Flexion-extension gap in cruciate-retaining versus posterior-stabilized total knee arthroplasty: a cadaveric study

We re-examined experimental model results using half-body specimens with intact extensor mechanisms and navigation to evaluate cruciate-retaining (CR) and posterior stabilized (PS) total knee arthroplasty (TKA) component gaps through an entire range of motion. Six sequential testing regimens were conducted with the knee intact, with a CR TKA in place, and with a PS TKA in place, with and without 22 N traction in place at each stage. Each of 10 knees was taken through six full ranges of motion from 0° to 120° at every stage using a navigated knee system to record component gapping. No significant difference was found between loaded and unloaded component gaps, and no significant differences were found in component gapping between CR and PS TKAs throughout a full range of motion. Flexion-extension gap measurements were significantly different from previously published data (at 90° flexion). No difference was found in kinematics when comparing CR and PS TKA component designs. Our results suggest that intact extensor mechanisms may be required to perform proper kinematic studies of TKA. Our findings provide evidence that the extensor mechanism may play a major role in the flexion-extension gaps in cadaveric knees.