While no objective measure exists to capture TKA instability, motion analysis instruments and radiographic stress tests show most potential: a scoping review.

BACKGROUND

Instability is a major cause of revision total knee arthroplasty (TKA). Diagnosis often relies on patient complaints and manual laxity tests, which poorly correlate with perceived instability. Since revisions without proper diagnosis yield poor outcomes, an objective, quantitative measure able to capture the patient's experience is essential for improved revision TKA outcomes. Therefore, this scoping review aimed to map subjective and objective measures, and patient and TKA factors described in published research that may help distinguish stable from unstable TKAs.

MATERIALS AND

METHODS

A search was conducted in PubMed, Embase, Web of Science, and Cochrane Reviews and Trials using terms related to TKA, instability and diagnosis. After duplicate removal, papers were screened on title and abstract using the AI tool ASReview Lab, followed by full-text screening. Data were extracted on quantitative instruments and corresponding parameters, measurement conditions, and patient-reported outcome measures (PROMs). All outcomes were assessed for ability to distinguish stable from unstable TKAs.

RESULTS

Of 6030 records, 29 studies were included showing substantial variety in investigated measures. Objective laxity assessment through applied knee or lower-leg loads could distinguish unstable from stable TKAs, particularly when assessed with stress radiographs. However, no consensus existed on laxity thresholds. Motion analysis systems, including wearable sensors and motion capture, successfully differentiated unstable from stable TKAs, especially via anteroposterior acceleration in dynamic, weight-bearing conditions. PROMs addressing weight-bearing activities also distinguished instability.

CONCLUSION

No golden standard was found distinguishing stable from unstable TKAs. Nevertheless, stress radiographs and motion analysis during dynamic activities hold discriminative potential.