Total Knee Replacement
Total knee replacement is a well proven and accepted procedure for the treatment of advanced knee arthritis. The procedure has evolved favorably since its development in the 1970s and consistently produces excellent long-term (15+ years) results.
Total knee replacement’s success depends on many factors including patient selection, prosthesis design, surgical technique—including proper soft tissue balancing and alignment—and post operative rehabilitation. The procedure’s durability has been enhanced by improvements in the implants, specifically the polyethylene (plastic) insert that sits between the metal components between the femur and the tibia. Efforts to improve total knee replacement’s predictability and longevity focus on the alignment of the components and balancing of the adjacent soft tissue.
The standard knee replacement is performed with the use of an intramedullary guide which is a rod placed in the marrow canal of the femur to allow measurements, bone cutting and placement of the femoral component. An extramedullary guide is used for preparation of the tibial surface. Proper alignment, achieved during this portion of the procedure, is extremely important in regards to durability of the procedure. Minor malpositioning contributes to early failure including loosening, wear and poor function. Although the development of extramedullary and intramedullary guidance systems has improved the accuracy of the procedure, misalignment still occurs. The inability to predictably achieve ideal alignment has spurred the development of computer-assistive or navigation technology.
Orthopaedic navigation technology is similar to directional tracking systems used in cars and ships, a global positioning system for the surgeon. Infrared sensors placed in the operating room act like satellites constantly monitoring the location of markers and instruments placed along a patient’s anatomy. As the surgeon moves an instrument within a patient’s joint, the infrared sensors calculate its position and smart, wireless instruments instantaneously transfer the data to a computer in the OR. This information is then displayed as an interactive model of the anatomy or blueprint that supplies the surgeon with the optimum angles, lines and measurements needed to align the implant within the patient. Other categories of computer-assistance in surgery include active robotic in which a robot performs some surgical tasks or semi-active robotic which may limit placement of surgical tools.
Computer navigation is an enhancement tool for total knee replacement, but is not artificial intelligence and does not substitute for a surgeon’s skills or judgment. It does provide quantitative data to enhance clinical decisions made during the procedure. The perceived and potential advantage of navigation is more consistent component alignment, which should contribute to enhanced component longevity. In addition, the elimination of the intramedullary technique diminishes associated risks including blood loss and fat embolization. Furthermore, navigation provides a more sophisticated assessment of component sizing in soft tissue balancing and creates a potential for downsizing the overall incision.
Future research and development of navigation systems should address the major challenges in total knee replacement which include ensuring consistent post-operative outcomes, the treatment of younger and more physically active patients, and enabling of less invasive surgery.
Additionally there is the concept of gender specific design. Knee osteoarthritis is more prevalent in women, and by virtue of that, total knee replacement is performed more commonly on women. In addition, there are known gender differences in the anatomy of the knee. In response, some manufacturers have introduced total knee designs with modified dimensions that attempt to better reproduce these anatomical differences. There is no available data that implies that this approach actually enhances the results of the procedure. The introduction of a gender-specific implant appears to have a marketing bias rather than scientific basis. There are several studies in progress that would allow a scientific perspective on this concept. The American Academy of Orthopaedic Surgeons has initiated an overview process with a five-year prospective study on the validity of gender design.
Another developing concept in total knee replacement is called patient-specific design. This system requires a preoperative MRI to construct a 3D model of the involved knee to assist in component sizing. Customized instrumentation is then created, which allows patient-specific bone resection. This concept is in the development stage by several manufacturers and is likely to be more prevalent in the future.
In summary, total knee replacement is a time-tested and highly successful option in the management of advanced knee arthritis. There are several areas of ongoing investigation that may further enhance its predictability and anticipated longevity.