Failure load of the femoral insertion site of the anterior cruciate ligament in a porcine model: comparison of different portions and knee flexion angles

Background This study compared the failure load of the femoral insertion site of the anterior cruciate ligament between different portions and knee flexion angles. Methods In total, 87 fresh-frozen, porcine knees were used in this study. Three knees were used for histological evaluation; the remaining 84 knees were randomly divided into 4 groups: anterior anteromedial bundle, posterior anteromedial bundle, anterior posterolateral bundle, and posterior posterolateral bundle groups (n=21 per group). The anterior cruciate ligament femoral insertion site was divided into these four areas and excised, leaving a 3-mm square attachment in the center of each bundle. Tibia-anterior cruciate ligament-femur complexes were placed in a material testing machine at 30°, 120°, and 150° of knee flexion (n=7), and the failure load for each portion was measured under anterior tibial loading (0.33 mm/s). Results Histological study showed that the anterior cruciate ligament femoral insertion site consisted of direct and indirect insertions. Comparison of the failure load between the knee flexion angles revealed that all the failure loads decreased with knee flexion; significant decreases were observed in the failure load between 30 and 150° knee flexion in the posterior anteromedial bundle and posterior posterolateral bundle groups. Comparison of the failure load according to different portions revealed a significant difference between the anteromedial and posterolateral bundle groups at 150° of knee flexion, but no significant difference among the groups at 30° of flexion. Conclusions Although the failure load of the posterior portion decreased significantly in the knee flexion position, it (mainly consisting of indirect insertion) plays a significant role against anterior tibial load in the knee extension position; this appears to be related to the characteristics of the insertion site. Reflecting the complex structure and function of the ACL, this study showed that the failure load of the femoral insertion site varies with differences in positions and knee flexion angles.

Anatomic and Biomechanical Properties of Flat Medial Patellofemoral Ligament Reconstruction Using an Adductor Magnus Tendon Graft: A Human Cadaveric Study

Background: In contrast to the majority of existing techniques for reconstruction of the medial patellofemoral ligament (MPFL), the technique described in this article uses the adductor magnus muscle tendon to gain a flat, broad graft, leaving its distal femoral insertion intact, and does not require drilling within or near the femoral physis. It also allows for soft tissue patellar fixation and could facilitate anatomic MPFL reconstruction in skeletally immature patients. Purpose: To evaluate the anatomic and structural properties of the native MPFL and the adductor tendon (AT), followed by biomechanical evaluation of the proposed reconstruction. Study Design: Descriptive laboratory study. Methods: The morphological and topographical features of the AT and MPFL were evaluated in 12 fresh-frozen cadaveric knees. The distance between the distal insertion of the AT on the adductor tubercle and the adductor hiatus, as well as the desired length of the graft, was measured to evaluate this graft’s application potential. Load-to-failure tests were performed to determine the biomechanical properties of the proposed reconstruction construct. The construct was placed in a uniaxial testing machine and cyclically loaded 500 times between 5 and 50 N, followed by load to failure, to measure the maximum elongation, stiffness, and maximum load. Results: The mean ± SD length of the AT was 12.6 ± 1.5 cm, and the mean distance between the insertion on the adductor tubercle and adductor hiatus was 10.8 ± 1.3 cm, exceeding the mean desired length of the graft (7.5 ± 0.5 cm) by 3.3 ± 0.7 cm. The distal insertion of the AT was slightly proximal and posterior to the insertion of the MPFL. The maximum elongation after cyclical loading was 1.9 ± 0.4 mm. Ultimately, the mean stiffness and load to failure were 26.2 ± 7.6 N/mm and 169.7 ± 19.2 N, respectively. The AT graft failed at patellar fixation in 2 of the initially tested specimens and at the femoral insertion in the remaining 10. Conclusion: The described reconstruction using the AT has potential for MPFL reconstruction. The AT graft presents a graft of significant volume, beneficial anatomic topography, and adequate tensile properties in comparison with the native MPFL following the data from previously published studies. Clinical Relevance: Given its advantageous anatomic relationship as an application that avoids femoral drilling and osseous patellar fixation, the AT may be considered a graft for MPFL reconstruction in skeletally immature patients.

Effect of Percentage of Femoral Anterior Cruciate Ligament Insertion Site Reconstructed With Hamstring Tendon on Knee Kinematics and Graft Force

