Abstract
Purpose of the study
To compare the patellofemoral kinematics and patella stability of a new TKR, with a continuous radius versus an established J shaped knee system and the natural knee. It was hypothesised that the high performance new TKR would be a better match to the natural knee and anatomical patella tracking would provide a more stable patella.
Methods
A cadaveric study using physiological loads examined the continuous kinematic behaviour (optical tracking system) of the tibiofemoral and patellofemoral compartments in 6 knees for the native, kinemax and new design triathlon knee systems.
Results
In all knees the patella shifted laterally as flexion increased. There were significant differences between the natural knee and the Triathlon knee from 10-40 degrees of flexion (p<0.001).
In patella spin the natural knee moved 7 degrees of adduction compared to 15 degrees for the Triathlon and 11 for the Kinemax.
Both the prosthetic patellae were tilted at 5 degrees of flexion and continued to tilt laterally to 7 degrees at 50 degrees where they remained. The natural knee tilted medially by 3 degrees up to 30 degrees of flexion, then laterally to 4 degrees at 90 degrees.
Both prostheses showed the patella to be flexed at full extension.
Fully extended, all knees required 100N to displace the patella 10mm medially. At 90 degrees of flexion the intact knee and the Triathlon knee needed 155N compared to 130N for the Kinemax knee. Around 110N was required in all knees for lateral displacement throughout flexion.
Discussion
Both TKRs were a good match to the natural knee patellofemoral joint kinematics and patella stability. There were no overall statistical differences.
