| ObjectiveOsteonecrosis of the femoral head(ONFH)is one of refractory chronic diseases which can easily ignored by sufferers,due to the slow development and concealed progressive course,especially in it's non-traumatic kind(NONFH).The mechanism of ONFH is complex and the collapse which can be regarded as one of the most critical aspects,so a effective prediction of collapse in such disease is valuable for clinical treatment.In the past clinical cases observation we had found that some patients received treatment could progressed to collapse stage even appeared subluxation of the hip.The subluxation of the hip could increase the clinical symptoms and lead to a worse outcome,but this phenomenon may not suddenly hit,or accompany with necrosis over the progression of the pathology.Methods1.A retrospective study was performed by collected the clinic general data and imaging data included JIC types,collapse grade,medial hip joint space,CE degree of the patients from first affiliated hospital of GuangZhou University of Traditional Chinese Medicine in the January 2010 to February 2016,all of them who suffered the NONFH without surgical interventions in it's first diagnosis time to latest fellow-up2.With series statistical analysis on those clinic date to find their relevance.Based on the distribution of medial hip joint space ratio(MSR)observed in clinic date,we constructed 14 kinds of 3D finite element(FE)models including necrosis and no-necrosis group,each one group of them had 7 kinds models with different medial hip joint space by the MSR change rate of 0.3.With the finite element analysis(FEA)Abaqus software,the stress distribution(MISES and CPRESS)and magnitude deformation of those model was analyzed and compared under loading condition to explore the correlated biomechanics.ResultsClinical research:1.General date:106 patients including 80 male cases,26 female cases,totaling 133 hips(68 left,65right)had been collected.Age was raged from 19 to 69,average in 44.73 ± 13.51 years old.All of those cases were in accurate diagnosis of ONFH without traumatic course and during the follow-up time(5 to 70 months,average in 26.89 ± 15.82 months)without surgical intervention.2.Survival analysis:With y collapse as end point event,survival time accounted in 5 to 70 month,average of 32.79±16.89 months,overall survival rate was 42.19%,the most notable survival rate change occurred in 12th-40th month,and slowed down after 40th month,maintained stability after 52th month.With ? collapse as end point event,survival time account in 5 to 70 month,average of 35.25 ± 18.3 months,overall survival rate was 19.9%,the most notable survival rate change occurred in 12th-51th month,and the lower survival rate could observed over entire period compared with ? collapse event.3.Survival analysis with variable medial hip joint space ratio in first visit(MSFS):P values in the log-rank test with ?,? collapse as end point event was less than 0.05,and survival rate among C,D,E group showed statistically significant,especially between E and C,D group.Survival analysis with ? collapse as end point event,survival rate in C,D group maintained above 52.23%which far greater than E group.In survival analysis which taken ? collapse as end point event,the survival rate between those groups had difference,but the rates in total groups were below 30%.4.Survival analysis with variable JIC types:survival rate among JIC B,JIC C1 and JIC C2 type showed statistically significant in ?,? collapse as end point event,and JIC B type maintained a high survival rate which far greater than those in JIC C1 and JIC C2 type.5.MSFS among JIC types without different distribution analyzed by Chi-square statistic test.5.Medial hip joint space change ratio(MSCR):MSCR distribution in different grade collapse showed significant difference analyzed by Kruskal-Wallis statistic test.Than we extracted the cases with widened joint gap,MSCR distribution in different grade collapse showed significant difference especially between ? collapse and each other group.Experimental study:1.Stress distribution in cartilage:Maximum CPRESS and MISES stress distribution in each model group appeared at the top of the cartilage of the femoral head and apex of acetabulum cartilage with the radial decline trend.The maximum stress value increases with the decrease of the medial hip joint space ratio(MSS),obviously during the phase which MSS less than 4.Contact area were inversely proportional to stress change.2.Stress distribution in cortical of femur head:The maximum MISES stress distribution on femoral cortical bone surface were located at the top of the partial anterolateral femoral head,both in necrosis group and non-necrosis group.In the necrosis group,the stress concentration on the cortical surface of femur head was more significant,the stress was far greater than the non-necrosis group when compared on same MSR level,and the maximum MISES occurred in the upper-outer aspect of weight-area.The maximum MISES averaged in all non-necrosis models was 14.67±0.1412 MPa,in all necrosis models was 22.61±0.4014 MPa.Stress change was significant in phase of MSR less than 4.3.Stress distribution and Magnitude deformation in the necrosis area(N area):The maximum MISES stress distribution in non-necrosis group was greater than necrosis group when compared in the same MSR level,the maximum MISES stress non-necrosis group was 0.6357 ± 0.002809 MPa,the maximum MISES stress necrosis group was 0.4439 ± 0.007005 MPa,and the maximum MISES stress in both two groups was increased with declined MSR,more notable change occurred in necrosis group.Magnitude deformation was increased with the declined MSR both in non-necrosis and necrosis groups.4.Stress distribution in the different elements of necrosis area(N area):Stress distribution in the different elements of N area was different,this difference was more significant in necrosis group.The sensitivity of stress changed with different MSR,and in the roof of N area varied most significantly,especially in phase of MSR less than 4.5.Stress transmission in proximal femur:In the model analysis,the stress transmission route blocked after necrosis,and stress loaded above could not transmitted downward which easily formatted the stress concentration.With the MSR changed the stress concentration was significant,especially in weight-area of femur head.Conclusion1.Medial hip joint space is significate to prognosticate the collapse of the osteonecrosis of the femoral head.1.1 Medial hip joint space and CE degree can be used to evaluate the head-cup relation of hip,and CE degree shows more sensitive,but medial hip joint space can be more objective and accurate to evaluate the head-cup relation,especially in the collapsed femur head.1.2 The change of medial hip joint space should be an important risk factor of the head collapse.The MSR change in 3-6 showed statistic significance to necrosis outcome,when necrosis hip comes in the phase of MSR less than 4,a high risk of collapse worth be noted.And if medial hip joint space were increasing in the progression,the risker collapse should be alerted.2.The mechanism of collapse mixed multiple factors,we can not accurately evaluate the outcome only by relying on a kind of indicator.3.Instable biomechanics of femur head after necrosis:3.1 The material property of bone tissue can be transformed after necrosis which lead to joint forces transmit and disperse ineffectively,and normal tissues can easily format the stress concentration,especially in the top area of cortical bone of femur head corresponding to the necrotic region.Altered distribution of stress transmission in the femur head can be regard as instable biomechanics after necrosis..3.2 The maximum contact stress regions in normal hip acetabulum is trimodal distribution occurring in the dome of acetabulum,anterior-inferior part and poster-inferior part of acetabulum.During the MSR increasing this trimodal distribution changes into unimodal which means head-cup contact style may take change,this phenomenon may represent to an instability in femur head which can be considered as "head-cup mapping unstably".3.3 As necrosis occurring,stress conduction abnormity in femur head causing instability will be the important factor for the collapse,and accompanying with the broadening of medial hip joint space may worse this collapse trend.4.Microcosmic differentiation theory and applying treatment based on"stability" theory can dramatically benefic to diagnosis and treatment of ONFH. |
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