Ultrastructural analyzes on mechanism of effects of stress shielding on the mechanical properties of the in situ frozen patellar tendon.

1.原位冷冻对髌腱的影响从生物力学的角度来看，冷冻在治疗后3周以上降低了髌腱的抗张强度。然而，最大失效载荷的减少是最小的，因为冷冻增加了髌腱的横截面积。超微结构，冷冻并没有改变超微结构的髌腱在3周。6周时，冷冻显著增加了直径小于90nm的细胶原纤维的数量，并使胶原纤维直径直方图由双峰变为单峰.应力遮挡对原位冷冻髌腱的影响从生物力学的角度来看，应力遮挡在1周内显著降低了原位冷冻髌腱的抗拉强度。尽管横截面积增加，最大破坏载荷显着降低。髌腱对应力遮挡的机械响应独立于活细胞发生。在髌腱冷冻原位，超微结构，应力屏蔽减少胶原纤维的总数和胶原纤维的总面积的比例，整个可视化面积在3周内，而它增加了粗胶原纤维的直径超过360 nm.应力遮挡对髌腱原位冷冻的影响机制应力遮挡作用于髌腱的基质，包括胶原蛋白，独立于活细胞。横截面中胶原原纤维的总面积的减小、胶原原纤维之间产生的摩擦力的减小以及胶原原纤维本身的拉伸强度的减小被认为是髌腱拉伸强度减小的原因。

1. Effects of in situ freezing on the patellar tendonBiomechanically, freezing reduced the tensile strength of the patellar tendon at more than 3 weeks after treatment. However, reduction of the maximum failurre load was minimum, because freezing increased the cross-sectional area of the patellar tendon. Ultrastructurally, freezing did not change the ultrastructure of the patellar tendon at 3 weeks. At 6 weeks, however, freezing significantly increased the number of thin collagen fibrils having the diameter of less than 90nm and changed the histogram of collagen fibril diameter from bimode into unimode.2. Effects of stress shielding on the patellar tendon frozen in situBiomechanically, stress shielding drastically reduced the tensile strength of the in situ frozen patellar tendon within 1 week. In spite of increase of the cross-sectional area, the maximum failure load significantly decreased. Mechanical response of the patellar tendon to stress shielding occurred independent of living cells. In the patellar tendon frozen in situ, ultrastructurally, stress shielding reduced the total number of collagen fibrils and the ratio of the total area of collagen fibrils to the whole visualized area within 3 weeks, while it increased thick collagen fibrils having the diameter of more than 360 nm.3. Mechanism of the effects of stress shielding on the patellar tendon frozen in situStress shielding affects the matrix of the patellar tendon that include collagen, independent of living cells. Reduction of the total area of collagen fibrils in the cross section, reduction of the frictional force developed between collagen fibrils, and decrease of the tensile strength of collagenfibril itself are considered as causes of the reduction in the tensile strength of the patellar tendon.