ArticleArthroplasty today2025
Defining "Paradoxical Instability" and Other Indications for Aseptic Single-Component Polyethylene Revision: A Cohort Study Including Mid-flexion Instability and Limited Arc of Motion.
Article in Arthroplasty today, 2025. The graph could read no effect estimate from its abstract, so it casts no vote on the map. Not yet cited in PubMed.
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Abstract
Background: Single-component polyethylene revision (SCPR) is a less invasive approach for addressing polyethylene wear in total knee arthroplasty by replacing only the tibial polyethylene component. While traditionally used for aseptic ligamentous mid-flexion instability and limited arc of motion, this study introduces paradoxical instability as a third indication, characterized by ligamentous laxity with knee effusion causing mid-flexion instability and secondary flexion contracture. Methods: A retrospective study analyzed 58 consecutive SCPR patients treated by a single fellowship-trained surgeon between 2012 and 2024, with a minimum 2-year follow-up. The cohort included 20 men (34%) and 38 women (66%), with a mean age of 70.2 years and average follow-up of 2.83 years. Patients were categorized into 3 groups: mid-flexion instability (n = 43), limited arc of motion (n = 9), and paradoxical instability (n = 6). Outcomes were assessed using clinical examinations and Knee Society Score 2011 and UCLA activity scores. Results: Clinical success rates defined as good to excellent clinical outcomes were 88.3% (38 of 43) for mid-flexion instability, 88.8% (8 of 9) for limited arc of motion, and 100% (6 of 6) for paradoxical instability patients. No readmissions or reoperations occurred within 90 days postsurgery. The mean hospital stay was 0.87 days. Conclusions: SCPR demonstrated effectiveness in treating all 3 indications, with particularly promising results for paradoxical instability cases. This study establishes paradoxical instability as a distinct clinical entity characterized by knee imbalance, mid-flexion instability, recurrent effusions, and limited motion arc. This limited motion arc is paradoxically treated with an increase of polyethylene thickness. The findings support SCPR as a viable treatment option for carefully selected patients with these conditions.
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