| The variation of acromion morphology was thought to be the cause of rotator cuff tearsand osteoarthritis. Some clinical research of the relation between these variation and shoulderdisease was complete. The imaging methods which to describe the acromion morphology wasfound and its clinical significance has been recognized.At present, relationship between the acromion index, the lateral acromion angle, thecritical shoulder angle and shoulder disease was researched. Many scholars believe thatfactors predisposing to tearing of the rotator cuff and can be used as auxiliary clinicalparameters for doctors to diagnose diseases. However, previous clinical studies focus oncontact between kinds of variation with specific disease. However, if one patient with thesevariations in the same time, namely the patient’s acromion has two or more characteristics atthe same time, such as the acromion index is larger and the lateral acromion angle is small,the role in the progress of the disease is synergism or antagonism? If it is synergy, which onehas more harm effect? It is rarely reported. This study was aim to explore the relationshipbetween the acromion index,the lateral acromion angle, the critical shoulder angle andshoulder diseases and study the inherent law between these parameters. Validate relatedproblem by the method of computer finite element analysis. To provide biomechanicaltheoretical basis for treatment of these diseases, facilitate the further application of thistechnology in the clinical. This study is divided into two parts of clinical research andcomputer numerical simulation analysis.Section one: the clinical research of acromion index in combination with lateralacromion angle. The purpose of this study is through a clinical research to analyze theconnection between acromion index, lateral acromion angle and the acute traumatic ofshoulder and rotator cuff tear. We use standardized true anteroposterior radiograph to measureacromion index and lateral acromion angle in the same patient. The patients were divided intothree study groups: asymptomatic and normal subjects; patients with rotator cuff tears; andpatients with acute shoulder injury. The group with acute injury consisted of61volunteers,the group with rotator cuff tears consisted of165volunteers, the control group consisted of63volunteers. The average AI was0.72±0.06and the average LAA was76.8°±7.02in shoulders with rotator cuff tears. The average AI was0.59±0.06and the average LAA was84.2°±7.81inshoulders with acute injury. The average AI was0.66±0.06and the average LAA was80.0°±7.33in normal shoulders. There was a statistical significance between the chronic and acutegroups in both the parameters (both p<0.01). In addition, LAA and AI were inverselyproportional to the symptoms in both groups. The rule revealed that the synergy effect ofacromion index and lateral acromion angle in the cause of the rotator cuff tears. Nyffeler findthat small acromion index may be the important risk factors of osteoarthritis. However, wedidn’t find causal relationship between small acromion index and osteoarthritis in this study.But we found that in patients with acute injury, its average acromion index significantly lessthan the control group. So we concluded that: with an increase in the lateral extension of theacromion, the angle between the acromion and glenoid decreases, which may increase the rateof impingement and provide an increased stability to the joint.Section two: the clinical research of acromion index in combination with lateralacromion angle and critical shoulder angle. We use standardized true anteroposteriorradiograph to measure acromion index and lateral acromion angle and critical shoulder anglein the same patient. The patients were divided into two study groups. The group A of patientsconsisted of105individuals with rotator cuff tears involving at least the supraspinatus tendonand the control group consisted of62asymptomatic volunteers in whom ultrasonography ofthe rotator cuff performed by an experienced musculoskeletal radiologist showed no signs oftendon degeneration or a tendon tear. The average AI (and standard deviation) was0.71±0.05in the patients with a rotator cuff tear, and0.64±0.06in the control group. The average LAA(and standard deviation) was77.2°±5.94in the patients with a rotator cuff tear, and82.0°±7.53in the control group. The average CSA (and standard deviation) was36.2°±4.61inthe patients with a rotator cuff tear, and31.7°±5.03in the control group. The differences in theindex between the patients with rotator cuff tear and the control groups were significant(p<0.01). The rule of the shape of acromion was found in two groups by correlation analysis.The negative linear relationship was found between AI and LAA in all groups. We named thisphenomenon shoulder is Acromion Rules. Because of the discovery of the rules, we prove thatin the patients with rotator cuff tears a large lateral extension of the acromion appears to beassociated with a small angle of anromion and glenoid. The AI and LAA is a synergy inpathological process of rotator cuff tears. However, it is unknown that are the different shapesof the acromion process congenital or acquired.Section three: To establish the3-D finite element model of