Accuracy and repeatability of a pressure measurement system in the patellofemoral joint

Wilson, David R.; Apreleva, Maria; Eichler, Markus; Harrold, Fraser

doi:10.1016/s0021-9290(03)00105-2

Cited by 86 publications

(87 citation statements)

References 12 publications

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“…Three commonly used indicators, the mean relative error (d), the standard deviation of the relative error (S), and the load deviation percentage (deviation), are selected to evaluate the simulation results [30,31]. The formulas are shown as followed:…”

Section: The Description Of the Entropy Weighting Methodsmentioning

confidence: 99%

Modeling Multi-Event Non-Point Source Pollution in a Data-Scarce Catchment Using ANN and Entropy Analysis

Chen

Cheng

Wang

et al. 2017

Entropy

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Event-based runoff-pollutant relationships have been the key for water quality management, but the scarcity of measured data results in poor model performance, especially for multiple rainfall events. In this study, a new framework was proposed for event-based non-point source (NPS) prediction and evaluation. The artificial neural network (ANN) was used to extend the runoff-pollutant relationship from complete data events to other data-scarce events. The interpolation method was then used to solve the problem of tail deviation in the simulated pollutographs. In addition, the entropy method was utilized to train the ANN for comprehensive evaluations. A case study was performed in the Three Gorges Reservoir Region, China. Results showed that the ANN performed well in the NPS simulation, especially for light rainfall events, and the phosphorus predictions were always more accurate than the nitrogen predictions under scarce data conditions. In addition, peak pollutant data scarcity had a significant impact on the model performance. Furthermore, these traditional indicators would lead to certain information loss during the model evaluation, but the entropy weighting method could provide a more accurate model evaluation. These results would be valuable for monitoring schemes and the quantitation of event-based NPS pollution, especially in data-poor catchments.

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Section: The Description Of the Entropy Weighting Methodsmentioning

confidence: 99%

Modeling Multi-Event Non-Point Source Pollution in a Data-Scarce Catchment Using ANN and Entropy Analysis

Chen

Cheng

Wang

et al. 2017

Entropy

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“…To minimize shear forces acting on the sensor, a protective Teflon film of 0,1mm is often applied [4, 17-19, 21, 22, 28, 29, 33]. Alternatively, a lubricant such as surgical lubricant [5] or vaseline [22] can be applied onto the sensor.…”

Section: Mounting Techniquesmentioning

confidence: 99%

“…Sensor behaviour in human knee joint One of the first problems that arise when using the Tekscan sensor for intra-articular contact pressure measurements is wrinkling of the sensor [5,7,10,[34][35][36]. As the sensor is made of a dimensionally stable substrate, it can nicely roll around a cylinder but it is difficult to wrap it around a ball shaped surface.…”

Section: 2mentioning

confidence: 99%

“…The electrical resistance of each cell is dependent of the force acting on that cell. By measuring the resistance of all cells, the pressure distribution on the sensor can be derived after an appropriate calibration [5,6] . To measure patellofemoral contact pressure, a sensor with measuring area of 55,9mm x 55,9mm and sensel density of 62/cm 2 is commonly used.…”

Section: Introductionmentioning

confidence: 99%

“…Figure 1: Construction Tekscan sensor [7] The success of this sensor can be attributed to the low thickness (0,1mm) and the real-time evaluation of contact pressures. As a result, this sensor is well suited to evaluate contact pressures during dynamic in vitro tests [5,[8][9][10]. Despite these favourable characteristics, there are also quite some drawbacks when this sensor is used to measure intra-articular contact pressures.…”

Section: Introductionmentioning

confidence: 99%

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Use of Tekscan pressure sensors for measuring contact pressures in the human knee joint

