Patellofermoral Issues After Total Knee Arthroplasty – Considerations with Different Alignments

Patellofemoral complications after total knee arthroplasty (TKA) are insidious and challenging, usually leading to poor outcomes and representing about 10% of complications. These consist of maltracking, lateral dislocation/subluxation, fractures, patellar clunk syndrome, and anterior pain. Risk factors identified by different papers could be patient-related, surgery-related, or implant-related. Patient-related factors include valgus deformity more than 10°, obesity, patellar thickness inferior to 18 mm, and history of patellar tilting or subluxation. Surgery-related factors include errors in bone cut when using the patellar component (i.e., asymmetrical bone cut or changing patellofemoral offset), errors in rotational alignment (i.e., malrotation of femoral and/or tibial component), or patellar blood supply compromise, especially during lateral retinacular release or after patellar fractures. Implant-related factors include shallow trochlear groove in femoral components, loosening, or error in positioning of the patellar component.[1] Historically, mechanical alignment with gap balancing technique was the gold standard for knee replacement, where tensioning the collateral ligaments in flexion identified femoral component rotation, and therefore the patellar tracking. In these cases, even with a standard and “fit for everyone” technique, different rotations could be identified. Otherwise, in the measured resection technique, the rotation of the femoral component is usually determined by the bone landmarks: the whiteside line, the transepicondylar axis, and the posterior condylar axis. Since the posterior condylar axis is 3° internally rotated than the transepicondylar axis and often no wear is present posteriorly, the rotation is usually fixed. Since mechanical alignment has been defined as a “nonpersonalized” and “systematic” technique, great attention was focused in recent years in the research of more patient-specific alignment. Howell first described the Kinematic Alignment (KA); this technique aims to restore the native position and rotation of the femur without ligament releases, and consequently reports the constitutional joint line orientation, in order to re-establish the knee alignment in its pre-arthritic condition. Despite the early enthusiasms and higher patient-related outcome measures, KA presents a difficult surgical technique without a statistically significant difference in complication rate against conventional techniques. Moreover, since the technique’s keystone is the femur, any other adjustment is performed on the tibial side, leading to a theoretical instability or early loosening.[2] Starting from KA, different alignment techniques are emerged to allow a gradual transition to KA and restrict the variability of combined tibiofemoral inclinations within ±3°.[3] Finally, MacDessi et al. described a comprehensive classification of nine different knee alignments basing on the combination of the arithmetic hip–knee–ankle angle (i.e., varus, neutral, or valgus) and the joint line obliquity (i.e., apex distal, neutral, and apex proximal).[4] Nevertheless, all of these different alignment techniques do not completely consider the patellofemoral joint. In fact, even if the femoral component is positioned in his natural position, it is not always possible to restore the trochlear groove anatomy, and in some cases, using KA, the femoral component is undersized.[5] Moreover, the only rotation of the femoral side is not enough to explain how the patella moves through the trochlear groove. The available femoral components are symmetrical and more prone to move in neutral alignment, with a fixed Q-angle of about 7°, except in cases of gender solutions, where the Q angle is about 10°. Furthermore, moving the femoral component in the coronal plane beyond values considered as outliers (usually 3°–5° in mechanical axis) could lead to serious problems in maltracking: the extreme varus femur brings the trochlear groove perpendicular to the floor, while the extreme valgus increases the Q angle and the risk of lateral dislocation. In conclusion, TKA still remains a reliable technique for pain relief and restore function, nowadays the stability and the orientation of the joint line is the main subject of debate. The available alignment techniques provide to match the prosthetic implant to the different knee morphotypes, but, whatever the chosen alignment, the goals should always remain the strict surgical technique, the stability of the joint on all planes, and the achievement of the best kinetic. Financial support and sponsorship Nil. Conflicts of interest There are no conflicts of interest.