Elastin content is high in the canine cruciate ligament and is associated with degeneration

Proteoglycans play a role in the viscoelastic behaviour of the canine cranial cruciate ligament

Proteoglycans (PGs) are minor extracellular matrix proteins, and their contributions to the mechanobiology of complex ligaments such as the cranial cruciate ligament (CCL) have not been determined to date. The CCLs are highly susceptible to injuries, and their extracellular matrix comprises higher PGs content than the other major knee ligaments. Hence these characteristics make CCLs an ideal specimen to use as a model in this study. This study addressed the hypothesis that PGs play a vital role in CCL mechanobiology by determining the biomechanical behaviour at low strain rates before and after altering PGs content. For the first time, this study qualitatively investigated the contribution of PGs to key viscoelastic characteristics, including strain rate dependency, hysteresis, creep and stress relaxation, in canine CCLs. Femur-CCL-tibia specimens (n = 6 pairs) were harvested from canine knee joints and categorised into a control group, where PGs were not depleted, and a treated group, where PGs were depleted. Specimens were preconditioned and cyclically loaded to 9.9 N at 0.1, 1 and 10%/min strain rates, followed by creep and stress relaxation tests. Low tensile loads were applied to focus on the toe-region of the stress-strain curves where the non-collagenous extracellular matrix components take significant effect. Biochemical assays were performed on the CCLs to determine PGs and water content. The PG content was ∼19% less in the treated group than in the control group. The qualitative study showed that the stress-strain curves in the treated group were strain rate dependent, similar to the control group. The CCLs in the treated group showed stiffer characteristics than the control group. Hysteresis, creep characteristics (creep strain, creep rate and creep compliance), and stress relaxation values were reduced in the treated group compared to the control group. This study suggests that altering PGs content changes the microstructural organisation of the CCLs, including water molecule contents which can lead to changes in CCL viscoelasticity. The change in mechanical properties of the CCLs may predispose to injury and lead to knee joint osteoarthritis. Future studies should focus on quantitatively identifying the effect of PG on the mechanics of intact knee ligaments across broader demography.

An off-the-shelf decellularized and sterilized human bone-ACL-bone allograft for anterior cruciate ligament reconstruction

Approximately 1% of active individuals participating in sports rupture their anterior cruciate ligaments (ACL) every year, which is currently reconstructed using tendon autografts. Upon reconstruction, clinical issues of concern are ACL graft rupture, persistent knee instability, limited return to sports, and early onset of osteoarthritis (OA). This happens because tendon autografts do not have the same compositional, structural, and mechanical properties as a native ACL. To overcome these problems, we propose to use decellularized bone-ACL-bone allografts in ACL reconstruction (ACLR) as a mechanically robust, biocompatible, and immunologically safe alternative to autografts. Here, a decellularization protocol combined with sterilization using supercritical carbon dioxide (scCO₂) was used to thoroughly decellularize porcine and human ACLs attached to tibial and femoral bone blocks. The specimens were named ultrACLean and their compositional, structural, and mechanical properties were determined. Our results indicate that: 1) decellularization of ultrACLean allografts leads to the removal of nearly 97% of donor cells, 2) ultrACLean has mechanical properties which are not different to native ACL, 3) ultrACLean maintained similar collagen content and decreased GAG content compared to native ACL, and 4) ultrACLean is not cytotoxic to seeded tendon-derived cells in vitro. Results from an in vivo pilot experiment showed that ultrACLean is biocompatible and elicits a moderate immunological response. In summary, ultrACLean has proven to be a mechanically competent and biocompatible graft with the potential to be used in ACLR surgery.

Relationship of mRNA Expression of Selected Genes in Peripheral Blood and Synovial Fluid in Cranial Cruciate Ligament Deficient Stifles of Dogs

