隨著年紀的增加，肩部功能障礙(Shoulder disorder)是很常見的肌肉骨骼疾病，尤其旋轉肌破裂(Rotator cuff tear)影響著龐大的病患人口，造成患者肩部虛弱無力、失去功能及反覆性的疼痛，在旋轉肌修復的手術中，縫合固定技術(Suture anchor technique)是其中一種主要修復方式，將穿有縫線(Suture)的鉚釘(Anchor)釘入肱骨大結後，再使縫線穿過破裂的肌腱，將肌腱拉回原本在骨頭上的附著處並固定之，藉由增加肌腱與骨頭的接觸面積，促進旋轉肌之再生及癒合。
儘管縫合固定技術能為病患提供很強的支撐力，於臨床上的使用率高，但經由手術後病患肌腱仍有很大的機率再次破裂，在縫線固定中使用之鉚釘材料，原本是以鈦合金為主，但近年來針對旋轉肌的術後復原狀況多以核磁共振造影(MRI)的方式來進行檢視，由於術後不會將鉚釘取出，鈦合金又不會在人體內降解，而金屬會影響MRI在判讀上的準確性，因此聚合物逐漸取代了鈦合金的使用，然而聚合物的力學強度仍然不及金屬，且聚合物在人體內的降解過程會產生酸性微環境，將帶來組織發炎等症狀的疑慮，不利於組織的癒合。
鎂合金具備良好的生物相容性，又擁有與骨質相近的輕量和高強度力學性質，近年來逐漸被視為新一代生物可降解型醫療用植入金屬，本研究使用開發之鎂鋅鋯合金ZK50為原料，以圓片先執行鎂合金於體外(in vitro)的抗腐蝕性測試、細胞毒性測試及細胞貼附測試，初步結果證實了試片經由氟化處理能有效地提升鎂合金的抗腐蝕性以及生物相容性。因此本研究接著以ZK50為原材加工成鉚釘，經由氟化處理後的鎂鉚釘與現有鈦合金鉚釘作為對照，進行體內(in vivo)測試，14隻活體大白兔隨機分為兩組: 鎂合金組及鈦合金組，於各組的每隻兔子雙側肩部執行旋轉肌斷裂的縫合固定手術，在左右兩邊的肱骨大結各植入一支鉚釘並縫合肌腱，經由電腦斷層掃描和組織切片分析，來觀察鎂合金植體的在術後4週(n=6)和12週(n=8)的降解及組織癒合情況並與鈦合金組做比較;另一方面，本研究於已犧牲的大白兔肩膀分別植入鎂合金和鈦合金鉚釘進行拉拔測試(n=5)，對照兩者在活體內的力學強度。
經由體內測試，植入大白兔體內的鎂合金鉚釘有效的支撐住斷裂肌腱的拉力，肌腱成功地與骨頭接合，同時，經由電腦斷層驗證了植體周遭組織良好的附著其上並隨著鎂合金的降解生成新生骨，拉拔測試證實了鎂合金與鈦合金相比能提供相媲美的力學性質。本研究是第一個發展出鎂合金在縫合固定技術上的應用，並且成功證實了鎂鉚釘在肩部旋轉肌修復的可行性，期能開發出新一代鎂製縫合固定鉚釘，對縫合固定材料於旋轉肌的修復上有所改善。

Suture anchor technique is one of the most commonly used surgical treatment of rotator cuff tear. The high retearing rate of repaired rotator cuff by anchor made of titanium alloy due to consistent foreign body reaction or polymers due to inferior mechanical strength and osteolysis concern remains a challenge in arthroscopic rotator cuff repair. Biodegradable material is the new generation of biomaterials served as the tissue integration scaffold for high regenerated tissue. Therefore, examination of a degradable magnesium (Mg) anchor is the aim of this study.
Recently, biodegradable magnesium alloy has attracted great attention because it has excellent biocompatibility, osteointegration ability and close mechanical properties to natural bone. However, the corrosion behavior of these metals in-vivo remains challenging.
In this study, a protective magnesium fluoride (MgF2) coating was deposited on the surface of Mg-5.0Zn-0.5Zr (ZK50) alloy. After a series of material analysis, it demonstrated its good corrosion resistance and the cell viability tests and cell adhesion tests showed that MgF2-coating could stimulate osteoblastic cell proliferation. So, the MgF2-coated ZK50 anchors were processed and used on rotator cuff repair of rabbits’ shoulders. Non-degradable titanium (Ti) anchors were used as control group in this approach. 14 New Zealand white rabbits were randomly divided into 2 groups: Mg group and Ti group, and the release of the supraspinatus tendon was performed at the base of the tendon insertion area. Anchor was inserted into greater tuberosity, then the detached tendon was repaired by Mason-Allen method. CT scans and histological analysis were performed at 4-week(n=6) and 12-week(n=8) post-operation to observe the biocompatibility of the implants and the change of degradation products. On the other hand, pullout tests (n=5) were conducted on euthanized rabbits’ shoulders to compare the initial fixation provided by suture anchor for the torn tendon.
The results showed good tendon-healing between supraspinatus and humeral head of rabbits with the implantation of MgF2-coated ZK50 anchors. The surrounding tissues of the implants could absorb the degradation products of the Mg anchors and the new bone replaced the space successfully. Furthermore, the strength provided by Mg anchor could be compatible to Ti anchor during the pullout tests, indicating that Mg anchor has sufficient mechanical strength. In conclusion, this is the first study that proved the feasibility of Mg anchors applied on rotator cuff repair. These results confirmed that MgF2-coated ZK50 anchor can degrade at proper time during tendon-bone healing and potentially offer a novel material for next-generation anchor application.

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