A New Twist for ACL Reconstruction Surgery
Abstract & Commentary
Synopsis: Pretensioning followed by rotating the ACL graft improved stability and graft tension. However, rotating the graft before tensioning did not have the same effect. The direction of rotation did not matter.
Source: Hame SL, et al. Arthroscopy. 2002;18:55-60.
Many authors support rotating the bone-patella tendon-bone (BTB) graft during anterior cruciate ligament reconstruction (ACLR). The purpose of this study was to determine the effects of rotating the BTB during ACLR on anteroposterior (AP) knee laxity and to determine the forces developed within the graft. Thirteen fresh cadaver knee specimens underwent ACLR and received BTB grafts that were pretensioned at 30° of flexion to restore normal AP knee laxity. AP knee laxity was then measured at 0°, 30°, and 90° of flexion with the graft placed in neutral, 90°, and 180° of internal and external rotation. Additionally, 5 knees received grafts that were first rotated, second tensioned, and finally tested.
In specimens tensioned and then rotated, AP laxity significantly decreased at most testing positions by about 1 mm. In general, AP laxity decreased and graft tension increased with increasing amounts of external or internal rotation of the graft.
In specimens where the graft was first rotated and then tensioned, rotation had no significant effect on laxity. Mean graft forces were significantly increased at a few positions but the increases was very small. For example, by rotating the graft 180° internally or externally, mean graft force increased at full extension by 25 N.
Hame and colleagues concluded that rotating the graft had small but significant effects on knee laxity and graft tension. However, the direction of rotation did not seem to be important.
Comment by James R. Slauterbeck, MD
Does twisting the BTB graft significantly alter the biomechanical properties for the graft? Keith Markolf’s biomechanics lab can begin to answer the question. He has published his technique of obtaining mechanical property and strain analysis for the ACL and PCL in many journals. The protocol cores out the ligament, leaving it intact on a long bony pedestal and maintains its origin or insertion in anatomic position. A load cell or strain gauge can be attached to one side of the ligament bone interface for measurement purposes.
In these experiments, the BTB graft was pretensioned at its original length then rotated, or it was rotated then pretensioned. The later condition was more clinically relevant since the twist is applied before the graft is pre-tensioned at surgery. The results show small differences in the properties when the ligament is tensioned then twisted, and no differences if twisted then pretensioned.
All in all, little effect is seen by twisting the graft, other than possibly exposing the graft to higher than desired pretensions and decreasing the knee laxity by 1 mm or so. The increase in the tension in the BTB tissue is low, relative to the approximately 500 N pullout strength for the bone-screw interface used in most ACL reconstructions. The effects of remodeling on a graft with higher tension are not known. Therefore, I would not recommend spending much time twisting the graft on insertion.
Dr. Slaughterbeck, Associate Professor, Department of Orthopedic Surgery, Texas Tech University Health Sciences Center, Lubbock, TX, is Associate Editor of Sports Medicine Reports.
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