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Background: Stacked screws is a commonly used technique in single-stage revision anterior cruciate ligament (ACL) reconstruction in the setting of bone loss, but there are limited data to support its use. Hypothesis: Two configurations of a biocomposite stacked screws construct have similar fixation strength and linear stiffness as a primary ACL reconstruction construct in a biomechanical model. Study Design: Controlled laboratory study. Methods: A total of 30 porcine legs were divided into 3 groups. Group 1 underwent primary ACL reconstruction with a patellar tendon graft fixed into the femur, with an 8-mm biocomposite interference screw of beta-tricalcium phosphate and poly lactide-co-glycolide. For a revision ACL reconstruction model, groups 2 and 3 had bone tunnels created and subsequently filled with 12-mm biocomposite screws. New bone tunnels were drilled through the filler screw and the surrounding bone, and the patellar bone plug was inserted. Group 2 was fixed with 8-mm biocomposite screws on the side of the graft opposite the filler screw, while group 3 had the interference screw interposed between the graft and the filler screw. The construct was loaded at 1.5 mm/s in line with the tunnel until failure. Load to failure, linear stiffness, and mode of failure were recorded. Results: The mean pullout strength for groups 1, 2, and 3 was 626 ± 145 N, 653 ± 152 N, and 720 ± 125 N, respectively (P =.328). The mean linear stiffness of the construct in groups 1, 2, and 3 was 71.4 ± 9.9 N/mm, 84.1 ± 11.1 N/mm, and 82.0 ± 10.8 N/mm, respectively. Group 2 was significantly stiffer than group 1 (P =.037). Conclusion: Two configurations of a biocomposite stacked screws construct for a single-stage revision ACL reconstruction in the setting of bone loss show a similar fixation strength and linear stiffness to a primary ACL reconstruction at time zero in a porcine model. Clinical Relevance: In the setting of bone loss from tunnel malpositioning, a single-stage revision ACL reconstruction using a stacked screws construct may provide adequate fixation strength and linear stiffness. [ABSTRACT FROM AUTHOR]

Background: Both anatomic anterolateral ligament (ALL) and nonanatomic anterolateral reconstructions are performed to improve the stability of anterior cruciate ligament (ACL)–deficient patients. However, the in vivo length change patterns and isometry of these anterolateral reconstructions are unknown. Purpose: To measure the theoretical length change patterns of the ALL and various anterolateral extra-articular reconstructions in healthy and ACL-deficient knees during in vivo weightbearing flexion. Study Design: Controlled laboratory study. Methods: Ten patients with an ACL injury in 1 knee and the contralateral side intact were included. By use of magnetic resonance and dual fluoroscopic imaging techniques, the changes in length of the ALL, modeled with its femoral attachment either anterior or posterior-proximal to the fibular collateral ligament (FCL) attachment, and nonanatomic extra-articular reconstructions were measured as a function of knee flexion and were compared between the intact and ACL-deficient knees. Results: The ALL, with its femoral attachment anterior to the FCL attachment, showed a consistent length increase of approximately 50% from 0° to 90° of knee flexion. The length change of the ALL was 20% ± 6% when its femoral attachment was placed posterior-proximal to the FCL. ACL deficiency did not affect ALL length. Even minor shifts in position around the rotational axis of the femur resulted in contrary ligament kinematic patterns. An extra-articular reconstruction with the femoral attachment proximal to the lateral epicondyle and the tibial attachment on the Gerdy tubercle increased 15% ± 4% in length from 0° to 60° and shortened at 90° of flexion. When the tibial fixation of the anatomic ALL with its femoral attachment posterior to the FCL was moved to the Gerdy tubercle, a 30% ± 4% length increase over 90° occurred, without the decrease in length at 90°. A significant length increase of both theoretical reconstruction grafts was seen at 0° in ACL-deficient knees. Conclusion: An anatomic ALL reconstruction as modeled based on recent anatomic studies was not isometric during in vivo knee flexion and was not affected by ACL deficiency. The nonanatomic extra-articular reconstructions demonstrated more biomechanically favorable length change patterns with the smallest percentage increase in elongation during knee flexion. Clinical Relevance: This study presents the first in vivo biomechanical data on the ALL, in both healthy and ACL-deficient knees, and provides surgical information that may be valuable for restoring normal anterolateral stability. [ABSTRACT FROM AUTHOR]

Background: The function of the anteromedial (AM) and posterolateral (PL) bundles of the anterior cruciate ligament (ACL) during gait has not been reported. Hypothesis: The AM and PL bundles have distinct functional behavior during the stance phase of treadmill gait. Study Design: Descriptive laboratory study. Methods: Three-dimensional models of the knee were created by magnetic resonance images from 8 healthy subjects. The contour of the 2 bundle attachments were constructed on each model. Each bundle was represented by a straight line connecting its tibial and femoral attachment centroids. Next, the knee kinematics during the stance phase of gait was determined with a dual fluoroscopic imaging system. The relative elongation, sagittal plane elevation, coronal plane elevation, and transverse plane deviation of the 2 bundles were measured directly from heel strike to toe-off. Results: At heel strike, the AM and PL bundles had first peak elongation of 9% ± 7% and 9% ± 13%, respectively. At 50% progress of the stance phase, both bundles were maximally elongated, 12% ± 7% for the AM bundle and 13% ± 15% for the PL bundle. No significant difference was found for each bundle between 40% and ±0% of the stance phase (P > .05). With increasing knee flexion, the sagittal plane and coronal plane elevations of the 2 bundles decreased, whereas the deviation angles increased. Conclusion: Both bundles are anisometric and function in a similar manner during the stance phase of gait. They were maximally elongated throughout the midstance where they were stretched maximally to resist anterior tibial translation. Clinical relevance: This information can be useful for further improving anatomical ACL reconstructions to better reproduce the 2 bundle functions. It may also be useful for designing postoperative rehabilitation regimens to prevent overstretch of the grafts. [ABSTRACT FROM AUTHOR]

Background: The in situ forces of the anteromedial (AM) and posterolateral bundles (PL) of the anterior cruciate ligament (ACL) under simulated functional loads such as simulated muscle loads have not been reported. These data are instrumental for improvement of the anatomical double-bundle ACL reconstruction. Hypothesis: The load-sharing patterns of the 2 bundles are complementary under simulated muscle loads. Study Design: Descriptive laboratory study. Methods: Eight cadaveric knees in this study were sequentially studied using a robotic testing system. Each knee was tested under 3 external loading conditions including (1) a 134-N anterior tibial load; (2) combined rotational loads of 10 N·m of valgus and 5 N·m internal tibial torques; and (3) a 400-N quadriceps muscle load with the knee at 0°, 15°, 30°, 60°, and 90° of flexion. The in situ forces of the 2 bundles of ACL were determined using the principle of superposition. Results: Under the anterior tibial load, the PL bundle carried peak loads at full extension and concurrently had significantly lower force than the AM bundle throughout the range of flexion (P<.05). Under the combined rotational loads, the PL bundle contributed to carrying the load between 0° and 30°, although less than the AM bundle. Under simulated muscle loads, both bundles carried loads between 0° and 30°. There was no significant difference between the 2 bundle forces at all flexion angles (P >.05). Conclusion: Under externally applied loads, in general, the AM bundle carried a greater portion of the load at all flexion angles, whereas the PL bundle only shared the load at low flexion angles. The bundles functioned in a complementary rather than a reciprocal manner to each other. Clinical Relevance: The data appear to support the concept that both bundles function in a complementary manner. Thus, how to re-create the 2 bundle functions in an ACL reconstruction should be further investigated. [ABSTRACT FROM AUTHOR]