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An important question is: does the placement of the acetabular component influence the risk of dislocation or revision surgery?
Improved placement of the acetabular cup – through use of navigation – is associated with reduced dislocation risk. Agarwal, et al.1 analysed Australian joint registry data from 2009 to 2019: using navigation to improve acetabular component placement was associated with lower risk of dislocation. Of the 269,848 total hip arthroplasties (THAs) for osteoarthritis, 6912 (2.6%) were navigated. The analyses were adjusted for the size of the femoral head, age, and gender. At 10 years, the cumulative risk of revision due to dislocation was significantly lower in navigated (0.4%) compared with non-navigated (0.8%) THAs. The authors also analysed the 5 most common combinations of THA components and found that the 10-year cumulative risk of all-cause revision was significantly lower for navigated (2.4%) than non-navigated (4.2%) THAs. These findings suggest that improved acetabular component placement explains a reduced dislocation risk beyond what might be expected for femoral head and some patient characteristics. Similarly, Davis, et al.2 assessed joint registry data from England, Wales, Northern Ireland, and the Isle of Man with respect to all-cause revision. The primary analysis was for all THAs treating osteoarthritis, with a further analysis of cementless-only THAs. At 10 years, the cumulative risk of all-cause revision was significantly lower in navigated (1.06%) compared with non-navigated (3.88%) THAs. Similarly, when limited to cementless-only THAs, the 10-year cumulative risk of all-cause revision was significantly lower for navigated (1.20%) than for non-navigated (3.99%) THAs. These two studies suggest that using navigation is associated with reduced revision due to dislocation and all-causes.
These registry results are consistent with findings that acetabular component orientation predicts hip loosening. In a study using both clinical research and finite element modelling of normal gait cycles, Patil, et al.3 investigated the influence of inclination angle on component loosening. In the hip wear simulation, significantly lower wear rates were found for acetabular liners oriented at an inclination of 45° (17.2 mg/million cycles) compared with 55° (21.7 mg/million cycles). The clinical study of 56 patients found a significant correlation between inclination angle and wear rate: as inclination increased, loosening increased. The authors concluded that acetabular component orientation is an important predictor of wear, osteolysis, and component loosening.
Suboptimal acetabular cup positioning is also related to avoidable revision surgery. Novikov, et al.4 conducted a review of 117 patients who had undergone revision or re-revision surgery within 5 years of their initial procedure. Three surgeons independently reviewed the patients’ radiographs and medical records to classify each revision as avoidable (errors in surgical planning or execution) or unavoidable (occurred despite optimal management). For the 51.3% of revision THAs which were deemed avoidable, the primary reason for revision was suboptimal positioning of the acetabular cup, accounting for 48.3%. A range of other factors were assessed and were not found to differ significantly between the avoidable and unavoidable group, including surgical approach, femoral head size, and bearing surface. These findings demonstrate a relationship between the position of the acetabular component and the risk of revision surgery.
Improving acetabular cup placement is associated with a reduced risk of dislocation. More broadly, acetabular cup placement is a significant predictor of the risk of revision surgeries.
- Agarwal S, Eckhard L, Walter WL, et al. The Use of Computer Navigation in Total Hip Arthroplasty Is Associated with a Reduced Rate of Revision for Dislocation: A Study of 6,912 Navigated THA Procedures from the Australian Orthopaedic Association National Joint Replacement Registry. JBJS 2021;103(17):10.2106/JBJS.20.00950. doi: 10.2106/jbjs.20.00950
- Davis ET, McKinney KD, Kamali A, et al. Reduced Risk of Revision with Computer-Guided Versus Non-Computer-Guided THA: An Analysis of Manufacturer-Specific Data from the National Joint Registry of England, Wales, Northern Ireland and the Isle of Man. JBJS Open Access 2021;6(3)
- Patil S, Bergula A, Chen PC, et al. Polyethylene wear and acetabular component orientation. J Bone Joint Surg Am 2003;85-A Suppl 4:56-63. doi: 10.2106/00004623-200300004-00007 [published Online First: 2003/12/04]
- Novikov D, Mercuri JJ, Schwarzkopf R, et al. Can some early revision total hip arthroplasties be avoided? The Bone & Joint Journal 2019;101-B(6_Supple_B):97-103. doi: 10.1302/0301-620X.101B6.BJJ-2018-1448.R1