This is a syndrome which occurs when a fibrous nodule forms on the joint capsule, just above the patella. This is a complication of Total Knee Replacement and once this develops the Knee starts making a loud clunk. At about 40 degrees of flexion this lump gets trapped between the anterior flange of the femoral component and hence the clunk.
According to the theories there are two causes:
Discomfort and pain in the knee, loud clunk on flexion, blocking of further movement, synovitis, effusion.
With the use of the newer designs of the total knee prosthesis very few cases of patella clunk have been seen. This is because the newer designs offer a much longer and deeper groove for the patella to fall back into the notch of the femur.
Removal of the lump by Arthroscopy of the Knee Joint.