| Part one:Establishment of denervated skeletal muscle in rabbit modelsPurpose:To establish denervated skeletal muscle in various nerve injury models in rabbits.Materials and methods:Twenty-seven male rabbits made up nine groups(Group A～I)with an injured left posterior sciatic nerve and one control group.There were three rabbits in each group.Group A-F:The nerve about 1cm below the sciatic notch was clipped with an intracranial aneurysm clip for 5,10,15,20,25,and 30 minutes,respectively;Group G:The nerve was transected and immediately sutured with nylon stiches;Group H:The nerve was transected and 1cm segment of nerve was removed,and the stump was tightly ligated with stitches to permanently prevent repair.The functional assessment of the injured sides was measured 1 day,3 days,5 days,lweek,2 weeks,3 weeks,4 weeks,6 weeks,8 weeks,10 weeks and 12 weeks after surgical injury.Specific acquisition points within groups were compared by using repeated measures analysis of variance.Comparisons across the five groups at each acquisition point were performed by using one-way analysis of variance.Results:The functional scores of the injured sides in Group A-G increased gradually and was significantly lower than the control group(P<0.05).The more severe the nerve damaged,the slower the function of injured side recovered.Comparisons across all of the groups at each time point showed:There were no significant differences in functional scores between group B and group A at any time point.There were no significant differences in functional scores between group B and group C at 1day,3 days,3～12weeks(P>0.05).There were no significant differences in functional scores between group D,E and group C,F at 1day,3 days,5 days,2～12weeks(P>0.05).There was significant differences in functional scores among group A,C,F,G,and H in different time point(P<0.05).Conclusions:There were significant differences among the three groups(group A with nerve clipped for 5 minutes,C for 15 minutes and F for 30 minutes),which combined with group G(reversible group)and H(irreversible group)form a comprehensive and stable model with various nerve injury animal models.Part Two:Multimodal MR imaging of denervated skeletal musclePurpose:To investigate the diagnostic value of multimodal MRI for denervated skeletal muscle in various nerve injury models in rabbits.Materials and methods:Thirty-six male rabbits made up six groups(Group A～I)with an injured left posterior sciatic nerve and one control group.There were six rabbits in each group.Group A-C:The nerve about 1cm below the sciatic notch was clipped with an intracranial aneurysm clip for 5,15,and 30 minutes,respectively;Group D:The nerve was transected and immediately sutured it with nylon stiches;Group E:The nerve was transected and 1cm segment of nerve was removed,and the stump was tightly ligated with stitches to permanently prevent repair.Multimodal MR imaging,EMG examination,and functional assessment of the injured sides were measured 1 day,3 days,5 days,1 week,2 weeks,3 weeks 4 weeks,6 weeks,8 weeks,10 weeks and 12 weeks after surgical injury.Specific acquisition points within groups were compared by using repeated measures analysis of variance.Comparisons across the five groups at each acquisition point were performed by using one-way analysis of variance.Results:The more severe the nerve damage,the higher the signal intensity on T2-weighted images.Changes in T2 values,D*,D,FA,Ktrans,Vp,and Ve correlate with the degree of nerve injury.T2 vlaue,D*,D,Ktrans,VP,Ve,and FA of the injured sides in Group A-B mostly increased or decreased gradually and reach peak or the bottom at 3 or 4 weeks follow-up,thereafter,they decreased or increased and were essentially normalized.T2 vlaue,D*,D,Ktrans,Vp,Ve,and FA in Group D increased or decreased gradually and reach peak or the bottom at 6 weeks follow-up,thereafter,they decreased or increased and were essentially normalized.T2 vlaue,D*,D,Ktrans,Vp,Ve,and FA in Group E increased or decreased gradually and reach peak or the bottom at 6 weeks follow-up,thereafter,they remain high or low throughout the remainder of the study period.There were significant differences between the degree of nerve injury and functional scores changes.The time course of functional scores is similar to that of MRI in injured sides.Spontaneous activity of EMG in all groups was observed at 2-week follow-up.Conclusions:Multimodal MRI can be used to diagnose denervated skeletal muscle,and MR findings can be used to predict nerve damage and its prognosis.Part three:Pathological mechanisms of multimodal MRI findings in denervated skeletal musclePurpose:To investigate the pathological mechanisms of multimodal MRI findings in denervated skeletal muscle.Materials and methods:Twelve male rabbits made up two groups(Group A and B).There were six rabbits in each group.Group A and B:The nerve was transected and 1cm segment of nerve was removed,and the stump was tightly ligated with stitches to permanently prevent repair.Multimodal MR imaging and EMG examination of the injured sides were measured 1 day,3 days,5 days,lweek,2 weeks,3weeks 4 weeks,6 weeks,8 weeks,10 weeks and 12 weeks after surgical injury,respectively.The correlation between MRI parameters and pathological results were performed by using Pearman’s correlation analysis.Results:T2-weighted images showed intermediate to high signal intensity in the target muscle beginning 5 days after surgery,and they showed high signal intensity at 2-week follow-up.For all rabbits in this group,signal intensity remained high until 12-week follow-up.T2 score,T2 vlaue,D*D,Ktrans,Vp,and Ve in Group E increased gradually and reach peak at 6 weeks follow-up,thereafter,they remain high or low throughout the remainder of the study period.Extracellular space percentage(ESP)and capillary number(CN)unit increased gradually from 1 day to 6 weeks after surgery and remained high throughout the remainder of the study period.Signal changes on T2 WI and T2 value positively correlated with ESP and CN,respectively(r = 0.925,0.919).There was positive correlation between D*and CN(r = 0.975).There was positive correlation between D and ESP(r = 0.97).Ktrans positively correlate with CN and ESP,respectively(r = 0.982,0.969).There was positive correlation between Vp and CN(r ＝0.987).There was positive correlation between Ve and ESP(r = 0.972).Conclusions:There are two possibilities of pathological mechanisms of multimodal MRI findings in denervated skeletal muscle including an increase in the extracellular and an enlargement of muscle capillaries. |
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