Simple Summary

The cranial cruciate ligament rupture is characterized by chronic inflammation, osteoarthritis of the stifle joint, and extracellular matrix degeneration of the ligament itself in dogs. Early pre-clinical cranial cruciate ligament alteration cannot be detected by clinical examination or standard radiography. Therefore, we assessed the possible relationship of inflammatory markers in peripheral blood and synovial fluid of affected stifle joints in comparison to a control. We also evaluated components of the extracellular matrix of ruptured ligaments and finally compared the tibial plateau angle and the anatomical-mechanical angle between groups. Some of the assessed inflammatory markers were significantly increased in both the peripheral blood and synovial fluid compared with the control, as were collagens. The tibial plateau angle was not significantly different; however, the anatomical-mechanical angle significantly increased in the ruptured ligaments. Our results suggest a possible positive relationship between inflammatory markers of blood and synovial fluid in cranial cruciate ligament deficient stifles compared to the control. These findings may support both local and systemic inflammation process at the same time during osteoarthritis progression. Based on this, it would be interesting to investigate the predictive osteoarthritis pathway of inflammatory cytokines, matrix metalloproteinases, and their effect on the extracellular matrix components of the cranial cruciate ligament in future studies.

Abstract

The cranial cruciate ligament rupture (CrCLR) is characterized by chronic inflammation and osteoarthritis (OA) of the stifle joint and extracellular matrix (ECM) degeneration of the ligament itself in dogs. Generally, OA may arise from chronic low-grade systemic inflammation. We assessed the possible relationship of inflammatory markers in the peripheral blood (PB) and synovial fluid (SF) of affected stifle joints in comparison to a control. Moreover, no study has shown the possible association between PB and SF levels of inflammatory markers in CrCLR stifles of dogs in veterinary medicine yet. We also evaluated components of ECM of CrCLR and finally compared the tibial plateau angle (TPA) and the anatomical-mechanical angle (AMA) between groups. Samples from PB and SF were examined for mRNA expression of interleukins, TNF-α and INF-γ. ECM components—collagen 1A1 and 3A1 and elastin—were examined for mRNA expression from SF. The level of relative expression for IL-1β, IL-8 and IFN-γ was significantly increased in both PB and SF in CrCLR stifles as compared with the control. Collagens were also significantly increased in CrCLR stifles. TPA was not significantly different; however, the AMA angle significantly increased in the CrCLR group. Our results suggest a possible relationship between PB and SF levels of inflammatory markers in CrCLR stifles of dogs.

Effects of long-term and high-dose administration of glucocorticoids on the cranial cruciate ligament in healthy beagle dogs

This study aimed to determine the effects of long-term and high-dose administration of glucocorticoids (GCs) on the histological and mechanical properties of the cranial cruciate ligament (CrCL) in healthy beagle dogs. A synthetic corticosteroid at 2 mg/kg every 12 h was administered for 84 days in nine dogs (18 CrCLs) (GC group). Twenty CrCLs from 12 healthy male beagles were used as the normal control (control group). CrCLs were histologically examined (n = 12 in the GC group and n = 14 in the control group) using hematoxylin-eosin, Alcian-Blue, Elastica-Eosin stains, and immunohistological staining of type 1 collagen and elastin. An additional 12 CrCLs were mechanically tested (n = 6 in the GC and n = 6 in the control groups) to determine failure pattern, maximum tensile strength, maximum stress, elastic modulus, and stress and strain at the transition point. The histological examination revealed a significant increase in interfascicular area and fibrillar disorientation at the tibial attachment in both groups. The ratios of mucopolysaccharide-positive area and positive areas of elastic fibers were significantly higher in the control group than in the GC group. The biomechanical examination demonstrated significantly lower stress at the transition point in the GC group than in the control group. The present study results indicate that high-dose corticosteroids may affect metabolism, such as mucopolysaccharides and elastic fibers production, although the effect on type 1 collagen production is small. These changes of the extracellular matrix had a small effect on the strength of the ligament. This study suggested that the ligamentous changes associated with GC are different from the degeneration observed in spontaneous canine CrCL disease.

Prophylactic Efficacy of Tibial Plateau Levelling Osteotomy for a Canine Model with Experimentally Induced Degeneration of the Cranial Cruciate Ligament

OBJECTIVE

 The aim of this study was to clarify the histological effects of tibial plateau levelling osteotomy on cranial cruciate ligament degeneration induced by excessive tibial plateau angle.

STUDY DESIGN

 Five female Beagles were used to bilaterally create excessive tibial plateau angle models surgically. A second tibial plateau levelling osteotomy was performed 11 months after the first surgery on the right stifle (tibial plateau levelling osteotomy group), and a sham operation that did not change the tibial plateau angle was performed on the left stifle (excessive tibial plateau angle group). At 6 months after the second surgery, the dogs were euthanatized. The cranial cruciate ligament was stained with haematoxylin-eosin to assess the cell density, Alcian-Blue to assess proteoglycans and Elastica-Eosin to assess elastic fibres, and immunohistochemically stained to assess type I (COL1) and type II collagen and SRY-type HMG box 9 (SOX9) expression.