Herregodts

Baets

Victor

et al. 2015

SCAD

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Abstract:The Tekscan pressure sensor is a common instrument to quantify in vitro tibiofemoral and patellofemoral contact pressures, which helps to understand the impact of surgical intervention such as total knee arthroplasty (TKA). As a result of the non-linear behavior of the sensor, the conditioning, normalization and calibration of the sensor are critical to achieve correct measurements. In this paper, a literature review is presented that provides insight in the correct use of these sensors, resulting in optimal accuracy. To guarantee the repeatability of the measurements, a secure and correct fixation of the sensor in the joint is required. Using the sensor for intra-articular measurements induces several unintended effects, which potentially lower the accuracy of the measurement. First, the uneven surface can result in wrinkling and destruction of the sensor, in turn leading to measurement results that can be corrupted. Second, the presence of shear forces on the sensor can lead to wear of the sensor and reduction in sensitivity with loss of accuracy as a result. Also the fixation method can worsen the accuracy. In literature, a deterioration of the accuracy from 3% under optimal conditions to errors of more than 50% are reported as a result of the aforementioned effects.

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Improving vastus medialis obliquus function reduces pressure applied to lateral patellofemoral cartilage

Elias

Kilambi

Goerke

et al. 2008

Journal Orthopaedic Research

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The current study was performed to characterize how improving vastus medialis obliquus (VMO) function influences the pressure applied to patellofemoral cartilage. An additional focus was characterizing how lateral and medial cartilage lesions influence cartilage pressures. Ten knees were flexed to 408, 608, and 808 in vitro, and forces were applied to represent the VMO and other muscles of the quadriceps group while a thin film sensor measured joint pressures. The knees were loaded with a normal VMO force, with the VMO force decreased by approximately 50%, and with the VMO unloaded. After tests were performed with the cartilage intact, all tests were repeated with a 12-mm-diameter lesion created within the lateral cartilage, with the lateral lesion repaired with silicone, and with a medial lesion created. Based on a two-way repeated measures ANOVA and post-hoc tests, increasing the force applied by the VMO significantly ( p < 0.05) decreased the maximum lateral pressure and significantly increased the maximum medial pressure at each flexion angle. A lateral cartilage lesion significantly increased the maximum lateral pressure, while a medial lesion did not significantly influence the maximum medial pressure. Improving VMO function can reduce the pressure applied to lateral cartilage when lateral lesions are present. Patellofemoral disorders are commonly attributed to an excessive lateral force applied to the patella. Due to the normal valgus orientation of the knee, the quadriceps muscles and the patella tendon act to shift and tilt the patella laterally. Passive resistance provided by the medial retinacular structures and forces due to contact with the trochlear groove resist the forces applied by the quadriceps and the patella tendon. 1,2 An excessive lateral force or inadequate resistance can lead to overloading of the lateral cartilage or lateral instability. 3 Overloading lateral cartilage can lead to areas of cartilage degradation, or lesions. 3,4 Instability episodes damage the medial retinacular restraints and can lead to lesions within the medial cartilage due to the medial facet of the patella contacting the bone on the lateral condyle of the femur. 5,6 Cartilage lesions increase the pressure applied to the surrounding cartilage 7 and can lead to pain due to overloading of the subchondral bone. 3,5,8 Physical therapy regimens prescribed for patellofemoral disorders commonly focus on improving the function of the vastus medialis obliquus (VMO). The force applied by the VMO has a medial component that can help resist the lateral force applied by the other quadriceps muscles. Some studies have indicated that patients with patellofemoral pain generate less force through the VMO than asymptomatic subjects. 9,10 The onset of VMO activity can also be delayed in patients with patellofemoral pain. [11][12][13][14][15] Although studies have indicated that training the VMO improves the strength 16 and activation timing 15 of the VMO, and provides better outcomes than a placebo treatment, 15,17 training ...

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Accuracy and repeatability of a pressure measurement system in the patellofemoral joint

Cited by 86 publications

References 12 publications

Modeling Multi-Event Non-Point Source Pollution in a Data-Scarce Catchment Using ANN and Entropy Analysis

Modeling Multi-Event Non-Point Source Pollution in a Data-Scarce Catchment Using ANN and Entropy Analysis

Use of Tekscan pressure sensors for measuring contact pressures in the human knee joint

Improving vastus medialis obliquus function reduces pressure applied to lateral patellofemoral cartilage

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