Abstract
Background
Traditionally, a standard femoral tunnel for a single-bundle anterior cruciate ligament (ACL) reconstruction is positioned 6 to 7 mm anterior to the posterior wall at an 11 o'clock orientation in the femoral notch (right knee). However, some surgeons have advocated placing the femoral tunnel at a more oblique orientation at or near the femoral footprint of the ACL's posterolateral bundle (at approximately 9:30 to 10 o'clock in the notch) to provide the graft with a better mechanical advantage for controlling tibial rotation and eliminating the pivot shift.
Hypothesis
Moving the femoral tunnel from the standard location to an oblique position in the femoral notch will significantly reduce the magnitude of a simulated pivot shift.
Study Design
Controlled laboratory study.
Methods
Internal-external tibial rotation and anteroposterior (AP) displacement of the lateral tibial plateau were measured in 17 fresh-frozen cadaveric knees during a simulated pivot-shift event with a single-bundle ACL reconstruction placed in standard and oblique femoral tunnels. Baseline kinematic measurements were taken with the graft tensioned to restore intact AP knee laxity at 30° of flexion. The measurements were repeated as graft tension was decreased to produce approximately 2-mm incremental increases in laxity (up to +10 mm). Correlations between lateral tibial plateau displacement and tibial rotation during the pivot shift were determined for both tunnels.
Results
There were no significant differences in tibial rotations or tibial plateau displacements during the pivot shift between standard and oblique femoral tunnels when the graft was tensioned to restore intact knee laxity. The relationship between pivot-shift magnitude and AP laxity was highly linear for each knee specimen over the range of laxities tested; the mean slopes for anteromedial (AM) and posterolateral (PL) tunnels were not significantly different. There were near perfect linear correlations (mean r2 > .98) between lateral plateau displacement and tibial rotation for both femoral tunnel positions; the slope of the regression line was not significantly different between tunnels.
Conclusion
Moving the femoral tunnel from the standard location to a more oblique position in the notch did not significantly alter pivot-shift kinematics. Lateral plateau displacement was strongly correlated with tibial rotation, and either can be used to quantify the pivot shift.
Clinical Relevance
The rationale for placing the femoral tunnel at an oblique position in the notch to reduce the pivot shift is questioned.
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