RESULTS

 In each group, the cranial cruciate ligament degeneration, especially on the tibial side, including the presence of Alcian-Blue- and Elastica-Eosin-positive regions, decreased in COL1-positive regions, and enhancement of SOX9 expression was observed. Besides, compared with the tibial plateau levelling osteotomy group, the excessive tibial plateau angle group showed increases in Alcian-Blue- and Elastica-Eosin-positive regions and a decrease in the COL1-positive regions.

CONCLUSION

 The results suggested that excessive tibial plateau angle-induced cranial cruciate ligament degeneration can be suppressed by reducing the biomechanical load on the cranial cruciate ligament by performing tibial plateau levelling osteotomy.

Characterisation of key proteoglycans in the cranial cruciate ligaments (CCLs) from two dog breeds with different predispositions to CCL disease and rupture

Cranial cruciate ligament disease and rupture (CCLD/R) is one of the most common orthopaedic conditions in dogs, eventually leading to osteoarthritis of the stifle joint. Certain dog breeds such as the Staffordshire bull terrier have an increased risk of developing CCLD/R. Previous studies into CCLD/R have found that glycosaminoglycan levels were elevated in cranial cruciate ligament (CCL) tissue from high-risk breeds when compared to the CCL from a low-risk breed to CCLD/R. Our objective was to determine specific proteoglycans/glycosaminoglycans in the CCL and to see whether their content was altered in dog breeds with differing predispositions to CCLD/R. Disease-free CCLs from Staffordshire bull terriers (moderate/high-risk to CCLD/R) and Greyhounds (low-risk to CCLD/R) were collected and key proteoglycan/glycosaminoglycans were determined by semi-quantitative Western blotting, quantitative biochemistry, quantitative reverse transcription polymerase chain reaction, and immunohistochemistry. Gene expression of fibromodulin (P = 0.03), aggrecan (P = 0.0003), and chondroitin-6-sulphate stubs (P = 0.01) were significantly increased, and for fibromodulin this correlated with an increase in protein content in Staffordshire bull terriers compared to Greyhound CCLs (P = 0.02). Decorin (P = 0.03) and ADAMTS-4 (P = 0.04) gene expression were significantly increased in Greyhounds compared to Staffordshire bull terrier CCLs. The increase of specific proteoglycans and glycosaminoglycans within the Staffordshire bull terrier CCLs may indicate a response to higher compressive loads, potentially altering their risk to traumatic injury. The higher decorin content in the Greyhound CCLs is essential for maintaining collagen fibril strength, while the increase of ADAMTS-4 indicates a higher rate of turnover helping to regulate normal CCL homeostasis in Greyhounds.

Elastic fibers in orthopedics: Form and function in tendons and ligaments, clinical implications, and future directions

Elastic fibers are an essential component of the extracellular matrix of connective tissues. The focus of both clinical management and scientific investigation of elastic fiber disorders has centered on the cardiovascular manifestations due to their significant impact on morbidity and mortality. As such, the current understanding of the orthopedic conditions experienced by these patients is limited. The musculoskeletal implications of more subtle elastic fiber abnormalities, whether due to allelic variants or age-related tissue degeneration, are also not well understood. Recent advances have begun to uncover the effects of elastic fiber deficiency on tendon and ligament biomechanics; future research must further elucidate mechanisms governing the role of elastic fibers in these tissues. The identification of population-based genetic variations in elastic fibers will also be essential. Minoxidil administration, modulation of protein expression with micro-RNA molecules, and direct injection of recombinant elastic fiber precursors have demonstrated promise for therapeutic intervention, but further work is required prior to consideration for orthopedic clinical application. This review provides an overview of the role of elastic fibers in musculoskeletal tissue, summarizes current knowledge of the orthopedic manifestations of elastic fiber abnormalities, and identifies opportunities for future investigation and clinical application.

