Patient-specific total knee arthroplasty

Abstract

Patient-specific instrumentation (PSI) is a computer navigation technology that leverages rapid prototyping as a way to remove traditional computer navigation from the surgical process. Instead, the computer navigation is done in the planning phase of a total knee arthroplasty (TKA) and is based on data from the patient’s preoperative MRI or CT scan. This “pre-navigation” aims to improve the accuracy of bony resection and component alignment without the steep learning curve and time required for traditional intraoperative computer navigation. During pre-navigation, an engineer and a surgeon collaborate to design and manufacture single-use custom cutting guides. Using these guides, precision and accuracy have been shown to be at least equivalent to conventional cutting guides, without the additional equipment and steps of either traditional or computer-navigated TKA. Cost has been a concern, with the required MRI and CT scans reducing the economic incentive to the technology’s widespread adoption. By simplifying navigation and reducing instrument trays and prosthesis inventory, PSI has the potential to improve operating room efficiency. By reducing surgical operating time and intraoperative bleeding beyond conventional instrumentation, it is hoped that PSI guides will be a major factor in reducing length of hospital stay and promoting earlier return to function. As with all TKA surgery, implant position should be combined with vigilant attention to ligament balancing and tensioning of the surrounding soft-tissue structures. While PSI aims to optimize the bony resections based on static anatomy, it does not yet have the ability to account for the soft-tissue envelope and its complex dynamics around the knee. Occasionally adjustments in size, position, rotation, and orientation of the guides are needed to achieve this ideal interplay. Various techniques are presented in this chapter which may guide the surgeon in the use and adjustment of PSI. At any point in time, conventional cutting guides can replace PSI guides if there is a concern about fit, bony resection or alignment. With the amount of adjustment possible with PSI, the technology has proven to be a very powerful method of primary knee reconstruction and can be used in nearly every circumstance.