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.     

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.     

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.     

The effects of ACL deficiency on mediolateral translation and varus-valgus rotation

Background The anterior cruciate ligament (ACL) constrains the anterior translation and axial rotation of the tibia. However, the effect of ACL injury on the mediolateral translation and varus-valgus rotation of the tibia is unknown. Because of the oblique orientation of the ACL, we hypothesized that ACL deficiency alters mediolateral translation and varus-valgus rotation.

Methods The kinematics of 9 cadavers from full extension to 90° of flexion under various loading conditions were measured before and after ACL resection using a robotic testing system.

Results ACL deficiency increased the medial translation of the tibia and valgus rotation, especially at 15° and 30° of flexion. For example, at 15°, ACL deficiency increased the medial translation from 1.2 (SD 0.9) mm to 1.8 (SD 1.1) mm in response to a quadriceps load. The valgus rotation also increased from 0.8° (SD 0.6) to 1.7° (SD 0.8).

Interpretation ACL deficiency altered both the mediolateral tibial translation and valgus-varus rotation under various loading conditions. The increased medial tibial translation could shift the contact in the medial compartment towards the medial tibial spine, a region where degeneration is observed in ACL-deficient patients. In addition to restoring anterior laxity, ACL reconstruction might need to restore the mediolateral translation of the tibia and varus-valgus rotation of the knee.     

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.     

Method for setting total graft force and load sharing in augmented ACL grafts

The objective of this study was to develop a method for obtaining a controllable and reproducible immediate postoperative mechanical state in a knee with an anterior cruciate ligament (ACL) reconstruction. This method, called the force-setting technique, was demonstrated using a composite graft consisting of the middle third of the patellar tendon with bone blocks (PT) and the ligament augmentation device (LAD). The total graft force was set to match the force in the intact ACL at 30 degrees flexion with the knee under the same standardized external load, while at the same time the load sharing between the biologic and augmentation components was controlled. The total graft force was set to match the ACL force three separate times in each knee, with ratios of load sharing set at the following levels: 50% PT-50% LAD, 25% PT-75% LAD, and 75% PT-25% LAD. ACL, PT, LAD, and collateral forces were measured using buckle transducers, and three-dimensional knee motion was measured using an instrumented spatial linkage as 90 N anteriorly directed tibial loads were applied to eight specimens at 0 degree, 30 degrees, 60 degrees, and 90 degrees flexion with an intact ACL, an excised ACL, and the three load-sharing reconstruction states. The total graft force could be consistently set to within an average of 2% of the intact ACL force at 30 degrees flexion, and load sharing between the graft segments could be set to within an average of 5.1% of the desired ratio at 30 degrees.(ABSTRACT TRUNCATED AT 250 WORDS)     

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.     

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.     

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。     

The effect of isolated popliteus tendon complex injury on graft force in anterior cruciate ligament reconstructed knees

Failure to diagnose injury to the posterolateral structures has been found to increase the forces experienced by the anterior cruciate ligament (ACL) and ACL grafts which may cause their subsequent failure. An isolated injury to the popliteus complex (PC) consisting of the popliteus tendon and popliteofibular ligament is not uncommon. Therefore, the purpose of this study was to discover if an isolated injury to the PC can significantly affect the forces experienced by the ACL graft under external loading conditions. We hypothesised that, under external tibial torque, the ACL graft will experience a significant increase in force, in knees with PC injury compared to the intact PC condition. Under varus tibial torque (10 N m), we observed minimal changes in the varus tibial rotation due to isolated sectioning of the PC in an ACL reconstructed knee (P > 0.05). Consequently, no significant increase in the ACL graft force was observed under varus tibial torque. In contrast, sectioning the PC resulted in a significant increase in the external tibial rotation compared to the intact PC knee condition under the external rotational tibial torque (5 N m) at all flexion angles (P < 0.05). These changes in kinematics under external tibial torque were manifested as elevated ACL graft forces at all selected flexion angles (P < 0.05). Prompt diagnosis of isolated PC injury and its treatment are warranted to prevent potential failure of ACL reconstruction.     

