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    Intraoperative Sensors for Dynamic Feedback during Soft Tissue Balancing

    Dr. Martin Roche describes a technology that can wirelessly transmit intraoperative data during a total knee arthroplasty, giving the surgeon real-time quantifiable data regarding alignment, rotation, and soft tissue balance.

    Total knee arthroplasty (TKA) is currently the second most-common orthopedic surgery procedure performed in the United States, exceeding 700,000 procedures annually and helping people of all ages live pain-free, active lives.

    However, not all TKAs are successful. The reasons for failures of implanted knees have changed over the past 15 years, with many failures today related to surgeon-dependent factors.

    Martin W. Roche, MD, Chief of Orthopedics and Director of the Holy Cross Orthopedic Institute, Fort Lauderdale, Florida, specializes in reconstructive knee surgery. According to Dr. Roche, “When we look at early failures leading to revisions in the past 2 years, infection is still the primary reason. But instability/stiffness, malrotation, and malalignment account for up to 35% of knee revisions. “

    “Even with all the technical advances in implant design,” he explained, “the revision burden remains unchanged at 8.2%, and these data reflect the importance of surgical techniques on patient outcomes.”

    The Challenge of Soft Tissue Balance

    Most surgeons who regularly perform TKAs say that soft tissue balancing is half the procedure. Nearly a decade ago, Dr. Roche stressed that the key to a well-functioning knee is a balanced knee, and that component placement and soft tissue balancing are critical to patient satisfaction and implant longevity.

    That said, soft tissue balancing during TKA is a challenge; it is a subjective art that is hard to master. “To date,” Dr. Roche said, “we still rely on our subjective feel and experience to define this important variable. Although we use measurement tools, intraoperatively, to define alignment, we lack quantifiable data regarding an individual’s knee balance and kinetic signature.”

    In response to this challenge, a growing number of surgeons have turned to computer-assisted navigation technology. Dr. Roche was a key part of the design team for a multifunctional, micro-electronic sensor system, the OrthoSensor VERASENSE Knee System (Knee Balancer). This system can wirelessly transmit intraoperative data, giving the surgeon real-time quantifiable data regarding alignment, rotation, and soft tissue balance.

    “We can only assess and improve on techniques with data we can measure; we can’t change what we can’t measure.” Dr. Roche said. “By defining the loads and knee position, the surgeon can identify the appropriate ligament complex to address and receive dynamic feedback while the soft tissue envelope is optimally tensioned through soft tissue releases.”

    Effects of Poor Soft Tissue Balance

    Soft tissue balance in the sagittal and coronal planes affects short- and long-term outcomes. “In the short term,” Dr. Roche explained, “the effects of over-tensioned ligaments lead to pain, stiffness, and limited range of motion. “

    “Long-term effects include accelerated polyethylene wear, osteolysis, and premature aseptic loosening,” he said.

    For patients, instability leads to pain, effusions, and problems navigating stairs, ramps, and inclines. “Instability can be seen both with cruciate-retaining and posterior-stabilized designs,” Dr. Roche said.

    A study on the importance of soft tissue balance related to patient outcomes was recently published in The Journal of Arthroplasty. [1] According to Dr. Roche, “Knee scores at 6 months specifically show improvements in knee function.” Long-term studies are underway.

    Refining the Intraoperative Algorithm

    The use of intraoperative sensors has impacted Dr Roche’s intraoperative algorithm. “In the past year, I have learned more intraoperatively regarding the effects of implant rotation, limb alignment, and soft tissue balance than I have in 15 years of practice,” he said.

    The effects of knee implant design are also an important element to soft tissue stability. The integrated sensor system allows surgeons to specifically address all ligament complexes through a full range of motion and identify the pathologic elements. Dr. Roche has been able to refine his algorithm using the alignment, rotation, and soft tissue tension data capabilities of the system.

    “I approach the knee with my standard bony cuts and initial releases based on the deformity. I then implant the trials with the corresponding sensorized tibial insert,” he explained. His approach is as follows:

    Set implant rotation and achieve implant-to-implant congruency using the femoral contact tracking on the tibial trial. Central patellar tracking is then assessed.

    Evaluate alignment of the bony cuts. This confirms that the overall mechanical axis has been restored and allows the surgeon to evaluate the effects of a malalinged tibia or femur on the soft tissue tension.

    When refinements of the bony cuts are made, the immediate effects on the soft tissue envelope are seen.

    Evaluate the dynamic soft tissue tension throughout full motion, which allows Dr. Roche to identify symmetrical or asymmetrical imbalance (instability/over-tensioning). The inter-compartmental pressure differential and contact points display the tension and femoral rollback with the capsule closed.

    The Interest in Navigation during TKA

    The need to improve soft-tissue balancing during TKA has long been recognized, driving new interest in navigation. The OrthoSensor™ VERASENSE™ Knee System is intended to address the leading causes of early implant failure in TKA: instability, malrotation, and malalignment.

    The advanced sensor and real-time data communications technologies empower surgeons to make evidence-based decisions regarding component placement, limb alignment, and soft tissue balance to achieve balance and stability through a full range of motion, with the goal of optimizing clinical outcomes and enhancing patient satisfaction.

    “Further outcome studies,” Dr. Roche concluded,” will be needed to show the effects of alignment and soft tissue tension on outcomes, function, and implant survival.”

    Reference

    1. Gustke KA, Golladay GJ, Roche MW, Elson LC, Anderson CR. A New Method for Defining Balance: Promising Short-Term Clinical Outcomes of Sensor-Guided TKA. J Arthroplasty. 2013 November 25 [Epub ahead of print].