Decreased posterior cruciate and altered collateral ligament loading following ACL transection: a longitudinal study in the ovine model

Adaptation of Fibril-Reinforced Poroviscoelastic Properties in Rabbit Collateral Ligaments 8 Weeks After Anterior Cruciate Ligament Transection

Ligaments of the knee provide stability and prevent excessive motions of the joint. Rupture of the anterior cruciate ligament (ACL), a common sports injury, results in an altered loading environment for other tissues in the joint, likely leading to their mechanical adaptation. In the collateral ligaments, the patterns and mechanisms of biomechanical adaptation following ACL transection (ACLT) remain unknown. We aimed to characterize the adaptation of elastic and viscoelastic properties of the lateral and medial collateral ligaments eight weeks after ACLT. Unilateral ACLT was performed in six rabbits, and collateral ligaments were harvested from transected and contralateral knee joints after eight weeks, and from an intact control group (eight knees from four animals). The cross-sectional areas were measured with micro-computed tomography. Stepwise tensile stress-relaxation testing was conducted up to 6% final strain, and the elastic and viscoelastic properties were characterized with a fibril-reinforced poroviscoelastic material model. We found that the cross-sectional area of the collateral ligaments in the ACL transected knees increased, the nonlinear elastic collagen network modulus of the LCL decreased, and the amount of fast relaxation in the MCL decreased. Our results indicate that rupture of the ACL leads to an early adaptation of the elastic and viscoelastic properties of the collagen fibrillar network in the collateral ligaments. These adaptations may be important to consider when evaluating whole knee joint mechanics after ACL rupture, and the results aid in understanding the consequences of ACL rupture on other tissues.

ACL microtrauma: healing through nutrition, modified sports training, and increased recovery time

PURPOSE

Sports injuries among youth and adolescent athletes are a growing concern, particularly at the knee. Based on our current understanding of microtrauma and anterior cruciate ligament (ACL) healing characteristics, this clinical commentary describes a comprehensive plan to better manage ACL microtrauma and mitigate the likelihood of progression to a non-contact macrotraumatic ACL rupture.

METHODS

Medical literature related to non-contact ACL injuries among youth and adolescent athletes, collagen and ACL extracellular matrix metabolism, ACL microtrauma and sudden failure, and concerns related to current sports training were reviewed and synthesized into a comprehensive intervention plan.

RESULTS

With consideration for biopsychosocial model health factors, proper nutrition and modified sports training with increased recovery time, a comprehensive primary ACL injury prevention plan is described for the purpose of better managing ACL microtrauma, thereby reducing the incidence of non-contact macrotraumatic ACL rupture among youth and adolescent athletes.

CONCLUSION

Preventing non-contact ACL injuries may require greater consideration for reducing accumulated ACL microtrauma. Proper nutrition including glycine-rich collagen peptides, or gelatin-vitamin C supplementation in combination with healthy sleep, and adjusted sports training periodization with increased recovery time may improve ACL extracellular matrix collagen deposition homeostasis, decreasing sudden non-contact ACL rupture incidence likelihood in youth and adolescent athletes. Successful implementation will require compliance from athletes, parents, coaches, the sports medicine healthcare team, and event organizers. Studies are needed to confirm the efficacy of these concepts.

LEVEL OF EVIDENCE

V.

The instrumented sheep knee to elucidate insights into osteoarthritis development and progression: A sensitive and reproducible platform for integrated research efforts

BACKGROUND

Osteoarthritis of the knee is a very common condition that has been difficult to treat. The majority of cases are considered idiopathic. Much research effort remains focused on biology rather than the biomechanics of such joints. Some new methods were developed and validated to better appreciate the subtleties of the biomechanical integrity of joints, and how changes in biomechanics can contribute to osteoarthritis.

METHODS

Over the past 15 years our lab has enhanced the sensitivity of the assessment of knee biomechanics of an instrumented, trained large animal model (sheep) of osteoarthritis and integrated the findings with biological and histological assessments. These new methods include gait analysis before and after injury followed by robotic validation post-sacrifice, and more recently using Fibre Bragg Grating sensors to detect alterations in cartilage stresses.

RESULTS

A review of the findings obtained with this model are presented. The findings indicate that sheep, like humans, exhibit individual characteristics. They also indicate that joint kinetics, rather than kinematics may better define the alterations induced by injury. With the addition of Fibre Bragg Grating sensors, it has been possible to measure with good accuracy, alterations to cartilage stresses following a controlled knee injury.

INTERPRETATION

Using this model as Proof of Concept, this sheep system can now be viewed as a sensitive platform to address many questions related to risk for development of idiopathic osteoarthritis of the human knee, the efficacy of potential interventions to correct biomechanical disruptions, and how joint biomechanics and biology are integrated during aging.

