Anatomy Study And Finite Element Analysis Of Proximal Humeral Fractures Treated With Locking Plates

BackgroundThe incidence of proximal humeral fractures is ranked the 3rd,behind those of the hip and the distal radius fractures,accounting for 4%-5%of all fractures in body.With the aging of society and the increasing incidence of osteoporosis,the incidence of proximal humeral fractures is tending to grow year by year.Compared to the young,the old are more prone to result in proximal humeral fractures under the same energy damage.Moreover fracture types are more complex.With the improvement of surgical techniques and implants,the proportion ofproximal humeral fractures taken with surgical treatment also gradually rose in order to decrease complications and get a better functional recovery.There are several surgical options for the fixation of proximal humeral fractures,such as percutaneous screw fixation,intramedullary nail fixation,locking plate fixation.To every option,there are its corresponding advantages and disadvantages.The current use of locking plate fixation of proximal humeral fractures obtain better clinical efficacy and it has been widely usedin the clinicalcases.At present,unstable proximal humeral fractures are mainly treated with the lateral locking plate(LLP).However,there are a variety of complications after surgery leading by varus deformity.So far,the domestic and foreign scholars are trying to evaluate and improve unstable proximal humeral fractures fixed with the lateral locking plate(LLP).The present studies suggest that the restoration of the integrity and strength of the medial cortex(or medial column)of the humerus is the key to the success of proximal humeral fractures fixed with the lateral locking plate(LLP).There are many ways to explore and apply the method of lateral lockinging plate(LLP)fixation for the treatment of proximal humeral fractures.Including:additional placing the kickstand screws in the lateral locking plate,filling medial bone defect with bone cement of calcium phosphate,anatomial reduction of medial column,medial strut supporting by allograft or autologous bone graft.The respective effects,advantages and disadvantages of various methods are reported and discussed in the literatures.Some scholars believe that the shoulder arthroplasty can be considered to treat unstable proximal humeral fractures.Considering the difficulty in operation,poor postoperative function and service life etc,at present,the shoulder arthroplasty is only used for a small part of the proximal humeral fractures.At present,there is a consensus on the treatment of unstable proximal humeral fractures at home and abroad:the lateral locking plate(LLP)fixation is the main method to treat unstable proximal humeral fractures.Besides protecting the blood vessels of the humeral head in operation,it is very important to restore the integrity of the medial column and the medial support.How to restore the integrity of the medial column and the medial support?We study on additional applying medial proximal humeral locking plate(MLP)which are specially designed to column and the medial surpport.The lateral locking plate and medial locking plate(L-MLP)fixation is more stable to reduce the risk of postoperative varus deformity and promote fractures healing.In this study,the anatomic parameters of the proximal humerus were measured to provide anatomical basis for the reduction of the proximal humeral fractures and the placement of the medial locking plate(MLP).Biomechanical study was finished by the finite element analysis(FEA).The study was carried out in the following three sections:The first part:Three-dimensional measurement of the proximal humerus and the applied anatomy for the medial locking plate fixationObjectiveBased on 30 cases(15males,15females,60 shoulders)three-dimensional imag es which were reconstructed by Mimics software on the basis of healthy adul ts CT scanning images from the medical imaging department of the Shandong Provincial Hospital.Anatomical landmarks of the proximal humerus were identi fied and a series of anatomical parameters were measured in order to provid e individualized anatomical data for surgical reduction and placing medial locki ng plate of the proximal humeral fractures.Methods30 cases(15 males,15 females,60 shoulders in total)healthy adult shoulder joint CT scanning images we selected from the same CT workstation of the medical imaging department of the Shandong Provincial Hospital.The CT scan ning images whose slice thickness was 1.0mm mage data were exported in DI COM format and saved.The digital three-dimensional visual models of hume rus were established by the application of medical interactive imaging softwar e Mimics16.0.Anatomical landmarks of the proximal humerus were calibrated and parameters including neck shaft angle,retroversion angle and medial are a surface distance were measured and performed statistical analysis.ResultsThe male