| Part I The effect of orientation of the cup on dislocation after total hip arthroplastyObjective To study the effect of prostheses orientation of the cup on dislocation after total hip arthroplasty which could be used as a basis to evaluate clinical practice. Methods From February 1999 to January 2009, 502 patients(538 hips) wereperformed with total hip arthroplasty in our hospital.Of whom 236 patients(248hips) met the selected criteria and were evaluated in this study.There were 106 men and 130 women.The average age of the 236 patients in this series was 57 years(range,21～72 years). The preoperative diagnosis for each of the patients was osteonecrosis in 70,osteoarthritis in 56,femoral neck fracture in 76,the crowe I and II congenital dysplasia in 22, ankylosing spondylitis in 12.The standardized anteroposterior radiographs of the hip and the cross-table lateral film of the hip were used for measuring of the abduction angle and the anteversion angle.The abduction angle was further classified as nomoral,if it was 30°～50°;horizontal ,if it was less than 30°;and vertical,if it was greater than 50°.The anteversion angle was also further classified as being anteverted (>25°),neutral(0°～25°),retroverted(<0°).The results were statistically analyzed ,with a P value less than 0.05 indicating significant difference.Results All the patients were followed up with an average of 3.1 years(range 3 months～9 years). Of the 248 THAs, there were 6 dislocations, the dislocation rate was 2.4%.All the hip dislocations occurred within the first 6 weeks after operation.And only posterior dislocation was occurred in this group.Closed reduction and the hip cast lasted 6 weeks were selected for all these patients,and all were successful.Recurrent dislocation occurred once in anthor one patient with 2 months after reduction.In the patients who had a dislocation ,the average acetabular component abduction angle was 39°±11.88°, whereas the average abduction angle for the other patients who did not dislocate was 38.98° ±8.65°(Mann-whitney U test P=0.449).And the patients who had a dislocation ,the average anteversion angle was 12.33°±14.89°,whereas the average anteversion angle for the patients who did not dislocate was 13.21°±11.52°(Mann-whitney U test P=0.131).There was no significant difference in the prevalence of dislocation between patients who were categorized as having a normal abduction angle(30°～50°) and patients who had a vertical or horizontal angle(Pearson'sχ2χ2=0.142,P=0.932 ;R=-0.02,P=0.824) ;And there also no significant difference between the anteversion angle(Pearson'sχ2 test.χ2=-0.183,P=0.913;R=0.062,P=0.368 ) . Conclusions In our study,we find that the acetabular abduction angle from 14°to 58°and antevertion angle from -15°to 35°have no effect on dislocation after THA.And we think that the inability to comply with instruction of rehabilitation perhaps contribute to the dislocation.Part II The effect of femoral head diameter on risk of dislocation after primary total hip arthroplastyObjective To discuss the effect of femoral head diameter on risk of dislocation after primary total hip arthroplasty.Because the outcome could be used as a basis when surgeons choose the diameter of femoral head for preventing the postoperative dislocation.Methods From March 1990 to August 2008, primary total hip arthroplasties with varying head sizes were performed in 706 patients (762 hips) in our hospital. There were 301 men and 405 women.The average age of the 706 patients in this series was 57 years(range 21～78 years). The preoperative diagnosis for each of the patients was osteonecrosis in 203, congenital dysplasia in 129(the crowe IV in 15 ), femoral neck fracture in190,osteoarthritis in 112, rheumatoid arthritis and ankylosing spondylitis in 58 and the other diagnosis in 14. The femoral head diameter was 22mm in 220 of the procedures, 26mm in 83, and 28mm in 459. All the operations were performed by a senior surgeon.Among the 762 THA's, a modified Harding approach was preferred in 95%, and a posterolateral approach was preferred in 5%. Patients routinely were followed at definite intervals and were specifically queried about dislocation.Results All the patients were followed up at least six months. Of the 762 THAs, there were 28 dislocations; the dislocation rate was 3.7%. In the subgroups, there were 7.3% (16/220) for 22mm heads.,4.8%(4/83) for 26mm heads, and 1.7%(8/459) for 28mm heads, and between the three groups, the difference were statistically significant(χ2=13.193,P=0.001;R=0.131,P=0﹤0.01).Conclusion In our study, we find that the femoral head diameter has a positive effect on risk of dislocation, using a larger femoral head could reduce the risk of dislocation after total hip arthroplasty. So, we advise when surgeons perform total hip arthroplasty, they should choose a larger femoral head for preventing the postoperative dislocation and avoid the usage of 22mm femoral heads. |
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