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

Abstract

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.

The effect of exercise on the protein profile of rat knee joint intra- and extra-articular ligaments

“…This study demonstrated that short-term strenuous treadmill exercise impacts ACL protein expression, whilst MCL proteome is not altered. These differences in response may be due to a difference in mechanical loading and previously identified structural and ECM compositional difference between the two tissue types [50].…”

“…In addition, a mean score was produced for each joint and these similarly were used to produce an overall 'average' mean grade in each group of rats [49]. The scoring for ligaments was adapted from Kharaz, Canty-Laird [50] and scoring was performed based on strength of ECM staining, cell hypertrophy, cell clustering, loss of alignment and ossification and were graded from 0-4 based on the extent of changes ((0= 0% increase; normal, 1= 5-25% increase; mild abnormality, 2= 26-50% increase; moderate abnormality, 3= 51-75% increase; marked abnormality, 4= 76-100% increase; severe abnormality). Inter and intra-observer variability was calculated with Cohen's Kappa statistics using an online software tool:…”

Comparison of elastic, viscoelastic and failure tensile material properties of knee ligaments and patellar tendon

“…Additionally, collateral ligaments have been shown to contain more smalldiameter fibrils than ACL, PCL and PT (Rumian et al, 2007), resulting in larger interaction areas between fibrils and other extracellular matrix constituents, which may affect viscoelasticity at the mesoscopic level. Finally, possibly lower elastin content compared to cruciate ligaments (Kharaz et al, 2018) might increase LCL viscosity, as elastin has been thought to be an elastic stabilizer restoring tissue back to its original shape.…”

“…The results might be explained by the higher collagen content in collateral ligaments (Hanada et al, 2014) and possibly more oriented collagen fibrils along the direction of the loading. Additionally, higher elastin (Kharaz et al, 2018) and GAG (Kharaz 2018, Rumian 2007 contents in cruciate ligaments might explain their differences to MCL, as presumably higher elastin and GAG contents lower the relative amount of collagen. Elastin has been shown to contribute only slightly to the stress-strain behavior outside the toe-region and the role of GAGs is more emphasized in compression (Korhonen and Jurvelin, 2010).…”

Active synthesis of type I collagen homotrimer in Dupuytren’s fibrosis is unaffected by anti-TNF-α treatment

“…obtained samples from the mid-metacarpal tendon region, far from any muscle, and utilised laser capture microdissection to prepare samples; hence contamination from surrounding tissues, or a long-range interdigitation of the myotendinous junction, seems unlikely. Ligament can contain a broader interfascicular matrix than tendon (Kharaz et al, 2018) hence muscle-related proteins in normal PF may arise from the interfascicular matrix and play a physiological role therein. The presence of proteins more usually associated with cartilage, such as cartilage intermediate layer protein 1 (CILP) and chondroadherin (CHAD) in normal PF, is consistent with previous findings of ourselves and others ligament, and may reflect the fibrocartilaginous nature of ligament regionally or throughout (Kharaz et al, 2016;Little et al, 2014).…”