Surgical technique in patellofemoral arthroplasty.

Patellofemoral arthroplasty (PFA) has seen its role validated over the last decade as a treatment for severe Iwano III or IV patellofemoral osteoarthritis (PFOA). The ideal indication is PFOA with femoral trochlear dysplasia. The accumulation of data on factors influencing the likelihood of PFA failure or success when using first- or second-generation implants has led to design changes, which have been incorporated into modern third-generation implants. These implants are positioned using anatomic cuts, with instrumentation kits that ensure accurate and reproducible alignment. Their design corrects the femoral trochlear dysplasia. Refinements in the indications of PFA, together with advances in prosthetic kinematics and improved understanding of the surgical technique, have strengthened the role for PFA. Although either a lateral or a medial approach can be used, the lateral approach deserves preference. Proper orientation of the femoral and patellar implants is crucial and can be achieved in an accurate and reproducible manner. Orientation of the coronal femoral cut is the only modifiable variable. The cut should be performed with the knee in neutral rotation to minimise both the tibial tuberosity-trochlear groove distance and the amount of extensor apparatus valgus. In the coronal plane, the femoral component must be positioned in valgus, to align the distal part of the trochlear implant with the lateral condylar cartilage. Medial positioning of the patellar component finalises the match between the femur and the patella. This coronal alignment of the two components promotes patellar engagement at the beginning of knee flexion. Thus, the technique brings the trochlea towards the patella and the patella towards the trochlea, thereby ensuring optimal patellofemoral tracking and ensuring a good final outcome. When these requirements are met, the functional and radiographic outcomes are predictable, of good quality, and sustained over time, provided the patient remains free of tibio-femoral osteoarthritis.