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     

Anterolateral rotatory instability of the knee: Cadaver study of extraarticular patellar-tendon transposition

A cadaver knee-testing system was used to analyze the effect of an extraarticular reconstruction for anterolateral rotatory instability in which the lateral one third of the patellar tendon with a patellar bone block was transposed to the lateral femoral condyle. Ligament and reconstruction tendon forces were measured using buckle transducers, and joint motion was measured using an instrumented spatial linkage as 90 N anteriorly directed tibial loads were applied to seven knee specimens at 0°, 30°, 60°, and 90° of flexion by a pneumatic load apparatus. This was done for each knee with first an intact, then an excised anterior cruciate ligament, and finally the extraarticular reconstruction.

Forces in the transposed graft exhibited an isotonic pattern over the flexion range, unlike the intact anterior cruciate ligament, which was more highly loaded in extension than in flexion. The transposition of the patellar tendon led to external rotation of the tibia In both unloaded and anterior load conditions throughout flexion. Collateral ligament forces increased with anterior cruciate ligament excision, with the force in the medial ligament remaining higher than normal with the reconstruction, while the lateral forces became lower than normal.     

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     

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.     

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.     

Determination of the in situ loads on the human anterior cruciate ligament

A noncontact, kinematic method was used to determine the lengths and in situ loads borne by portions of the human anterior cruciate ligament (ACL) by the combination of kinematic data from the intact knee and load-length curves of the isolated ACL. Specimens from knees of cadavers of young people were tested in passive flexion and extension as well as with 100 N of anterior tibial drawer at 0, 30, 45, and 90° of flexion. The results showed that the in situ load on the whole ACL (as much as 129 N) can exceed the magnitude of the applied anterior tibial drawer. The load distribution within the ligament changes with flexion of the knee. The anterior and posterior portions share the anterior drawer force equally toward full extension. However, at flexion >45°, the anterior portion supports 90–95% of the load. This information is important for the determination of the function of the entire ACL and of its subportions in response to external loading of the intact knee. In particular, the preferential loading found for one of the portions of the ACL demonstrates that successful operative reconstruction of this ligament may not be achieved simply by reproduction of its gross anatomy; consideration of the role of the ligament in the overall kinematics of the knee is necessary.     

A quantitative analysis of valgus torque on the ACL: a human cadaveric study.

The loads needed to elicit a positive pivot shift test in a knee with an anterior cruciate ligament (ACL) rupture have not been quantified. The coupled anterior tibial translation (ATT), coupled internal tibial rotation (ITR), and the in situ force in the ACL in response to a valgus torque, an inherent component of the pivot shift test, were measured in 10 human cadaveric knee specimens. Using a robotic/universal force-moment sensor testing system, valgus torques ranging from 0.0 to 10.0 Nm were applied in nine increments on the intact and ACL-deficient knee in flexion ranging from 0 degrees to 90 degrees. At 15 degrees of knee flexion, the coupled ATT and ITR were significantly increased in the ACL-deficient knee when compared to the intact knee. Coupled ATT increased a maximum of 291% (6.7 mm, p<0.05), while coupled ITR increased a maximum of 85% (5.1 degrees, p<0.05). At 30 degrees, the increases in coupled ATT and ITR were significant at valgus loads of 3.3 Nm and greater with a maximum increase in coupled ATT of 137% (6.3 mm, p<0.05) and a maximum increase in coupled ITR of 38% (3.6 degrees, p<0.05). At 45 degrees, coupled ATT increased significantly (maximum of 69%, 4.4 mm, p<0.05), but only at torques > or =6.7 Nm. The in situ force in the ACL was less than 20 N for all flexion angles when a torque between 3.3 and 5.0 Nm was applied. Low valgus torque elicited tibial subluxation in the ACL-deficient knee with low in situ ACL forces, similar to a positive pivot shift test. Thus, application of a valgus torque may be suitable to evaluate ACL-deficient and ACL-reconstructed knees, since subluxation can be achieved with minimal harm to the ACL graft. This work is important in understanding one load component needed for the pivot shift examination; further studies quantifying other load components are essential for better comprehension of the in vivo pivot shift examination.