Knee stability and graft function following anterior cruciate ligament reconstruction: Comparison between 11 o'clock and 10 o'clock femoral tunnel placement

Purpose: 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. Type of Study: Biomechanical experiment using human cadaveric specimens. Methods: 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°, 30°, 60°, and 90° 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° and 30° of flexion. The resulting kinematics of the reconstructed knee and in situ forces in the ACL graft were determined for each femoral tunnel position. Results: 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° of knee flexion as well as at 60° 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° 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° and 30° of flexion. For the 10 o'clock position, the coupled ATT was not significantly different from the intact knee at 15° of flexion and approximately 120% of that for the intact knee at 30° of flexion. Coupled ATT for the 10 o'clock position was significantly smaller than for the 11 o'clock position at 15° and 30° 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° of flexion in response to the same loading condition (70 ± 18 N v 60 ± 15 N, respectively). Conclusions: 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.Arthroscopy: The Journal of Arthroscopic and Related Surgery, Vol 19, No 3 (March), 2003: pp 297–304     

Distribution of in situ forces in the anterior cruciate ligament in response to rotatory loads.

The anterior cruciate ligament (ACL) can be anatomically divided into anteromedial (AM) and posterolateral (PL) bundles. Current ACL reconstruction techniques focus primarily on reproducing the AM bundle, but are insufficient in response to rotatory loads. The objective of this study was to determine the distribution of in situ force between the two bundles when the knee is subjected to anterior tibial and rotatory loads. Ten cadaveric knees (50+/-10 years) were tested using a robotic/universal force-moment sensor (UFS) testing system. Two external loading conditions were applied: a 134 N anterior tibial load at full knee extension and 15 degrees, 30 degrees, 60 degrees, and 90 degrees of flexion and a combined rotatory load of 10 Nm valgus and 5 Nm internal tibial torque at 15 degrees and 30 degrees of flexion. The resulting 6 degrees of freedom kinematics of the knee and the in situ forces in the ACL and its two bundles were determined. Under an anterior tibial load, the in situ force in the PL bundle was the highest at full extension (67+/-30 N) and decreased with increasing flexion. The in situ force in the AM bundle was lower than in the PL bundle at full extension, but increased with increasing flexion, reaching a maximum (90+/-17 N) at 60 degrees of flexion and then decreasing at 90 degrees. Under a combined rotatory load, the in situ force of the PL bundle was higher at 15 degrees (21+/-11 N) and lower at 30 degrees of flexion (14+/-6 N). The in situ force in the AM bundle was similar at 15 degrees and 30 degrees of knee flexion (30+/-15 vs. 35+/-16 N, respectively). Comparing these two external loading conditions demonstrated the importance of the PL bundle, especially when the knee is near full extension. These findings provide a better understanding of the function of the two bundles of the ACL and could serve as a basis for future considerations of surgical reconstruction in the replacement of the ACL.     

Interaction between the ACL graft and MCL in a combined ACL+MCL knee injury using a goat model

The optimal treatment for the MCL in the combined ACL and MCL-injured knee is still controversial. Therefore, we designed this study to examine the mechanical interaction between the ACL graft and the MCL in a goat model using a robotic/universal force-moment sensor testing system. The kinematics of intact, ACL-deficient, ACL-reconstructed, and ACL-reconstructed/MCL-deficient knees, as well as the in situ forces in the ACL, ACL graft, and MCL were determined in response to two external loading conditions: 1) anterior tibial load of 67 N and 2) valgus moment of 5 N-m. With an anterior tibial load, anterior tibial translation in the ACL-deficient knee significantly increased from 2.0 and 2.2 mm to 15.7 and 18.1 mm at 30° and 60° of knee flexion, respectively. The in situ forces in the MCL also increased from 8 to 27 N at 60° of knee flexion. ACL reconstruction reduced the anterior tibial translation to within 2 mm of the intact knee and significantly reduced the in situ force in the MCL to 17 N. However, in response to a valgus moment, the in situ forces in the ACL graft increased significantly by 34 N after transecting the MCL. These findings show that ACL deficiency can increase the in situ forces in the MCL while ACL reconstruction can reduce the in situ forces in the MCL in response to an anterior tibial load. On the other hand, the ACL graft is subjected to significantly higher in situ forces with MCL deficiency during an applied valgus moment. Therefore, the ACL-reconstructed knee with a combined ACL and MCL injury should be protected from high valgus moments during early healing to avoid excessive loading on the graft.     

