The effect of anterior cruciate ligament graft rotation on knee laxity and graft tension: An in vitro biomechanical analysis.

PURPOSE: The purpose of this study was to determine the effects of rotating a bone-patellar tendon- bone allograft during anterior cruciate ligament reconstruction on anteroposterior (AP) knee laxity and forces developed within the graft.

TYPE OF STUDY: In vitro biomechanical study using human cadaveric knees.

METHODS

Thirteen fresh-frozen knee specimens received bone-patella tendon-bone allografts that were pretensioned at 30 degrees of flexion to restore AP laxity to that of the intact knee. AP laxity was then measured at 0 degrees, 30 degrees, and 90 degrees of knee flexion with the graft in neutral rotation and in 90 degrees and 180 degrees of internal and external rotation. Five specimens received allografts that were rotated to 90 degrees internally and externally and then tensioned. Two knee specimens were used to measure the effects of graft rotation on graft force at full extension; 1 received 7 separate allografts and the other received 10 allografts. During testing, the potted end of the allograft that was connected to a tibial load cell was rotated.

RESULTS

In specimens tensioned and then rotated, AP laxity at 30 degrees of knee flexion decreased an average of 0.9 mm with 90 degrees of graft rotation in either direction. At 180 degrees of external rotation, the mean decrease in laxity of 1.8 mm was significantly greater than that for 180 degrees of internal rotation (P <.05). When significant, all mean laxity reductions at 0 degrees and 90 degrees of flexion were less than those at 30 degrees of flexion. In specimens where the graft was rotated and then tensioned, rotation had no significant effect on laxity. With the exception of 90 degrees of external rotation, rotation of the graft increased graft tension at full extension; 90 degrees of internal rotation increased mean graft force by 11 N (P <.05). Rotating the graft 180 degrees in either direction increased mean graft force at full extension by 25 N (P <.05).

CONCLUSIONS

Although minor, rotating the graft had significant effects on knee laxity and graft tension. In general, AP laxity decreased and graft tension increased with increasing rotation of the graft. The direction of rotation did not seem to be important. As a result, clinicians who choose to rotate their patellar tendon grafts can expect that the biomechanical changes in the graft with rotation will have little clinical importance.