Introduction Abnormal patellar tracking is the most common complication of TKA. the most important variable in proper patellar tracking is preservation of a normal Q angle. Abnormal Q angle an increase in the Q angle will lead to an increased lateral subluxation forces on the patella relative to the trochlear groove possible pain, mechanical symptoms, accelerated wear, and even dislocation. it is critical to avoid techniques that lead to increase Q angle. Common errors include internal rotation of the femoral prosthesis medialization of the femoral component internal rotation or medialization of the tibial prosthesis placing the patellar prosthesis lateral on the patella Anatomy Q Angle the Q angle is defined as angle between axis of extensor mechanism (ASIS to center of patella) axis of patellar tendon (center of patella to tibial tuberosity) Imaging CT scan malrotation of components is best diagnosed with CT scan of the knee Femoral Prosthesis There are three reference axis that one may use: anteroposterior axis defined as a line running from the center of the trochlear groove to the top of the intercondylar notch a line perpendicular to this defines the neutral rotational axis transepicondylar axis defined as a line running from the medial and lateral epicondyles the epicondylar axis is parallel to the cut tibial surface a posterior femoral cut parallel to the epicondylar axis will create the appropriate rectangular flexion gap posterior condylar axis defined as a line running across the tips of the two posterior condyles this line is in ~ 3 degrees of internal rotation from the transepicondylar axis, the femoral prosthesis should be externally rotated 3 degrees from this axis to produce a rectangular flexion gap if the lateral femoral condyle is hypoplastic, use of the posterior condylar axis may lead to internal rotation of the femoral component WARNING: the average posterior condylar twist angle is 3º but the range is 1-10º. Therefore vary angle of femoral rotation based on variances in femoral anatomy. Internal Rotation of Femoral Prosthesis will Increase Q angle by internally rotating the femoral prosthesis, you are effectively bringing the groove and the patella medially. This will increase the Q angle to the tibial tubercle will also make the medial compartment tight in flexion with subsequent TKA stiffness Medialization of the Femoral Prosthesis will Increase Q angle a medialized femoral prosthesis will bring the trochlear groove to a more medial position, and thus bring the patella medial with it, thus increasing the Q angle therefore, you want the femoral component to be slighly lateral if anything Tibial Prosthesis The preferred rotation of the tibial component is neutral, with no internal or external rotation. the best way to obtain this is to have the tibial component centered over the medial third of the tibial tubercle this may leave a portion of the posteromedial tibia uncovered and some overhang of the prosthesis over the tibia on the posterolateral tibia. Internal Rotation of Tibial Prosthesis will increase Q angle internal rotation of the tibial component effectively results in relative external rotation of the tibial tubercle and an increase in the Q angle Medialization of tibia will increase Q angle Patellar Prosthesis The preferred position of the patellar prosthesis is to be either centered over the patella or medialized medializing the patellar component is one strategy to decrease the Q angle. results in uncoverage of lateral facet. Consider removing to lessen risk of lateral facet syndrome. another alternative is use of an oval shaped patella with the apex medialized. Lateralization of the patellar prosthesis will increase the Q angle and increase maltracking Intraoperative lateral subluxation of the patella if patella laterally subluxes intraoperatively during trialing, deflate tourniquet and recheck before performing a lateral release Indications for resurfacing absolute inflammatory arthritis patella maltracking patellofemoral arthritis as the main indication for TKA Options for resurfacing during TKA always resurface never resurface option to perform patelloplasty excision of marginal osteophytes, reshaping of patella selective resurfacing Patella resurfacing vs. Non-resurfacing less anterior knee pain with resurfacing less revision rates with resurfacing inferior results with secondary resurfacing similar patient satisfaction rates trochlear design important: “patellar friendly” thinner anterior flange anatomic trochlear groove