The Vivo Study Of Finite Helical Axis In Patients With Recurrent Patellar Dislocation Based On Three-dimensional Patellofemoral Dynamic Model Based Methodology

Objective:Up to date,long-term satisfactory curative effect of recurrent patellar dislocation still remain difficult to be obtained, the primary cause is that the theory based on the matching of patellofemoral joint articular surface to study the biomechanics of recurrent patellar dislocation is flawed. Basically, forcemoment acting on the patellofemoral joint is the driver of joint movement and stress,the finite helical axis,as a new perspective to research the biomechanics of recurrent patellar dislocation could be more scientific.this study aims to create a new method to reconstruct the three-dimensional patellofemoral motion model based on static magnetic resonance imagings,and calculate patellar tracking and finite helical axis of patellofemoral joint by using reconstructed dynamic model.The differences of patellar tracking,finite helical axis between patients with recurrent patellar dislocation and normal human will be analysed to provide new scientific basis for the research of biomechanics.Methods:An adult female patient with recurrent patellar dislocation(24 years old, weight 68kg,170cm tall, BMI23.52kg/m2) and an healthy adult female(26 years old, weight 60kg,165cm tall, BMI22.04kg/m2) were assembled randomly,relatively from patients cured in our hospital and normal volunteers.the adult female patient act as the subject,and the healthy adult female play the role of control.The right knee of the subject and the control were scanned with the same magnetic resonance machine (Siemens 3.0T, Germany) at 0°,30°,60°,90° and 120°of knee flexion using fat suppression/two-dimensional fast low angle stimulateing/T1 weighted gradient echo sequence and flexible coil;only the sagittal plane was scanned;The layer thickness arrange from 0.8 to 1.5mm,and the scan slices arrange from 90 to 110 layers; scaned once or twice.First of all,import the magnetic resonance images of healthy adult female(the control) into the Mimics in Dicom format, then extract the shape of patella, patellar cartilage, distal femur and femoral cartilage by utilizing the 3DLivewire segmentation,manually calculate the static three-dimensional model of patellofemoral joint at the five flexion angles by utilizing the 3DCaculation. After optimizing the Geometry of three-dimensional model through using the FEA module and Remesh function, import the five static models into RapidForm at the same coordinate system to realise registrating the discrete static patellofemoral joint model for dynamic three-dimensional motion model using spline interpolation algorithm, calculate the patella tracking in the three-dimensional coordinate system and the results were compared with previous vivo research to validate it’s accuracy.The FHA of patellofemoral. joint is calculated based on the known patella tracking in the reverse engineering software.use the same method to calculate the FHA of patients with recurrent patellar dislocation and analyse the results comparing with the results of healthy adult female.Results:l.The dynamic 3-dimensional patellofemoral model is successfully reconstructed which included patella, patellar cartilage, distal femur and femoral cartilage and cover the whole process from fully extension to the maximum flextion.The patellar tacking and the FHA could be calculated basing on the reconstructed model within the range of in vivo experimental measurements in literatures.2.The sagittal plane view of dynamic FHA trajectory arising from the patient with recurrent patellar dislocation approximate "ε" shape, and respectively approximate "C" shape arising from the normal volunteer.3.The FHA fluctuation range of normal volunteer is small, contrarily the FHA fluctuation range of patients with recurrent patellar dislocation is much bigger.4.The differences of FHA between patients with recurrent patellar dislocation and normal volunteer are significant,and can be quantified to mearure the sagittal plane angle between FHA and EA(or CA) using the spatial coordinates of FHA.5.The patellar tacking,FHA,and Angle between FHA arid EA (or CA) arising from the patients with recurrent patellar dislocation and normal volunteer have significant differences, especially in early stage of knee flexion.6.The FHA of normal volunteer is closer to the CA in whole process of knee flexion.Conclusions:1.Basing on static magnetic resonance images can reconstruct accurate tree-dimensional patellofemoral motion model,and the reconstructed model can be used for the calculation of patellar tracking and FHA.2.The FHA of recurrent patellar dislocation can be observed dynamically and quantified successfully,and is practicable as a new perspective to research the biomechanics of recurrent patellar dislocation.3.The differences of FHA between patients with recurrent patellar dislocation and normal human are significant,moreover such differences can be quantified successfully.The FHA could be recognized as a quantitative index to observe and assess the patients with recurrent patella dislocation.