Accuracy and reproducibility of visual estimation of the acetabular cup positioning in total hip arthroplasty on plain radiographs by orthopaedic surgeons

Objectives

To examine whether trauma and orthopaedic surgeons could visually assess the anteversion and inclination of a total hip replacement acetabular component from standard anteroposterior radiograph and anteversion on a standard lateral radiograph with accuracy or reproducibility.

Main outcome measurement: The main outcome was accuracy of visual estimations of angles. The secondary outcome was whether these estimations were reproducible though intra-observer variability.

Results

Mean angles of anteversion on the anteroposterior, inclination on the anteroposterior and anteversion on the lateral on formal measurements were 15.2°, 45.4° and 19.9°; and the visual estimates were 17.5°, 45.9° and 18.2°, respectively. When comparing the visual estimates of surgeons and formal measurements, the results ranged from very poor to very good. Intra-observer reproducibility was moderate for all angles. The difference between the consultants and speciality registrars was not significant.

Conclusion

This study illustrated that not all orthopaedic surgeons were able to visually estimate angles well. Although some of our participants were very accurate, there were some who statistically were very poor. This level of inaccuracy can lead to inconsistency and we strongly suggested specialist software is used to assess acetabular cup position on postoperative plane radiographs rather than relying on ‘visual estimations’.