A biomechanical investigation of the anteromedial and posterolateral bands of the porcine anterior cruciate ligament

Effects of various load magnitudes on ACL: an in vitro study using adolescent porcine stifle joints

INTRODUCTION

The escalating incidence of anterior cruciate ligament (ACL) injuries, particularly among adolescents, is a pressing concern. The study of ACL biomechanics in this demographic presents challenges due to the scarcity of cadaveric specimens. This research endeavors to validate the adolescent porcine stifle joint as a fitting model for ACL studies.

METHODS

We conducted experiments on 30 fresh porcine stifle knee joints. (Breed: Yorkshire, Weight: avg 90 lbs, Age Range: 2-4 months). They were stored at - 22 °C and a subsequent 24-h thaw at room temperature before being prepared for the experiment. These joints were randomly assigned to three groups. The first group served as a control and underwent only the load-to-failure test. The remaining two groups were subjected to 100 cycles, with forces of 300N and 520N, respectively. The load values of 300N and 520N correspond to three and five times the body weight (BW) of our juvenile porcine, respectively.

RESULT

The 520N force demonstrated a higher strain than the 300N, indicating a direct correlation between ACL strain and augmented loads. A significant difference in load-to-failure (p = 0.014) was observed between non-cyclically loaded ACLs and those subjected to 100 cycles at 520N. Three of the ten samples in the 520N group failed before completing 100 cycles. The ruptured ACLs from these tests closely resembled adolescent ACL injuries in detachment patterns. ACL stiffness was also measured post-cyclical loading by applying force and pulling the ACL at a rate of 1 mm per sec. Moreover, ACL stiffness measurements decreased from 152.46 N/mm in the control group to 129.42 N/mm after 100 cycles at 300N and a more significant drop to 86.90 N/mm after 100 cycles at 520N. A one-way analysis of variance (ANOVA) and t-test were chosen for statistical analysis.

CONCLUSIONS

The porcine stifle joint is an appropriate model for understanding ACL biomechanics in the skeletally immature demographic. The results emphasize the ligament's susceptibility to injury under high-impact loads pertinent to sports activities. The study advocates for further research into different loading scenarios and the protective role of muscle co-activation in ACL injury prevention.

Mechanical properties of animal ligaments: a review and comparative study for the identification of the most suitable human ligament surrogates

The interest in the properties of animal soft tissues is often related to the desire to find an animal model to replace human counterparts due to the unsteady availability of human tissues for experimental purposes. Once the most appropriate animal model is identified, it is possible to carry out ex-vivo and in-vivo studies for the repair of ligamentous tissues and performance testing of replacement and support healing devices. This work aims to present a systematic review of the mechanical properties of ligaments reported in the scientific literature by considering different anatomical regions in humans and several animal species. This study was conducted according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) method. Moreover, considering the lack of a standard protocol for preconditioning of tissues, this aspect is also addressed. Ninety-six studies were selected for the systematic review and analysed. The mechanical properties of different animal species are reported and summarised in tables. Only results from studies reporting the strain rate parameter were considered for comparison with human ligaments, as they were deemed more reliable. Elastic modulus, ultimate tensile stress, and ultimate strain properties are graphically reported identifying the range of values for each animal species and to facilitate comparison between values reported in the scientific literature in animal and human ligaments. Useful similarities between the mechanical properties of swine, cow, and rat and human ligaments have been found.

Dynamic tensile properties of porcine knee ligament

BACKGROUND

The knee plays an essential role in movement. There are four major ligaments in the knee which all have crucial functionalities for human activities. The anterior cruciate ligament (ACL) is the most commonly injured ligament in the knee, especially in athletes.

OBJECTIVE

The aim of this study was to investigate the dynamic tensile response of the porcine ACL at strain rates from 800 to 1500 s-1 for simulations of acute injury from sudden impact or collision.

METHODS

Split Hopkinson Tension Bar (SHTB) was utilized to create a dynamic tensile wave on the ACL. Stress-strain curves of strain rates between 800 s-1 to 1500 s-1 were recorded.

RESULTS

The results demonstrated that the elastic modulus of the porcine ACL at higher strain rates was six to eight times higher than that of porcine and human specimens at quasi-static strain rate. However, the failure stress was quite similar while the strain was much smaller than that at the lower strain rate.

CONCLUSIONS

ACL is highly strain rate sensitive and easier to break with lower failure strain when the strain rates increased to more than 1000 s-1. The stress-strain curves indicated that the sketching crimps at the slack region did not happen but switched to the sliding process of collagen fibers and was accompanied by some ruptures, which can develop into tears when strain and stress were large enough. On the other hand, the viscoelastic properties of the ligament, depending on the proteoglycan matrix and the cross-link, showed a limited value in the studied strain rate range.

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.

A study of knee anterior cruciate ligament biomechanics with respect to energy and relaxation

BACKGROUND

This research aimed to study the biomechanical properties of sheep tendon under torsion and the tendon energy absorption performance with an externally imposed initial force.

METHODS

Tendons of nine healthy knees of sheep were investigated. In both tests, we investigated energy and relaxation at rotations of 0°, 90°, 180°, and 360°. For both tensile force and tensile displacement at a sampling period of 100 milliseconds, the maximum value of 89 N was selected as the maximum tension state for 600 s of relaxation duration for testing relaxation, and analysed of the average force of the last 30 s.

