Screw home motion after total knee replacement

The objective of this study was to evaluate the effect of muscle force and the posterior cruciate ligament on screw home motion in patients with total knee replacement in a posterior cruciate ligament retaining prosthesis (10 knees) and a posterior cruciate ligament substituting prosthesis (10 knees ), Screw home motion was examined with only active extension and with two t ypes of externally loaded active extension (2 kg and body weight). Screw ho me motion was measured with a 6 degrees of freedom electrogoniometer (instr umented spatial linkage), Retaining the posterior cruciate ligament maintai ned screw home motion, with and without external load to muscles, whereas s ubstituting the posterior cruciate ligament maintained screw home motion on ly under the full external load of body weight, This was not seen with a 2- kg external load, As for the normal knee, it appears that screw home motion of a prosthetic knee is influenced, not only by the presence of ligamentou s structures, but also by the activity of the muscles. The activity of the muscles may have a much greater effect on screw home motion with currently used prosthetic designs than does the presence of ligamentous structures.