In-situ force in the medial and lateral structures of intact and ACL-deficient knees

The anterior cruciate ligament (ACL) is the major contributor to limit excessive anterior tibial translation (ATT) when the knee is subjected to an anterior tibial load. However, the importance of the medial and lateral structures of the knee can also play a significant role in resisting anterior tibial loads, especially in the event of an ACL injury. Therefore, the objective of this study was to determine quantitatively the increase in the in-situ forces in the medial collateral ligament (MCL) and posterolateral structures (PLS) of the knee associated with ACL deficiency. Eight fresh-frozen cadaveric human knees were subjected to a 134-N anterior tibial load at full extension and at 15°, 30°, 60°, and 90° of knee flexion. The resulting 5 degrees of freedom kinematics were measured for the intact and the ACL-deficient knees. A robotic/universal force-moment sensor testing system was used for this purpose, as well as to determine the in-situ force in the MCL and PLS in the intact and ACL-deficient knees. For the intact knee, the in-situ forces in both the MCL and PLS were less than 20 N for all five flexion angles tested. But in the ACL-deficient knee, the in-situ forces in the MCL and PLS, respectively, were approximately two and five times as large as those in the intact knee (P < 0.05). The results of this study demonstrate that, although both the MCL and PLS play only a minor role in resisting anterior tibial loads in the intact knee, they become significant after ACL injury. Received: December 3, 1999 / Accepted: July 19, 2000     

单隧道双束前交叉韧带重建不同移植物固定角度的生物力学研究

目的探讨在何种初始张力及屈膝角度下进行移植物固定能够使单隧道双束前交叉韧带（ACL）重建术后的膝关节更好地恢复原有的运动学功能。方法将16具新鲜冰冻尸体膝关节随机分为四组，每四个膝关节为一组，分别为T20A20（在20N的初始张力下屈膝20。固定）、T20A45、T40A20及T40A45。使用BOSE—ElectroForce材料生物力学性能测试仪定量测量上述四组膝关节在屈曲30。及90。时胫前载荷（134N）下的胫前位移和旋转载荷（5N×m胫骨内旋）下胫骨内旋角度。所有组均采用直径相等的自体胭绳肌腱、相同的隧道定位方法及固定装置进行韧带重建。结果（1）胫前载荷（134N）下的胫前位移：T20A20、T20A45与完整组比较无统计学差异（F=0．56，P〉0．05），T40A20、T40A45与完整组比较有统计学差异（F=85．35，P〈0．05）；（2）旋转载荷（5N×m胫骨内旋）下的胫骨内旋角度：T20A20、T40A20与完整组比较无统计学差异（F=0．74，P〉0．05），T20A45、T40A45与完整组比较有统计学差异（F=145．24，P〈0．05）。40N初始张力下进行韧带固定会使重建术后膝关节伸屈约束过度，而屈膝45。进行韧带固定则使重建术后膝关节内旋约束过度。在20N的初始张力下屈膝20。进行韧带固定能使重建术后膝关节的前后及旋转稳定性更接近于正常。结论单隧道双束ACL重建术中，两束韧带分别在20N的初始张力下屈膝20°进行固定能够恢复膝关节的前后及旋转稳定性，从而更好地恢复原有的运动学功能。     

ACL forces and knee kinematics produced by axial tibial compression during a passive flexion–extension cycle

