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David H. Perrin is an associate professor and Director of Graduate Athletic Training and Bruce M. Gansneder is an associate professor of Educational Studies at the Curry School of Education at the University of Virginia.
David E. Martin is an assistant professor in the Department of Radiology at the University of Virginia Medical Center. He was a doctoral candidate in Sports Medicine at the Curry School of Education at the time this research was completed.
David M. Kahler is an assistant professor of Orthopedic Surgery and Frank C. McCue is an Alfred R. Shands Professor of Orthopedic Surgery and Plastic Surgery of the Hand. Both are associated with the Department of Orthopedics at the University of Virginia.
The anterior cruciate ligament (ACL) is the primary restraint to anterior translation of the tibia on the femur. Research suggests that resistance to anterior translation changes as the tibia is rotated internally and externally. This study assessed the degree to which ACL reconstruction and tibial rotation affects anterior knee laxity. Nine subjects with ACL lesions and functional instabilities participated in the study. Subjects were measured 1 to 10 days before surgery and 6 to 8 months after ACL reconstruction using the KT-1000 knee arthrometer. A mechanical leg stabilizer was used to assess anterior translation at 20° of knee flexion in three positions: internal rotation of 15°, neutral, and external rotation of 15°. Subjects were measured at 89 and 67 N of anterior force. Data were analyzed with a three-factor (test × position × force) repeated measures ANOVA. Following surgery, reduction in laxity (mm) for the three positions (internal rotation, neutral, and external rotation) was 1.9, 2.8, and 3.4, respectively, at 89 N and 1.5, 2.0, and 2.6, respectively, at 67 N. The degree of reduction in laxity (presurgery to postsurgery) was dependent upon rotation and force, and was greatest in external rotation and least in internal rotation pre- to postsurgery. We concluded that ACL reconstruction using a patellar tendon graft significantly decreased anterior tibial translation at all three positions, but a greater amount of reduction was observed postsurgically at the externally rotated position. This supports the theory that mechanical blocks and secondary restraints such as a taut mid-third of the iliotibial tract may interfere with clinical laxity tests in some positions of tibial rotation. Fixing the tibia in an externally rotated position may decrease the effect of secondary restraints and improve sensitivity in testing for ACL laxity.