Abstract
Observations of knee arthroplasty kinematics generally show differences in anteroposterior translation when comparing posterior cruciate retaining (CR) and posterior stabilised (PS) designs. However, the PS cam/post mechanism is not engaged in extension. We hypothe-sised that there would be little difference between CR and PS knee kinematics during stance in gait.
Videofluoroscopy and shape matching techniques were used to quantify motions of 47 fixed-bearing knee arthroplasties (24 CR, 23 PS) during gait and stair-climbing in consenting patients with excellent clinical/ functional performance at least one year post-surgery. The average centre of rotation (COR) was computed for each knee during the two activities; a lateral COR (−50% to 0%) indicates anterior femoral translation with flexion, a medial COR (0% to +50%) indicates posterior femoral translation with flexion.
There was a significant difference between the average COR in the PS (+9%) and CR (−15%) knees for the stair climbing activity (p< 0.001), but not the stance phase of gait (−5% vs. −14%, respectively, p=0.664). The COR was more lateral for the stance phase of gait than for stair climbing in the PS knees (p=0.008), but not the CR knees (p=0.948). All knees showed more axial rotation during the stair activity (8°) than the stance phase of gait (5°, p< 0.001).
During stance in gait, there were small but not significant differences in the centre of rotation between the CR and PS knees. For stair climbing, there were significant differences between CR and PS knee kinematics. These observations are consistent with the hypothesis that CR and PS kinematics ought to be similar near extension, where the articular constraints are similar, but might differ in deeper flexion activities where the intrinsic constraints of the arthroplasty are different. An improved understanding of arthroplasty function should facilitate further evolution of design, surgical techniques, and numerical analyses to optimise patient performance.
The abstracts were prepared by Nico Verdoschot. Correspondence should be addressed to him at Orthopaedic Research Laboratory, Universitair Medisch Centrum, Orthopaedie / CSS1, Huispost 800, Postbus 9101, 6500 HB Nijmegen, Th. Craanenlaan 7, 6525 GH Nijmegen, The Netherlands.
