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a joint structure determines its combination of strength and flexibility. at one end of the spectrum are joints that permit no movement and thus very strong, but inflexible. in contrast, other joints afford fairly free movement and are thus flexible but not as strong. in general, the closer the fit at the point of contact, the stronger the joint. at tightly fitted joints, movement is obviously more restricted. the looser the fit, the greater the movement. however, loosely fitted joints are prone to displacement of the articulating bones from their normal positions (dislocation). movement at joints is also determined by the shape of the articulating bones, the flexibility (tension or tautness) of the ligaments that bind the bones together and the tension of associated muscles and tendons. joint flexibility may also be affected by hormones. for example, toward the end of pregnancy, a hormone called relaxin increases the flexibility of the fibrocartilage of the pubic
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最后更新: 2014-03-02
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