Accuracy of Manual Surgeon-Defined Assessment of Soft Tissue Balance in TKA In Comparison to Sensor-Guided Measures and its Effect on Final Balance

OBJECTIVES: Present literature supports the importance of final alignment and soft tissue balance in total knee arthroplasty (TKA) on implant survivorship and clinical outcomes. Current soft tissue balance techniques mostly depend on subjective static measures that don’t allow for quantitative determination of ligament tension. Sensor guided technique (Verasense, Orthosensor) allows demonstration of the magnitude and location of load in a dynamic way providing quantitative data about knee balance. The aim of this study is to test the accuracy of the surgeon’s manual assessment in judging knee balance in comparison to Verasense. We also aimed to determine whether Verasense can assist in achieving soft tissue balance from the unbalanced state. METHODS: 58 patients were enrolled in this prospective cohort study. The level of agreement between SDA and Verasense at 10, 45, 90 degrees was recorded. Initial trial pressures and final pressures after release or re-cut were recorded and compared. Final pressure measurements were then documented to assess whether appropriate knee balance (differential compartmental pressure of 15 lb/inch on 2 or more angular positions) had been achieved. RESULTS: The mean age of the cohort was 67.5 years with deformities ranging from -16 degrees of varus to +20 degrees of valgus (mean -1.26 degrees varus). The capacity for the surgeon to manually identify an unbalanced knee was low with a test sensitivity of 33.3%. Manual test specificity to define a balanced knee was better with a specificity of 77.3%. The manual test had a positive predicitive value of 59.2% and a negative predictive value of 54%. There were 46.5% (27 of 58) of cases where the Verasense lead to a different surgical plan to that initially determined by the manual assessment. In 23 cases, either ligament release or tibial bone recut was performed. In the remaining 4 cases, the Verasense prevented a ligament release being performed. 95% of cases achieved a balanced state within 15lb/inch of pressure between compartments, with 100% balanced within 25 lb/inch. CONCLUSION: Manual surgeon assessment of soft tissue balance is a poor predictor of unbalanced knees. Verasense has the capacity to subsequently balance the knee within an acceptable pressure range as defined by prior studies. Further analysis to determine the impact on patient outcomes and implant survivorship is warranted.