Tendons and ligaments are anatomically distinct but overlap in molecular and morphological features—a comparative study in an ovine model

Abstract

Tendons and ligaments are similar in composition but differ in function. Simple anatomical definitions do not reflect the fact individual tendons and ligaments have unique properties due to their adaptation to a specific role. The patellar tendon is a structure of particular clinical interest. A null hypothesis was declared stating that the patellar tendon is not significantly different in terms of matrix composition and collagen fibril diameter to other tendons. The lateral and medial collateral ligaments (LCL, MCL), anterior and posterior cruciate ligaments (ACL, PCL), together with the long digital extensor, superficial digital extensor, and patellar tendons (LDET, SDFT, PT) were harvested from three cadaveric ovine hindlimbs. The extracellular matrix was assessed in terms of water, collagen, and total sulphated glycosaminoglycan (GAG) content. The organization of the collagen component was determined by an ultrastructural analysis of collagen fibril diameter distributions, together with values for the collagen fibril index (CFI) and massaverage diameter (MAD). There were significant differences between ligaments and tendons. The PT had a bimodal collagen fibril diameter distribution with CFI 72.9%, MAD 202 nm, water content 53.1%, GAG content 2.3 mg/mg, and collagen content 73.7%, which was not significantly different from the other tendons. The results of this study support the null hypothesis suggesting that the patellar tendon is similar to other tendons and demonstrate that tendons have different characteristics to ligaments. ß

Lower strength of the human posterior patellar tendon seems unrelated to mature collagen cross-linking and fibril morphology

“…Anatomically, the posterior portion of patellar tendon connects the patellar sesamoid bone to the tibial tuberosity, whereas the anterior portion appears as a continuity of the quadriceps tendon. Furthermore, compared with tendon, ligaments have increased concentration of the immature cross-link dihydroxylysinonorleucine (DHLNL) [which is a precursor of HP (37)], a higher concentration of pyridinoline (36), and a larger number of small fibrils (35), which corresponds well with the present data, although obviously further studies are warranted.…”

Viscoelastic Relaxation and Recovery of Tendon

“…1 Rumian et al found differences in the extracellular matrix between an assortment of tendons and ligaments in sheep, finding differences not only between the tendon and ligament groups, but also between the various ligaments and tendons themselves, including fibril diameter distributions, water content, and glycosaminoglycan content. 30 These findings show that tendon and ligament properties vary with position and function in the body. Whether these variations are due to site-specific mechanical adaptation or are predetermined genetically remains unknown.…”

Evidence against proteoglycan mediated collagen fibril load transmission and dynamic viscoelasticity in tendon

“…This limitation has been pointed out by other researchers who have suggested that the structure-function relationships found in the tail might not generally apply to all tendons (Robinson et al, 2005). However the biochemical composition (Rumian et al, 2007), collagen-PG architecture (Wang et al, 2006) and mechanical characteristics (Nagasawa et al, 2008;Schechtman and Bader, 1994;Schwerdt et al, 1980) of RTTFs fall within the range of other skeletal tendons.…”