Instrumented analysis of the pivot shift phenomenon after reconstruction of the anterior cruciate ligament.

The pivot shift was analysed using an electrogoniometer linkage (OSI, CA, USA) in 27 patients 18 to 24 months after reconstruction of the anterior cruciate ligament (ACL). The static passive AP-displacement of the tibia was also measured by a laxity tester in 20 degrees of knee flexion with a load of 90N. All patients had a positive pivot shift on manual examination before surgery. At follow-up 18 patients had normal subjective knee function according to the Lysholm score and 18 patients had returned to their preinjury, competitive activity level. Only three patients had a positive pivot shift on manual testing. In contrast a pivot shift curve was registered with the electrogoniometer in 18/27 in the operated knee. Their mean maximum tibial translation in the operated knee during the pivot shift test was 8.1 +/- 4.3 mm. In 10 of these patients a pivot shift-like motion pattern was recorded also in the non-operated knee. Generally patients with passive sagittal A-P displacement difference of the tibia of > +2 mm in comparison to the non-operated knee also had positive instrumented pivot shift tests. In six control subjects without previous knee injury the electrogoniometer revealed no pivot shift curve and the mean maximum sagittal translation was only 3.4 +/- 1.3 mm. It seems that pathologic knee motions can be provoked manually in many patients two years after reconstruction of the ACL in spite of a generally good clinical result. In some patients also the non-operated knee shows a pathologic motion pattern that could not be demonstrated in normal subjects. Computerized registration of the pivot shift phenomenon was more sensitive than ordinary manual testing. These findings are in line with results previously found in vitro.