| A | B |
|---|
| function of tendons | attach muscle to bone. transmits tensile loads from muscle to bone |
| function of ligaments | connect bone to bone. augments the mechanical stability of joints. guides motion of joints. prevents excessive joint motion |
| structure of tendons and ligaments | are dense connective tissue referred to as parallel-fibered collagenous tissue. sparsely vascularized. composed largely of collagen. great mechanical stability of collagen gives tendons and ligament their strength and flexibility. both consist of relatively few cells called fibroblasts (20%) and an extra-cellular matrix (80%) |
| tendons and aponeurosis | muscles attach to bones in one of three ways: directly into bone, via a tendon, via an aponeurosis |
| tendon | transmits force from the associated muscle to the bone. connects to the muscle at the myotendinous junction. are surrounded by a loose connective tissue that forms a sheath that protects it during gliding. in areas where subjected to high friction forces (e.g. wrist joint), a synovial layer is found beneath the sheath |
| collagen fibers in tendon | have an orderly parallel arrangement that allows the tendon to handle high tensile forces |
| ligaments | connects one bone to another bone. role is to augment the mechanical stability of the joints, to guide motion and to prevent excessive motion. structure is much like that of a tendon. do appear to not act in the mid-range movement of the joint but only at the end range of the motion. surrounded by a loose connective sheath also |
| ligaments and tensile forces | sustain tensile forces in one predominant direction. bear smaller tensile loads in other directions. collagen fibers are not completely parallel but are closely interlaced with one another |
| insertion into bone consists of four zones. | 1. at the end of the tendon. 2. the collagen fibers intermesh with fibro-cartilage. 3. fibro-cartilage become mineralized fibro-cartilage. 4. mineralized fibrocartilage merges into cortical bone. this gradual change produces a change in mechanical properties of the tissue (i.e. the increased stiffness and decreased stress concentration at the insertion of the stiffer bone) |
| mechanical behavior | both viscoelastic structures. tendons are strong to sustain high tensile forces resulting from muscle contraction. tendons are flexible enough to angulate around bony surfaces to change direction of muscle pull. ligaments are pliable and flexible allowing natural movements of bones. ligaments are sufficiently strong and inextensible to offer resistance to applied forces |
| biomechanical properties | both tendons and ligaments sustain predominatley tensile loads |
| physiological loading | under normal conditions in vivo, tendons and ligaments are stressed only to about 1/3 of Pmax. the upper limit for physiological strain in tendons and ligaments if from 2-5% (during running and jumping). experiments suggest that, during normal activity, a tendon in vivo is subjected to less than 1/4 of its ultimate stress |
| injury mechanism | similar for tendons and ligaments. when ligament subjected to loading that exceeds the physiologic range, microfailure takes place even before yield point. when Plin is exceeded, the ligament begins to undergo gross failure and the joint begins to displace abnormally |
| category 1 ligament injury | produce negligible clinical symptoms but some pain and no joint instability |
| category 2 ligament injury | produce severe pain, some joint instability; progressive failure of collagen fibers; strength and stiffness decrease by 50% |
| category 3 ligament injury | severe pain during trauma but less afterward; joint completely unstable; most collagen fibers are ruptured |
| viscoelastic behavior | both exhibit rate dependent behavior. with higher strain rates ligaments and tendons store more energy, require more force to rupture and undergo greater elongation. during cyclic loading, the stress-strain curve is displaced to the right along the deformation axis with each loading cycle. micro-failure can occur within the physiologic range if frequent loading is imposed on an already damaged structure |
| aging affects on biobmechanical properties | physical properties of collagen closely associated with number and quality of cross-links. during maturation, number and quality of cross-links increase thus increasing tensile strength. as agin progresses, collagen reaches a plateau as to strength and stiffness eventually decreasing |
| immoblization affects on biobmechanical properties | tissues remodel in response to mechanical demands. physical training increases tensile strength in tendons and ligament-bone interface |