Peripheral mechanisms of arthritic pain: A proposal to leverage large animals for in vitro studies

Pain arising from musculoskeletal disorders such as arthritis is one of the leading causes of disability. Whereas the past 20-years has seen an increase in targeted therapies for rheumatoid arthritis (RA), other arthritis conditions, especially osteoarthritis, remain poorly treated. Although modulation of central pain pathways occurs in chronic arthritis, multiple lines of evidence indicate that peripherally driven pain is important in arthritic pain. To understand the peripheral mechanisms of arthritic pain, various in vitro and in vivo models have been developed, largely in rodents. Although rodent models provide numerous advantages for studying arthritis pathogenesis and treatment, the anatomy and biomechanics of rodent joints differ considerably to those of humans. By contrast, the anatomy and biomechanics of joints in larger animals, such as dogs, show greater similarity to human joints and thus studying them can provide novel insight for arthritis research. The purpose of this article is firstly to review models of arthritis and behavioral outcomes commonly used in large animals. Secondly, we review the existing in vitro models and assays used to study arthritic pain, primarily in rodents, and discuss the potential for adopting these strategies, as well as likely limitations, in large animals. We believe that exploring peripheral mechanisms of arthritic pain in vitro in large animals has the potential to reduce the veterinary burden of arthritis in commonly afflicted species like dogs, as well as to improve translatability of pain research into the clinic.

Three-dimensional in vivo kinematics and finite helical axis variables of the ovine stifle joint following partial anterior cruciate ligament transection

Partial anterior cruciate ligament (p-ACL) rupture is a common injury, but the impact of a p-ACL injury on in vivo joint kinematics has yet to be determined in an animal model. The in vivo kinematics of the ovine stifle joint were assessed during 'normal' gait, and at 20 and 40 weeks after p-ACL transection (Tx). Gross morphological scoring of the knee was conducted. p-ACL Tx creates significant progressive post-traumatic osteoarthritis (PTOA)-like damage by 40 weeks. Statistically significant increases for flexion angles at hoof-strike (HS) and mid-stance (MST) were seen at 20 weeks post p-ACL Tx and the HS and hoof-off (HO) points at 40 weeks post p-ACL-Tx, therefore increased flexion angles occurred during stance phase. Statistically significant increases in posterior tibial shift at the mid-flexion (MF) and mid-extension (ME) points were seen during the swing phase of the gait cycle at 40 weeks post p-ACL Tx. Correlation analysis showed a strong and significant correlation between kinematic changes (instabilities) and gross morphological score in the inferior-superior direction at 40 weeks post p-ACL Tx at MST, HO, and MF. Further, there was a significant correlation between change in gross morphological combined score (ΔGCS) and the change in location of the helical axis in the anterior direction (ΔsAP) after p-ACL Tx for all points analyzed through the gait cycle. This study quantified in vivo joint kinematics before and after p-ACL Tx knee injury during gait, and demonstrated that a p-ACL knee injury leads to both PTOA-like damage and kinematic changes.

Posttraumatic Osteoarthritis Development and Progression in an Ovine Model of Partial Anterior Cruciate Ligament Transection and Effect of Repeated Intra-articular Methylprednisolone Acetate Injections on Early Disease

BACKGROUND

Partial anterior cruciate ligament (p-ACL) ruptures are a common injury of athletes. However, few preclinical models have investigated the natural history and treatment of p-ACL injuries.

PURPOSE

To (1) demonstrate whether a controlled p-ACL injury model (anteromedial band transection) develops progressive gross morphological and histological posttraumatic osteoarthritis (PTOA)-like changes at 20 and 40 weeks after the injury and (2) investigate the efficacy of repeated (0, 5, 10, and 15 weeks) intra-articular injections of methylprednisolone acetate (MPA; 80 mg/mL) in the mitigation of potential PTOA-like changes after p-ACL transection.

STUDY DESIGN

Controlled laboratory study.

METHODS

Twenty-one 3- to 5-year-old female Suffolk-cross sheep were allocated to 4 groups: (1) nonoperative controls (n = 5), (2) 20 weeks after p-ACL transection (n = 5), (3) 40 weeks after p-ACL transection (n = 6), and (4) 20 weeks after p-ACL transection + MPA (n = 5). Gross morphological grading and histological analyses were conducted. mRNA expression levels for inflammatory, degradative, and structural molecules were assessed.

RESULTS

p-ACL transection led to significantly more combined gross damage ( P = .008) and significant aggregate histological damage ( P = .009) at 40 weeks after p-ACL transection than the nonoperative controls, and damage was progressive over time. Macroscopically, MPA appeared to slightly mitigate gross damage at 20 weeks after p-ACL transection in some animals. However, microscopic analysis revealed that repeated MPA injections after p-ACL transection led to significant loss in proteoglycan content compared with the nonoperative controls and 20 weeks after p-ACL transection ( P = .008 and P = .008, respectively).

CONCLUSION

p-ACL transection led to significant gross and histological damage by 40 weeks, which was progressive over time. Multiple repeated MPA injections were not appropriate to mitigate injury-related damage in a p-ACL transection ovine model as significant proteoglycan loss was observed in MPA-treated knees.

