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Ligaments have similarities yet differences from tendons in important respects. Ligaments have a similar hierarchical organization of collagen structures as tendons, although the collagen fibers tend to be more loosely packed in ligaments (the collagen fibrils are slightly less in volume fraction and organization than tendon). However, ligaments have a higher percentage of proteoglycan matrix than tendons. Another significant difference in structure between ligaments and tendons is the amount of elastin found in ligaments. Elastin comprises less than 4% of the dry weight of tendons; in contrast, typical ligaments exhibit 4–9% elastin as dry weight, while some highly extensible ligaments have over 70% elastin as dry weight. The elastin network in the ligament resides along and between the collagen fibers (Zitnay & Weiss, 2018).

Figure 3.20 Ligaments. (a) A diagram showing the ligament of the knee: lateral collateral ligament (LCL), medial collateral ligament (MCL), anterior and posterior cruciate ligaments (ACL and PCL), and several other tendons. Sensory receptors present in the ligaments are listed and include free nerve endings (pain endings), Ruffini endings (pressure receptors), and Golgi tendon organs (tension receptors).

From Cabuk, H., & Kuşku Çabuk, F. (2016). Mechanoreceptors of the ligaments and tendons around the knee. Clinical Anatomy, 29,(6),789–795. doi: 10.1002/ca.22743.

(b) An image of a ligament joining carpal bones.

Table 3.6 Summary of Cells, Extracellular Matrix (ECM), Subtypes, and Function of Ligaments Under Normal Conditions

Characteristic	Description
Tissue type	Dense regular connective tissues
Cells	Fibroblastic synoviocyte‐like type cells
ECM	Collagen, proteoglycans, elastin (varies from 4 to 70% of dry weight dependent on ligament)
Subtypes	Typical (4–9% elastin) to highly extensible (up to 70% extensible)
Function	Support and strength to joints