Evaluation Of The Coracoid Bone Tunnel Placement On Dog Bone Button Fixation For Acromioclavicular Joint Dislocation:A Cadaver Study Combined With Finite Element Analysis

Background and Purpose:Dog Bone button fixation is one of the treatment methods for acromioclavicular joint dislocation.However,several studies have reported various complications after fixation,including clavicle fractures,coracoid fractures,erosion of the clavicle and coracoid bone by the buttons,and other related postoperative complications.Therefore,the purpose of this study was to investigate the effect of the coracoid bone tunnel location on the treatment of acromioclavicular joint dislocation with Dog Bone button single-tunnel coracoclavicular ligament reconstruction through the cadaveric biomechanical test(BT)and finite element analysis(FEA).Methods: 1.Cadaveric BT: Six cadaveric shoulders were used.The cadaveric biomechanical tests were performed on each cadaver acromioclavicular joint under five conditions:(1)Firstly,with a normal acromioclavicular joint(Gn).(2)Secondly,the acromioclavicular ligaments and coracoclavicular ligaments were removed and no Dog Bone buttons were used for the coracoclavicular ligaments reconstruction(G0).Next,the coracoclavicular ligament reconstruction was performed using the Dog Bone technique.Here,the coracoid bone tunnel was at one of three locations:(3)either it was at the center of the base of the coracoid(G1),(4)or 5 mm distal from the G1 site,along the axis of the coracoid(G2),(5)or 10 mm distal from the G1 site,along the axis of the coracoid(G3).We applied the same load(30 N)to the distal clavicles under different conditions to produce pronation or supination movements of the clavicles.Following,the rotational stability of the clavicles was evaluated under different conditions by comparing the rotation angles of the clavicles between the different groups.2.FEA: Throughout FEA,a single finite element model of the scapula and clavicle was created using computed tomography(CT)images from the normal shoulder.A singletunnel coracoclavicular ligaments reconstruction of the dislocated acromioclavicular joint was performed using the Dog Bone buttons.Here,Model 1(M1),Model 2(M2),and Model 3(M3)correspond to the cadaveric models of G1,G2,and G3,respectively.A bone bending threshold of 70 N was used as a vertical upward load added to the distal clavicle to simulate mild physical rehabilitation stress.Consequently,the von Mises stress peak value,the strain LE along the FiberWire and the displacement nephogram of the three models have been obtained.Results: 1.Cadaveric BT: After single-tunnel coracoclavicular ligament reconstruction using the Dog Bone technique.Under a load of 30 N,the pronation and supination angles of the clavicle in the G2 group were 20.50(19.50,21.25)° and 20.00(18.75,21.25)°,respectively,showing the best rotational stability.2.FEA: The von Mises stress peak values along the FiberWire in M1,M2,and M3 were121.70 MPa,33.110 MPa,and 64.710 MPa,respectively.The strain LE along the FiberWire in M1,M2,and M3 were 0.010080,0.006227,and 0.017090,respectively.Finally,the displacement nephogram for the three models provided a maximum displacement of the clavicle,which measured 1.5610 mm at M1,0.4244 mm at M2,and 2.4420 mm at M3.Conclusions: When the coracoid bone tunnel was located 5 mm anterior to the center of the coracoid base(along the axis of the coracoid),the clavicle showed greater rotational stability.