Can Intraoperative Sensors Determine the "Target" Ligament Balance? Early Outcomes in Total Knee Arthroplasty.

BACKGROUND: The optimal "target" ligament balance for each patient undergoing total knee arthroplasty (TKA) remains unknown. The study purpose was to determine if patient outcomes are affected by intraoperative ligament balance measured with force-sensing implant trials and if an optimal "target" balance exists. METHODS: A multicenter, retrospective study reviewed consecutive TKAs performed by 3 surgeons. TKA's were performed with standard surgical techniques and ligament releases. After final implants were made, sensor-embedded smart tibial trials were inserted, and compartment forces recorded throughout the range of motion. Clinical outcome measures were obtained preoperatively and at 4 months. Statistical analysis correlated ligament balance with clinical outcomes. RESULTS: One hundred eighty-nine consecutive TKAs were analyzed. Patients were grouped by average medial and lateral compartment force differences. Twenty-nine TKAs (15%) were balanced within 15 lbs and 53 (28%) were "balanced" greater than 75 lbs. Greater improvement in University of California Los Angeles activity level was associated with a mediolateral force difference <60 lbs. (P = .006). Knee Society objective, function, and satisfaction scores, and self-reported health state were unrelated to mediolateral balance in the knee. CONCLUSION: Intraoperative force-sensing has potential in providing real-time objective data to optimize TKA outcomes. These data support some early outcomes may improve by balancing TKAs within 60 lbs difference. Close follow-up is warranted to determine if gait pattern adaptations affect longer term outcomes with greater or less ligament "imbalance."

Functional Improvement and Expectations Are Diminished in Total Knee Arthroplasty Patients Revised for Flexion Instability Compared to Aseptic Loosening and Infection.

BACKGROUND: Instability has emerged as the most common noninfectious cause necessitating early revision after total knee arthroplasty (TKA). Although studies have documented improvement in outcomes with revision for flexion instability, it remains unknown how the outcomes compare to patients revised for other failure etiologies. The study purpose was to compare outcomes after revision TKA based on failure etiology. METHODS: A retrospective review of our prospectively collected revision TKA database was performed on patients who underwent revision TKA from October 1, 2010 to November 19, 2014. Demographic data; minimum 1-year Knee Society Scores; and University of California, Los Angeles activity level scores were obtained. RESULTS: One hundred seventy-seven consecutive revision TKAs were evaluated. After exclusion of revisions with confounding variables and diagnosis groups with small numbers, 92 patients with a revision diagnosis of flexion instability, infection, or loosening/osteolysis were compared. There were no group differences in Knee Society objective (P ≥ .460) and satisfaction (P ≥ .112) scores or UCLA activity level scores at final follow-up (P ≥ .118). Preoperative Knee Society function scores were significantly higher in patients with flexion instability (P = .019), but the amount of improvement in function relative to baseline was equivalent in the 3 groups (P = .170). Patients revised for flexion instability were significantly more likely than patients in the other 2 groups to report that their expectations were not met (P = .028). CONCLUSION: Patients and surgeons can expect that revision for isolated flexion instability may only obtain modest improvement compared with other diagnoses, potentially in part due to a higher preoperative functional level in patients with instability.