Application of axial tibial force to the knee at a fixed flexion angle has been shown to generate ACL force. However, direct measurements of ACL force under an applied axial tibial force have not been reported during a passive flexion–extension cycle. We hypothesized that ACL forces and knee kinematics during knee extension would be significantly different than those during knee flexion, and that ACL removal would significantly increase all kinematic measurements. A 500 N axial tibial force was applied to intact knees during knee flexion–extension between 0° and 50°. Contact force on the sloping lateral tibial plateau produced a coupled internal + valgus rotation of the tibia, anterior tibial displacement, and elevated ACL forces. ACL forces during knee extension were significantly greater than those during knee flexion between 5° and 50°. During knee extension, ACL removal significantly increased anterior tibial displacement between 0° and 50°, valgus rotation between 5° and 50°, and internal tibial rotation between 5° and 15°. With the ACL removed, kinematic measurements during knee extension were significantly greater than those during knee flexion between 5° and 45°. The direction of knee flexion–extension movement is an important variable in determining ACL forces and knee kinematics produced by axial tibial force. © 2013 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 32:89–95, 2014.     

Comparison of the ACL and ACL graft forces before and after ACL reconstruction an in-vitro robotic investigation

Background?Long-term follow-up studies have indi-cated that there is an increased incidence of arthrosis following anterior cruciate ligament (ACL) reconstruc-tion, suggesting that the reconstruction may not repro-duce intact ACL biomechanics. We studied not only the magnitude but also the orientation of the ACL and ACL graft forces

Methods?10 knee specimens were tested on a robotic testing system with the ACL intact, deficient, and recon-structed (using a bone-patella tendon-bone graft). The magnitude and orientation of the ACL and ACL graft forces were determined under an anterior tibial load of 130?N at full extension, and 15, 30, 60, and 90° of flexion. Orientation was described using elevation angle (the angle formed with the tibial plateau in the sagit-tal plane) and deviation angle (the angle formed with respect to the anteroposterior direction in the transverse plane)

Results?ACL reconstruction restored anterior tibial translation to within 2.6?mm of that of the intact knee under the 130-N anterior load. Average internal tibial rotation was reduced after ACL reconstruction at all flexion angles. The force vector of the ACL graft was significantly different from the ACL force vector. The average values of the elevation and deviation angles of the ACL graft forces were higher than that of the intact ACL at all flexion angles

Interpretation?Contemporary single bundle ACL reconstruction restores anterior tibial translation under anterior tibial load with different forces (both magni-tude and orientation) in the graft compared to the intact ACL. Such graft function might alter knee kinematics in other degrees of freedom and could overly constrain the tibial rotation. An anatomic ACL reconstruction should reproduce the magnitude and orientation of the intact ACL force vector, so that the 6-degrees-of-freedom knee kinematics and joint reaction forces can be restored.     

The forces in the anterior cruciate ligament and knee kinematics during a simulated pivot shift test: A human cadaveric study using robotic technology

Purpose: Although it is well known that the anterior cruciate ligament (ACL) is a primary restraint of the knee under anterior tibial load, the role of the ACL in resisting internal tibial torque and the pivot shift test is controversial. The objective of this study was to determine the effect of these 2 external loading conditions on the kinematics of the intact and ACL-deficient knee and the in situ force in the ACL. Type of Study: This study was a biomechanical study that used cadaveric knees with the intact knee of the specimen serving as a control. Materials and Methods: Twelve human cadaveric knees were tested using a robotic/universal force-moment sensor testing system. This system applied (1) a 10–Newton meter (Nm) internal tibial torque and (2) a combined 10-Nm valgus and 10-Nm internal tibial torque (simulated pivot shift test) to the intact and the ACL-deficient knee. Results: In the ACL-deficient knee, the isolated internal tibial torque significantly increased coupled anterior tibial translation over that of the intact knee by 94%, 48%, and 19% at full extension, 15°, and 30° of flexion, respectively (P <.05). In the case of the simulated pivot shift test, there were similar increases in anterior tibial translation, i.e., 103%, 61%, and 32%, respectively (P <.05). Furthermore, the anterior tibial translation under the simulated pivot shift test was significantly greater than under an isolated internal tibial torque (P <.05). Under the simulated pivot shift test, the in situ forces in the ACL were 83 ± 16 N at full extension and 93 ± 23 N at 15° of knee flexion. These forces were also significantly higher when compared with those for an isolated internal tibial torque (P <.05). Conclusion: Our data indicate that the ACL plays an important role in restraining coupled anterior tibial translation in response to the simulated pivot shift test as well as under an isolated internal tibial torque, especially when the knee is near extension. These findings are also consistent with the clinical observation of anterior tibial subluxation during the pivot shift test with the knee near extension.Arthroscopy: The Journal of Arthroscopic and Related surgery, Vol 16, No 6 (September), 2000: pp 633–639     

