Effect of an iliac bone plate on the subsidence of iliac screw after fatigue loading

English Keywords:Spino-pelvic reconstruction  Iliac screw  Iliac bone plate  Biomechanics

English Abstract:

  【Abstract】 Objective：To evaluate the biomechanical effect of a self-designed iliac bone plate on the subsidence of iliac screw after fatigue loading.Method：Lumbo-pelvic specimens from 6 adult fresh cadavers were used in this study，their mean bone mineral densities（BMD） of L1-L4 were measured by using dual-energy radiograph absorptiometry.The iliac bone plate was randomly placed at the iliac screw entry point of one-side ilium（group A），while the other side without iliac bone plate served as the control（group B）.Then，the iliac screws with 70mm length and 7.5mm diameter were inserted into the ilium bilaterally.On a MTS testing machine，a dynamic compressive loading of 100-400N was added to the screw head for 20000 cycles.The screw subsidence displacements following each 5000 cyclic loadings were measured and compared between two groups.Result：The average BMD value of 6 specimens was 0.89±0.06g/cm2，ranged from 0.78g/cm2 to 1.06g/cm2.All the screws passed the 20000 cyclic loadings smoothly.At the time-points of the 5000th，10000th，15000th，and 20000th cyclic loadings，the subsidence displacements of iliac screw in group A were 0.28mm，0.36mm，0.48mm and 0.66mm respectively；while those in group B were 0.34mm，0.69mm，0.88mm and 1.07mm respectively.After the first 5000 cyclic loadings，no significance with respect to subsidence displacement was detected between two groups（P>0.05）.However，at the 10000th，15000th and 20000th cycles，significant difference was noted between two groups（P<0.05）.After the 20000 cyclic loadings，no screw in group A and 5 screws in group B were found loosen under radiograph.Conclusion：The iliac bone plate can effectively resist the subsidence of iliac screw following fatigue loading and protect iliac screw against loosening.