Biomechanical Evaluation Of The Stability Of The Posterior Wall Fracture Of The Acetabulum And Its Fixations

1. Biomechanical evaluation of the stability of the simulated fractures of the posterior wall of acetabulumOBJECTS To study the effects of various proportions of the posterior wall fractures of acetabulum on the hip stability and the function of posterior capsule of hip and to offer a reference to the clinical treatment.METHODS Fourteen preserved cadaveric hip joints were divided into two groups randomly. All soft-tissue structures were stripped in group A and left the posterior capsule intact in group B. The simulated posterior wall fracture models were created by osteotomy from outer rim of the acetabulum to the cotyloid fossa in the proportions of 20% ,30%,40%,50%,60% .Then tests were performed on each model in the state of 90?flexing of the hip .Measure the deformations of the acetabulum and its axial stiffness and the loadings when the femoral heads dislocated.RESULTS The acetabular deformation increased as the proportions of osteotomy added when loading. There was no significant difference between group 20% and group 30% (P>0.05), yet significant difference between group30% and group 40%, 50%, 60% (P<0.01). The variance of axial stiffness showed the same trend. All joints dislocated except 20% and 30% osteotomy group when the load was 800N.There was no significant difference between group A and group B either in deformations or in axial stiffness.CONCLUSION Fragments of posterior acetabulum involving 30% or less do not affect the stability of hip while fragments involving 40% or more do and need to internal fixed. Posterior capsule has no moreeffect on maintaining the stability of hip than acetabulum.2. Biomechanical evaluation of the fixations of the simulated fractures ofthe posterior wall of acetabulumOBJECTS Try to define the optimal internal fixation method by means of studying the strength of various internal fixations of simulated fractures of posterior acetabular wall.METHODS Eighteen preserved cadaveric hip joints were divided into three groups randomly. The simulated big isolated posterior wall fracture models were created by osteotomy in the middle of the outer rim of posterior acetabulum and the incisura ischiadica major. The models were fixed with one of the three different methods: two cortical screws (CS), reconstruction plate (RP) and buttress plate plus two cortical screws (CS+RP). Then tests were performed on each model with 90?flexing of the hip. Measure the displacements of the fragments and the loadings when the displacements were 3mm.RESULTS The displacements of fragments increased as the loading added. There have high significant difference between the CS and RP or RP+CS (P<0.01), but no significance between the RP and CS+RP (P>0.05).CONCLUSION The ideal method of internal fixation of posterior acetabular wall fracture is RP. The strength of CS only cannot maintain the stability of the fragment while RP+CS is not stronger than RP only and it may add more operative trauma and difficulty to operation.