| BackgroundAtlantoaxial joint dysfunction syndrome(AADS)is caused by neck degeneration and strain,which leads to changes in the relative position of the atlantoaxial axis and produces corresponding symptoms and signs.It is also called atlantoaxial joint malalignment,which belongs to the category of malalignment of the tendon and groove bone.In recent years,due to the popularisation of electronic devices and the change in people’s lifestyle,the incidence of this disease has increased year by year,and its condition is easy to repeat,seriously affecting the lives and work of patients,resulting in a serious social and economic burden,which has become the focus of and the difficulty to be solved in clinical practice.Previous studies have suggested that the anatomical basis of its pathogenesis includes abnormalities of blood vessels,nerves,and muscles,and the reduction of vertebral artery blood supply and nerve compression may be its pathogenesis.These mechanisms can explain how atlantoaxial joint dislocation causes various symptoms,but how atlantoaxial dislocation affects other structures of the cervical spine is still unclear.In terms of biomechanics,the cervical spine is a whole,and the change of any one structure will affect the whole cervical spine.The key pathogenesis of atlantoaxial joint disorders is muscle and bone imbalance.According to the theory of tendons and bones,tendons and bones are mutually dependent on each other in physiology and affect each other in pathology.When the neck is exposed to wind,cold,or strain,there will be pathological states such as clonus and constriction of tendons,and bone misalignment is easy to occur after the binding function of tendons to bones decreases.Tendon injury may be the initial factor in muscle and bone imbalance,but there is still a lack of relevant research on the biomechanical effect of tendon injury on the upper cervical spine,and the biomechanical mechanism of cervical bone malalignment caused by tendon injury is still unclear.In addition,the biomechanical effects of atlantoaxial joint disorders on the upper cervical structure are not clear.The development of finite element technology provides a new way to solve the above problems.The finite element technology is based on the patient’s image data,which can better simulate the geometry and material properties of the cervical spine and can analyse the stress and strain inside the structure under physiological load.The biomechanical characteristics of the cervical spine can be visually displayed in the form of a cloud map,which provides a direction for the early prevention and precise treatment of the disease.Therefore,based on the wide application and rapid development of finite element technology in the field of bone injuries in traditional Chinese medicine,this study attempts to explain the pathogenesis of atlantoaxial joint disorders from the perspective of biomechanics and to study the role of muscle dysfunction and the mechanical influence of vertebral malalignment on the cervical spine as the entry point to study the role of muscle and bone imbalance in the pathogenesis of atlantoaxial joint disorders.further enrich the scientific connotation of "tendon out of groove,bone staggered" in traditional Chinese medicine..ObjectiveBased on the three-dimensional finite element technology,the biomechanical mechanism of atlantoaxial joint disorder was discussed under the guidance of the theory of tendons and bones in traditional Chinese medicine,and the role of tendons and bones imbalance in the pathogenesis of atlantoaxial joint disorder was expated,so as to provide reference for the prevention and treatment of the disease.Content1.Construct a healthy finite element model of the upper cervical spine based on cadaveric specimens,simulate various types of muscle dysfunction by modifying the material properties of the muscle,and analyze the biomechanical characteristics of the upper cervical spine when the muscle dysfunction occurs.2.Construct the finite element model of atlantoaxial joint disorder based on the patient’s imaging data,analyze the stress and strain of cervical spine structure under physiological load,and analyze the influence of atlantoaxial dislocation on the biomechanics of the upper cervical spine.Methods1.Finite element analysis of the effect of muscle dysfunction on the biomechanics of the upper cervical spineThe finite element model of C0-C3 upper cervical vertebrae with normal bone structure was constructed using the CT images of the upper cervical vertebrae of cadaveric specimens,and the validity of the model was verified according to the experimental data in vitro.At the same time,the material properties of the muscles were changed to simulate the normal,increased tension and unbalanced(asymmetrical increased tension)states of the upper cervical muscles.The simulation calculated the Lateral Atlantoaxial joint(LAAJ),atlantodens joint(ADJ),intervertebral Disc under physiological load of the upper cervical spine under different states.To analyze the biomechanical characteristics of the upper cervical spine during muscle dysfunction.2.Establishment of finite element model and biomechanical analysis of atlantoaxial joint disorderA patient with typical symptoms of atlantoaxial joint disorder was selected according to strict inclusion and exclusion criteria.After signing an informed consent form and recording the patient’s medical history and personal information in detail,the original data were stored in Dicon format after taking cervical spine CT in the supine position.Mimics 15,Geomagic Wrap 2015,Solidwork 2021,Ansys 19 and other software were used to complete the geometric model construction,mesh division,material properties definition,load loading and other