shoulder joint and finite element analysis of the impingement of different shapes of acromion. To establish the3-Dfinite element model of two groups with rotator cuff tears and asymptomatic volunteers. Touse the CT data from patients and volunteers establish3-D finite element model of scapulaand humerus by Mimics. Its initial position is affected by the postures of patients due tocomputed tomography (CT) to establish the model, therefore, adjust the position of the3-Dmodel unified is necessary in order to accurately measure the AI, LAA, CSA. Measure thoseparameters on each model. Select a shoulder model in patients and volunteers respectively toestablish the3-D finite element model of joint capsule, the supraspinatus tendon, articularcartilage. Optimize the model by Geomagic Studio. Give all parts material properties byAbaqus and take the finite element analysis of impingement in scapular plane. Analyze VonMises stress and strain in tendon and articular cartilage of different shapes of acromion.Results show that the Von Mises stress between tendon and acromion is172.6MPa (average12.57MPa) in the model of rotator cuff tears, significantly greater than42.99MPa (average5.108MPa) of healthy people model. The results show that rotator cuff tear model canproduce more stress concentration in the tendon. Rotator cuff tear model outreach impactbetween the head of the humerus and glenoid cavity cartilage after the stress of69.91MPa(average16.06MPa) greater than healthy people model of53.41MPa (average12.61MPa),proved that show the impact when the rotator cuff tear out model in dishes humerus jointsbetween stress is higher than normal models. The experiment proved that stress inhumeral-glenoid of rotator cuff tears model is higher than normal when shoulder in abduction.Section four: Virtual surgery and finite element analysis of anterior acromioplasty.Anterior acromioplasty is an effective treatment for the shoulder impingement syndrome byarthroscopy. This surgery through the revision the shape of cortex on anterior acromion torelieve subacromial impingement with or without rotator cuff tears. But it is unknown thatwhether this surgery can relieve the impingement when shoulder abduction on scapular plan.Select the rotator cuff tears model in third section to simulate the anterior acromioplasty byMagics software (Polyline Cut). Mark the area of2.5cm from anterior part of acromion onrotator cuff tear model. Grind bone cortex on this area and removed the8mm bone cortexfrom front of acromion. The CT-AI was0.60and the CT-LAA was76.8°and the CT-CSA was28.56°virtual surgery. To see the operation does not improve the outer edge of the acromion.The humerus was abducted to the position of impingement and was take the finite elementanalysis. Results show that the maximum stress was81.59MPa (average6.658MPa) betweentendon and acromion after impingement. The stress in the tendon reduced compared with rotator cuff model. However, there was a large concentration of stress compared with normalmodel.Section five: Virtual surgery and finite element analysis of cut the acromion lateralmargin. Based on the previous results, we found that the anterior acromioplasty can improvestress concentration between acromion and tendon, but the effect is limited. Therefore, we putforward a kind of operation scheme for cut outer rim of acromion according to thephysiological anatomy. Base on the model of rotator cuff tears in section three. Remove partof the bone cortex from outer rim of acromion uniform in Magics software by Polyline Cut.The mass of excision was without a fixed value. It is aim to make the AI, LAA, CSA is basicconsistent with healthy model after this operation scheme. The CT-AI was0.45and theCT-LAA was86.25°and the CT-CSA was28.56°after the virtual surgery. Various parameterswas basic consistent with wealthy people model. Results of the finite element analysis showthat stress between acromion and tendon decreased to75.01MPa(average6.025MPa). Thismethod can reduce the impingement by modify the outer edge of acromion. We found that thestress from articular cartilage reduced to43.81MPa (average12.74MPa). This is aninteresting phenomenon，the reduction of stress in glenohumeral joint after impingement iscause by decrease of AI. The phenomenon was contrary to the hypothesis from Nyffyle. Itmeans that the stress from didn’t increase with the decrease of the AI.Through the above research we found that a large lateral extension and gradient of theacromion appears to be associated with tearing of the rotator cuff, however, a small lateralextension and gradient of the acromion appears to be associated with osteoarthritis. AI，LAA，CSA can be used as auxiliary index for predisposing to rotator cuff tears and osteoarthritis.The study found that an obvious stress concentration in tendon will be produced when abductthe shoulder on scapular plane of patients with rotator cuff tears. The stress concentrationalleviate by anterior acromioplasty. The concentration of stress between acromion and tendoncan a greater extent eased by excise lateral margin of acromion to normal range. However, itis a hypothesis after biomechanical study, there are still many questions need to solve. |
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