IN-VIVO KNEE KINEMATICS DERIVED USING AN INVERSE PERSPECTIVE TECHNIQUE

Sixty-four subjects having implanted and nonimplanted knees were studi ed using fluoroscopic videos, Each subject, flexing in the sagittal pl ane, performed successive deep knee bends under fluoroscopic surveilla nce, Femorotibial contact in the sagittal plane was then determined us ing image matching and discrete digitization. At full extension, the m ean contact point of the normal and posterior stabilized implanted fem urs was anterior to the tibial midpoint in the sagittal plane, The ave rage position was 6.49 mm (+3 - +13 mm) for the normal knees and 0.30 mm (0- +4 mm) for the posterior stabilized knees, The implanted poster ior cruciate retaining and anterior cruciate ligament deficient knees differed from the other knee types. Their average initial contact was posterior, The average contact at full extension for the posterior cru ciate retaining and anterior cruciate ligament deficient knees was 5.1 3 mm (-2 - -8 mm) and -5.45 mm (-2 - -14 mm), respectively, The femur of the normal knee contacts the tibia anterior to the midpoint in the sagittal plane in full extension and translates posteriorly during fle xion, The femur of the posterior stabilized knee contacts the tibia an teriorly, slightly less than the normal knee, and rolls back posterior ly during flexion similar to normal knees, The femurs of the posterior cruciate retaining and anterior cruciate ligament deficient knees con tact the tibia posterior in extension, but translate anteriorly during midflexion in a substantial number of cases, which is kinematically o pposite of the normal knees. The abnormal anterior femoral translation observed in the posterior cruciate retaining knees may be a factor in the premature polyethylene wear seen in retrieval studies.