Revision Total Knee Arthroplasty for Mid-Flexion or Combined Mid-Flexion and Flexion Instability: Survivorship and Outcomes.

Background: As patients place higher demand on their implants, mid-flexion instability is increasingly recognized as a contributor to dissatisfaction after total knee arthroplasty. However, the outcomes of revision surgery to address mid-flexion instability have not been categorized.

Methods: The study cohort was composed of 52 patients who underwent revision surgery for mid-flexion or combined flexion and mid-flexion instability by a single surgeon between 2015 and 2022. The mean follow-up duration was 2.76 years. Patient characteristics, implants used, and complications were recorded. Range of motion and patient reported outcomes (collected using the Knee injury and Osteoarthritis Outcome Score for Joint Replacement (KOOS Jr.) and EQ-5D-5L questionnaires) were compared before surgery and at final follow up.

Results: Five patients (9.6%) required an additional operation. Causes of reoperations included component loosening, persistent wound drainage, recurrent instability, and arthrofibrosis. KOOS Jr. scores improved from 46 preoperatively to 60 postoperatively (p<0.01). EQ-5D-5L scores demonstrated a reduction in pain/discomfort and an improvement in ability to perform usual activities (p<0.05). A trend was observed toward increased mobility (p=0.05). The most common 30-day complications were transfusion (11.5%), readmission (11.5%), renal complications including acute kidney injury (9.6%), and wound complications (5.8%). Patients had improvements in maximum flexion and total arc of motion postoperatively (p<0.05).

Conclusion: This study includes the largest cohort of patients undergoing revision for mid-flexion instability and demonstrates that appropriately selected patients can have improved outcomes while maintaining their range of motion.