Jonathan Hugo Jürgens-Lahnstein, Johanne Frost Teilmann, Emil Toft Petersen, Søren Rytter, Maiken Stilling, Elise Laende
Inducible displacement may indicate functional stability. The existing literature provides no threshold to identify at-risk implants and reporting was too heterogeneous to support a cut-off value. SLWB was the most common protocol. Prospective studies with standardized protocols and clinical endpoints are necessary.
BACKGROUND AND PURPOSE: Radiostereometric analysis (RSA) is the gold standard for assessing implant migration, with 1-year migration thresholds predicting later revision. While inducible displacement under immediate load may enable single-session functional stability assessment, no established threshold exists. We systematically reviewed RSA-measured inducible displacement after primary knee arthroplasty to determine whether a threshold identifying at-risk implants can be derived from the existing literature, and to characterize responses to loading, differences between fixation methods, temporal patterns, and the relationship to migration.
METHODS: We searched PubMed, Web of Science, Scopus, and Embase (April 2025) for studies reporting in vivo RSA-measured inducible displacement after primary knee arthroplasty, requiring quantitative data with specified reference and load conditions. Studies were evaluated for links between inducible displacement and supine, non-weightbearing migration. We assessed bias risk using RoB 2 and ROBINS-E. Due to high heterogeneity, a descriptive synthesis was performed; meta-analysis and regression were not feasible (PROSPERO CRD420251043748).
RESULTS: 23 studies were included. The most common outcome was maximum total point motion (MTPM) during supine-to-single-leg weightbearing (SLWB). Cemented tibial components tended to show greater displacement than cementless designs. Rotatory stress tests produced the largest absolute displacements; differences within the same study from SLWB were minimal. Predictive evidence remained limited.
CONCLUSION: Inducible displacement may indicate functional stability. The existing literature provides no threshold to identify at-risk implants and reporting was too heterogeneous to support a cut-off value. SLWB was the most common protocol. Prospective studies with standardized protocols and clinical endpoints are necessary.