FINDINGS

The difference of energy levels of the tendons are significant between twisted groups (180° and 360°) and untwisted group (0°) (P < 0.05); The relaxation force decreases significantly with twisted groups (90°,180°, and 360°) and untwists group (0°) (P < 0.05). The nine-group tendons show no significant difference at torsion 90° and 180° (P = 0.466). Peak force test shows significant differences between the twisted groups (90°,180°, and 360°) and untwisted group (0°) (P < 0.05).

INTERPRETATION

The torsion tendon has lower energy absorption and relaxation than the untwisted counterparts; thus, it may be more prone to damage. These results are useful for providing guidance on anterior cruciate ligament reconstruction.

Large Animal Models for Anterior Cruciate Ligament Research

Large animal (non-rodent mammal) models are commonly used in ACL research, but no species is currently considered the gold standard. Important considerations when selecting a large animal model include anatomical differences, the natural course of ACL pathology in that species, and biomechanical differences between humans and the chosen model. This article summarizes recent reports related to anatomy, pathology, and biomechanics of the ACL for large animal species (dog, goat, sheep, pig, and rabbit) commonly used in ACL research. Each species has unique features and benefits as well as potential drawbacks, which are highlighted in this review. This information may be useful in the selection process when designing future studies.

Tensile properties of a split quadriceps graft for ACL reconstruction

PURPOSE

Anatomic double-bundle ACL reconstruction can be performed using different grafts, such as quadriceps tendon. Grafts can be split in either coronal or sagittal planes to approximate the two bundles of the native ACL, but it is unknown whether a difference exists in the graft tensile properties depending on splitting plane. The purpose of this study was to evaluate the tensile properties of split human quadriceps tendon-bone grafts.

METHODS

Twenty full-thickness quadriceps tendon-bone grafts were prepared to mimic grafts for double-bundle ACL reconstruction. Ten grafts were split in the sagittal plane, and ten were split in the coronal plane. Each graft underwent cyclic creep testing and load-to-failure testing to compare creep, ultimate load, ultimate elongation, stiffness, and tangent modulus between splitting planes. All parameters were compared between splitting groups (significance p < 0.05).

RESULTS

Lateral halves of grafts split in the sagittal plane exhibited a percent creep of 42.5 ± 12.4 %, ultimate load of 445 ± 210 N, ultimate elongation of 7.3 ± 1.9 mm, stiffness of 75.7 ± 19.9 N/mm, and tangent modulus of 174.0 ± 99.8 MPa. No differences were found between halves within split tendons or between splitting planes (n.s.).

CONCLUSIONS

Overall, splitting quadriceps tendon grafts for anatomic double-bundle ACL reconstruction results in similar tensile properties regardless of splitting plane. Surgeons can split quadriceps tendon in either splitting plane, but should take care to preserve fibres as much as possible. This study provides data that support the use of both coronal and sagittal splits of quadriceps tendons for anatomic double-bundle ACL reconstruction.

Effect of ACL graft material on joint forces during a simulated in vivo motion in the porcine knee: examining force during the initial cycles

This study compared three-dimensional forces in knees containing anterior cruciate ligament (ACL) graft materials versus the native porcine ACL. A six-degree-of-freedom (DOF) robot simulated gait while recording the joint forces and moments. Knees were subjected to 10 cycles of simulated gait in intact, ACL-deficient, and ACL-reconstructed knee states to examine time zero biomechanical performance. Reconstruction was performed using bone-patellar tendon-bone allograft (BPTB), reconstructive porcine tissue matrix (RTM), and an RTM-polymer hybrid (Hybrid). Forces and moments were examined about anatomic DOFs throughout the gait cycle and at three key points during gait: heel strike (HS), mid stance (MS), toe off (TO). Compared to native ACL, each graft restored antero-posterior (A-P) forces throughout gait. However, all failed to mimic normal joint forces in other DOFs. For example, each reconstructed knee showed greater compressive forces at HS and TO compared to the native ACL knee. Overall, the Hybrid graft restored more of the native ACL forces following reconstruction than did BPTB, while RTM grafts were the least successful. If early onset osteoarthritis is in part caused by altered knee kinematics, then understanding how reconstruction materials restore critical force generation during gait is an essential step in improving a patient's long-term prognosis.

A novel core biopsy technique for anterior cruciate ligament preserves ligament structural integrity: a porcine study

PURPOSE

The objective of this study was to validate a new technique to safely obtain core biopsy specimens of the anterior cruciate ligament (ACL) without jeopardizing the ACL's biomechanical properties.

METHODS

Eleven pairs of fresh porcine femur-ACL-tibia complexes were tested in a loading frame. The ACL of one knee was biopsied using a spring-loaded core biopsy device, whereas the contralateral ACL was tested as the control. Biomechanical properties of the biopsied and control ACLs were compared.

RESULTS

The ultimate load to failure was 1,202 N ± 171.1 N and 1,193 N ± 228.7 N (P = .8984) for biopsied and non-biopsied ACLs, respectively. No significant differences were noted for maximal elongation at failure, maximal strain, absorbed energy, and stiffness between biopsied and non-biopsied ACLs.

CONCLUSIONS

The results of this study indicate that a new ACL core biopsy technique can be performed while preserving the ligament's structural integrity.

CLINICAL RELEVANCE

The presented core biopsy technique could be regarded as a dedicated tool to elucidate the poorly understood (patho)biological processes occurring in both the native and reconstructed ACLs.