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Poor healing response after rotator cuff reconstruction is multifactorial, with the inflammatory microenvironment and deficiency of stem cell differentiation factors at the lesion site being most relevant. However, there is a lack of effective tissue engineering strategies that can simultaneously exert anti-inflammatory and pro-differentiation effects to promote rotator cuff healing. Methods: In this study, we synthesized and characterized a novel active drug delivery vector that successfully overcame the challenge of simultaneous high-efficiency loading and controlled release of Mg2+ and curcumin. The anti-inflammatory and pro-differentiation effects of the composite hydrogel were evaluated in vitro and in vivo. Moreover, healing of the rotator cuff tendon-to-bone interface was studied by histology, immunofluorescence, and biomechanical tests. Results: The composite hydrogel exhibited excellent biocompatibility and injectability, good adhesiveness, and rapid self-healing. The released curcumin showed obvious anti-inflammatory and antioxidation effects, which protected stem cells and tendon matrix. Furthermore, released Mg2+ promoted stem cell aggregation and chondrogenesis. Moreover, biomechanical tests and histological results of a rat rotator cuff tear model at 8 weeks after surgery indicated that the composite hydrogel significantly enhanced tendon-to-bone healing. Conclusions: The composite hydrogel mediated sustained in situ release of curcumin and Mg2+ to effectively promote rotator cuff tendon-to-bone healing via anti-inflammatory and pro-differentiation effects. Therefore, this composite hydrogel offers significant promise for rotator cuff repair.

Background Clavicular hook plates are frequently used in clinical orthopedics to treat acromioclavicular joint dislocation. However, patients often exhibit acromial osteolysis and peri-implant fracture after hook plate fixation. To solve the above problems, we developed a novel double-hook clavicular plate and used finite element analysis (FEA) to investigate its biomechanical properties. Methods A finite element (FE) model was constructed and validated. Then, a double-hook clavicular plate, a single-hook clavicular plate, and an anatomical double-hook clavicular plate was implanted into the acromioclavicular joint and fixed with screws in groups 1, 2 and 3, respectively. Finally, a load was applied, and some indicators were recorded and analyzed. Results For both the proximal clavicular rotation angle and the distal clavicular displacement, the range of motion in groups 1 and 3 was more than 90% lower than that in group 2. The maximum von Mises stress of the clavicle in groups 1 and 3 was more than 45% lower than that in group 2. The maximum stress of the acromion in group 2 was significantly higher than that in groups 1 and 3, and that in group 3 was less than that in group 1, for both cortical and cancellous bone. Conclusions The double-hook clavicular plate could immediately reconstruct the stability of the acromioclavicular joint, effectively reducing the stress of the bone around the clavicle and screws. Additionally, the double-hook clavicular plate could reduce the peak stress of the acromion and produce a more uniform stress distribution.

Stability of space frame structures with bone cement screw reinforcement by biomechanical testing was analyzed. Seven complete human spine specimens with osteoporosis were selected. Three specimens were separated into 18 vertebral bodies. Nine vertebral bodies were randomly selected and bone cement screws were implanted on both sides. Bone cement was used to form a bridge at the front end of the two screws (single vertebral group A). The other nine vertebral bodies were implanted with cement screws on both sides, but the front ends of the two screws were not bridged (single vertebral group B). The remaining spine specimens were used for biomechanical testing of the overall stability of the three-dimensional frame. The four specimens were osteotomized, and then two specimens were randomly selected. Bone cement screws were implanted on both sides of the vertebral body, and a bone cement bridge was formed at the front end of the two screws to establish a three-dimensional frame structure (multi-vertebral group A). The other two spine specimens were implanted with cement screws on both sides of the vertebral body, but the front ends of the two screws were not bridged (multi-vertebral group B). A statistical difference was found between the extractive force of bridged and non-bridged specimens. Group B showed some loosening of screws after the test. The stability of the triangle structure screw, which was formed after the bridge was established at the front end of the single-vertebral bone cement screw, was significantly enhanced. Moreover, the stability was significantly improved after the three-dimensional frame structure was established in the multi-vertebral body group, providing a new method for clinical improvement of the stability and reliability of internal fixation in patients with severe osteoporosis and spinal disease.