Biomechanical Study Of The Influence Of Coracoglenoid Space On Scapular Neck Fracture Stability

ObjectiveThe anatomical variation of the coracoglenoid space has the potential to influence the stability of scapular neck fractures.This study aimed to investigate the anatomic variation of the coracoglenoid space by constructing three-dimensional(3D)computed tomography(CT)reconstruction models and measuring the scapular morphology.Subsequently,the biomechanical mechanism underlying the influence of different coracoglenoid space types on scapular neck fractures was investigated by finite element analysis(FEA)and vitro biomechanical experiments.MethodsThe shoulder CT data of 60 healthy adult volunteers were used to construct the 3D recongstruction models and a total of 68 scapular specimens were used to analyze the anatomical variability of the coracoglenoid space.Mimics software was used to measure the 3D-CT reconstruction model,and the bone specimens were directly measured with a cursor caliper.Two variables,the length of the coracoglenoid distance(CGD)and the coracoglenoid notch(CGN),were measured respectively.The differences between these two variables in gender and side were compared.The distribution of CGN/CGD?100%was used to identify the morphology of the coracoglenoid space.Geomagic Studio and Solidworks software were applied to complete the pre-processing of the 3D solid model of scapula.Ansys Workbench software was applied to perform FEA tests on the 3D solid model to record the distribution of Von-Mises stress and variation of displacement.In vitro biomechanical tests,each specimen was tested for failure under static axial compression loading.The average failure load,stiffness,and energy were calculated.The fracture patterns of scapula were observed.ResultsTwo coracoglenoid space types,typeⅠ(‘‘hook’’shape)and typeⅡ(‘‘square bracket’’shape),were identified in the population.There was a similar incidence of two different types.In the 3D-CT reconstruction model,the average CGD for type I and TypeⅡwere 13.88±00.68 mm and 11.68±0.93 mm,respectively.The average CGN for the two types were 4.78±0.52 mm and 2.63±0.81 mm,respectively.In the vitro direction vision measurement,the CGD and CGN were significantly higher for typeⅠthan typeⅡ(13.81±0.74 mm vs.11.50±1.03 mm,P<0.05;4.74±0.45 mm vs.2.61±0.45mm,P<0.05).The results of the scapular 3D reconstruction model were similar to those of the measured in vitro,and the parameters of the coracoglenoid space in type I were significantly greater than those in typeⅡ(P<0.05).There was a significant linear correlation between CGD and CGN in the pcoracoglenoid space of typeⅠand typeⅡ(R~2=0.774,P<0.001).However,there were no statistically significant differences between the two parameters between sex and side(P>0.05).The FEA results of the scapular 3D model showed that there was obvious stress concentration in the area of the scapular notch and the spinoglenoidal notch.The average Von-Mises stress(4.710±1.719 MPa)and displacement(0.080±0.033 mm)of typeⅠwere smaller than those of typeⅡ(Von-Mises stress:5.723±2.320 MPa;displacement:0.065±0.037 mm).In the vitro biomechanical test of the scapula,the proximal fracture line started from the scapular notch area and the distal fracture line tended to run into the spinoglenoidal notch.The average maximum failure load of the two types was 1270.82±318.85 N and1529.18±467.29 N,respectively(P=0.011).The stiffness and energy were significantly higher for typeⅡthan typeⅠ(896.75±281.14 N/mm vs.692.91±217.95 N/mm,P=0.001;2.10±0.65 J vs.1.71±0.63 J,P=0.015).ConclusionsThe study confirmed that there was great inter-individual variation in the anatomical morphology of the coracoglenoid space based on the 3D-CT reconstruction models and the vitro measurement of the scapula.From the anatomical and biomechanical perspective,there is a correlation between the anatomical variation of coracoglenoid space and the scapular neck fracture stability.The“hooked”coracoglenoid spaces bore lower forces and less stiff,which may constitute an anatomical factor to scapular neck fractures.This study can provide anatomical and biomechanical basis for the identification and repair of scapular neck fractures in the future.