Anatomy and biomechanics of the patellofemoral joint. Physiological conditions and changes after total knee arthroplasty

The patellofemoral joint constitutes a complex anatomical and functional entity. The tensile force of the quadriceps femoris muscle is transmitted through the patella and patellar ligament onto the tibial tuberosity. This particular three-dimensional arrangement increases the torsional moment acting on the knee joint. Dynamic alignment of the patella is determined by trochlear geometry and is supported by active muscular and passive connective tissue stabilizers. In addition to the retinaculum of the patella, the medial patellofemoral ligament is attracting increasing clinical attention. Multidirectional motion of the patella is closely connected to retropatellar pressure distribution which can be modulated by moving the patellar ligament insertion. Implantation of a knee endoprosthesis changes the joint surface geometry and consequently patella kinematics and retropatellar pressure distribution. Finite element analysis provides the possibility to assess retropatellar pressure distribution before and after implantation of prostheses.