Roentgen stereophotogrammetry allows one to localize the position of an object in space using roentgen rays. For orthopaedic purposes it was developed 35 years ago by Göran Selvik, and since that time many investigators have refined the radiostereometric calculations and evaluative software. Many uses and mathematical algorithms have been developed, and advancements in computer programs and digital radiography continue to expand its capabilities. Despite these advances, improvements in the technical accuracy and type of kinematic analyses possible have been relatively modest. However, radiostereometric analysis is now easier and less time consuming to use, with a resolution in clinical practice almost equal to what could only previously be obtained under ideal laboratory conditions. The ability to measure skeletal and implant movements with high resolution in vivo images was an important progressive step for the orthopaedic community. Radiostereometric analysis has helped develop new fields in clinical orthopaedic research and continues to improve advancements in orthopaedic health care.

Background: The dual-mobility acetabular cup (DMC) has an additional bearing consisting of a mobile polyethylene component between the prosthetic head and the outer metal shell. This design has gained popularity in revision total hip arthroplasty (THA) and in primary treatment of femoral neck fractures with the anticipation of a reduced risk of THA instability. Our primary aim was to evaluate the overall revision risk of these cups on the basis of data from the Nordic Arthroplasty Register Association (NARA) database, and our secondary aim was to study specific revision causes including dislocation. Methods: Propensity score matching for age, sex, fixation of the cup and stem, and the year of surgery (2001 to 2014) was used to match 4,520 hip fractures treated with a DMC to 4,520 hip fractures treated with conventional THA (control group). Competing risk regression analyses with revision or death as the end point were used. Revision was defined as a secondary surgical procedure in which any component of the implant was removed or exchanged. In addition, revision of the cup was analyzed. Results: The DMCs had a lower risk of revision compared with conventional THA, with an adjusted hazard ratio (AHR) of 0.75 (95% confidence interval [CI] = 0.62 to 0.92). This was consistent after adjusting for surgical approach. DMCs had a lower risk of revision due to dislocation (AHR = 0.45 [95% CI = 0.30 to 0.68]) but we found no difference regarding revision for deep infection. Revision of the acetabular component, both in general and due to dislocation, was more frequent with the use of conventional cups. The risk of death was higher in the DMC group (AHR = 1.49 [95% CI = 1.40 to 1.59]). Conclusions: The use of a DMC as primary treatment for hip fracture was associated with a lower risk of revision in general and due to dislocation in particular. The total number of DMCs analyzed (4,520) likely exceeds any cohort of DMC-treated fractures published to date. Level of Evidence: Therapeutic Level III. See Instructions for Authors for a complete description of levels of evidence.

The effects of surgical approach in total hip replacement on health-related quality of life and long-term pain and satisfaction are unknown. From the Swedish Hip Arthroplasty Register, we extracted data on all patients that had received a total hip replacement for osteoarthritis through either the posterior or the direct lateral approach, with complete pre- and one-year post-operative Patient Reported Outcome Measures (PROMs). A total of 42 233 patients met the inclusion criteria and of these 4962 also had complete six-year PROM data. The posterior approach resulted in an increased mean satisfaction score of 15 (sd 19) vs 18 (sd 22) (p < 0.001) compared with the direct lateral approach. The mean pain score was 13 (sd 17) vs 15 (sd 19) (p < 0.001) and the proportion of patients with no or minimal pain was 78% vs 74% (p < 0.001) favouring the posterior approach. The patients in the posterior approach group reported a superior mean EQ-5D index of 0.79 (sd 0.23) vs 0.77 (sd 0.24) (p < 0.001) and mean EQ score of 76 (sd 20) vs 75 (sd 20) (p < 0.001). All observed differences between the groups persisted after six years follow-up. Although PROMs after THR in general are very good regardless of surgical approach, the results indicate that some patients operated by the direct lateral approach report an inferior outcome compared with the posterior approach. The large number of procedures and the seemingly sustained differences make it likely these findings are clinically relevant.

Opening remarks: These guidelines are the result of discussions within a diverse group of RSA researchers. They were approved in December 2023 by the board and selected members of the International Radiostereometry Society to update the guidelines by Valstar et al. [1]. By adhering to these guidelines, RSA studies will become more transparent and consistent in execution, presentation, reporting, and interpretation. Both authors and reviewers of scientific papers using RSA may use these guidelines, summarized in the Checklist, as a reference. Deviations from these guidelines should have the underlying rationale stated.