SIMULTANEOUS MEASUREMENTS OF SAGITTAL KNEE LAXITY WITH AN EXTERNAL DEVICE AND RADIOSTEREOMETRIC ANALYSIS

We obtained simultaneous measurements of sagittal knee laxity in 12 co nsecutive patients after reconstruction of the anterior cruciate ligam ent (ACL), using the Stryker laxity tester and radiostereometric analy sis (RSA). The mean anteroposterior (AP) displacement when a 90 N load was applied in both directions was 5.3 +/- 2.7 mm with RSA and 9.8 +/ - 1.6 mm with the external device (p < 0.001). The corresponding measu rements at a load of 180 N were 5.7 +/- 2.4 mm and 13.8 +/- 3.7 mm, re spectively (p < 0.001). More than 50% of the sagittal knee movement, a s measured by the external device at a load of 180 N, was not true fem orotibial displacement of the joint but was due to soft-tissue deforma tion.