Lessons Learned from Sensor Technology

    In his presentation at ICJR Australia, Dr. Jimmy Chow said this technology can help surgeons improve their total knee arthroplasty technique – which can lead to better patient satisfaction.

    A recent independent poll queried orthopaedic surgeons about what areas of practice needed to be addressed to improve outcomes of total knee arthroplasty (TKA). Respondents answered ligament balancing techniques, surgeon training, and surgical skills.

    One new surgical tool aimed at helping to improve ligament balancing in TKA is intraoperative sensors. These “smart trials” – a trial polyethylene tibia implant with embedded sensors – can provide the surgeon with ligament balance and implant positioning information in real time during the procedure.

    This is important: Patient satisfaction can play a significant role in care delivery and surgeon compensation. Yet about 20% of patients are still dissatisfied after TKA.

    According to Jimmy Chow, MD, from Hedley Orthopaedic Institute in Phoenix, Arizona, anecdotally, patients who undergo TKA in which intraoperative sensors were used are reporting that they feel better at 3 to 4 weeks after the procedure than patients in whom intraoperative sensors were not used. They have less need for pain medication and an easier time with physical therapy.

    At ICJR Australia, Dr. Chow reviewed his experience using intraoperative sensors in TKA, noting that, “sensor-based navigation is teaching the surgeon things about how to be a better surgeon.”

    A common complaint about computer navigation is that it is guiding implant placement and alignment, but the surgeon is still “inferring” ligament balance based on movement and excursion during ROM. Although intraoperative sensors are still translating pressure into inferred ligament strain/tension, they are measuring pressure across the knee joint as induced by ligament tension.

    Because of this, Dr. Chow believes that sensors provide additional information that allows surgeons to refine what they already know how to do.

    Dr. Chow reviewed the lessons he has learned through the use of intraoperative sensors:

    • Cementing is important. Even 0.5mm of additional cement can change the pressures across the tibial polyethylene by 10 lbs/inch2
    • How the implants are impacted during cementing changes how the knee is balanced. Dr. Chow now bases ligament balancing on the thickness of the cement mantle.
    • Dr. Chow uses a cruciate retaining implant and has found that optimal implant choice changes subtly throughout the procedure. After tibial insertion, the posterior cruciate and medial collateral ligaments are lax, often requiring a 1-mm thicker poly after cementing.
    • Small changes make a big difference in balancing – even a 1-mm thicker poly matters. Thicker polyethylene does not impact ligament tightness equally on both sides – one side will tighten up quicker than the other. This can cause the tibial polyethylene to act as a fulcrum, which can lead to lift-off on one side.

    Using sensors have made Dr. Chow re-evaluate the importance of ligament balance. He is now able to under-release at the beginning of the surgery, and then later in the procedure, he sequentially performs micro-balances or “precision releases” by palpating for tight bands and release those bands with a 16- to 18-gauge needle. This allows him to better calibrate the releases.

    Dr. Chow concluded that, “I’m not as good as I thought I was, but I’m trying to improve, and sensors are helping me do that.”

    Click the image below to watch Dr. Chow’s presentation.