Interaction between the ACL graft and MCL in a combined ACL+MCL knee injury using a goat model

The optimal treatment for the MCL in the combined ACL and MCL-injured knee is still controversial. Therefore, we designed this study to examine the mechanical interaction between the ACL graft and the MCL in a goat model using a robotic/universal force-moment sensor testing system. The kinematics of intact, ACL-deficient, ACL-reconstructed, and ACL-reconstructed/ MCL-deficient knees, as well as the in situ forces in the ACL, ACL graft, and MCL were determined in response to two external loading conditions: 1) anterior tibial load of 67 N and 2) valgus moment of 5 N-m. With an anterior tibial load, anterior tibial translation in the ACL-deficient knee significantly increased from 2.0 and 2.2 mm to 15.7 and 18.1 mm at 30 degrees and 60 degrees of knee flexion, respectively. The in situ forces in the MCL also increased from 8 to 27 N at 60 degrees of knee flexion. ACL reconstruction reduced the anterior tibial translation to within 2 mm of the intact knee and significantly reduced the in situ force in the MCL to 17 N. However, in response to a valgus moment, the in situ forces in the ACL graft increased significantly by 34 N after transecting the MCL. These findings show that ACL deficiency can increase the in situ forces in the MCL while ACL reconstruction can reduce the in situ forces in the MCL in response to an anterior tibial load. On the other hand, the ACL graft is subjected to significantly higher in situ forces with MCL deficiency during an applied valgus moment. Therefore, the ACL-reconstructed knee with a combined ACL and MCL injury should be protected from high valgus moments during early healing to avoid excessive loading on the graft.     

Interaction between the ACL graft and MCL in a combined ACL+MCL knee injury using a goat model

The optimal treatment for the MCL in the combined ACL and MCL-injured knee is still controversial. Therefore, we designed this study to examine the mechanical interaction between the ACL graft and the MCL in a goat model using a robotic/universal force-moment sensor testing system. The kinematics of intact, ACL-deficient, ACL-reconstructed, and ACL-reconstructed/MCL-deficient knees, as well as the in situ forces in the ACL, ACL graft, and MCL were determined in response to two external loading conditions: 1) anterior tibial load of 67 N and 2) valgus moment of 5 N-m. With an anterior tibial load, anterior tibial translation in the ACL-deficient knee significantly increased from 2.0 and 2.2 mm to 15.7 and 18.1 mm at 30° and 60° of knee flexion, respectively. The in situ forces in the MCL also increased from 8 to 27 N at 60° of knee flexion. ACL reconstruction reduced the anterior tibial translation to within 2 mm of the intact knee and significantly reduced the in situ force in the MCL to 17 N. However, in response to a valgus moment, the in situ forces in the ACL graft increased significantly by 34 N after transecting the MCL. These findings show that ACL deficiency can increase the in situ forces in the MCL while ACL reconstruction can reduce the in situ forces in the MCL in response to an anterior tibial load. On the other hand, the ACL graft is subjected to significantly higher in situ forces with MCL deficiency during an applied valgus moment. Therefore, the ACL-reconstructed knee with a combined ACL and MCL injury should be protected from high valgus moments during early healing to avoid excessive loading on the graft.     