CLINICAL RELEVANCE

A p-ACL injury leads to slow and progressive PTOA-like joint damage, and multiple repeated injections of glucocorticoids may be detrimental to the knee joint in the long term.

Use of pre-clinical surgically induced models to understand biomechanical and biological consequences of PTOA development

Post-traumatic osteoarthritis (PTOA) development is often observed following traumatic knee injuries involving key stabilising structures such as the cruciate ligaments or the menisci. Both biomechanical and biological alterations that follow knee injuries have been implicated in PTOA development, although it has not been possible to differentiate clearly between the two causal factors. This review critically examines the outcomes from pre-clinical lapine and ovine injury models arising in the authors' laboratories and differing in severity of PTOA development and progression. Specifically, we focus on how varying severity of knee injuries influence the subsequent alterations in kinematics, kinetics, and biological outcomes. The immediate impact of injury on the lubrication capacity of the joint is examined in the context of its influence on biomechanical alterations, thus linking the biological changes to abnormal kinematics, leading to a focus on the potential areas for interventions to inhibit or prevent development of the disease. We believe that PTOA results from altered cartilage surface interactions where biological and biomechanical factors intersect, and mitigating acute joint inflammation may be critical to prolonging PTOA development. © 2017 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 35:454-465, 2017.

Ligament and meniscus loading in the ovine stifle joint during normal gait

BACKGROUND

The ovine stifle joint is an ideal preclinical model to study knee joint biomechanics. Knowledge of the ovine ligamentous and meniscal loading during normal gait is currently limited.

METHODS

The in vivo kinematics of the ovine stifle joint (N=4) were measured during "normal" gait using a highly accurate instrumented spatial linkage (ISL, 0.3±0.2mm). These motions were reproduced in vitro using a unique robotic testing platform and the loads carried by the anterior/posterior cruciate ligaments (ACL/PCL), medial/lateral collateral ligaments (MCL/LCL), and medial/lateral menisci (MM/LM) during gait were determined.

RESULTS

Considerable inter-subject variability in tissue loads was observed. The load in the ACL was near zero at hoof-strike (0% gait) and reached a peak (100 to 300N) during early-stance (~10% gait). The PCL reached a peak load (200 to 500N) just after hoof-strike (~5% gait) and was mostly unloaded throughout the remainder of stance. Load in the MCL was substantially lower than the cruciate ligaments, reaching a maximum of 50 to 100N near the beginning of stance. The LCL carried a negligible amount of load through the entire gait cycle. There was also a major contribution of the MM and LM to load transfer from the femur to the tibia during normal gait. The total meniscal load reached a maximum average between 350 and 550N during gait.

CONCLUSION

Knowledge of joint function during normal motion is essential for understanding normal and pathologic joint states. The considerable variability in the magnitudes and patterns of tissue loads among animals simulates clinical variability in humans.

LEVEL OF EVIDENCE

III.

Crimp morphology in the ovine anterior cruciate ligament

While the crimp morphology in ligaments and tendons has been described in detail in the literature, its relative distribution within the tissue has not been studied, especially in relation to the complex multi-bundle arrangement as is found in the anterior cruciate ligament (ACL). In this study, the crimp morphology of the ovine ACL was examined topologically and with respect to its double-bundle structure. The crimp morphologies were compared with the knee in three knee positions, namely stance, maximum extension and maximum flexion. As a control, the crimp morphology of the ACL free from its bony attachments was determined. In the control samples, the anterior-medial (AM) bundle contained a combination of coarse and fine crimp, whereas the posterior-lateral (PL) bundle manifested only a coarse crimp. Using the extent of crimp loss observed when subjecting the knee to the respective positions, and comparing with the controls, the crimp morphologies show that the AM bundle of the ACL is most active in the stance position, whereas for the maximum extension and flexion positions the PL bundle is most active. We propose that these differences in crimp morphologies have relevance to ACL design and function.

Increased meniscal loading after anterior cruciate ligament transection in vivo: a longitudinal study in sheep

INTRODUCTION

Meniscal injury has been well documented as a frequent consequence of both acute and chronic ACL deficiency. The purpose of this study was to evaluate the effect of ACL deficiency on meniscal loads in vivo and determine how these loads would change over time after ACL injury.

METHODS

The in vivo kinematics of the stifle joint of five sheep were measured during normal gait, as well as 4 and 20 weeks after ACL transection. A unique robotic testing platform was then programmed to reproduce all the previously recorded kinematics and the loads carried by medial and lateral menisci during gait were estimated.

RESULTS

The results demonstrated a significant increase in both medial and lateral meniscal loads 20 weeks following ACL transection, mainly during mid-stance phase of gait (p = 0.007 and p = 0.003, respectively), with interesting inter-subject variability. A moderate correlation (R(2) ≥ 0.5) between in situ meniscal loads and anterior tibial translations was also detected over time after injury, increased translations post injury generally corresponded to larger meniscal loads.

CONCLUSION

The dramatic increase in meniscal loads long term post ACL transection probably explains the meniscal changes or injuries reported clinically in many chronic ACL-deficient knees.