Abstract
Introduction
Accurate prosthetic cup placement is very important in total hip arthroplasty (THA). When the surgeon is impacting the acetabular cup, it is assumed that the patient's pelvis is perpendicular to the operating table. In reality the pelvis may not be truly lateral, and error in patient positioning may influence the resultant cup orientation.
Objectives
The primary aim of this study was to examine the accuracy of patient positioning prior to THA. A secondary aim was to see if patient BMI influenced the accuracy of positioning.
Method
A consecutive series of 36 patients undergoing total hip arthroplasty were investigated. Once the lead surgeon believed that the patient had been correctly positioned in lateral decubitus, a lateral fluoroscopic image of the pelvis was taken. The C-arm of the image intensifier was manipulated in two planes until a proper lateral view of the hip was obtained, defined as when the native acetabulae overlapped. The number of degrees of positioning error in two planes (coronal, axial) was recorded, along with the patient's BMI.
Results
Only 6 patients (17%) were positioned within 2° of true lateral in both planes. A further 20 patients (56%) had an error of 5° or more in at least one plane. In the axial plane the mean error was 2.9° and 7 patients (19%) were tilted by 5 degrees or more. In the coronal plane the mean error was 3.1° and 14 patients (39%) were tilted by 5 degrees or more. A statistically significant correlation was shown between patient BMI and combined error in the two planes (R=0.47, P < 0.01).
Conclusion
Large errors can occur frequently and these may pass by unnoticed without the use of an image intensifier. Further research into the clinical significance of this finding would help decide if the use of fluoroscopy to aid patient positioning should be routine.