Comparison of the ACL and ACL graft forces before and after ACL reconstruction: an in-vitro robotic investigation

Background Long-term follow-up studies have indi-cated that there is an increased incidence of arthrosis following anterior cruciate ligament (ACL) reconstruc-tion, suggesting that the reconstruction may not repro-duce intact ACL biomechanics. We studied not only the magnitude but also the orientation of the ACL and ACL graft forces

Methods 10 knee specimens were tested on a robotic testing system with the ACL intact, deficient, and recon-structed (using a bone-patella tendon-bone graft). The magnitude and orientation of the ACL and ACL graft forces were determined under an anterior tibial load of 130 N at full extension, and 15, 30, 60, and 90° of flexion. Orientation was described using elevation angle (the angle formed with the tibial plateau in the sagit-tal plane) and deviation angle (the angle formed with respect to the anteroposterior direction in the transverse plane)

Results ACL reconstruction restored anterior tibial translation to within 2.6 mm of that of the intact knee under the 130-N anterior load. Average internal tibial rotation was reduced after ACL reconstruction at all flexion angles. The force vector of the ACL graft was significantly different from the ACL force vector. The average values of the elevation and deviation angles of the ACL graft forces were higher than that of the intact ACL at all flexion angles

Interpretation Contemporary single bundle ACL reconstruction restores anterior tibial translation under anterior tibial load with different forces (both magni-tude and orientation) in the graft compared to the intact ACL. Such graft function might alter knee kinematics in other degrees of freedom and could overly constrain the tibial rotation. An anatomic ACL reconstruction should reproduce the magnitude and orientation of the intact ACL force vector, so that the 6-degrees-of-freedom knee kinematics and joint reaction forces can be restored.     

Effect of the iliotibial band on knee biomechanics during a simulated pivot shift test.

The purpose of this study was to evaluate the effect of the iliotibial band (ITB) on the kinematics of anterior cruciate ligament (ACL) intact and deficient knees and also on the in situ force in the ACL during a simulated pivot shift test. A combination of 10 N-m valgus and 5 N-m internal tibial torques was applied to 10 human cadaveric knees at 15 degrees, 30 degrees, 45 degrees, and 60 degrees of flexion using a robotic/universal force-moment sensor testing system. ITB forces of 0, 22, 44, and 88 N were also applied. An 88 N ITB force significantly decreased coupled anterior tibial translation of ACL deficient knees by 32%-45% at high flexion angles, but did not have a significant effect at low flexion angles. Further, an 88 N ITB force significantly decreased in situ forces in the ACL at all flexion angles by 23%-40%. These results indicate that during the pivot shift test, the ITB can improve tibial reduction at high flexion angles while not affecting subluxation at low flexion angles. Additionally, the action of the ITB as an ACL agonist suggests that its use as an ACL graft might hinder knee stability in response to rotatory load.     

Single– versus two–femoral socket anterior cruciate ligament reconstruction technique: Biomechanical analysis using a robotic simulator

Purpose: Although anterior cruciate ligament (ACL) reconstruction with multistrand autogenous hamstring tendons has been widely performed using a single femoral socket (SS), it is currently advocated to individually reconstruct 2 bundles of the ACL using 2 femoral sockets (TS). However, the difference in biomechanical characteristics between them is unknown. The objective of this study was to clarify their biomechanical differences. Type of Study: This is a cross-over trial using cadaveric knees. Methods: Seven intact human cadaveric knees were mounted in a robotic simulator developed in our laboratory. By applying anterior and posterior tibial load up to ± 100 N at 0°, 15°, 30°, 60°, and 90° of flexion, tibial displacement and load were recorded. After cutting the ACL, the knees underwent ACL reconstruction using TS, followed by that using SS, with 44 or 88 N of initial grafts tension at 20° of flexion. The above-mentioned tests were performed on each reconstructed knee. Results: The tibial displacement in the TS technique was significantly smaller than that in the SS at smaller flexion angles in response to anterior and posterior tibial load of ± 100 N, and the in situ force in the former was significantly greater than that in the latter at smaller flexion angles. Furthermore, in the TS technique, the posterolateral graft acted dominantly in extension, while the anteromedial graft mainly resisted against anterior tibial load in flexion. However, in the SS technique, the anteriorly located graft functioned more predominantly than the posteriorly located graft at all flexion angles. Conclusions: The ACL reconstruction via TS using quadrupled hamstring tendons provides better anterior-posterior stability compared with the conventional reconstruction using a single socket.Arthroscopy: The Journal of Arthroscopic and Related Surgery, Vol 17, No 7 (September), 2001: pp 708–716     

