Optimal acetabular orientation for hip resurfacing

Abstract

Pseudotumours are a rare complication of hip resurfacing. They are thought to be a response to metal debris which may be caused by edge loading due to poor orientation of the acetabular component. Our aim was to determine the optimal acetabular orientation to minimise the risk of pseudotumour formation. We matched 31 hip resurfacings revised for pseudotumour formation with 58 controls who had a satisfactory outcome from this procedure. The radiographic inclination and anteversion angles of the acetabular component were measured on anteroposterior radiographs of the pelvis using Einzel-Bild-Roentgen-Analyse software. The mean inclination angle (47 degrees, 10 degrees to 81 degrees) and anteversion angle (14 degrees, 4 degrees to 34 degrees) of the pseudotumour cases were the same (p = 0.8, p = 0.2) as the controls, 46 degrees (29 degrees to 60 degrees) and 16 degrees (4 degrees to 30 degrees) respectively, but the variation was greater. Assuming an accuracy of implantation of +/- 10 degrees about a target position, the optimal radiographic position was found to be approximately 45 degrees of inclination and 20 degrees of anteversion. The incidence of pseudotumours inside the zone was four times lower (p = 0.007) than outside the zone. In order to minimise the risk of pseudotumour formation we recommend that surgeons implant the acetabular component at an inclination of 45 degrees (+/- 10) and anteversion of 20 degrees (+/- 10) on post-operative radiographs. Because of differences between the radiographic and the operative angles, this may be best achieved by aiming for an inclination of 40 degrees and an anteversion of 25 degrees.

The Canadian Arthroplasty Society’s experience with hip resurfacing arthroplasty

“…1,3,11,[13][14][15][16][17][18][19][20] The higher revision rate in women can be attributed partly to the differences in the proportion of men and women who receive smaller femoral heads. Data from the Australian registry show that after adjusting for femoral head size, female gender no longer remained an independent risk factor.…”

“…1,3,5 In addition, high levels of circulating metal ions and reactive lesions have been identified in some patients. [6][7][8][9][10] Suboptimal acetabular component positioning has been recognised as an important factor in failure of HRA, 5,6,11 leaving little margin of error for the surgeon as far as implantation of the acetabular component is concerned. These factors have led to a decrease in the number of HRAs performed annually in recent years.…”

“…12 Many factors have the potential to contribute to HRA failure. 3 Various single-centre studies have implicated implant type or position, component size, female gender, age and surgical experience as risks for failure, 11,[13][14][15][16] and several multicentre and registry-based studies from all over the world have supported these findings. 1,3,[17][18][19][20] National registry data have demonstrated that not all HRAs behave in the same manner, and that factors such as implant design, diametrical clearance and heat treatment influence the outcome.…”

Squeaking: Current knowledge and how to avoid it

“…8 of the 10 patients had well positioned components according to AP radiographs though we were unable to measure anteversion at the time. It would be useful to revisit these cases to remeasure inclination and anteversion with the latest validated software such as EBRA [38].…”

Effects of coordinate-system construction methods on postoperative computed tomography evaluation of implant orientation after total hip arthroplasty

“…[1][2][3][4][5][6] Therefore, it is recommended that in modern THA with a conventional femoral head size, [7] surgeons use an inclination of [40][41][42][43][44][45] and anteversion based on combined anteversion theory for acetabular cup orientation, and indeed it has recently been reported that precise implantation prevents such complications. [8,9] Although many helpful techniques have been developed to achieve accurate implantation, [8][9][10][11][12][13][14] such as computed tomographybased (CT-based) navigation, imageless navigation, and patient-specific surgical guides, it is also important to assess postoperative implant orientation and the accuracy of these estimation modalities.…”