Abstract
Besides the numerous variations of TKR designs addressing fixation, wear, or specific indications, there are variations from competing design philosophies such as conformity and shape of the articulating surfaces and mobile versus fixed bearing designs. With the same resected ACL and retained PCL ligament combinations and similar surgical procedure, the subset of different implants for these very indications should be expected to produce only minor variations in kinematics. This study set out on a comprehensive series of detailed and intricately controlled in-vitro tests to examine this hypothesis. Six different posterior cruciate retaining medium size knees from different manufacturers were used. Four were fixed bearing condylar types of low to high constraint; and two mobile bearing ones which allowed rotational and translational freedom, one fully and one partially conforming. The implants were aligned according to the manufacturer’s recommendations and subjected to the same ISO force-control simulation. The kinematics captured from the averaged simulated cycles of walking showed AP displacement contained within an envelope of 4 mm for most of the stance phase. This increased with most to a maximum range of 5mm just before toe-off at the end of the stance phase. In rotation, the designs showed ranges during stance from about 2–13 degrees. The kinematics from the different implant designs were thus significantly different; a controversial answer regarding the hypothesis posed. This means the “performance” must be different between these implants if installed “ideally” on the same patient with the PCL retained. Studies are worthwhile to determine if these differences in performance are reflected in clinical functional conditions.
The abstracts were prepared by Nico Verdonschot. Correspondence should be addressed to him at Orthopaedic Research Laboratory, University Medical Centre, PO Box 9101, 6500 HB Nijmegen, The Netherlands.