Combined knee loading states that generate high anterior cruciate ligament forces

Injuries to the anterior cruciate ligament frequently occur under combined mechanisms of loading. This in vitro study was designed to measure levels of ligament force under dual combinations of individual loading states and to determine which combinations generated high force. Resultant force was recorded as the knee was extended passively from 90° of flexion to 5° of hyperextension under constant tibial loadings. The individual loading states were 100 N of anterior tibial force, 10 Nm of varus and valgus moment, and 10 Nm of internal and external tibial torque. Straight anterior tibial force was the most direct loading, mechanism; the mean ligament force was approximately equal to applied anterior tibial force near 30° of flexion and to 150% of applied tibial force at full extension. The addition of internal tibial torque to a knee loaded by anterior tibial force produced dramatic increases of force at full extension and hyperextension. This loading combination produced the highest ligament forces recorded in the study and is the most dangerous in terms of potential injury to the ligament. In direct contrast, the addition of external tibial torque to a knee loaded by anterior tibial force decreased the force dramatically for flexed positions of the knee; at close to 90° of flexion, the anterior cruciate ligament became completely unloaded. The addition of varus moment to a knee loaded by anterior tibial force increased the force in extension and hyperextension, whereas the addition of valgus moment increased the force at flexed positions. These states of combined loading also could present an increased risk for injury. Internal tibial torque is an important loading mechanism of the anterior cruciate ligament for an extended knee. The overall risk of injury to the ligament from varus or valgus moment applied in combination with internal tibial torque is similar to the risk from internal tibial torque alone. External tibial torque was a relatively unimportant mechanism for generating anterior cruciate ligament force.     

单隧道双束和单束ACL重建的生物力学比较研究

目的比较单隧道双束和单隧道单束ACL重建膝关节稳定性的差异。方法选用6侧人体膝关节标本,保留完整的关节囊及周围韧带,行单隧道双束和单束ACL重建,在MTS-858生物材料试验系统上测试膝关节在胫前加载(134N)和旋转加载(5N·m内旋胫骨)下屈曲0°、15°、30°、60°、90°位时的运动学反应。每个膝关节在4个不同条件下进行测试:ACL完整、ACL损伤、单隧道双束重建ACL以及单隧道单束重建ACL,其中单隧道双束及单束ACL均采用双股腘绳肌腱。结果 (1)胫前加载:双束组在屈曲30°、60°和90°位,单束组在屈曲90°位时关节前后稳定性获得良好恢复(P0.05);在屈曲60°位时双束组的胫前位移明显低于单束组,差异有统计学意义(P0.05)。(2)旋转加载:与ACL完整组相比较,双束组的胫骨内旋角度在屈曲0°、60°位时无明显变化(P0.05),屈曲90°位时明显减少(P0.05);单束组在屈曲0°时无明显变化(P0.05)。屈曲60°和90°位时双束组的胫骨内旋角度明显小于单束组,差异有统计学意义(P0.05)。结论与单隧道单束ACL重建相比,单隧道双束ACL重建能够更好地恢复膝关节前后稳定性及旋转稳定性。     

In situ forces in the anterior cruciate ligament and its bundles in response to anterior tibial loads

