Increased Rate Of Dislocation Of Total Hip Arthroplasty With Cementless Implants: Accuracy Of Acetabular Inclination.

摘要

Accurate positioning of acetabular component in total hip arthroplasty is essential for stability. There is some evidence that cementless components are more difficult to position than cemented and have a higher dislocation rate. Our aim was to obtain information about rates of dislocation from the National Joint Registry (NJR) of England and Wales and to compare accuracy of acetabular component position of cemented and cementless implants. Methods: We made an enquiry of the NJR regarding number of dislocations during 2004-9 and compared rates of dislocation for cemented and cementless implants. We examined 126 post operative radiographs at our institution, assessing the angle of acetabular inclination to determine if there was a difference in the number of implants positioned within <±5° of the target angle. Results: There was a significant difference in rate of revision for dislocation with cementless implants (262/69,822) compared with cemented (266/92,928; c2=12.1, p<.001; odds ratio 1.35, 95% confidence interval 1.14 to 1.60). Discussion: The greater accuracy of acetabular component positioning of cemented implants with, perhaps consequent, higher rates of revision due to dislocation should be considered when selecting mode of fixation for THA. Introduction Dislocation of the hip following total hip arthroplasty (THA) is a major short term complication not infrequently resulting in revision arthroplasty. Malposition of the acetabular component in total hip arthroplasty (THA) results in a higher rate of dislocation as well as increased wear and osteolysis. , , , There is evidence that acetabular position is more accurate with cemented implants13,11,12.A difference in the rate of dislocation between cemented and cementless implants has been reported elsewhere using joint registries. Dislocation is a relatively infrequent event so it is difficult to detect a significant difference in dislocation rates between cemented and cementless implants with the number of THA performed within a single institution. A compilation of data from multiple centres is therefore more likely to detect any difference. We aimed to gain further information about whether there is a difference in dislocation rate of THA between cemented and cementless implants using the National Joint Registry of England and Wales. We assessed accuracy of acetabular component positioning at our institution, comparing cemented with cementless components and examined a possible reason for the findings. Patients, materials and methods An enquiry was made to the NJR about the number of revision THA procedures performed for which dislocation was stated as the indication over the five year period 2004-9. To estimate dislocation rate we compared the number of revisions for dislocation with the total number of primary THA, cemented and cementless over this period. We used the ?2 test and calculated an odds ratio to assess whether there was a significant difference between the number of cemented and cementless implants undergoing revision due to dislocation. For all THAs performed in our hospital in 2008, we assessed angle of acetabular inclination. Our measurement technique was based on that described by Lewinnek et al but for our assessment the angle measuring feature of the picture archiving and communication system (PACS) software was used (Sectra Imtec AB, Link?ping, Sweden). Assessment of angle was performed using the anteroposteror pelvic radiograph taken at the first the first post-operative outpatient follow-up appointment. Acetabular inclination was taken as the angle between a line drawn level with the inferior margins of the pubes and another in alignment with the extremes of the acetabular component. For cemented implants a line was drawn intersecting the extremes of the radio-opaque metal ellipse of the acetabular component (figure 1)