Monica Linde-Rosen

Comparison of In Situ Forces and Knee Kinematics in Anteromedial and High Anteromedial Bundle Augmentation for Partially Ruptured Anterior Cruciate Ligament

Background: High tunnel placement is common in single- and double-bundle anterior cruciate ligament (ACL) reconstructions. Similar nonanatomic tunnel placement may also occur in ACL augmentation surgery. Purpose: In this study, in situ forces and knee kinematics were compared between nonanatomic high anteromedial (AM) and anatomic AM augmentation in a knee with isolated AM bundle injury. Study Design: Controlled laboratory study. Methods: Seven fresh-frozen cadaver knees were used (age, 48 ± 12.5 years). First, intact knee kinematics was tested with a robotic–universal force sensor testing system under 2 loading conditions. An 89-N anterior load was applied, and an anterior tibial translation was measured at knee flexion angles of 0°, 30°, 60°, and 90°. Then, combined rotatory loads of 7-N·m valgus and 5-N·m internal tibial rotation were applied at 15° and 30° of knee flexion angles, which mimic the pivot shift. Afterward, only the AM bundle of the ACL was cut arthroscopically, keeping the posterolateral bundle intact. The knee was again tested using the intact knee kinematics to measure the in situ force of the AM bundle. Then, arthroscopic anatomic AM bundle reconstruction was performed with an allograft, and the knee was tested to give the in situ force of the reconstructed AM bundle. Knee kinematics under the 3 conditions (intact, anatomic AM augmentation, and nonanatomic high AM augmentation) and the in situ force were compared and analyzed. Result: The high AM graft had significantly lower in situ force than the intact and anatomic reconstructed AM bundle at 0° of knee flexion (P < .05) and the intact AM bundle at 30° of knee flexion under anterior tibial loading. There were no differences between anatomic graft and intact AM bundle. The high AM graft also had a significantly lower in situ force than the intact and anatomic reconstructed AM with simulated pivot-shift loading at 15° and 30° of flexion (P < .05). Under anterior tibial and rotatory loading, there was a difference in tibial displacement between anatomic and high AM reconstructions and between the high AM graft and intact ACL under rotational loading with the knee at 15° of flexion. Clinical Relevance: Anatomic AM augmentation can lead to biomechanical advantages at time zero when compared with the nonanatomic (high AM) augmentation. Anatomic AM augmentation better restores the knee kinematics to the intact ACL state.

Measurement of the End-to-End Distances Between the Femoral and Tibial Insertion Sites of the Anterior Cruciate Ligament During Knee Flexion and With Rotational Torque

PURPOSE The aim of this study was to determine the end-to-end distance changes in anterior cruciate ligament (ACL) fibers during flexion/extension and internal/external rotation of the knee. METHODS The positional relation between the femur and tibia of 10 knees was digitized on a robotic system during flexion/extension and with an internal/external rotational torque (5 Nm). The ACL insertion site data, acquired by 3-dimensional scanning, were superimposed on the positional data. The end-to-end distances of 5 representative points on the femoral and tibial insertion sites of the ACL were calculated. RESULTS The end-to-end distances of all representative points except the most anterior points were longest at full extension and shortest at 90°. The distances of the anteromedial (AM) and posterolateral (PL) bundles were 37.2 ± 2.1 mm and 27.5 ± 2.8 mm, respectively, at full extension and 34.7 ± 2.4 mm and 20.7 ± 2.3 mm, respectively, at 90°. Only 4 knees had an isometric point, which was 1 of the 3 anterior points. Under an internal torque, both bundles became longer with statistical meaning at all flexion angles (P = .005). The end-to-end distances of all points became longest with internal torque at full extension and shortest with an external torque at 90°. CONCLUSIONS Only 4 of 10 specimens had an isometric point at a variable anterior point. The end-to-end distances of the AM and PL bundles were longer in extension and shorter in flexion. CLINICAL RELEVANCE The nonisometric tendency of the ACL and the end-to-end distance change during knee flexion/extension and internal/external rotation should be considered during ACL reconstruction to avoid overconstraint of the graft.