The anterior cruciate ligament has a complex fiber anatomy and is not considered to be a uniform structure. Current anterior cruciate ligament reconstructions succeed in stabilizing the knee, but they neither fully restore normal knee kinematics nor reproduce normal ligament, function. To improve the outcome of the reconstruction, it may be necessary to reproduce the complex function of the intact anterior cruciate ligament in the replacement graft. We examined the in situ forces in nine human anterior cruciate ligaments as well as the force distribution between the anteromedial and posterolateral bundles of the ligament in response to applied anterioi tibial loads ranging from 22 to 110 N at knee flexion angles of 0–90°. The analysis was performed using a robotic manipulator in conjunction with a universal force-moment sensor. The in situ forces were determined with no device attached to the ligament, while the knee was permitted to move freely in response to the applied loads. We found that the in situ forces in the anterior cruciate ligament ranged from 12.8 ± 7.3 N under 22 N of anterior tibial load applied at 90° of knee flexion to 110.6 ± 14.8 N under 110 N of applied load at 15° of flexion. The magnitude of the in situ force in the posterolateral bundle was larger than that in the anteromedial bundle at knee flexion angles between 0 and 45°, reaching a maximum of 75.2 ± 18.3 N at 15° of knee flexion under an anterior tibial load of 110 N. The magnitude of the in situ force in the posterolateral bundle was significantly affected by knee flexion angle and anterior tibial load in a fashion remarkably similar to that seen in the anterior cruciate ligament. The magnitude of the in situ force in the anteromedial bundle, in contrast, remained relatively constant, not changing with flexion angle. Significant differences in the direction of the in situ force between the anteromedial bundle and the posterolateral bundle were found only at flexion angles of 0 and 60° and only under applied anterior tibial loads greater than 66 N. We have demonstrated the nonuniformity of the anterior cruciate ligament under unconstrained anterior tibial loads. Our data further suggest that in order for the anterior cruciate ligament replacement graft to reproduce the in situ forces of the normal anterior cruciate ligament, reconstruction techniques should take into account the role of the posterolateral bundle in addition to that of the anteromedial bundle.     

In situ forces in the human posterior cruciate ligament in response to muscle loads: a cadaveric study.

The objectives of this study were to determine the effects of hamstrings and quadriceps muscle loads on knee kinematics and in situ forces in the posterior cruciate ligament of the knee and to evaluate how the effects of these muscle loads change with knee flexion. Nine human cadaveric knees were studied with a robotic manipulator/universal force-moment sensor testing system. The knees were subjected to an isolated hamstrings load (40 N to both the biceps and the semimembranosus), a combined hamstrings and quadriceps load (the hamstrings load and a 200-N quadriceps load), and an isolated quadriceps load of 200 N. Each load was applied with the knee at full extension and at 30, 60, 90, and 120 degrees of flexion. Without muscle loads, in situ forces in the posterior cruciate ligament were small, ranging from 6+/-5 N at 30 degrees of flexion to 15+/-3 N at 90 degrees. Under an isolated hamstrings load, the in situ force in the posterior cruciate ligament increased significantly throughout all angles of knee flexion, from 13+/-6 N at full extension to 86+/-19 N at 90 degrees. A posterior tibial translation ranging from 1.3+/-0.6 to 2.5+/-0.5 mm was also observed from full extension to 30 degrees of flexion under the hamstrings load. With a combined hamstrings and quadriceps load, tibial translation was 2.2+/-0.7 mm posteriorly at 120 degrees of flexion ut was as high as 4.6+/-1.7 mm anteriorly at 30 degrees. The in situ force in the posterior cruciate ligament decreased significantly under this loading condition compared with under an isolated hamstrings load, ranging from 6+/-7 to 58+/-13 N from 30 to 120 degrees of flexion. With an isolated quadriceps load of 200 N, the in situ forces in the posterior cruciate ligament ranged from 4+/-3 N at 60 degrees of flexion to 34+/-12 N at 120 degrees. Our findings support the notion that, compared with an isolated hamstrings load, combined hamstrings and quadriceps loads significantly reduce the in situ force in the posterior cruciate ligament. These data are in direct contrast to those for the anterior cruciate ligament. Furthermore, we have demonstrated that the effects of muscle loads depend significantly on the angle of knee flexion.     

