Persistent anterior knee pain, subluxation or dislocation of the patella as well as early aseptic loosening and increased polyethylene wear of the patella implant are common clinical problems after total knee arthroplasty (TKA) which are associated with the patellofemoral joint. In addition to patellar resurfacing, the design of the patellofemoral joint surfaces is attributed a large influence. While for patients without patella resurfacing, the native patella is sliding on the standardized femoral component and therefore the possibility of a reduced surface matching is high, patella resurfacing has been shown to decrease the joint contact area and yield to increased patellofemoral pressure. With regard to a further design optimization, the current study examined patellar biomechanics after TKA without and with resurfacing, comparing 5 differently designed patellofemoral joint surfaces of the femoral implant. The femoral implant of the Genesis II prosthesis (Smith & Nephew) was scanned and an adaptable CAD-model was built using CATIA. Five different designs of the patellofemoral groove were created: original completely flat laterally elevated (+2mm lateral, −1mm medial) medially elevated (+2mm medial, −1mm lateral) laterally & medially elevated (+3mm lateral+medial) The tibiofemoral joint as well as patellofemoral groove path and radius remained unchanged. Rapid Prototyping was used to produce prototypes made of polyamide. A dynamic muscle loaded knee squat was simulated on 10 fresh frozen knee specimens with an upright knee simulator. The patellofemoral pressure distribution was measured using a flexible, resistive force sensor (TEKSCAN) while tibiofemoral and patellofemoral kinematics were recorded with an ultrasonic motion tracking system (ZEBRIS). In addition, patellar stability was measured in different flexion angles on another 10 specimens using a robot (KUKA). Measurements were taken on the native knee as well as after TKA and after additional patellar resurfacing with alternating femoral implant.Introduction
Methods
