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

As patients place higher demand on their implants, mid-flexion instability is increasingly recognized as a contributor to dissatisfaction after total knee arthroplasty (TKA). However, the outcomes of revision surgery to address mid-flexion instability have not been categorized. 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 EuroQol-5 Dimensions-5 Levels [EQ-5D-5L] questionnaires) were compared before surgery and at final follow-up. 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 (<i>p</i> < 0.01). EQ-5D-5L scores demonstrated a reduction in pain/discomfort and an improvement in the ability to perform usual activities (<i>p</i> < 0.05). A trend was observed toward increased mobility (<i>p</i> = 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 (<i>p</i> < 0.05). 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.