Abstract
Component and limb alignment are important considerations during Total Knee Arthroplasty (TKA). Three-dimensional positioning of TKA implants has an effect on implant loosening, polyethylene stresses, and gait. Furthermore, alignment, in conjunction with other implant and patient variables such as body mass index (BMI) influence osseous loading and failure rates. Fortunately, implant survivorship after TKA has been reported to be greater than 95% at 20 years, despite up to 28% of TKAs having component position greater than 3 degrees from neutral. How good are we at positioning TKA implants? Ritter, et al examined 6,070 primary TKAs and found that from 2–7 degrees of valgus, the failure rate was 0.5% for limb alignment. Importantly 28% of the TKAs were outside the 2–7 degree range in the hands of experienced surgeons. Clearly there is room for improvement in surgical technique, but this improvement must be (1) time efficient and cost effective; (2) have a low complication rate, and (3) be reproducible with a minimal learning curve. A number of technologies have been developed to help surgeons implant and position TKA components including intramedullary guides, patient matched guides based on pre-operative imaging, Computer Assisted Surgery (CAS) based on line-of-sight navigation, and most recently, hand-held navigation. All of these techniques have distinct advantages and disadvantages, but we have found that hand-held navigation in TKA meets the prerequisites. Nam, et al reported the first series with a handheld device in 42 knees, and was able to position 95% of the tibial components within 2 degrees of targeted sagittal slope and 96% within 3 degrees of coronal alignment. Advantages of hand-held navigation include low cost, minimal learning curve, reproducibility surgeon to surgeon, and time efficiency (usually taking less than 3 minutes). The disposable device can be used on all patients with all deformities, including those with retained hardware. Hand held navigation devices create a virtual alignment framework from known osseous landmarks, and this framework is used to position tibial and femoral cutting guides on the bone. Using tibial osseous landmarks, including the ACL footprint proximally and the medial and lateral malleoli distally, the device allows real-time feedback of tibial slope and coronal alignment. On the femur, the device locates and references the centre of rotation of the hip and the centre of the distal femur, which allows for real-time calculation of distal femoral valgus and flexion for the distal femoral cutting block. Receiving three-dimensional, real-time feedback of coronal and sagittal alignment, as well as resection depth, combining limited mechanical instruments aided by hand-held navigation devices is a significant step forward. Thus, this technology represents a significant help to the surgeon and patient.
