Abstract
Fifteen-year survivorships studies demonstrate that total knee replacements have excellent survivorship, with reports of 85 to 97%. However, excellent survivorship does not equate to excellent patient reported outcomes. Total knee imbalance with either too tight or loose soft tissues account for up to 54% of revisions in one series. This may account for many of the 20% unsatisfactory total knee arthroplasty outcomes.
Soft tissue balancing technique is more like an art. The surgeon relies on subjective feel for appropriate ligamentous tension. Surgical experience and case volume play a major role in each surgeon's relative skill in balancing the knee properly.
New technology of “smart trials” with embedded microelectronics and accelerometers, used in the knee with the medial retinaculum closed, can provide dynamic, intraoperative feedback regarding knee quantitative compartment pressures and component tracking. After all bone cuts are made using the surgeon's preferred techniques, trial components with the sensor tibial trial are inserted and the knee is taken through a passive range of motion. After visualizing the resultant compartment pressures and tracking data on a graphical interface, imbalance situations such as a too tight MCL or ITB, an incompetent or too tight PCL, or malrotated femoral or tibial component can be identified. A decision can be made as to whether to recut the bone to realign components, do a soft tissue release, or a combination of both. Soft tissue releases can be titrated while observing equalizing compartment pressures.
Sensor feedback improves soft tissue balancing. More balanced compartments occur using a sensor trial than with standard soft tissue balancing technique blinded to sensor information. A multicenter three year study has shown that having the medial and lateral compartments in flexion and extension balanced within 15 pounds provides better outcomes. Patients with quantitatively balanced TKA with <15lbf mediolateral load differential have better forgotten knee scores at six weeks and six months. Use of smart trials is a new approach to total knee replacement surgery allowing fine tune balancing and takes soft tissue balancing from art to science.
