Correlation between morphological features of the anterior cruciate ligament: A quantitative study using a porcine model.

Introduction: Knowledge of the morphological features of the anterior cruciate ligament (ACL) is critical for accurate reconstruction of it. This study aimed to explore the quantitative correlations among different morphological features of the ACL, thus to provide useful information for improving anatomical reconstruction techniques and designing artificial ligaments. Methods: 19 porcine knees were fixed at full extension using 10% formalin and were dissected to expose the ACL. ACL lengths were measured using a caliper. Mid-substances of the ACL were cut and scanned using X-ray microscopy, and the cross-sectional area (CSA) was measured at the isthmus. Margins of direct and indirect bone insertion sites were distinguished and marked. Measurements were performed on digital photographs to obtain the areas of bone insertions. Statistical analysis using nonlinear regression was used to identify potential correlations among the measurements. Results: The results showed that the CSA at the isthmus was significantly correlated with the total area of the bone insertion sites and the area of tibial insertion. The area of the tibial insertion was significantly correlated with the area of its direct insertion site. In contrast, the area of the femoral insertion was significantly correlated with the area of its indirect insertion site. The area of the indirect tibial insertion showed a weak correlation with the length of ACL, whereas the length of the ACL was not able to predict or be predicted by any other parameters. Conclusions: The CSA at the ACL isthmus is more representative for assessing the size of the ACL. However, ACL length has little correlation with the CSA of the isthmus or bone insertion sites, and thus should be evaluated independently for ACL reconstruction.

Comparison of the morphology of the anterior cruciate ligament and related bony structures between pigs and humans.

Introduction: Pigs are widely used for clinical research on the anterior cruciate ligament (ACL) because of the similarity of the knee structure to the human knee. But evidence to support the suitability of using porcine samples to guide clinical practices is limited. This study aims to explore the qualitative and quantitative morphological features of the porcine knee and ACL, and to compare these with data on humans reported in literature. Methods: Nineteen porcine knees were used for this study. The bone structures were measured on coronal X-ray images. The length of the ACL was measured using a caliper. The ACL bone insertion sites were marked and measured on a digital photograph. The lengths of the long and short axis of the ACL isthmus were measured on the X-ray microscopy reconstructed images. The outcomes were compared with previously reported data on humans using an abstract independent-samples T test. Results: Qualitative observation indicated a similar location, orientation and general morphology of the porcine ACL to human ACLs. The major difference was the location of the ACL tibial insertion with respect to the anterior horn of the lateral meniscus (AHLM). The porcine ACL was split into AM and PL bundles by the AHLM, while the AHLM was adjacent to the anterolateral border of the ACL tibial insertion in human knees. The quantitative comparison showed no significant difference between the human and porcine ACL in terms of the length of the ACL, the width of the femoral condyle and tibial plateau, and the tibial interspinal width. However, the CSA, the lengths of the long and short axis of the ACL isthmus, and the femoral and tibial insertion areas of the porcine ACL were all significantly larger than the reported features in human knees. Conclusion: The location, orientation and basic morphology of the porcine ACL and knee are similar to humans. However, the two-bundle structure is more distinct in a porcine ACL, and the dimensions of the porcine ACL are generally larger. This study may provide useful information to researchers when assessing the feasibility and limitations of using porcine samples for research on the human ACL and knee.

Graft Diameter Should Reflect the Size of the Native Anterior Cruciate Ligament (ACL) to Improve the Outcome of ACL Reconstruction: A Finite Element Analysis.

The size of the anterior cruciate ligament (ACL) often varies between individuals, but such variation is not typically considered during ACL reconstruction (ACLR). This study aimed to explore how the size of the ACL affects the selection of a suitable graft diameter. A finite element model of a human knee was implanted with intact ACLs of different dimensions (0.95, 1 and 1.05 times the size of the original ACL) and with grafts of different diameters, to simulate ACLR (diameter 7.5-12 mm in 0.5 mm increments). The knee models were flexed to 30° and loaded with an anterior tibial load of 103 N, internal tibial moment of 7.5 Nm, and valgus tibial moment of 6.9 Nm. Knee kinematics (anterior tibial translation (ATT), internal tibial rotation (ITR) and valgus tibial rotation (VTR)) and ligament forces were recorded and compared among the different groups. The results showed that, compared with the intact knee, a graft diameter of 7.5 mm was found to increase the ATT and VTR, but reduce the graft force. Increasing the graft diameter reduced knee laxity and increased the graft force. A 10% increase in the size of the ACL corresponded to a 3 mm larger graft diameter required to restore knee stability and graft force after ACLR. It was concluded that the graft diameter should be selected according to the dimensions of the native ACL, for better restoration of knee functionality. This study may help to improve the clinical treatment of ACL ruptures.

Correlation between ACL size and dimensions of bony structures in the knee joint.

