外部反覆衝擊力對骨中結構及膝關節退化之尚在被研究中, 尤其是針對顯
微裂縫及OA產生之初期。至於骨如何修補顯微裂縫, 和如何影響骨骼機械
性質至今仍未有全面性之瞭解。此外骨骼在體內 (In-vivo)及體外(In
vitro )疲勞試驗之結果存在極大差異.本實驗中設計一機械式機構, 將兔
子自一定高度, 以自由落體方式落下 ,反覆此動作, 以產生膝關節退化之
情形, 並利用超音波量測設備及骨組織學觀察, 探討衝擊力對骨機械性質
變化及關節軟骨變化之關係以求更進一步了解膝關節退化之機轉.從實驗
結果顯示出受落體試驗之兔子, 在進行跳躍運動期間的前二至三個星期,
其脛骨彈性係數有增加的趨勢 ,可知在骨骼細胞系統內存在有一個較敏感
的機制, 只需非常少的重覆荷重就會刺激一個調適的反應, 這種反應是在
骨材和組織損壞裂縫累積之前就已經發生 ,而運動二至三星期後其脛骨彈
性係數有減低的趨勢 .至於脛骨超音波量測則以縱向量測所之值最大 ,橫
向量測之值次之 ,而拉伸試驗所得之值最小; 這與骨骼為一非均質, 非等
向性之材質有關 .在 SEM 觀察方面,發現關節軟骨表面會隨著實驗期增長
而有逐漸粗糙的現象 .此表面粗糙度的變化, 相信為關節退化初期之重要
訊息, 因此未來表面粗糙度的定量化與衝擊力之關係為一重要課題 .

Repeated impact forces cause bone and joint degeneration.
Changes of bony microstructure due to repeated loading is a
popular topic nowadays.How these cyclic stresses affect the
generation of microcracks remains unknown. It is know that
microdamages jeopardize mechanical properties of bone. However,
in-vivo and in-vitro fatigue tsts showed very much different
results. Thus, we design a mechanical apparatus to implement a
falling body test. From repeated impact forces on rabbits, the
variations of mechanical properties and the generation of
microcracks in their tibia of hind limb can be measured through
a ultrasound technique and histology examination,respectively .
By performing the above experiments, a thorough understanding
of the occurrence of joint degeneration is a ultimate goal.
Results showed that after experiment,the rabbits' tibia elastic
modulus increased. This means that rabbit's bone went though an
adaptation process. Meanwhile,the unchanged material properties
from ultrasound measurement would suggest that microdamages did
not accumulate until the forth week, then the bone's elastic
modulus decreased. Scanning electron microscoppy was used to
examine surface of articular cartilage , the surface became
rough.It is believed that the change of surface roughness is an
important indication of the initial of OA .Thus , the
quantitative relation between surface rought and impact
conditions would be very important in the future.