Growth plate cartilage has limited self-repair ability, leading to poor bone bridge formation post-injury and ultimately limb growth defects in children. The current corrective surgeries are highly invasive, and outcomes can be unpredictable. Following growth plate injury, the direct loss of extracellular matrix (ECM) coupled with further ECM depletion due to the inhibitory effects of inflammation on the cartilage matrix protein greatly hinder chondrocyte regeneration. We designed an exosome (Exo) derived from bone marrow mesenchymal stem cells (BMSCs) loaded ECM-mimic hydrogel to promote cartilage repair by directly supplementing ECM and anti-inflammatory properties. Aldehyde-functionalized chondroitin sulfate (OCS) was introduced into gelatin methacryloyl (GM) to form GMOCS hydrogel. Our results uncovered that GMOCS hydrogel could significantly promote the synthesis of ECM due to the doping of OCS. In addition, the GMOCS-Exos hydrogel could further promote the anabolism of chondrocytes by inhibiting inflammation and ultimately promote growth plate injury repair through ECM remodeling.

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Background: Derotational osteotomy remains the most commonly performed procedure in patients with congenital radioulnar synostosis (CRUS). Bone fixation is mostly performed using K-wires or plates. Many scars, loss of correction and neurovascular complications in the form were the most common complications across the studies. This report introduces a novel, minimally-invasive surgical approach, and reviews our experience.Methods: Twenty-seven children with CRUS were treated using the new technique, including bilateral forearms in 12 cases and unilateral forearm in 15 cases. A transverse osteotomy was performed at the ulnar and radial fusion site, the forearm was derotated osteotomy to the target position, intramedullary nailing was performed, and the elbow was flexed 90 degrees with a long-arm cast after surgery. One week after surgery, the forearm swelling disappeared, the long-arm cast was replaced, the elbow flexed at 90 degrees, and the forearm fixed in the maximum supination position for 4 weeks. Pre-and post-operative positions of the forearm were recorded; the pre-and post-operative activities of daily living (ADL) item scores were recorded for each patient.Results: All patients were followed up postoperatively for a mean duration of 20.7 months. The mean initial pronation deformity was 59.7±12.20 (40 to 100) degrees. The mean correction achieved was 51.2±14.50 degrees, resulting in a mean final position of 8.59±8.10 degrees of supination. The fixed angles of forearm pronation after surgery were corrected to 0-20°, with a mean of 8.33º [standard deviation (SD) 7.98°), and the difference was statistically significant compared with that before surgery (P<0.01). The patients' preand post-operative ADL item scores were 3.6 and 4.5, respectively, which was a 0.9-point change and was statistically significant (P<0.01). After surgery, 26 patients obtained good healing, and only one patient had delayed union, which was healed with forearm immobilization for a further month.Conclusions: Rotational osteotomy with single incision and elastic fixation for CRUS in children is a simple operation, and provides advantages including small trauma, fewer postoperative complications, and good efficacy.

Recent breakthroughs in cell transplantation therapy have revealed the promising potential of bone marrow mesenchymal stem cells (BMSCs) for promoting the regeneration of growth plate cartilage injury. However, the high apoptosis rate and the uncertainty of the differentiation direction of cells often lead to poor therapeutic effects. Cells are often grown under three-dimensional (3D) conditions in vivo, and the stiffness and components of the extracellular matrix (ECM) are important regulators of stem cell differentiation. To this end, a 3D cartilage-like ECM hydrogel with tunable mechanical properties was designed and synthesized mainly from gelatin methacrylate (GM) and oxidized chondroitin sulfate (OCS) via dynamic Schiff base bonding under UV. The effects of scaffold stiffness and composition on the survival and differentiation of BMSCs in vitro were investigated. A rat model of growth plate injury was developed to validate the effect of the GMOCS hydrogels encapsulated with BMSCs on the repair of growth plate injury. The results showed that 3D GMOCS hydrogels with an appropriate modulus significantly promoted chondrogenic differentiation of BMSCs, and GMOCS/ BMSC transplantation could effectively inhibit bone bridge formation and promote the repair of damaged growth plates. Accordingly, GMOCS/BMSC therapy can be engineered as a promising therapeutic candidate for growth plate injury.