The complex interplay between the tibiofemoral and patellofemoral joint still leads to unsatisfied patients after total knee arthroplasty. In this context, the role of patella height is controversially discussed. Furthermore, patella alta is a risk factor for retro-patellar cartilage lesions. Therefore, this computational study aims to analyze the biomechanical effect of different patella heights on patellofemoral (PF) dynamics during active knee movement.
A previously validated musculoskeletal multibody model [Kebbach et al. 2020] of a male subject (88 years, 66.7 kg) equipped with a posterior cruciate-retaining bicondylar total knee endoprosthesis with a patellar button (P.F.C. Sigma, DePuy Synthes, Warsaw, IN, U.S.A.) was adapted to examine different patella heights. The model of the lower extremity resembled a dynamic squat motion. Relevant ligaments and muscle structures were implemented within the multibody model. It served as a basis for the parameter analyses in which the effect of different patella heights (baja, normal, and alta) was evaluated by the PF contact force and patellar tilt during flexion movement from 0 to 90°.
As knee flexion increased, the PF contact force increased as well. Patella alta resulted in higher PF contact forces in extension as well as flexion movements by up to 14%. In contrast, patella baja was associated with decreased PF forces by about 8% compared to normal patella height. The difference between patella baja and alta configurations amounts to up to 25% of the overall PF contact force calculated. Concerning PF kinematics, patella alta yielded in a more lateral tilt compared to the patella baja configuration.
Our computational study indicates that patella alta yields higher PF contact forces than patella baja, which is contrary to common belief. This might be a factor that should be considered in the generation and diagnosis of patellofemoral pain after total knee arthroplasty. Furthermore, our data may also explain why patella alta is a risk factor for retropatellar cartilage lesions due to increased contact forces.