A new and improved acetabular cup digital templating method and its clinical application

Preoperative acetabular cup templating has an important auxiliary effect on hip surgery. The traditional acetabular cup templating method requires the measuring person to have some experience in total hip replacement (THA) surgery since the measurement results vary from person to person with differences between different measuring persons. To obtain stable templating results, we designed a new acetabular cup templating method and tested the inter-person measuring differences and measurement accuracy of this method. Meanwhile, the clinical application of this method was preliminarily explored.

The pattern of this new method was manual labeling of imaging characteristic points and then programmed automatic measurements. The measurement process was performed entirely by orthopedic graduate students without any experience in hip replacement surgery. The inter-person measuring difference was evaluated by comparing the templating results of three measuring persons. The accuracy of the templating was evaluated by comparing the templating results with the actual size of the prosthesis in the surgery. The correlation between the position of the acetabular cup and the templating error was analyzed to explore the clinical significance of the templating results. This study was a retrospective study which included templating in a total of 406 cases for total hip replacement with cementless cup prosthesis. Digital measurements were performed using the Matlab software from MathWorks. The statistical comparison was performed using Kendall's W test.

The results of the three measuring persons were completely identical in 61.8% (251/406) of cases, and the variation in 38.2% (155/406) of cases did not exceed one size of the acetabular cup. The Kendall's W coefficient was 0.977, and p < 0.01. The measurement accuracy is not as good as the traditional method in exactly accurate measurement and ±1 cup size, but it is similar to the traditional method in the ±2 cup sizes. The correlation between the templating error and the position evaluation of the implanted acetabular cups reveals: (1) larger the templating error, larger the proportion of the acetabular cups with poor position; (2) the proportion of acetabular cup with poor position slowly increased when the templating error was from 0 to 1 size, and the proportion rapidly increased when the templating error was from 1 to 2 size.

All the patients with clear teardrop bottom and lateral superior edge of acetabulum were able to use our method to predict the size of the acetabular cup. The method has the following advantages: (1) it does not require the measuring person to have any previous experience of the THA surgery, which reduces the labor cost of the templating; (2) the differences between the measuring persons is small, the measurement result can be repeated; (3) it can predict the probability of acetabular cup with poor positioning according to the templating error, and thereby reminding the surgeon to recheck and correct the position of the acetabular cup in time during the surgery.