Risk Factors Of Contralateral Femoral Head Collapse After Unilateral Replacement For Bilateral Femoral Head Ecrosis

Objective:To evaluate the risk of contralateral femoral head collapse after unilateral total hip replacement in patients with bilateral femoral head failure,and analyze the risk factors of contralateral femoral head collapse through clinical data and imaging examination.Methods:From January 2017 to January 2020,the patients who were hospitalized in our hospital for bilateral ONFH and received unilateral THA were analyzed retrospectively.A total of 67 patients were included,aged 41-71 when they first received THA,with an average age of 58.3 years,including 35 males and 32 females.Follow-up for an average of 3 years,according to whether the contralateral femoral head collapsed,they were divided into collapsed group and non-collapsed group.The multivariate Cox risk ratio model was used to evaluate the risk factors of contralateral femoral head collapse,which was meaningful for multivariate analysis.The x-tile software was used to find the optimal cutoff value.Kaplan-Meier(K-M)survival analysis was used,and the survival rate between groups was compared with log-rank test to evaluate the risk of contralateral femoral head collapse.Results:1.There were 38 patients(56.7%)with contralateral femoral head collapse.The risk of contralateral femoral head collapse was 17.9% one year after operation and 53.7% three years after operation.2.JIC classification is highly related to the risk of contralateral femoral head collapse.In JIC classification,the average survival time of C2 type contralateral femoral head is 19.9 months(95%Cl:14.8-24.9),and the collapse rate is 90% after3 years.3.Sex,age,BMI,etiology,first THA operation side(left/right),contralateral ONFH international bone circulation research institute(ARCO)staging,acetabular angle(Sharp angle),Medial space ratio of hip joint,MSR),Acetabular depth ratio,ADR)and the length of the contralateral lower limb compared with the replacement side(longer/shorter)are not risk factors for the progression of contralateral femoral head collapse.JIC classification of contralateral femoral head(hazard ratio =3.361),length difference of both lower limbs(hazard ratio =1.496),center edge angle(CE angle)of contralateral femoral head(hazard ratio =0.768)and Harris hip score,HHS)(hazard ratio =0.886)one month after THA were as follows.4.Patients with lower limb length difference ≥5.2mm,contralateral central edge angle < 28.9°,and Harris score < 70 on the operating side one month after total hip replacement have higher risk of contralateral femoral head collapse.Conclusion:1.Patients with bilateral femoral head necrosis will have some contralateral femoral head collapse after unilateral total hip replacement.It is of great clinical significance to observe the extent of contralateral femoral head necrosis involving the weight-bearing area.JIC classification C2 has a high risk of femoral head collapse.2.After unilateral total hip replacement for patients with bilateral femoral head necrosis,the length difference of both lower limbs,the central edge angle of the contralateral hip joint and the function of the operative hip joint are independent risk factors for contralateral femoral head collapse.Reducing the length difference of both lower limbs after operation and restoring the function of the operative hip joint early can reduce the risk of contralateral femoral head collapse,and measuring the central edge angle of the contralateral hip joint can be used as an important factor to predict contralateral femoral head collapse.