a potential impact in knee loads.

Effects of conventional and minimalist footwear on patellofemoral and Achilles tendon kinetics during netball specific movements

Netball is a physically demanding sport that is associated with a high incidence of chronic injuries. Currently there is a trend towards the utilisation of minimalist footwear in netball players as opposed to more conventional netball trainers. The current investigation aimed to examine the effects of netball specific and minimalist footwear on patellofemoral and Achilles tendon loads during netball specific motions. Fifteen female netballers performed both run and cut movements when wearing conventional netball footwear and also a minimalist trainer. Kinematics of the lower extremities were quantified using a motion analysis system alongside ground reaction force information which was obtained using a force platform. Patellofemoral force (PTF), patellofemoral pressure (PP) and Achilles tendon forces (ATF) were quantified using predictive methods and examined between footwear using repeated measures ANOVA. The results indicate that patellofemoral loads (run – PTF: netball specific = 5.56 / minimalist = 4.74 body weight (BW); – PP: netball specific = 13.17 / minimalist = 11.89 MPa; cut – PTF: netball specific = 5.65 / minimalist = 4.82 BW; – PP; netball specific = 14.05 / minimalist = 12.88 MPa) were significantly larger in the conventional footwear compared to minimalist in both movements. Achilles tendon forces (run: netball specific = 4.43 / minimalist = 5.47; cut: netball specific = 4.32 / minimalist = 5.29 BW) were however significantly larger in the minimalist compared to the conventional footwear. Taking the proposed association between knee loading and patellofemoral pathology, the risk from knee injuries in netballers may be reduced via minimalist footwear. However, taking into account the equivalent increases in Achilles tendon forces, this may increase the likelihood of overuse Achilles tendon injuries.

Discrete Element Analysis for Characterizing the Patellofemoral Pressure Distribution: Model Evaluation

The current study was performed to evaluate the accuracy of computational assessment of the influence of the orientation of the patellar tendon on the patellofemoral pressure distribution. Computational models were created to represent eight knees previously tested at 40 deg, 60 deg, and 80 deg of flexion to evaluate the influence of hamstrings loading on the patellofemoral pressure distribution. Hamstrings loading increased the lateral and posterior orientation of the patellar tendon, with the change for each test determined from experimentally measured variations in tibiofemoral alignment. The patellar tendon and the cartilage on the femur and patella were represented with springs. After loading the quadriceps, the total potential energy was minimized to determine the force within the patellar tendon. The forces applied by the quadriceps and patellar tendon produced patellar translation and rotation. The deformation of each cartilage spring was determined from overlap of the cartilage surfaces on the femur and patella and related to force using linear elastic theory. The patella was iteratively adjusted until the extension moment, tilt moment, compression, and lateral force acting on the patella were in equilibrium. For the maximum pressure applied to lateral cartilage and the ratio of the lateral compression to the total compression, paired t-tests were performed at each flexion angle to determine if the output varied significantly (p < 0.05) between the two loading conditions. For both the computational and experimental data, loading the hamstrings significantly increased the lateral force ratio and the maximum lateral pressure at multiple flexion angles. For the computational data, loading the hamstrings increased the average lateral force ratio and maximum lateral pressure by approximately 0.04 and 0.3 MPa, respectively, compared to experimental increases of 0.06 and 0.4 MPa, respectively. The computational modeling technique accurately characterized variations in the patellofemoral pressure distribution caused by altering the orientation of the patellar tendon.