operations to construct the finite element model of atlantoaxial joint disorder.Physiological loads such as flexion,extension,lateral flexion and rotation were applied to the model,the stresses of the articular surface,intervertebral disc and muscle in the model were calculated,and the mechanical effects of atlantoaxial joint disorder on the upper cervical spine structure were analyzed.Result1.Finite element analysis of the effect of muscle dysfunction on the biomechanics of the upper cervical spineThe range of motion(ROM)of the finite element model of C0-C3 segment is within the range of the measured results in vitro,and the established model is effective.Under forward flexion load,the maximum stress of lateral joints in the muscle imbalance model was higher than that in the normal muscle model and the hypertonia model.Under forward flexion load,the maximum stress of the intervertebral disc in the model with increased muscle tension was higher than that in the normal model and the imbalance model.The atlantodontal joint is under the maximum stress under the extension load.Muscle imbalance and increased tension do not cause the maximum stress and abnormal stress distribution of the atlantodontal joint.2.Establishment of finite element model and biomechanical analysis of atlantoaxial joint disorderThe established finite element model of atlantoaxial joint disorder contains 50913 elements and 130005 nodes.The atlantoaxial dislocation can be obviously observed in the appearance of the model.The range of motion of the model under flexion,extension and lateral flexion conditions is consistent with the data in the literature,indicating that the finite element model established in this study is real and reliable in geometric morphology and mechanical properties,and can be used for biomechanical analysis of atlantoaxial joint disorders.The results of finite element analysis showed that the stress of the right side of the model was higher than that of the left side under flexion and extension load,and the stress of the lateral atlantoaxial joint and the C2/3 facet joint were the most significant.Moreover,the stress distribution of atlantoaxial lateral joints and intervertebral discs under physiological load was uneven,and the stress distribution of atlantoaxial lateral joints and posterior intervertebral discs on the deviated side was more obvious.The muscle stress distribution of the upper cervical spine after atlantoaxial joint malalignment was abnormal,and there was a significant stress concentration at the attachment point of the axial spinous process of the posterior rectus maj or muscle.Conclusion1.When the bone structure is normal,muscle dysfunction will lead to uneven stress distribution and abnormal stress increase in the lateral atlantoaxial joint during cervical flexion,which may increase the risk of atlantoaxial joint disorders;And increased muscle tension will lead to increased stress in the intervertebral disc,which may increase the risk of intervertebral disc lesions.Therefore,early intervention of muscle dysfunction and reduction of cervical flexion can help prevent neck diseases.The finite element model established in this study explained the influence of tendon imbalance on cervical spine from the perspective of biomechanics,indicating that tendon imbalance may be the cause and risk factor of bone malalignment,which is conducive to enriching the scientific connotation of TCM theory of tendon and bone imbalance and guiding clinical practice.2.After the onset of atlantoaxial joint disorder,the overall mechanical balance of the upper cervical spine was destroyed,and the lateral stress of the odontoid process was greater than that of the lateral one;There will be abnormal stress increase or stress concentration in the lateral atlantoaxial articular surface and intervertebral disc after malocclusion,and there will be obvious stress concentration at the insertion of the posterior rectus capitis maximus muscle attached to the axis spinous process,which may lead to paraspinal pain of the axis.In the clinical treatment of neck pain caused by atlantoaxial joint disorder,the stress concentration site can be focused on to achieve better efficacy.The finite element analysis of atlantoaxial joint disorder reveals the biomechanical characteristics of the upper cervical spine after bone malalignment,indicating that the pathological interaction between tendons and bones,tendon imbalance may lead to the occurrence of bone malalignment,and bone malalignment further aggravates tendon injury,so the principle of "both muscles and bones" should be followed in the treatment.3.The terms "tendon and bone dislocation" and "muscle and bone imbalance" may include the increase of tension and force imbalance of neck muscles,the change of position of bone structure,and other diseases.The uneven stress of joint surface is an objective response of "bone dislocation".The treatment concept of "tendon first" is conducive to the early prevention and precise treatment of diseases.Innovation1.Comprehensively analyzed the role and mechanism of muscle and bone before and after the onset of atlantoaxial joint disorders by finite element technology,and scientifically and objectively elaborated the role of muscle and bone imbalance in the pathogenesis of atlantoaxial joint disorders.2.The new technology based on modern biomechanics has further enriched the scientific connotation of traditional Chinese medicine terms "muscle and bone imbalance","tendon out of groove,bone dislocation",which is conducive to the"prevention of disease" and precise treatment of cervical spine diseases,and to a certain extent,promotes the modernization of traditional Chinese medicine. |
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