group:Medial inclination angle of the humeral head(MIA):134.23±2.36°in the left side,134.44±2.50° in the rightside.Retroversion angle(RA):27.00±2.26° in the left side,26.73±2.66° in the right side.Superior surface di stance(SSD):53.57±1.33 mm in the left side,53.65 ± 1.37mm in the right side.Inferior surface distance(ISD):32.82±1.04mmin the left side,32.98±1.01mmin the right side.The female group:Medial inclination angle of the humeral head(MIA):133.51±1.86° in the left side,133.72±2.58° in the rightside.Retroversion angle(RA):25.78±2.31° in the left side,25.88±2.36° in the right side.Superior surface distance(SSD):51.95± 1.24mm in the left side,51.79 ± 1.20mm in the right sid e.Inferior surface distance(ISD):31.62±0.84mmin the left side,31.80±0.59mmi n the right side.The paired t test between the left and the right sides of each parameter wa s done.The results of the paired t test were all P>0.05,namely,there was no statistical difference on these parameters between the left and right sides of the same individual.Conclusions1.The digital three-dimensional visual models of humerus which were establis hed by the application of medical interactive imaging software Mimics16.0 via CT scanning images had good shape and clear boundary.The identification o f humeral anatomical landmarks and the measurement of corresponding para meters were accurate and simple.2.There was no statistical difference on these parameters between the left a nd right sides of the same individual.It was feasible and practical to apply h ealthy side parameters to guide the reduction and fixation of fracture in the affected side.3.It was more appropriate to place the medial locking plate in the medial a pproach at the place of half of the SSD and the ISD after the surface of the small tubercle of humerus which was coincident with the central axis of the medial plate in an actual operation.Meanwhile,themedial locking plate(MLP)was assembled according to the position in further finite element analysis.The second part:Three-dimensional finite element analysis of proximal humeral fractures with an unstable medial column treated with lateral locking plateObjectiveThe aim of this study was to test its biomechanical characteristicsunder di fferent load conditions by three-dimensional finite element analysis on the ap plication of lateral locking plate fixation of proximal humeral fracture with an unstable medial column.The results were compared with those analyzed on t he application of doublelocking plates fixation of proximal humeral fracture wi th an unstable medial column.MethodsThe study was performed at the Shandong Provincial Hospital and permissi on was obtained from the hospital ethics committee.Authors hadto obtain pa tient consent before enrolling participants inthis study.One adult healthy fem ale volunteer was enrolled in the study.After CT scan,the CT cross sectional images of 1.0mm were obtained,and the images were imported into Mimics software to establish the three-dimensional model of the proximal humerus.Then the model of proximal humeral fracture with an unstable medial column was established.The model was optimized in Geomagic Studio software befor e it was imported into Abaqus software for further three-dimensional finite el ement analysis.According to the respective of cortical or cancellous bone whic h were different between the normal bone and the osteoporosis bone,the el astic modulus is assignedto simulate the normal bone and the osteoporosis b one group respectively.Three-dimensional model of the lateral locking plate a nd screws were fitted to the model according to a standard surgical procedur e.After a series of processing including mesh and contact,the model of the proximal humeral fracture with an unstable medial column treated with lateral locking plate was established for further finite element analysis.The function of the shoulder joint,including abduction,adduction,flexion,extension,axial compression,internal rotation and external rotation was simu lated by the application of horizontal rotation and axial compression load(Fig.2).The displacement was measured in the point(a),point(b),point(c),and p oint(d)respectively.The stability of fracture area was evaluated by the displac ement of fracture space.The stiffness tested in the study stood for the stabil ity of the whole structure of the proximal humeral fracture treated with later al locking plate.Von Meese stress distribution and the maximum stress on im plants were measured on the conditions of different shoulder function and dif ferent load respectively.ResultsThe overall structure stability of the normal bone group was stronger than that of the osteoporosis group under the axial compression and,particularly under the condition of the horizontal rotation load.However,as to the maxim um von stress on the LLP,the osteoporosis group were higher than those of the normal group under conditions of abduction,adduction,flexion,extension,axial