Technology and the Anterior Approach: Pros and Cons

    Total hip arthroplasty (THA) is one of the most successful orthopaedic procedures, reliably producing good patient outcomes such as improved mobility and pain relief.

    Failures do occur, however. Orthopaedic surgeons have turned to technology in an effort to decrease failures caused by improper implant positioning. This technology includes:

    • Imaging systems
    • Computer navigation systems
    • Robotics

    Whether technology has a role in improving implant placement in direct anterior approach THA remains controversial, as was evident in a series of lectures at ICJR’s annual Anterior Hip Course in Houston, Texas.

    Anthony Unger, MD, of George Washington University argued that technology does not improve outcomes with the anterior approach and thus does not add any value to the procedure. Technology, he said, is of questionable help in alleviating the major complications of THA – infection, loosening, instability, and length-length discrepancy.

    Dr. Unger mentioned a study that reported no difference in outcomes between freehand placement of acetabular cups and computer-assisted placement. He said that most studies that show an improvement with technology-aided guidance were for THAs using the posterior rather than the anterior approach.

    This lack of improvement for THA using the anterior approach could be due to the fact that joint stability is a dynamic entity that cannot be adequately assessed by static measurements obtained with available technology systems. Dr. Unger contended that preoperative templating and intraoperative assessment of dynamic stability are still the best ways to evaluate THA.

    Three other speakers had more favorable views about the role of technology in anterior approach THA:

    • Joel Matta, MD, of Saint John’s Health Center in Santa Monica, California, discussed the use of x-ray navigation
    • Douglas Padgett, MD, of the Hospital for Special Surgery in New York City, shared his insights on robotic-aided implant placement
    • Adam Freedhand, MD, of the University of Texas Health Science Center in Houston, discussed the use of computer navigation

    Dr. Matta described how x-ray navigation can help maximize the accuracy of the cup position, leg length, and offset in a direct anterior approach THA. If the orthopaedic surgeon gets those right, the hip will be stable, he said.

    Some surgeons have shied away from the anterior approach because they believe it must be done with x-rays. That is a misperception, Dr. Matta said. X-rays are not required during the procedure, but with the patient in the supine position on a radiolucent table, it is very easy to take intraoperative x-rays to check inclination and anteversion, he said.

    One of the greatest benefits he has found from intraoperative x-rays is confirmation of leg length, which he said is more difficult to accomplish than cup position. When the leg length and offset are right, the patients biomechanics are restored – key in proper functioning.

    Dr. Matta briefly discussed computer guidance, which he believes is not as accurate as x-ray because it produces a virtual picture of the hip, not the actual picture of the joint provided by x-ray. He said computer guidance offers consistency in cup inclination, but anteversion can be variable. In addition, the computer as satisfactory for leg length in standard cases, but is less accurate in more difficult cases.

    Dr. Padgett presented the key features of robotics-assisted THA. He noted that instability is the most frequent cause of THA failure, and that surgeon factors – including component positioning – play a role in instability.

    In 2005, he and his colleagues published a study in which they used positioners and guides to place the cup in THA, and although they achieved a mean of the desired 40° of abduction, the range was 22° to 57°. A study from Massachusetts General Hospital in 2011 had similar results: Only 50% of cups in that study were within range for version and abduction.

    Robotic-assisted surgery is intended to correct issues with positioning of the cup in the pelvis. It is both a visual and a tactile technology (computer-assisted navigation is purely visual). And it can be active – the robot “drives” the procedure – or semi-passive (haptic) – the surgeon is still in control.

    The robot can be used to guide reaming and impaction and provide real-time assessments of both processes, with an error smaller than that obtained with manual methods. Dr. Padgett said the perceived advantages of robotics are:

    • Improved accuracy of bone preparation, as well as precision of delivery
    • Possible improved ability to restore leg length and offset through 3D planning and execution

    Early results from a multicenter study in which Dr. Padgett is participating have been encouraging. Despite that, Dr. Padgett recognized that higher costs and longer surgery time, as well as institutional reluctance to invest in both, are drawbacks. Further studies are needed to fully understand the impact of robotics on outcomes in THA.

    Dr. Freedhand discussed computer-assisted navigation, which may be either image-based or imageless. A number of these systems are available and have been validated as fairly accurate, he said.

    He shared data from a meta-analysis by Dr. Joseph Moskal that compared studies of freehand and computer-assisted acetabular cup placement. About 1,500 THAs were included in the study. Dr. Moskal found that 80% of cups were placed in the “safe zone” with computer navigation versus 63% of cups placed freehand. In addition, the dislocation rate was only 1% in the computer-navigated THAs, compared with 2.49% in the freehand group.

    Dr. Freedhand said that although the concept of the safe zone is not perfect, it provides a target for cup positioning that can possibly minimize complications related to THA. He suggested that orthopaedic researchers need to define a similar safe zone for the femur.

    He concluded that computer-navigated systems work, have been validated for accuracy, and have been shown in some studies to improve patient outcomes. Improvements need to be made, however, in understanding of kinematics. Dr. Freedhand speculated that as computer-navigated systems, robotics, and implants improve, orthpaedic surgeons will be able to reliably and reproducibly restore kinematics to normal gait patterns.

    Click on the links below to watch the presentations.

    No Modern Technology Needed, Anthony Unger, MD

    The Art of Using Imaging, Joel Matta, MD

    The Art of Using Robotics, Douglas Padgett, MD

    The Art of Using Computer Assistive Surgery, Adam Freedhand, MD