Effect Of The Hip Offset And The Center Of Rotation Of The Hip In Total Hip Arthroplasty

Objective:To investigate the effect of the hip offset recovery on postoperative hip function and leg length discrepancy after total hip arthroplasty and to investigate the effect of the change of the center rotation(COR)of the hip on postoperative hip functional outcome.Materials and methods:The patients who were treated with total hip arthroplasty(THA)by a surgeon at the First Affiliated Hospital of Suzhou University from January 2012 to December 2017 were counted.We collected the basic information and medical history of these patients using the Haitai system and imaging data through the imaging system.106 patients who met the inclusion criteria were included in the clinical follow-up and imaging data collection.The parameters were measured and collected by imaging software.Patients are divided into different groups by different parameters obtained.The hip function after THA was evaluated by the improved Harris score and the excellent rate of the improved Harris score was calculated and analyzed.We analyzed the data obtained by SPSS23.0 software.Results:A total of 106 patients with complete follow-up data was obtained.The average improved Harris score at the last follow-up was 87.80±6.90,of which 97 patients had excellent hip function(Hams score?80),and the optimal rate was 91.50%.The ratio of hip offset(the ratio of the surgical side to the healthy side)accounted for 75.47%of patients with 90%to 110%.Patients whose ratio of hip offset were 90-110%had a better clinical outcome,their improved Harris score was better than the patients outside the zone,the difference was statistically significant(P<0.05).The optimal rate of postoperative function was 96.3%,which was also higher than other patients.The difference was statistically significant(P<0.05).When the HO ratio was within this range,90%of patients had a leg length difference within 1 cm.When the HO ratio exceeded this range,only 72.3%of patients had a leg length difference within 1 cm,the difference between them was statistically significant(P<0.05).In addition,the relative change(?H)in the vertical direction of the COR(center of rotation)of the hip before and after the operation was within 3 mm in 68 patients(64.2%),within 3 to 6 mm in 25 patients(23.6%),and there was a ?H?6 mm in 13 patients(12.2%).A higher Harris score and optimal rate were also observed in the group with a smaller ?H,and there was a statistical difference between these groups(P<0.05).There was no statistical difference in the improved Harris score and excellent rate between the groups whose changes of horizontal position of the COR were different(P>0.05).Conclusion:1.After THA,patients with a ratio of hip offset within the range of 90-110%had a better functional recovery and a less difference of the limb length.2.The positional change of the COR(center of rotation)of the hip in the vertical direction has an effect on the functional outcome(P<0.05),The functional recovery of patients whose change of the vertical position of the COR was within 6 mm was significantly better than patients whose change was greater than or equal to 6 mm(P<0.05).