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The goal of this study was to determine the effects of peak knee valgus angle and peak knee abductor moment on the anterior, medial, and lateral tibial translations (ATT, MTT, LTT) in the "at risk" female knee during drop landing. Fifteen female subjects performed drop landings from 40 cm. Three-dimension knee motion was simultaneously recorded using a high speed, biplane fluoroscopy system, and a video-based motion analysis system. Valgus knee angles and knee abduction moments were stratified into low, intermediate, and high groups and peak ATT, MTT, and LTT were compared between these groups with ANOVA (α = 0.05). Significant differences were observed between stratified groups in peak knee valgus angle (p0.0001) and peak knee abduction moment (p0.0001). However, no corresponding differences in peak ATT, LTT, and MTT between groups exhibiting low to high-peak knee valgus angles (ATT: p = 0.80; LTT: p = 0.25; MTT: p = 0.72); or, in peak ATT (p = 0.61), LTT (p = 0.26) and MTT (p = 0.96) translations when stratified according to low to high knee abduction moments, were found. We conclude that the healthy female knee is tightly regulated with regard to translations even when motion analysis derived knee valgus angles and abduction moments are high.

The measurement of anterior or posterior tibial translation depends on the existence of a repeatable and accurate reference position of the knee from which the corresponding translation is measured.Clinical measurements of posterior tibial translation alone do not accurately reflect the laxity of posterior cruciate ligament-reconstructed knees.Controlled laboratory study.Ten human cadaveric knees were tested by using a robotic/universal force-moment sensor testing system. The reference positions and the resulting kinematics in response to a 134-N anterior-posterior tibial load were determined for the intact and reconstructed knees. Posterior cruciate ligament reconstruction was performed with the graft tensioned and fixed at two different positions: 1) 90 degrees of knee flexion with a 134-N anterior tibial load and 2) full extension with no load.Posterior cruciate ligament reconstruction with graft fixation at full extension with no load resulted in anterior shift of the reference position by 1.5 to 3.2 mm. The reconstruction resulted in an overconstrained knee with significantly decreased total anterior-posterior translation of 2.6 to 3.2 mm. However, the posterior tibial translation measured was not significantly different from that of the intact knee. Posterior cruciate ligament reconstruction with graft fixation performed at 90 degrees of flexion with a 134-N anterior tibial load resulted in kinematics similar to those of the intact knee.Posterior tibial translations that are measured clinically can be misleading because the reference position of the knee can be shifted significantly after posterior cruciate ligament reconstruction.The measurement of total anterior-posterior translation may be a more accurate way to assess kinematics of the reconstructed knee.

To study how well an anterior cruciate ligament (ACL) graft fixed at the 10 and 11 o'clock positions can restore knee function in response to both externally applied anterior tibial and combined rotatory loads by comparing the biomechanical results with each other and with the intact knee.Biomechanical experiment using human cadaveric specimens.Ten human cadaveric knees (age, 41+/-13 years) were reconstructed by placing a bone-patellar tendon-bone graft at the 10 and 11 o'clock positions, in a randomized order, and then tested using a robotic/universal force-moment sensor testing system. Two external loading conditions were applied: (1) 134 N anterior tibial load with the knee at full extension, 15 degrees, 30 degrees, 60 degrees, and 90 degrees of flexion, and (2) a combined rotatory load of 10 N-m valgus and 5 N-m internal tibial torque with the knee at 15 degrees and 30 degrees of flexion. The resulting kinematics of the reconstructed knee and in situ forces in the ACL graft were determined for each femoral tunnel position.In response to a 134-N anterior tibial load, anterior tibial translation (ATT) for both femoral tunnel positions was not significantly different from the intact knee except at 90 degrees of knee flexion as well as at 60 degrees of knee flexion for the 10 o'clock position. There was no significant difference in the ATT between the 10 and 11 o'clock positions, except at 90 degrees of knee flexion. Under a combined rotatory load, however, the coupled ATT for the 11 o'clock position was approximately 130% of that for the intact knee at 15 degrees and 30 degrees of flexion. For the 10 o'clock position, the coupled ATT was not significantly different from the intact knee at 15 degrees of flexion and approximately 120% of that for the intact knee at 30 degrees of flexion. Coupled ATT for the 10 o'clock position was significantly smaller than for the 11 o'clock position at 15 degrees and 30 degrees of flexion. The in situ force in the ACL graft was also significantly higher for the 10 o'clock position than the 11 o'clock position at 30 degrees of flexion in response to the same loading condition (70 +/- 18 N v 60 +/- 15 N, respectively).The 10 o'clock position more effectively resists rotatory loads when compared with the 11 o'clock position as evidenced by smaller ATT and higher in situ force in the graft. Despite the fact that ACL grafts placed at the 10 or 11 o'clock positions are equally effective under an anterior tibial load, neither femoral tunnel position was able to fully restore knee stability to the level of the intact knee.

Various techniques are used to produce the pivot shift phenomenon after anterior cruciate ligament (ACL) injury. In particular, the amount of applied axial tibial torque varies among examiners. Thus, the objective of this study was to determine the effect of the magnitude and direction of axial tibial torque in combination with valgus torque on the resulting knee kinematics during such a simulated pivot shift test.This was a biomechanical study that used cadaveric knees with the intact knee of the same specimen serving as a control.On 19 human cadaveric knees (age, 26 to 69 years), a constant 10-Nm valgus torque was applied at 15 degrees of knee flexion. Then, internal and external tibial torque was applied incrementally from 0 to 10 Nm and the resulting kinematics of the ACL-intact and ACL-deficient knee, as well as the in situ force in the ACL, were measured using a robotic/universal force-moment sensor testing system.In response to isolated valgus torque, the coupled anterior tibial translation for the ACL-intact and ACL-deficient knee was 1.6 +/- 2.4 mm and 8.5 +/- 4.7 mm, respectively; therefore the difference between the ACL-intact and ACL-deficient knee was 6.9 +/- 3.4 mm. With an external tibial torque greater than 5 Nm, the tibia translated up to 4 mm posteriorly for both the ACL-intact and ACL-deficient knee. Whereas, internal tibial torque greater than 1.6 Nm caused a rapid increase in coupled anterior tibial translation up to 10.2 mm in the ACL-deficient knee, while causing only a gradual increase for the ACL-intact knee. With excessive internal torque of 10 Nm, the difference in coupled anterior tibial translation was only 4.4 +/- 2.2 mm, suggesting a decrease in the sensitivity of the test. Correspondingly, the in situ force in the ACL under 10 Nm valgus tibial torque was 43 +/- 17 N, and increased up to 87 +/- 32 N as a 10-Nm internal torque was added. By applying a 3.3-Nm external tibial torque in addition to the 10-Nm valgus torque, the in situ force decreased to 21 +/- 14 N.This study showed that a minimal amount of internal torque in combination with valgus torque may be a suitable way to elicit a pivot shift from an ACL-deficient knee.