The effectiveness of reconstruction of the anterior cruciate ligament with hamstrings and patellar tendon . A cadaveric study comparing anterior tibial and rotational loads

BACKGROUND: The objective of this study was to evaluate the effectiveness of reconstructions of the anterior cruciate ligament to resist anterior tibial and rotational loads. We hypothesized that current reconstruction techniques, which are designed mainly to provide resistance to anterior tibial loads, are less effective in limiting knee instability in response to combined rotational loads. METHODS: Twelve fresh-frozen young human cadaveric knees (from individuals with a mean age [and standard deviation] of 37 +/- 13 years at the time of death) were tested with use of a robotic/universal force-moment sensor testing system. The loading conditions included (1) a 134-N anterior tibial load with the knee at full extension and at 15 degrees, 30 degrees, and 90 degrees of flexion, and (2) a combined rotational load of 10 N-m of valgus torque and 10 N-m of internal tibial torque with the knee at 15 degrees and 30 degrees of flexion. The kinematics of the knees with an intact and a deficient anterior cruciate ligament, as well as the in situ force in the intact anterior cruciate ligament, were determined in response to both loads. Each knee then underwent reconstruction of the anterior cruciate ligament with use of a quadruple semitendinosus-gracilis tendon graft and was tested. A second reconstruction was performed with a bone-patellar tendon-bone graft, and the same knee was tested again. The kinematics of the reconstructed knees and the in situ forces in both grafts were determined. RESULTS: The results demonstrated that both reconstructions were successful in limiting anterior tibial translation under anterior tibial loads. Furthermore, the mean in situ forces in the grafts under a 134-N anterior tibial load were restored to within 78% to 100% of that in the intact knee. However, in response to a combined rotational load, reconstruction with either of the two grafts was not as effective in reducing anterior tibial translation. This insufficiency was further revealed by the lower in situ forces in the grafts, which ranged from 45% to 65% of that in the intact knee. CONCLUSIONS: In current reconstruction procedures, the graft is placed close to the central axis of the tibia and femur, which makes it inadequate for resisting rotational loads. Our findings suggest that improved reconstruction procedures that restore the anatomy of the anterior cruciate ligament may be needed.     

Anterior tibial post impingement in a posterior stabilized total knee arthroplasty.

Despite the numerous long-term success reports of posterior stabilized (PS) total knee arthroplasty (TKA), recent retrieval studies of various PS TKA designs revealed wear and deformation on the anterior side of the tibial post. This study investigated the mechanisms of anterior impingement of the post with the femoral component. Seven cadaveric knees were tested to study kinematics and tibial post biomechanics during simulated heel strike using an in vitro robotic testing system. Intact knee kinematics and in situ anterior cruciate ligament (ACL) forces were determined at hyperextension (0 degree to -9 degrees) and low flexion angles (0 degrees to 30 degrees) under the applied loads. The same knee was reconstructed using a PS TKA. The kinematics and the tibial post contact forces of the TKA were measured under the same loading condition. The ACL in the intact knee carried load and contributed to knee stability at low flexion angles and hyperextension. After TKA, substantial in situ contact forces (252.4 +/- 173 N at 9 degrees of hyperextension) occurred in the tibial post, indicating anterior impingement with the femoral component. Consequently, the TKA showed less posterior femoral translation compared to the intact knee after the impingement. At 9 degrees of hyperextension, the medial condyle of the intact knee translated 0.1 +/- 1.1 mm whereas the medial condyle of the TKA knee translated 5.6 +/- 6.9 mm anteriorly. The lateral condyle of the intact knee translated 1.5 +/- 1.0 mm anteriorly whereas the lateral condyle of the TKA knee translated 2.1 +/- 5.8 mm anteriorly. The data demonstrated that anterior tibial post impingement functions as a substitute for the ACL during hyperextension, contributing to anterior stability. However, anterior post impingement may result in additional polyethylene wear and tibial post failure. Transmitted impingement forces might cause backside wear and component loosening. Understanding the advantages and disadvantages of the tibial post function at low flexion angles may help to further improve component design and surgical techniques and thus enhance knee stability and component longevity after TKA.