Investigation of fibrillin microfibrils in the canine cruciate ligament in dogs with different predispositions to ligament rupture

Cranial cruciate ligament disease (CCLD) is the most common cause of pelvic limb lameness in dogs but its precise aetiopathogenesis is uncertain. Fibrillin microfibrils (FM) are complex macro-molecular assemblies found in many tissues including ligaments, where they are thought to play an important mechanical role. We hypothesised that FM ultrastructural variation correlates with the differing predisposition of canine breeds to CCLD. Non-diseased cranial and caudal cruciate ligaments (CCLs and CaCLs) were obtained from Greyhound (GH) and Staffordshire Bull Terrier (SBT) cadavers. Fibrillin microfibrils were extracted from the ligaments by bacterial collagenase digestion, purified by size-exclusion chromatography and subsequently visualized by atomic force microscopy (AFM). With AFM, FMs have a characteristic beads-on-a-string appearance. For each FM, periodicity (bead-bead distance) and length (number of beads/FM) was measured. Fibrillin microfibril length was found to be similar for GH and SBT, with non-significant inter-breed and inter-ligament differences. Fibrillin microfibril periodicity varied when comparing GH and SBT for CCL (GH 60.2 ± 1.4 nm; SBT 56.2 ± 0.8 nm) and CaCL (GH 55.5 ± 1.6 nm; SBT 61.2 ± 1.2 nm). A significant difference was found in the periodicity distribution when comparing CCL for both breeds (P < 0.00001), further, intra-breed differences in CCL vs CaCL were statistically significant within both breeds (P < 0.00001). The breed at low risk of CCLD exhibited a periodicity profile which may be suggestive of a repair and remodelling within the CCL.

Is the T-ligament a ligament? A histological study in equine cadaver forelimbs

Foot pain is a frequent cause of lameness in horses and can involve multiple structures within the hoof. The T-ligament (an anatomical structure connecting the synovium of the distal interphalangeal joint, the digital flexor tendon sheath and the navicular bursa) is poorly described. Five pairs of equine cadaver distal forelimbs were collected from a slaughterhouse. Sagittal sections (medial, middle and lateral) were obtained and processed with Haematoxylin Eosin Safran, Unna's Orcein, and Picrosirius red stains. Histological assessment revealed that the T-ligament was covered by the surrounding synovia of the distal interphalangeal joint, the digital flexor tendon sheath and the navicular bursa. Its collagen content was lower (30.01%±10.15) than that of the collateral sesamoidean ligament (89.48%±5.8; P = .0008) and the middle phalanx (85.72%±3.67; P = .0008). Under polarized light microscopy, it showed a slight heterogeneous pattern of birefringence, with angle-related changes. Elastic fibres were more numerous (21.76%±8.72) than in the collateral sesamoidean ligament (0.28%±0.45), or deep digital flexor tendon (0.04%±0.02); and were more densely packed. Mean cell count was higher for the T-ligament than for other tissues (P = .0007). Blood vessels were identified in the T-ligament and were penetrating the deep digital flexor tendon (8/10 limbs, 5/5 horses). In conclusion, the T-ligament looked like a vinculum for the deep digital flexor tendon, with a central elastic core, surrounding loose connective tissue and blood vessels. It is not a ligament. Its clinical relevance still needs to be determined.

Histologic examination of the shoulder capsule shows new layer of elastic fibres between synovial and fibrous membrane

Purpose

In the present study, a systematic histological analysis of the glenohumeral joint capsule was conducted.

Materials and methods

12 cadaveric shoulders were examined. Inclusion criteria were: 1) intact joint capsule and 2) fixation in neutral position. The tissue samples were Elastica Hematoxylin-van-Gieson-(ElHvG) stained and diameter, quantity, and distribution patterns were analyzed.

Results

We detected a new layer (elastic boundary layer, EBL) between the synovial and fibrous membrane. The elastic fibres of the EBL differ considerably in diameter, quantity, and distribution pattern.

Conclusions

A previously undescribed layer was noticed, which we named elastic boundary layer for now.