Acl Graft Position Affects in Situ Graft Force Following Acl Reconstruction

BACKGROUND The purpose of our study was to evaluate the relationship between graft placement and in situ graft force after anterior cruciate ligament (ACL) reconstruction. METHODS Magnetic resonance imaging (MRI) was obtained for twelve human cadaveric knees. The knees, in intact and deficient-ACL states, were subjected to external loading conditions as follows: an anterior tibial load of 89 N at 0°, 15°, 30°, 45°, 60°, and 90° of flexion and a combined rotatory (simulated pivot-shift) load of 5 Nm of internal tibial torque and 7 Nm of valgus torque at 0°, 15°, and 30° of flexion. Three ACL reconstructions were performed in a randomized order: from the center of the tibial insertion site to the center of the femoral insertion site (Mid), the center of the tibial insertion site to a more vertical femoral position (S1), and the center of the tibial insertion site to an even more vertical femoral position (S2). The reconstructions were tested following the same protocol used for the intact state, and graft in situ force was calculated for the two loadings at each flexion angle. MRI was used to measure the graft inclination angle after each ACL reconstruction. RESULTS The mean inclination angle (and standard deviation) was 51.7° ± 5.0° for the native ACL, 51.6° ± 4.1° for the Mid reconstruction (p = 0.85), 58.7° ± 5.4° for S1 (p < 0.001), and 64.7° ± 6.5° for S2 (p < 0.001). At 0°, 15°, and 30° of knee flexion, the Mid reconstruction showed in situ graft force that was closer to that of the native ACL during both anterior tibial loading and simulated pivot-shift loading than was the case for S1 and S2 reconstructions. At greater flexion angles, S1 and S2 had in situ graft force that was closer to that of the native ACL than was the case for the Mid reconstruction. CONCLUSIONS Anatomic ACL reconstruction exposes grafts to higher loads at lower angles of knee flexion. CLINICAL RELEVANCE Rehabilitation and return to sports progression may need to be modified to protect an anatomically placed graft after ACL reconstruction.

A Biomechanical Comparison of 2 Femoral Fixation Techniques for Anterior Cruciate Ligament Reconstruction in Skeletally Immature Patients: Over-the-Top Fixation Versus Transphyseal Technique

PURPOSE The purpose of this study was to compare knee kinematics and in situ forces of the graft between 2 femoral fixation techniques of anterior cruciate ligament (ACL) reconstruction: the over-the-top (OTT) fixation and transphyseal (TP) techniques. METHODS ACL reconstruction in skeletally immature patients is a challenging procedure. Regarding the femoral fixation techniques, 2 methods are commonly used: the OTT fixation and TP techniques. Ten cadaveric knees (mean age, 57 years; range, 48 to 65 years) were tested with the robotic/universal force-moment sensor system by use of (1) an 89-N anterior tibial load at full extension and 15°, 30°, 60°, and 90° of knee flexion and (2) a combined 7-Nm valgus torque and 5-Nm internal tibial rotation torque at 15° and 30° of knee flexion. RESULTS Both OTT and TP ACL reconstruction techniques closely restored the intact knee kinematics and had a significant reduction in anterior tibial translation under an anterior tibial load and in coupled anterior tibial translation under a combined rotatory load when compared with an ACL-deficient knee. When both ACL reconstruction techniques were compared, the only difference found was that the in situ force of the ACL graft reconstructed with the OTT technique in response to a combined rotatory load at 30° of flexion was significantly lower than the ACL graft reconstructed with the TP technique (5.3 ± 3.3 N and 10.7 ± 6.0 N, respectively; P = .013). CONCLUSIONS This time 0 testing showed that both ACL reconstruction techniques, OTT and TP, can reproduce the kinematics of the intact knee in response to an anterior tibial load and a combined rotatory load. CLINICAL RELEVANCE Both femoral fixation techniques exhibited comparable time 0 kinematics when subjected to simulated clinical examination loading conditions.

Effects of knee flexion angle and loading conditions on the end-to-end distance of the posterior cruciate ligament: a comparison of the roles of the anterolateral and posteromedial bundles.

Background: It is commonly accepted that the anterolateral (AL) bundle of the posterior cruciate ligament (PCL) is tight in flexion and that the posteromedial (PM) bundle is tight in extension. However, a recent in vivo study showed that both bundles were tight in extension. Purpose: To investigate the effects of knee flexion angle, rotational torque, and anterior/posterior translational force on the end-to-end distance between the femoral and tibial insertion sites of each bundle of the PCL. Study Design: Descriptive laboratory study. Methods: Cadaveric knees (10 specimens) were mounted on a robotic system, and the relative positional data between the femur and tibia were acquired during passive flexion/extension, with an applied 5-N·m rotational torque and an applied 89-N translational force. The bony surface and PCL insertion data were acquired with a 3-dimensional scanner after gross dissection and were superimposed onto the positional data. The end-to-end distance between the 2 PCL insertion sites of the femur and tibia was measured. Results: The end-to-end distance increased from full extension to 90° for both the AL (9.2 ± 1.8 mm; from 30.0 to 39.2 mm) and PM bundles (5.8 ± 2.2 mm; from 32.0 to 37.7 mm). With an internal rotational torque, the end-to-end distance of the PM bundle increased significantly (P < .05) at 0°, 30°, and 60° of knee flexion. Under a posterior translational force at 90° of knee flexion, the length of both bundles increased to their longest measurements (AM bundle: 40.6 ± 4.2 mm; PM bundle: 38.4 ± 3.8 mm). Conclusion: The end-to-end distance of the AL and PM bundles of the PCL increased in flexion, and this pattern was maintained during tests with posterior translational force. The PM bundle was more affected by the rotational torque than was the AL bundle. Clinical Relevance: Both bundles of the PCL may serve a greater functional role in flexion than in extension. The PM bundle might be more important for the control of rotation than the AL bundle. Posterior translation at 90° of knee flexion could be the most stressful condition for both bundles of the PCL, which may have implications for an injury mechanism.