New Technology Brings Intelligence, Accuracy to TKA Instrumentation

    3 orthopaedic surgeons discuss their experience with developing, testing, and using the iASSIST Knee technology in TKAs

    In December 2012, Zimmer received clearance from the U.S. Food and Drug Administration (FDA) to market its iASSIST Knee technology, which Giles R. Scuderi, MD, one of the principles involves in its development, describes as “an accurate and efficient guidance/navigation system for total knee arthroplasty.”

    Dr. Scuderi worked with an international team of orthopaedic surgeons and the Zimmer CAS group of engineers to develop iASSIST, which has been available in Canada and internationally for several years. Dr. Scuderi is Attending Orthopedic Surgeon at Lenox Hill Hospital and Franklin Medical Center, Assistant Clinical Professor of Orthopedic Surgery at Albert Einstein College of Medicine, and one of the Directors of the Insall Scott Kelly Institute for Orthopedics and Sports Medicine in New York, New York.

    How does iASSIST technology work? According to Dr. Scuderi, it “provides intelligence and accuracy to TKA instrumentation with pods that incorporate radiofrequency Bluetooth-like technology, gyroscopes, accelerometers, and temperature sensors – all within a small battery operated pod that communicates with the other pods through its own internal network.”

    The disposable pod components used at the surgical site provide immediate alignment validation through a simple electronic display.  The pods are manipulated within the surgical field with positioning information provided by a series of internal accelerometers. iASSIST does not require the use of pins or additional incisions and does not rely on external systems or stimulus.

    Benefits for Surgeons and Patients

    David Camarata, MD, a board-certified orthopaedic surgeon at OrthoArizona, Arizona Bone & Joint Specialists, Phoenix, Arizona, is an enthusiastic early adopter of iASSIST, calling it a “remarkable feat of mechanical and computer engineering.” He originally tested the device on a number of cadavers last spring and adopted it in the operating room as soon as it received FDA approval.

    “The benefit for using iASSIST for surgeons is that it ensures 100% accurate bony cuts every time,” said Dr. Camarata. “And we verify these cuts and know that we are correct before moving on.”

    He said iASSIST is easy to use, with no-start up costs for the hospital. The surgeon can be confident that there will be no outliers or bony cuts that are out of alignment. “I have never used traditional navigation,” said Dr. Camarata, “yet I was able to adopt this technology immediately to my surgeries with no down time.”

    The benefits to patients, Dr. Camarata, says, is clear. “Patients benefit from having accurate mechanical alignment, which we believe can lead to better early outcomes and a longer-lasting prosthesis.”

    Paul Gilbert, MD, a board-certified orthopaedic surgeon who practices at Huntington Memorial Hospital in Pasadena, California, agrees.

    He, too, got involved with the early cadaver labs where prototypes were tested and orthopaedic surgeons gave feedback on their effectiveness and usability. He said iASSIST is easy to use and gives “immediate, accurate feedback on component position. Accurate placement of the prosthesis contributes to better outcomes for patients. iASSIST facilitates accurate positioning in virtually every case.”

    Dr. Gilbert has long used computer navigation in his TKA cases because it increases accuracy and eliminates outliers. He acknowledges that most surgeons have been reluctant to work through the steep learning curve and accept what he calls “the hassle factor” involved with previously available computer navigation systems for TKA. “There is time involved to apply the device, a stereo camera that needs to ‘see’ the field which is a problem for some assistants, and there is also a capital outlay” with computer navigation systems, Dr. Gilbert said.

    iASSIST is different. “iASSIST provides similar information during the case, without the hassle,” he said. “In fact, the instruments are designed to mimic current instrumentation. The hope is that it will see wide acceptance by surgeons and thus improve outcomes for all.”