Intraarticular Ligament Degeneration Is Interrelated with Cartilage and Bone Destruction in Osteoarthritis

Osteoarthritis (OA) induces inflammation and degeneration of all joint components including cartilage, joint capsule, bone and bone marrow, and ligaments. Particularly intraarticular ligaments, which connect the articulating bones such as the anterior cruciate ligament (ACL) and meniscotibial ligaments, fixing the fibrocartilaginous menisci to the tibial bone, are prone to the inflamed joint milieu in OA. However, the pathogenesis of ligament degeneration on the cellular level, most likely triggered by OA associated inflammation, remains poorly understood. Hence, this review sheds light into the intimate interrelation between ligament degeneration, synovitis, joint cartilage degradation, and dysbalanced subchondral bone remodeling. Various features of ligament degeneration accompanying joint cartilage degradation have been reported including chondroid metaplasia, cyst formation, heterotopic ossification, and mucoid and fatty degenerations. The entheses of ligaments, fixing ligaments to the subchondral bone, possibly influence the localization of subchondral bone lesions. The transforming growth factor (TGF)β/bone morphogenetic (BMP) pathway could present a link between degeneration of the osteochondral unit and ligaments with misrouted stem cell differentiation as one likely reason for ligament degeneration, but less studied pathways such as complement activation could also contribute to inflammation. Facilitation of OA progression by changed biomechanics of degenerated ligaments should be addressed in more detail in the future.

Variations in internal structure, composition and protein distribution between intra- and extra-articular knee ligaments and tendons

Tendons and ligaments play key roles in the musculoskeletal system in both man and animals. Both tissues can undergo traumatic injury, age‐related degeneration and chronic disease, causing discomfort, pain and increased susceptibility to wider degenerative joint disease. To date, tendon and ligament ultrastructural biology is relatively under‐studied in healthy, non‐diseased tissues. This information is essential to understand the pathology of these tissues with regard to function‐related injury and to assist with the future development of tissue‐engineered tendon and ligament structures. This study investigated the morphological, compositional and extracellular matrix protein distribution differences between tendons and ligaments around the non‐diseased canine stifle joint. The morphological, structural characteristics of different regions of the periarticular tendons and ligaments (the intra‐articular anterior cruciate ligament, the extra‐articular medial collateral ligament, the positional long digital extensor tendon and energy‐storing superficial digital flexor tendons) were identified using a novel semi‐objective histological scoring analysis and by determining their biochemical composition. Protein distribution of extracellular matrix collagens, proteoglycans and elastic fibre proteins in anterior cruciate ligament and long digital extensor tendon were also determined using immunostaining techniques. The anterior cruciate ligament was found to have significant morphological differences in comparison with the other three tissues, including less compact collagen architecture, differences in cell nuclei phenotype and increased glycosaminoglycan and elastin content. Intra‐ and interobserver differences of histology scoring resulted in an average score 0.7, indicative of good agreement between observers. Statistically significant differences were also found in the extracellular matrix composition in terms of glycosaminoglycan and elastin content, being more prominent in the anterior cruciate ligament than in the other three tissues. A different distribution of several extracellular matrix proteins was also found between long digital extensor tendon and anterior cruciate ligament, with a significantly increased immunostaining of aggrecan and versican in the anterior cruciate ligament. These findings directly relate to the different functions of tendon and ligament and indicate that the intra‐articular anterior cruciate ligament is subjected to more compressive forces, reflecting an adaptive response to normal or increased loads and resulting in different extracellular matrix composition and arrangement to protect the tissue from damage.

Three dimensional microstructural network of elastin, collagen, and cells in Achilles tendons

Similar to most biological tissues, the biomechanical, and functional characteristics of the Achilles tendon are closely related to its composition and microstructure. It is commonly reported that type I collagen is the predominant component of tendons and is mainly responsible for the tissue's function. Although elastin has been found in varying proportions in other connective tissues, previous studies report that tendons contain very small quantities of elastin. However, the morphology and the microstructural relationship among the elastic fibres, collagen, and cells in tendon tissue have not been well examined. We hypothesize the elastic fibres, as another fibrillar component in the extracellular matrix, have a unique role in mechanical function and microstructural arrangement in Achilles tendons. It has been shown that elastic fibres present a close connection with the tenocytes. The close relationship of the three components has been revealed as a distinct, integrated and complex microstructural network. Notably, a "spiral" structure within fibril bundles in Achilles tendons was observed in some samples in specialized regions. This study substantiates the hierarchical system of the spatial microstructure of tendon, including the mapping of collagen, elastin and tenocytes, with 3-dimensional confocal images. © 2017 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 35:1203-1214, 2017.