A Randomized Control Trial Comparing an Anatomical Axis Aligned and Conventional Mechanical Axis Total Knee Arthroplasty Using Patient-Specific Instrumentation

The reference standard for total knee replacement or total knee arthroplasty (TKA) has historically been based on a 2-dimensional "mechanical axis" of the knee which surgically creates a joint line parallel to the ground. This is based on the idea that this alignment will evenly distribute the stress on the prosthesis, thus improving the wear characteristics and longevity of the replacement. More recent studies have shown that TKAs with greater than 3 degree deviation (in either valgus or varus) from this previously accepted ideal does not convey a survival benefit over a 15 year period. This is not to say that alignment does not play a role in survivorship as gross deviation from neutral does result in earlier implant failure, but a simple 2-D model may not be the ideal approach to TKAs. With the developments and improvements in patient-specific technology (or patient-specific instrumentation (PSI)), our ability to create TKAs that reproduce the patient's original anatomic or kinematic alignment in 3-Dimensions has dramatically improved. Early research with respect to function and survivorship has shown that PSIs are at least equivalent when compared to conventional TKAs. Some studies have also suggested improvements with respect to shorter operating times, less blood loss and increased range of motion. Most of the current PSI TKA literature has placed an emphasis on the technology's effect on TKA alignment or to show that it is bioequivalent with respect to range of motion or early prosthesis survivorship when compared to conventional TKAs. Although a single study using PSIs (Howell et al., 2013) has shown improvement in Oxford Knee Scores when comparing patients preoperatively to postoperatively, to our knowledge there is no research done to directly compare the functional knee scores between a mechanically-aligned and anatomically aligned TKA. This randomized control trial will compare these two approaches using implants from the same manufacturer and also hope to identify more subtle functional differences using power testing and gait analysis, in addition to assessing other perioperative outcomes such as blood loss, hospital stay duration and operative time.