The Effect Of The Size Relation Between Femoral Head And External Cup Of Bipolar Head On The Dislocation After Bipolar Hemiarthroplasty

Objective: There are many studies on the risk factors for postoperative dislocation after Bipolar Hemiarthroplasty(BHA),but no relatives report on the impact of the femoral head diameter and the size of the bipolar external cup on postoperative dislocation after BHA.The aim of this study is to investigate the effect of the difference between the diameter of the femoral head and the external cup diameter of the bipolar head prosthesis on the postoperative dislocation in the treatment of femoral neck fracture(FNF)by BHA.Effect of the selection of the external cup of the prosthesis by different ways of measuring the femoral head on the postoperative dislocation is also observed.Methods: From August 2013 to February 2018,567 elderly patients who underwent posterolateral cement-unilateral BHA due to femoral neck fracture were included in this study.The follow-up period was 6~63 months.Surgical records of all patients were reviewed,including intraoperative measurement of femoral head diameter and the use of the prosthesis size;Postoperative radiographic examination of all patients was recorded and analyzed.We used the head-cup difference to represent the relationship between the femoral head diameter and the external cup diameter of the bipolar head prosthesis.Head-cup difference means the diameter of the patient's own femoral head minus the external cup diameter of the bipolar head.We regarded the patients without dislocation as the control group and compared the patients with dislocation to analyze the influence of head-cup difference on the dislocation of prosthesis after BHA surgery.In addition,according to selection of measured diameter of femoral head(the maximum or minimum),the patients were divided into two sub-groups with matching gender and age.The incidence of postoperative BHA dislocation was analyzed to study the effect of maximum or minimum diameters of femoral head diameter.Results: Among the 567 patients,the postoperative dislocation rate was 6.88%(39/567).When the head-cup difference fluctuated between-1.8mm-1.4mm,there was no significant difference between the dislocation group and the control group(0.026±0.629 mm vs.0.022±0.564 mm,P=0.971).The rate of dislocation of BHA when selecting the maximum diameter of femoral head was 5.95%(5/84),and the rate of dislocation of BHA when selecting the minimum diameter of femoral head was 7.69%(3/39).There was no significant difference(P=0.716).Conclusions: When the difference between femoral head diameter and external cup diameter of bipolar head prosthesis is in a certain range(head cup difference was within-1.8mm-1.4mm),it has no effect on the dislocation rate of BHA.The surgeon can choose the size of the external cup of the prosthesis according to his own habits in the above range,and it has no effect on dislocation.When the femoral head was measured intraoperatively,the choice of maximum or minimum diameter of the femoral head to select the size of the prosthetic cup had no effect on postoperative prosthesis dislocation.