A new radiographic acetabular cup anteversion measurement method in total hip arthroplasty: a clinical study

Assessing the Reliability of Postoperative Cross-Table Radiographs Compared to CT Scans for Measuring Acetabular Anteversion Angle Following Total Hip Arthroplasty

AIM

This study aimed to evaluate acetabular anteversion following total hip arthroplasty (THA) using cross-table lateral radiographs and CT scans and to determine the reliability of cross-table lateral radiographs compared to computed tomography (CT) scans for measuring acetabular anteversion.

MATERIALS AND METHODS

We conducted a cross-sectional study of patients undergoing THA at Justice K.S. Hegde Charitable Hospital, Deralakatte, Mangalore, from January 2020 to June 2021. Radiographs are typically taken in both anteroposterior (AP) and lateral views after THA. However, for this study, a cross-table lateral view was used instead of the usual lateral radiograph to measure the angle of anteversion. The anteversion was calculated using the method described by Woo and Morrey. Additionally, CT scans were performed on all patients as part of the study protocol. The anteversion measured in these scans was compared to that in the cross-table radiographs to assess the latter's reliability for routine use. The risk of radiation exposure from CT scans was minimized by adhering to the ALARA (As Low as Reasonably Achievable) principle, with only axial sections of the acetabular cup being scanned.

RESULTS

 The results show that the radiographic acetabular anteversion and CT scan measurements have a mean difference of 0.3036. There is a positive correlation between these measurements. The p-value is not statistically significant (p=0.698). Therefore, the measurements are correlated with each other with a linear relationship (r=0.919). For anteversion measurements using the X-ray method, the mean was 27.16 degrees with a standard deviation of ±9.49. The median was 27.26 degrees, ranging from 10.27 to 42.58 degrees. In comparison, the CT method yielded a mean anteversion of 27.40 degrees with a standard deviation of ±8.50 degrees. The median was 27.64 degrees, ranging from 12.35 to 43.11 degrees.

CONCLUSION

Cross-table lateral radiographs are a reliable and comparable method to CT scans for measuring acetabular anteversion following total hip arthroplasty.

Vitamin E-blended highly cross-linked polyethylene liners in total hip arthroplasty: a randomized, multicenter trial using virtual CAD-based wear analysis at 5-year follow-up

BACKGROUND

Progressive oxidation of highly cross-linked ultra-high molecular weight (UHMPWE-X) liners is considered to be a risk factor for material failure in THA. Antioxidants such as vitamin E (alpha-tocopherol) (UHMWPE-XE) were supplemented into the latest generation of polyethylene liners. To prevent inhomogenous vitamin E distribution within the polymer, blending was established as an alternative manufacturing process to diffusion. The purpose of the present study was to investigate the in vivo wear behavior of UHMWPE-XE in comparison with conventional UHMWPE-X liners using virtual CAD-based radiographs.

METHODS

Until now, 94 patients from a prospective, randomized, controlled, multicenter study were reviewed at 5-year follow-up. Of these, 51 (54%) received UHMWPE-XE and 43 (46%) UHMWPE-X liners. Anteroposterior pelvic radiographs were made immediately after surgery and at 1 and 5 years postoperatively. The radiographs were analyzed using the observer-independent analysis software RayMatch^® (Raylytic GmbH, Leipzig, Germany).

RESULTS

The mean wear rate was measured to be 23.6 μm/year (SD 13.7; range 0.7-71.8 μm). There were no significant differences between the two cohorts (UHMWPE-X: 23.2 μm/year vs. UHMWPE-XE: 24.0 μm/year, p = 0.73). Cup anteversion significantly changed within the 1st year after implantation independent from the type of polyethylene liner [UHMWPE-X: 18.2-23.9° (p = 0.0001); UHMWPE-XE: 21.0-25.5° (p = 0.002)]. No further significant changes of cup anteversion in both groups were found between year 1 and 5 after implantation [UHMWPE-X (p = 0.46); UHMWPE-XE (p = 0.56)].

CONCLUSION

The present study demonstrates that the addition of vitamin E does not adversely affect the midterm wear behavior of UHMWPE-X. The antioxidative benefit of vitamin E is expected to become evident in long-term follow-up. Cup anteversion increment by 5° within the 1st year is likely a result of the released hip flexion contracture resulting in an enhanced posterior pelvic tilt. Therefore, a reassessment of target values in acetabular cup placement might be considered.

Radiographic assessment of the cup orientation after total hip arthroplasty: a literature review

Optimal acetabular cup orientation is of substantial importance to good long-term function and low complication rates after total hip arthroplasty (THA). The radiographic anteversion (RA) and inclination (RI) angles of the cup are typically studied due to the practicability, simplicity, and ease of interpretation of their measurements. A great number of methods have been developed to date, most of which have been performed on pelvic or hip anteroposterior radiographs. However, there are primarily two influencing factors for these methods: X-ray offset and pelvic rotation. In addition, there are three types of pelvic rotations about the transverse, longitudinal, and anteroposterior axes of the body. Their effects on the RA and RI angles of the cup are interactively correlated with the position and true orientation of the cup. To date, various fitted or analytical models have been established to disclose the correlations between the X-ray offset and pelvic rotation and the RA and RI angles of the cup. Most of these models do not incorporate all the potential influencing parameters. Advanced methods for performing X-ray offset and pelvic rotation corrections are mainly performed on a single pelvic AP radiograph, two synchronized radiographs, or a two-dimensional/three-dimensional (2D-3D) registration system. Some measurement systems, originally developed for evaluating implant migration or wear, could also be used for correcting the X-ray offset and pelvic rotation simultaneously, but some drawbacks still exist with these systems. Above all, the 2D-3D registration technique might be an alternative and powerful tool for accurately measuring cup orientation. In addition to the current methods used for postoperative assessment, navigation systems and augmented reality are also used for the preoperative planning and intraoperative guidance of cup placement. With the continuing development of artificial intelligence and machine learning, these techniques could be incorporated into robot-assisted orthopaedic surgery in the future.