It is difficult to measure the dimensions of the anterior cruciate ligament (ACL) in vivo, which makes choosing an individualized graft size for ACL reconstruction particularly troublesome. The morphology and function of porcine ACL have been reported to be similar to the native human ACL. This study aimed to identify bony morphological parameters on X-ray images that were significantly correlated with features of the native ACL. Anteroposterior X-ray images of 19 porcine knees were obtained. The width, height and area of the femoral notch, the widths of the femoral and tibial condyles and the width and area of the interspinal fossa of the tibia were measured. ACL length was measured using a caliper. The ACL was then resected and the outline of the bone insertion sites were marked and photographed for measuring the areas of the insertion sites. The excised ACL substance was scanned using X-ray microscopy and reconstructed to measure the medial-lateral (ML) and anterior-posterior (AP) widths, the long and short axes and cross-sectional area of the ACL isthmus. Linear regression analyses showed that the area of the interspinal fossa of the tibia was significantly correlated with the long axis and ML width of the ACL, and with the AP / ML width (p value = 0.038, 0.032 and 0.016 respectively). The width of the femoral condyle was significantly correlated with the area of the tibial insertion and the length and ML width of the ACL (p value = 0.013, 0.000 and 0.038 respectively). The area of the interspinal fossa of the tibia / notch width index (NWI) was significantly correlated with the long axis / short axis of the ACL (p value = 0.016). The width of the interspinal fossa of tibia / NWI was significantly correlated with the short axis of the ACL isthmus (p value = 0.009). However, the dimensions of the femoral intercondylar notch and the width of the interspinal fossa of the tibia were not significantly correlated with any of the ACL parameters. In conclusion, the dimension of the interspinal fossa of the tibia and the width of the femoral condyle measured from X-ray images might be used to estimate the shape and size of the ACL, which might be helpful for choosing a suitable graft size for ACL reconstruction. DATA STATEMENT: All data relevant to the study are included in the article.

Hourglass-shaped grafts are superior to conventional grafts for restoring knee stability and graft force at knee flexion angle of 30° following anterior cruciate ligament reconstruction: A finite element analysis.

Background: Anterior cruciate ligament reconstruction (ACLR) using a generally columnar graft is considered the gold standard for treating anterior cruciate ligament ruptures, but such grafts cannot replicate the geometry and mechanical properties of the native anterior cruciate ligament. Purpose: To evaluate the effectiveness of an innovative hourglass-shaped graft versus a traditional columnar graft for restoring joint stability and graft force, while avoiding notch impingement following anterior cruciate ligament reconstruction. Methods: Finite element models of a human knee were developed to simulate ① An intact state, ② anterior cruciate ligament reconstruction using columnar grafts with different diameters (7.5-12 mm in 0.5 mm increments), ③ anterior cruciate ligament reconstruction using columnar grafts with different Young's moduli (129.4, 168.0 and 362.2 MPa) and ④ anterior cruciate ligament reconstruction using hourglass-shaped grafts with different Young's moduli. The knee model was flexed to 30° and loaded with an anterior tibial load of 103 N, internal tibial moment of 7.5 Nm, and valgus tibial moment of 6.9 Nm. The risk of notch impingement, knee stability and graft forces were compared among the different groups. Results: This study found that columnar grafts could not simultaneously restore knee stability in different degree of freedoms (DOFs) and graft force to a level similar to that of the intact knee. The anterior tibial translation and graft force were restored to a near-normal condition when the internal tibial rotation was over-restrained and valgus tibial rotation was lax. A graft diameter of at least 10 mm was needed to restore knee stability and graft force to physiological levels, but such large grafts were found to be at high risk of notch impingement. In contrast, the hourglass-shaped graft was able to simultaneously restore both knee stability and graft force at knee flexion of 30° while also having a much lower risk of impingement. Conclusion: Under knee flexion angle of 30°, an hourglass-shaped graft was better able to restore joint stability and graft force to a near-physiological level than columnar grafts, while also reducing the risk of notch impingement.

Research on Transportation-Related Emissions: Current Status and Future Directions.

Transportation-related emissions are the dominant contributing source of air pollutants today. Considering the negative impacts of transportation-related emissions on our social and economic environment, extensive efforts have been made by researchers and practitioners attempting to find solutions to reduce the emissions. To synthesize these research efforts, researchers have conducted various reviews of relevant studies. However, because of the diversity of the topics, most of existing reviews have only focused on specific and narrowed areas. Furthermore, none of the existing reviews have attempted to summarize the researchers' opinions on the current research and their prospects of the future research directions. Therefore, this paper is intended to fill this gap by conducting an extensive survey of transportation emissions professionals. In the paper, a review of existing research and developments on each of the emissions-related topics is provided, followed by a presentation of the respective survey results and analysis. At the conclusion of these reviews and the analysis of the survey, some future research directions in this field are presented.