State of the Art in Radiostereometric Analysis for Tibial Baseplate Migration and Future Research Directions.

Radiostereometric analysis (RSA) measures movement (migration) of a baseplate relative to the underlying tibia after total knee arthroplasty (TKA) and has been used extensively to evaluate safety of new implant designs and/or surgical techniques regarding baseplate loosening. Because RSA is a complex methodology which involves various choices that researchers make, including whether to use marker-based or model-based methods, which migration metric to report, how to relate short-term migrations to long-term risk, and how these choices impact error, the objectives of this review were to: (1) lay out a comprehensive structure illustrating the multiple components/considerations for RSA and their interrelations, (2) review components of the structure using the latest RSA literature, and (3) use the preceding review as a context for identifying future areas of study. The components to be reviewed were structured using the following topics: type of RSA, migration metrics, sources of error, studies/reports of error, stability limits, and studies of error in stability limits. Based on the current RSA literature and knowledge gaps which exist, the following future research directions were identified: (1) revising the ISO standard to require reporting of clinical measurement error (bias) and recommending use of a local baseplate coordinate system, (2) identifying the migration metric and associated threshold most predictive of baseplate loosening for individual patients, (3) creating a method for data sharing to improve individual patient diagnostics, and (4) determining an appropriate stability limit for model-based RSA for group stability and individual patient diagnostics.