    Dr. Camarata added that “iASSIST specifically eliminates the need to instrument the medullary canals of the tibia and, in particular, the femur. This theoretically can decrease the risk of postoperative bleeding, deep venous thrombosis, pulmonary embolus, and postoperative confusion by eliminating embolization of marrow contents. In addition, it is far more accurate than conventional instrumentation in terms of restoring mechanical alignment of the limb through bony cuts.

    iASSIST allows us to verify all of our osteotomies after we make them, ensuring precise mechanical alignment.”

    Improving Alignment, with Reproducible, Accurate Results

    What Drs. Camarata and Gilbert have experienced is exactly what the developers had intended for iASSIST. The impetus for designing this system, Dr Scuderi said, “centers around the need to improve alignment in TKA and be able to have reproducible and accurate results.”

    He noted that “computer navigation has moved us in that direction, but has the burden of preoperative imaging, registration of multiple anatomic landmarks, and line-of-sight optical trackers, not to mention the capital investment for the equipment.

    “The advantage of iASSIST is that the system is an accurate guidance system that can be performed without the application of multiple optical trackers,” Dr. Scuderi said, “which eliminates the need for the placement of multiple additional pins in the femur and tibia (which have been shown to create stress risers and increase the risk of fracture), as well as eliminates the issue of line-of-sight with the optical trackers.”

    Dr. Scuderi said iASSIST should satisfy all surgeons. “For the conventional instrument user, iASSIST adds intelligence and accuracy to the instruments,” he said. “For the navigation user, it adds simplicity to the procedure with comparable accuracy.”

    He shared some of the internal accuracy and validation data gathered during the development process, comparing iASSIST with an optical navigation system.

    iASSIST Comparison with Optical Navigation System


    No. knees

    Coronal difference with optical navigation

    Sagittal Difference with Optical Navigation

    Validation Difference with Optical Navigation



    0.35˚ + 1.4˚

    0.18˚ + 1.1˚

    0.4˚ + 1.3˚



    0.08 + 1.0˚

    0.31˚ + 1.2˚

    0.5˚ + 1.2˚


    Comparison of iASSIST vs. Optical Navigation Relative to Radiographic Measurement of the Mechanical Axis


    Femur (n+5)

    Tibia (n=7)

    iASSIST vs Fluoro

    0.52˚+ 0.77˚

    0.23˚+ 1.26˚

    Optical vs Fluoro

    1.26˚ + 0.92˚

    0.01˚ + 1.52˚


    So far, Dr. Camarata has done approximately 50 knee replacements using the iASSIST, and although it is very early in the follow-up period, his patients have done uniformly well. All of my postop X-rays have been in neutral mechanical alignment, with zero outliers,” he said. “I am seeing patients with results at 6 weeks that previously took 6 months to attain.”

    Minimal Learning Curve

    The learning curve for orthopaedic surgeons who want to adopt iASSIST is minimal, Dr. Scuderi said, because “the use of iASSISt does not change the flow of the procedure and adds intelligence to instruments that are very familiar to surgeons who use conventional instruments. For those surgeons who are familiar with computer navigation, they have found the setup to be simple and more rapid than the more elaborate setup of optical navigation system.”

    Dr. Scuderi has run a number of training sessions for orthopaedic surgeons, and “I have found surgeons to be very excited about iASSIST and quickly adapt to the surgical technique. They were also amazed at the accuracy and reproducibility of the technology.”

    Dr. Camarata and Dr. Gilbert agree with this assessment.

    “The look and feel are the same for most surgeons,” said Dr. Camarata. “It is not a great leap of faith to use iASSIST, and it is simple to convert to conventional arthroplasty if there is any uncertainty during the procedure.”

    Initially, using iASSIST added 3 to 5 minutes to his knee procedures. “Now,” Dr. Camarata said, “it’s down to our normal time.”

    Dr. Gilbert noted that “every new instrument has a ‘feel’ that different surgeons acquire at different rates. Still, iASSIST is easy to learn and the curve is short. This is one of its strongest advantages.”