Regarding the current materials used for suture anchors for rotator cuff repair, there are still limitations in terms of degradability, mechanical properties, and bioactivities in clinical applications. Magnesium alloys have preliminarily been shown to promote tendon-bone healing with good prospects for application as anchor materials. However, the design of anchor structures for the degradation characteristics of magnesium alloy materials has not been considered, which is critical for the practical application of magnesium alloy anchors. The mechanism by which magnesium promotes tendon bone healing remains to be clarified. Here, we proposed a novel split hollowed magnesium alloy suture anchors for the repair of rabbit rotator cuff injury. We found that novel split hollowed magnesium alloy anchors structure effectively solved the problem of failure due to degradation of traditional eyelet structure, providing reliable suture fixation. The open architecture facilitates the metabolic resorption of the degradation products of and promotes the ingrowth of bone tissue. Histological staining showed that magnesium anchors have better ability to promote regeneration at the fibrocartilage interface compared to PLLA anchors. The higher expression of fibrocartilage markers (Aggrecan, COL2A1, and Sox9) at the tendon-bone interface in magnesium anchors, which promotes chondrocyte differentiation at the tendon-bone interface and matrix formation, which is more conducive to achieving regeneration and maturation of fibrocartilage enthesis. Hence, this study provides a basis for further research on the clinical application of degradable magnesium alloy suture anchors.

Despite transosseous rotator cuff tear repair using sutures is widely accepted for tendon-bone fixation, the fibrocartilaginous enthesis regeneration is still hardly achieved with the traditional sutures. In the present work, degradable magnesium (Mg) alloy wire was applied to suture supraspinatus tendon in a rat acute rotator cuff tear model with Vicryl Plus 4–0 absorbable suture as control. The shoulder joint humerus-supraspinatus tendon complex specimens were retrieved at 4, 8, and 12 weeks after operation. The Mg alloy suture groups showed better biomechanical properties in terms of ultimate load to failure. Gross observation showed that hyperplastic response of the scar tissue at the tendon-bone interface is progressively alleviated over time in the both Mg alloy suture and Vicryl suture groups. In the histological analysis, for Mg alloy suture groups, chondrocytes appear to proliferate at 4 weeks postoperatively, and the tendon-bone interface showed an orderly structural transition zone at 8 weeks postoperatively. The collagenous fiber tended to be aligned and the tendon-bone interlocking structures apparently formed, where transitional structure from unmineralized fibrocartilage to mineralized fibrocartilage was closer to the native fibrocartilaginous enthesis. In vivo degradation of the magnesium alloy wire was completed within 12 weeks. The results indicated that Mg alloy wire was promising as degradable suture with the potential to promotes fibrocartilaginous interface regeneration in rotator cuff repair.