彈性髓內釘適用於一般長骨骨幹骨折，尤其是青少年和兒童之骨幹骨折，因為使用彈性髓內釘來進行骨折之固定可以避免傷害生長板，同時兼具傷口小、不傷害骨頭周圍軟組織、手術時間短、術後恢復快等優點，故為臨床常用之方式。然而，因為彈性髓內釘之作用方式與一般鎖固式髓內釘不同，沒有使用螺釘進行固定，所以固定力相對較弱，對於體重超過50公斤或是年紀大於13歲之患者會有較高之失敗率及併發症之發生。此外，在使用彈性髓內釘進行骨折之固定時，髓內釘在術前之預彎為目前臨床上使用之基本技巧，以增加植入後對骨折固定之整體穩定度，但是目前對於預彎幅度及其做用機制仍不甚清楚。本研究之目的為分析探討不同預彎幅度之彈性髓內釘對於脛骨骨幹骨折固定之影響，包含整體穩定度、骨折斷面之位最大移量、髓內釘末端之位移量等等；此外，有無使用固定螺帽對於整體穩定度的影響亦在本研究中一併探討。
本研究先建立一完整之脛骨實體模型，並在脛骨骨幹建立一橫斷骨折，總共包含三種骨折模式：骨折處位於骨幹之近端、中端和遠端，分別植入三種不同預彎之鈦合金髓內釘，包含預彎幅度等於髓腔寬度以及預彎幅度為髓腔寬度之2和3倍；髓內釘之外徑依據髓腔寬度設定為3.5 mm。固定螺帽之使用則以一拘束等式將髓內釘末端與其周圍之骨頭緊密結合來模擬，使得骨頭與髓內釘末端無法產生任何相對之位移。無使用固定螺帽之模型則讓髓內釘末端可以自由滑動。本研究探討之負載包含150N 之軸向負載、150 N彎曲負載以及10度之扭轉，計算骨折處之最大位移量和髓內釘末端之最大滑動量做為結構穩定度評估判斷之指標。
結果顯示使用固定螺帽可以防止髓內釘末端之滑動，進而防止骨折處之塌陷；而在沒有使用固定螺帽的組別中，則需要預彎幅度達到髓腔寬度之3倍時才能有效降低髓內釘之滑動和阻止骨折處之塌陷。在髓內釘預彎幅度不足同時又沒有使用固定螺帽的情況下承受負載，會造成骨折處塌陷以及髓內釘末端在穿入脛骨處之滑動。
在使用彈性髓內釘進行脛骨骨幹骨折之固定時，建議使用固定螺帽或是增加髓內釘之預彎幅度達到髓腔寬度之3倍以有效防止髓內釘之滑動進而增加結構穩定度同時減少骨折處之位移。對於近端脛骨骨幹骨折，則建議要使用固定螺帽且增加髓內釘預彎幅度達到髓腔寬度之3倍以有效固定骨折。

Elastic stable intramedullary nailing (ESIN) is a treatment strategy for the management of diaphyseal long-bone fractures in adolescents and children, but few studies have investigated the mechanical stability and the stability mechanism of tibial diaphyseal fractures treated with various degrees of prebending of the elastic nails. Therefore, the aim of this study was to compare the mechanical stability, including the gap deformation and nail dropping, of a tibia fracture with various fracture sites and fixed with various degrees of prebending of the elastic nails. The stability mechanism of prebent nails was examined through nail deformation during implantation into the intramedullary canal. Furthermore, the contribution of end caps to stability was taken into consideration in the simulation.
A tibia model based on the CT images of a healthy subject was developed with a transverse fracture at the proximal, middle and distal parts of the diaphysis, and fixed with three degrees of prebending of elastic nails, including those equal to, two times and three times the diameter of the intramedullary canal. The outer diameter of the nail used in the computation was 3.5 mm, and the fractured tibia was fixed with two elastic double C-type nails. Furthermore, the proximal end of each nail was set to free or being tied to the surrounding bone by a constraint equation to simulate with or without using end caps.
The results indicated that using end caps can prevent the fracture gap from collapsing by stopping the ends of the nails from dropping back in all prebending conditions and fracture patterns, and increasing the prebending of the nails to a degree three times the diameter of the canal reduced the gap shortening and the dropping distance of the nail end in those without using end caps under axial compression and bending. Insufficient prebending of the nails and not using end caps caused the gap to collapse and the nail to drop back at the entry point under loading.
Using end caps or increasing the prebending of the nails to three times the diameter of the canal is suggested to stop the nail from dropping back and thus produce a more stable structure, with less gap deformation and less nail dropping, in the management of a simulated tibial diapyhseal fracture by using titanium elastic nails with a double C-shape.

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