The Investigation Of Frog Lateral View Type And Its Reliability In Predicting The Prognosis Of Osteonecrosis Of The Femoral Head

Background The osteonecrosis of the femoral head(ONFH)causes serious pain and dysfunction in patients,and often leads to secondary osteoarthritis with the progression of the disease.Many factors,such as the presence of pain,lesion size,location of the necrotic area,and radiographic evidence of collapse,determine clinical definitions and management of ONFH,so as to influence the prevalence of collapse and prognosis.Many evidence have confirmed that the location and size of necrotic lesions are primary factors that predict the prognosis of ONFH.The Japanese Investigation Committee(JIC)classification system,based on the location of the necrotic lesion,has been widely accepted and applied around the world.However,there are few opinions in regard to significance of the different spatial localization of necrotic sites in JIC classification.In particular,there is no report about whether the location of the necrotic area in lateral view may affect the prognosis predicted initially by the JIC classification.Consequently,this classification system may neglect the effect of the three-dimensional structure of the femoral head and necrosis because the classifying method is based on the two-dimensional anteroposterior(AP)radiographs or coronal magnetic resonance imaging(MRI).Purposes The purpose of this study was to investigate whether the location of the necrotic area in the frog leg lateral(FL)view may affect the prognosis predicted initially by the JIC classification.Methods From January 2011 to December 2013,we diagnosed the ONFH before femoral head collapse in 175 hips of 142 patients on plain radiographs.85 hips in 66 patients were excluded as a result of death or loss to follow up(47 hips in 36 patients),or receiving hip-preserving surgery at the initial visits of diagnosis(38 hips in 30 patients).The remaining 90 hips in 76 patients were analyzed in this study.All patients received standard radiographs including an AP and a FL view of the affected hip.The percentage of the necrotic area were measured and compared in AP and FL view.The area was measured by using an image processing program.Hips with ONFH were categorized using the JIC classification and the FL view type and inter-and intraobserver reliability were compared between them.The cumulative survival rate with subsequent collapse and requirement for further hip surgery as the endpoints was evaluated for the two classification systems.Results The percentage of the necrotic area was found to be significantly greater in the FL views(47.0%±1.5%)than that in the AP views(37.7%± 1.7%,p<0.0001).Our comparisons also included subdivisions of the JIC classification system that type A showed parameter of 23.3%± 1.0%in the AP views and 35.1%± 1.6%in the FL views(p<0.0001),type B showed parameter of 27.9%±0.9%in the AP views and 43.2%± 2.2%in the FL views(p<0.0001),type C1 showed parameter of 36.8%±3.0%in the AP views and 46.8%± 3.2%in the FL views(p=0.0263),and type C2 showed parameter of 41.6%± 1.7%in the AP views and 53.0%± 2.3%in the FL views(p=0.0002).Intraobserver reliability in the JIC classification(mean 0.91,range 0.85 to 0.98)was higher than that in the FL view type(mean 0.77,range 0.63 to 0.89;p<0.001),as well as the interobserver reliability in the JIC classification(mean 0.74,range 0.38 to 0.87)was higher than that in the FL view type(mean 0.58,range 0.31 to 0.76;p<0.001).At the latest follow-up.there were 36 hips(40%)collapsed(Fig.6)(mean,30.2 months;range 5 to 73 months)and 34 hips(37.8%)underwent hip arthroplasty(mean,20.5 months;range 1 to 67 months)during the follow-up period,and 20 hips(22.2%)remained pain tolerable and mobility acceptable and without evidence of collapse for more than five years(mean,69.5 months;range 60 to 83 months).Comparisons of survival curves showed that Type III in FL view type had the worst prognosis than other two divisions,following the Type II.The Type I was likely to gain optimal outcomes.Conclusion The JIC classification is a convenient and reliable method in evaluating the ONFH.The location to which necrosis extended in the FL view is a reliable indicator in predicting the prognosis.It would be more helpful to add the FL view type as a supplement.Further investigation is essential to standardize clinical applications and guide the therapeutic strategies.