Liaw's Ellipse Anteversion Method for Distinguishing Acetabular Component Retroversion from Anteversion on Plain Radiographs

Improper acetabulum component position is a significant risk factor for postoperative dislocation after total hip arthroplasty. Several radiographic two‐dimensional methods exist for measuring acetabulum component anteversion, but they cannot distinguish between anteversion and retroversion. “Liaw's version,” initially proposed as a simple mathematical standardized two‐dimensional method, was modified to the computerized ellipse method, proving superior accuracy to traditional two‐dimensional methods. In this article, we demonstrated its application in detecting and measuring retroverted acetabulum component. We obtained anteroposterior pelvis radiographs from a patient undergoing total hip arthroplasty on the day of surgery and 2 weeks postoperatively. The computerized ellipse method was used to measure the acetabulum component orientation. Upon comparison, the difference between θ assigned to be retroverted (9.52–8.56 = 0.96) is much smaller than the difference between θ assigned to be anteverted (23.81–18.86 = 4.95), leading us to determine retroversion. This was further confirmed by computed tomography at the 6‐week follow‐up. We propose that using the computerized ellipse method to measure Liaw's version can be a valuable tool in identifying acetabulum component retroversion on anteroposterior radiographs during routine postoperative follow‐up and retrospective assessments of total hip arthroplasty patients. The computerized ellipse method, as far as we know, is the first two‐dimensional radiographic method capable of distinguishing retroverted acetabular components in plain radiographs. The Elliversion software facilitates a quick and easy measurement process. Although further cases are necessary to determine the reliability of this method, it can be suggested as a tool for detecting acetabular component retroversion on anteroposterior radiographs during routine postoperative follow‐up and retrospective reviews of patients who have undergone THA.