Background: Previous studies have stated that closely matching the size of the anterior cruciate ligament (ACL) insertion site footprint is important for biomechanical function and clinical stability after ACL reconstruction. However, the ACL varies widely regarding the area of femoral insertion, tibial insertion, and midsubstance of ACL, and reconstructing the insertion site area with a uniform diameter graft can result in a cross-sectional area that is greater than that of the midsubstance of the native ACL. Therefore, understanding the effect of relative graft size in ACL reconstruction on knee biomechanics is important for surgical planning. Purpose: To assess how the percentage of femoral insertion site affects knee biomechanics in single- and double-bundle ACL reconstruction. Study Design: Controlled laboratory study. Methods: A total of 14 human cadaveric knees were scanned with magnetic resonance imaging and tested using a robotic system under an anterior tibial load and a combined rotational load. In total, 7 knee states were evaluated: intact ACL; deficient ACL; single-bundle ACL reconstruction with approximate graft sizes 25% (small), 50% (medium), and 75% (large) of the femoral insertion site; and double-bundle reconstruction of approximately 50% (medium) and 75% (large) of the femoral insertion site, based on the ratio of the cross-sectional area of the graft to the area of the femoral ACL insertion site determined by magnetic resonance imaging. Results: Anterior tibial translation was not significantly larger than the intact state in single-bundle and double-bundle medium graft reconstructions ( P > .05) and was significantly greater in the single-bundle small graft reconstruction ( P < .05). Anterior knee translation in single-bundle medium graft and large graft reconstructions was not statistically different ( P > .05). In contrast, the anterior tibial translation for double-bundle large graft reconstruction was significantly smaller than for double-bundle medium graft reconstruction at low flexion angles ( P < .05). The single-bundle small graft force was significantly different from the intact ACL in situ force ( P < .05). The graft force with double-bundle large reconstruction was significantly greater than that with the double-bundle medium reconstruction ( P < .05) but was not significantly different from that of the intact ACL ( P > .05). Conclusion: Knee biomechanics with a single-bundle small graft tended to be significantly different from those of the intact knee. In the kinematic and kinetic data for the single- and double-bundle medium graft reconstruction, only the anterior translation at full extension for the single-bundle reconstruction was significantly different (lower) from that of intact knee. This was a time zero study. Clinical Relevance: This study can provide surgeons with guidance in selecting the graft size for ACL reconstruction.

Length change pattern of the medial structures of the knee and related reconstructions

Introduction: Aim of the study was to investigate the length changes of the medial structures and related reconstructions. It was assumed that the three fibre sections (anterior/middle/posterior) of the superficial medial collateral ligament (sMCL) have different length change patterns, which cannot be imitated by current reconstructions. Hypotheses: The three fibre sections (anterior/middle/posterior) of the superficial medial collateral ligament (sMCL) cannot be imitated by current reconstructions. Methods: Measurements were made on eight cadaveric knees. The knee joints were clamped in a custom-made open chain extension structure. For this purpose, the portions of the quadriceps and the iliotibial tract were aligned according to their fibre direction and statically loaded using hanging weights. The respective tibial and femoral insertion points of the sMCL anterior/middle/posterior fibres were marked by small pins. Similarly, pins were inserted at the tibial and femoral attachment sites of the posterior oblique ligament (POL). In order to imitate the Lind reconstruction, a pin was additionally inserted on the tibial semitendinosus insertion site. Pin combinations accounting for the anterior/middle/posterior sMCL, the POL, and the Lind reconstruction were connected using a high resistant suture. Then the length change patterns were measured using a rotary encoder from 0-120° knee flexion. Statistical analysis was performed using 2-way repeated-measures ANOVA and a post-hoc Bonferroni correction (p <0.05). Results: The anterior and posterior fibres of the sMCL showed a reciprocal behaviour (p< 0.001). The anterior fibres showed a length reduction (2%) up to a flexion of 20°, followed by an elongation of 5% at 120° flexion, which means that the anterior fibres are tight in knee flexion. Conversely, the posterior fibres of the MCL showed an initial length reduction of 4% at 20° flexion. This was followed by an isometric range (20° - 80°) and a further length reduction of 8% in deep flexion (120°). Thus, the posterior fibres of the MCL were tight in extension. The three parts of the POL showed a constant reduction of 25% between 0° and 120°. The Lind reconstruction with the tibial pin at the semitendinosus insertion site showed similar length changes compared to the sMCL (n.s.). Furthermore, the Lind reconstruction was dependent on the femoral placement of the pins (p <.001). The tibial placement had no significant influence. Conclusion: The anterior portion of the sMCL was tight in flexion, whereas the posterior portion was tight in extension. This reciprocal behavior could not be imitated by a single point to point reconstruction. When surgically applying these reconstructions, special attention should be paid to the femoral insertion.

CT scan of the placement of the femoral tunnel in combined anterior cruciate ligament and anterior lateral ligament reconstruction by a single femoral tunnel using the outside-in technique

Background: The main difficulty with this ALL reconstruction method is the placement of the femoral tunnel as isometrically as possible. The femoral insertion of the ALL is usually located one centimeter posteriorly and proximal to the lateral epicondyle, at the level of the Lemaire vessels. The purpose of our study was to evaluate the placement of the femoral tunnel in ligament reconstruction by combined ACL and ALL reconstruction with a single femoral tunnel using the outside-in technique. Our hypothesis was that a single femoral tunnel by outside-in technique would allow satisfactory placement of the femoral insertion of the ALL.. Methods: We conducted a retrospective bi-centric study of all patients who underwent combined ACL and ALL reconstruction surgery with a common outside-in femoral technique. A postoperative low-dose knee CT scan with multiplane reconstructions was performed after patient consent. After locating the top of the epicondyle on three-dimensional CT scan reconstructions, the distances between the top of the lateral epicondyle and the center of the femoral tunnel in the frontal and sagittal planes were measured. These measurements were taken by a surgeon and a radiologist. Results: 45 patients were included and the average age was 29 years (17-39). 30 patients had a CT scan. Analysis of the placement of the femoral tunnel showed that 10 tunnels were placed posteriorly and proximal to the top of the lateral epicondyle. Conclusion: This study did not confirm our hypothesis. Combined ACL and ALL reconstruction by a single tunnel did not provide access to the isometric point of the femoral insertion of the ALL in a reproducible manner, despite open intra-operative identification of this point. This study highlights the difficulty of locating the femoral isometric point with a standard outside-in femoral guide. Developing a specific femoral guide might be useful.