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Which data sources may be used to efficiently generate subject-specific knee models to meet clinical questions?

par Pianigiani, Silvia
Président du jury Delchambre, Alain
Promoteur Innocenti, Bernardo
Publication Non publié, 2016-05-20

Thèse de doctorat

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Résumé :

Knee joint kinematics is the result of a complex roto-translation movementcharacteristic of the tibio-femoral (TF) and patello-femoral (PF) articulations.This movement depends on the shape of the femur, the tibial plateau andthe patella. Moreover, it depends also on the morphological and mechanicalproperties of the soft tissues of the knee joint. In fact, the knee is characterizedby an extrinsic stability due to the active constraints (muscles and tendons)and passive soft tissues (menisci, retinaculum and ligaments) that surround it.As a result, knee kinematics and kinetics are different in each human being, andsometimes, even in the same person, with the right knee behaving differentlycompared to the left one.The ideal total knee arthroplasty TKA, used to correct pathologies that couldaffect the knee joint, should enable the restoration of the patient’s functionalknee kinematics and kinetics, so that the patient does not normally notice theTKA implant.Nowadays, TKA surgery is a well-established procedure and surgeons maychoose from among the broad range of TKA solutions available on the marketto meet the patient’s request. Prostheses may differ because of shape, materials,and mechanical constraints of their components. Consequently, the restorationof the knee joint biomechanics is limited by the degrees of freedom guaranteedby the adopted design solution.Despite the success of TKAs, pain and limited motor skills are reportedto still affect the clinical outcomes and not all patients are shown to be happyafter a TKA.Current complaints regarding post-TKA surgery might be related to the absenceof a proven tool that enables predicting patient-specific outcomes based ondifferent TKA solutions and providing guidelines to surgeons. In fact, surgicalpre-planning is usually based on a patient’s evaluation that the clinician canmake also based on medical images, and clinical experience. Data reported inthe literature can help in guiding the surgeon to a final decision regarding thebest subject-specific solution.Numerical methods, able to simulate knee biomechanics for various configurations,can be fundamental for the development of the appropriate reliableand effective tools to support clinically-tailored responses to a question.In particular, they can be used for subject-specific analyses on the intact kneeand for supporting the surgical pre-planning phase by comparing the effect ofdifferent solutions.When developing a subject-specific knee model, different kinds of datainputsare needed, such as the knee shapes and alignment information, softtissuesbehavior and boundary conditions describing the investigated motortasks. Often, most of this requested data are unlikely to be available (e.g.subject-specific soft-tissues material properties). Consequently, it is a commonoperating procedure to integrate literature data with subject-specific informationin order to develop knee models for collecting personalized outputsthat could be used to address research and clinical questions.However, up to now, the resulting effect of different generalized sources, asa mix of subject-specific and literature data, still needs to be evaluated for itsimpact on personalized outputs concerning knee behaviour.Furthermore, clinical questions are often focused on specific requests thatpartially use features of more complex knee models that could require too muchtime to be efficiently incorporated into daily clinical evaluations.For these reasons, the principal aims of this research have been to assess,first, the impact of differently derived generalized sources on the developmentof an intact subject-specific knee model or after a TKA; second,to provide guidelines to identify efficient clinically-tailored data sourcesused in and for knee modeling.To accomplish these tasks, a numerical knee model of an intact knee wasdeveloped based on both subject-specific and literature data sources. Theinfluence of different approaches to deal with a subject’s information, such asthe reconstruction of the knee geometries from different imaging sources, hasiiibeen evaluated. Moreover, a sensitivity analysis was performed to understandthe potential changes on kinetics and kinematics outcomes due to differentlyderived literature inputs, such as models and the properties that characterizethe joint materials and ligaments description. The outputs collected after finiteelement analyses were analyzed and compared with already published experimentaloutcomes for the same analyzed specimen and replicated boundaryconditions.Additionally, the effects on knee joint contact forces and kinematics afterTKA surgery and due to the mis-alignment of implant components or misidentificationsof ligament insertions were evaluated in another sensitivityanalysis performed with a rigid body analysis for four different TKA designsimplanted in a subject-specific knee model. As for the intact knee model, theanalyzed configurations were compared against already published experimentaloutputs or literature data replicating similar boundary conditions.Moreover, several dedicated knee models were developed to address specificclinical questions, such as the lack of biomechanical explanations for certainbehaviours of TKA designs.Once compared to already published experimental or literature data, the resultsof the developed models agree.The main results from the numerical simulations performed show that, changingthe values of some of the parameters used as inputs, the knee model kinematicsis less influenced than the contact forces and stresses outputs.In particular, in developing an intact knee model, the main effecting parameteris the material properties selection for the knee cartilage layers. Among theconfigurations analyzed using subject-specific knee models with TKAs, theposition of the tibial component and the height of the patellar buttonare the most effecting inputs.Exploring the different chapters of this research thesis, several specific resultsare shown regarding each main step followed in developing a knee numericalmodel. For example, new approaches based on MRIs have been suggested andtested proving that they are suitable for collecting subject-specific informationregarding geometrical shapes and landmark definitions. Moreover, a newgraphical method was proposed resulting more effective and immediate thanconventional representations in reporting huge amount of data. In particular,the method is the favourite to show complex biomechanical analyses especiallyfor the clinical audience that replied to a survey. Furthermore, the differentmodels tailored to address specific clinical questions collected useful biomechanicalresults, to provide clinical advice or industrial guidelines, and can beconsidered as examples of what should be included in a knee model for similarscenarios.The results of this thesis offer several contributions. Generally, these findingscould provide useful guidelines for knee-model developers to achievea more balanced approach to subject-specific intact knee models based upongeneral sources in order to improve the understanding of personalized kneebiomechanics.To address a general comment to the title of this thesis, there is no singleanswer. In fact, the selection of data sources is case-dependent using, forexample, the subject’s or literature available data to describe material’s behavioror the boundary conditions of a specific motor task. Moreover, differentclinical questions can be addressed with different numerical approaches, e.g.,finite element analysis is necessary especially in the case that stress outputs arerequested, but can be too time-consuming for addressing complex sensitivityanalyses.Once the knee model developer has identified the necessary data sources andthe approaches to be implemented, the question-tailored knee models can thusbe used for several applications such as predicting subject-specific abnormalknee kinematics and kinetics for different TKA designs, polyethylene wear,patellofemoral dislocation and bone remodeling, choosing the best fitting TKAdesign for a specific patient, and developing a procedure to optimize TKAimplant designs.