Simulated pivot-shift testing with single and double-bundle anterior cruciate ligament reconstructions.

BACKGROUND

One of the principal rationales for performing a double-bundle reconstruction of the anterior cruciate ligament is the suggestion that it may be superior to a single-bundle reconstruction in restoring a normal pivot-shift sign. The purpose of this study was to measure the abilities of single-bundle and anatomic double-bundle reconstructions to restore normal knee kinematics and graft forces during a simulated pivot-shift test.

METHODS

Graft force and knee kinematics were recorded during a simulated pivot-shift event with and without the anterior cruciate ligament and after graft reconstructions. With a single bundle, the graft was tensioned to restore anterior-posterior laxity at 30 degrees of flexion. With double-bundle reconstructions, the anteromedial graft was first tensioned as above and then the posterolateral graft tension was set with use of one of four protocols: posterolateral tension = anteromedial tension at 10 degrees of flexion (DB1); posterolateral tension = anteromedial tension at 30 degrees (DB2); posterolateral tension = (anteromedial tension + 30 N) at 10 degrees (DB3); and posterolateral tension = (anteromedial tension + 30 N) at 30 degrees (DB4).

RESULTS

A single-bundle reconstruction restored all displacements and rotations during the pivot shift to the intact knee levels. The mean tibial rotations and lateral plateau displacements during the pivot shift with DB2, DB3, and DB4 reconstructions were less than those in the intact knee and also less than those in a single-bundle reconstruction. Before the pivot shift, the mean graft forces with all reconstructions were greater than that of the intact knee; the mean graft forces with the DB3 and DB4 reconstructions were also greater than that of a single-bundle reconstruction. After the pivot shift, the mean graft forces for all reconstructions were less than the levels before the pivot shift with single-bundle forces lower than intact knee levels and DB4 forces higher than intact knee levels.

CONCLUSIONS

Reduction or elimination of the pivot-shift sign is an important goal for anterior cruciate ligament reconstruction. In our model, the results show that a single-bundle reconstruction was sufficient to restore intact knee kinematics during a simulated pivot-shift event. The higher graft forces with some double-bundle graft-tensioning protocols reduced the coupled rotations and displacements from an applied valgus moment to less than the intact levels. This overcorrection should theoretically make the knee less likely to pivot but could have unknown clinical consequences.