compression,internal rotation and external rotation.The stress distributi on focused on area where the plate deform from wide to narrow under the shoulder abduction and adduction.When shoulder flexed or extended,the ma ximum stress appeared in the locking screw which located at either end of t he plate.Under the axial compression,the maximum stress occurredon area where the plate deform from wide to narrow and the locking screw which to cated at either end of the plate.The stress distribution on the LLP was the smallest under the conditions of internal rotation or external rotation.The dis placement measured in point a,b,c,d,of the osteoporosis group waslonger than those of the normal bone group under flexion,extension and axial compressi on conditions.On the whole,the stability of the osteoporosis group was wea ker than that of the normal bone group.ConclusionsThe three-dimensional model of proximal humerus was successfully establis hed on the basis of the shoulder joint CT scan.The three-dimensional finite element analysis of the proximal humeral fracture only fixed with lateral lock ing plate(LLP)was established to analyze its biomechanical properties under different loading conditions,the result showed that:the application of lateral locking plate(LLP)fixation of the proximal humeral fracture with an unstable medial column,the LLP provided support indirectly,there was a risk of stress concentration in the LLP.The results were consistent with the clinical observ ations,and the validity of the model was verified.In the furrther study,we w ill compare the resluts with those of the application of of bilateral proximal I ocking plate(L-MLP)fixation of the proximal humeral fracture with an unstabl e medial column.The third part:Three-dimensional finite element analysis of proximal humeral fractures with an unstable medial column treated with lateral locking plate and medial locking plateObjectiveThe biomechanical properties of proximal humeral fractures treated with me dial and lateral dual locking platesin both the normal bone and the osteopor osis groups we re obtained through the finite element analysis under different s imulating load conditions.The results were analyzed and compared to those of proximal humeral fractures with an unstable medial column fixed with later al locking plate.MethodsOn the basis of the above three-dimensional finite element analysis humeral proximal fractures with an unstable medial columntreated with lateral locking plate fixation,both the lateral and medial locking plates and corresponding scr ews were assembled according to the standard and the way of the assembly to the proximal humeral fracture with an unstable medial column of by the Abaqus software.The normal bone and the osteoporosis group were establishe d through assignment,mesh and contact processing model respectively.Both axial compression and horizontal rotation load were applied to test models un der 7 simulating conditions including shoulder abduction,adduction,flexion,e xtension,internal rotationand external rotation.Test methods were the same as those applied in the three-dimensional finite element analysis of proximal hu meral fractures treated with lateral locking plate fixation.The measured stiffnes s value stood for the stability of the integral structure containing humerus an d implants.The displacement of the fracture gap measured under different sho ulder functional positions and different load conditions was used to evaluate t he stability of fracture zone.Records of von Meese stress distribution on impla nts and the maximum stress was analyzed and compared tothose of proximal humeral fractures treated with lateral locking plate fixationResultsThe results of the Nor group and the Ost group fixed with LLP respectively were analyzed and recorded:the integral structure stiffness represented by sti ffness under horizontal rotation and axial compression load,the maximum vo n Meese stress on the LLP and the stress distribution of the implants under different conditions,the displacement of point a,b,c and d.ConclusionsThe double locking plates fixation providing both internal and external supp ort could reduce the stress of the lateral plate and the micro displacement o f the fracture area in both the normal boneand the osteoporosis groups.On the contrary,the stress of unilateral locking plate fixation increasedue to the lack of medial column support.In the osteoporotic group,proximal humeral fr actures with an unstable medial column fixed with single lateral locking plate was more likely to result in the failure of surgical fixation than those fixed w ith double locking plates including lateral locking plate and medial locking plat e.In conclusion,the lateral locking plate and medial locking plate fixation of p roximal humeral fractures with an unstable medial columncould provide a stro nger support for the medial column of the humerus than single lateral lockin g plate fixation.